Surgical method and apparatus for positioning a diagnostic or therapeutic element within the body

A surgical method and apparatus for positioning a diagnostic or therapeutic element within the body. The apparatus may be catheter-based or a probe including a relatively short shaft.

BACKGROUND OF THE INVENTIONS

1. Field of Invention

The present inventions relate generally to structures for positioning one or more diagnostic or therapeutic elements within the body and, more particularly, to devices which are particularly well suited for treatment of cardiac conditions.

2. Description of the Related Art

There are many instances where diagnostic and therapeutic elements must be inserted into the body. One instance involves the treatment of cardiac conditions such as atrial fibrillation and atrial flutter which lead to an unpleasant, irregular heart beat, called arrhythmia.

Normal sinus rhythm of the heart begins with the sinoatrial node (or “SA node”) generating an electrical impulse. The impulse usually propagates uniformly across the right and left atria and the atrial septum to the atrioventricular node (or “AV node”). This propagation causes the atria to contract in an organized way to transport blood from the atria to the ventricles, and to provide timed stimulation of the ventricles. The AV node regulates the propagation delay to the atrioventricular bundle (or “HIS” bundle). This coordination of the electrical activity of the heart causes atrial systole during ventricular diastole. This, in turn, improves the mechanical function of the heart. Atrial fibrillation occurs when anatomical obstacles in the heart disrupt the normally uniform propagation of electrical impulses in the atria. These anatomical obstacles (called “conduction blocks”) can cause the electrical impulse to degenerate into several circular wavelets that circulate about the obstacles. These wavelets, called “reentry circuits,” disrupt the normally uniform activation of the left and right atria.

Because of a loss of atrioventricular synchrony, the people who suffer from atrial fibrillation and flutter also suffer the consequences of impaired hemodynamics and loss of cardiac efficiency. They are also at greater risk of stroke and other thromboembolic complications because of loss of effective contraction and atrial stasis.

Although pharmacological treatment is available for atrial fibrillation and flutter, the treatment is far from perfect. For example, certain antiarrhythmic drugs, like quinidine and procainamide, can reduce both the incidence and the duration of atrial fibrillation episodes. Yet, these drugs often fail to maintain sinus rhythm in the patient. Cardioactive drugs, like digitalis, Beta blockers, and calcium channel blockers, can also be given to control the ventricular response. However, many people are intolerant to such drugs. Anticoagulant therapy also combats thromboembolic complications, but does not eliminate them. Unfortunately, pharmacological remedies often do not remedy the subjective symptoms associated with an irregular heartbeat. They also do not restore cardiac hemodynamics to normal and remove the risk of thromboembolism.

Many believe that the only way to really treat all three detrimental results of atrial fibrillation and flutter is to actively interrupt all of the potential pathways for atrial reentry circuits.

One surgical method of treating atrial fibrillation by interrupting pathways for reentry circuits is the so-called “maze procedure” which relies on a prescribed pattern of incisions to anatomically create a convoluted path, or maze, for electrical propagation within the left and right atria. The incisions direct the electrical impulse from the SA node along a specified route through all regions of both atria, causing uniform contraction required for normal atrial transport function. The incisions finally direct the impulse to the AV node to activate the ventricles, restoring normal atrioventricular synchrony. The incisions are also carefully placed to interrupt the conduction routes of the most common reentry circuits. The maze procedure has been found very effective in curing atrial fibrillation. However, the maze procedure is technically difficult to do. It also requires open heart surgery and is very expensive. Thus, despite its considerable clinical success, only a few maze procedures are done each year.

More recently, maze-like procedures have been developed utilizing catheters which can form lesions on the endocardium to effectively create a maze for electrical conduction in a predetermined path. Exemplary catheters are disclosed in commonly assigned U.S. Pat. No. 5,582,609. Typically, the lesions are formed by ablating tissue with an electrode carried by the catheter. Electromagnetic radio frequency (“RF”) energy applied by the electrode heats, and eventually kills (i.e. “ablates”), the tissue to form a lesion. During the ablation of soft tissue (i.e. tissue other than blood, bone and connective tissue), tissue coagulation occurs and it is the coagulation that kills the tissue. Thus, references to the ablation of soft tissue are necessarily references to soft tissue coagulation. “Tissue coagulation” is the process of cross-linking proteins in tissue to cause the tissue to jell. In soft tissue, it is the fluid within the tissue cell membranes that jells to kill the cells, thereby killing the tissue.

Catheters used to create lesions (the lesions being 3 to 15 cm in length) typically include a relatively long and relatively flexible body portion that has an ablation electrode on its distal end. The portion of the catheter body portion that is inserted into the patient is typically from 23 to 55 inches in length and there may be another 8 to 15 inches, including a handle, outside the patient. The proximal end of the catheter body is connected to the handle which includes steering controls. The length and flexibility of the catheter body allow the catheter to be inserted into a main vein or artery (typically the femoral artery), directed into the interior of the heart, and then manipulated such that the ablation electrode contacts the tissue that is to be ablated. Fluoroscopic imaging is used to provide the physician with a visual indication of the location of the catheter.

Atrial appendages are primary potential sources of thrombus formation. The atrial appendages are especially important in the transport of blood because they have a sack-like geometry with a neck potentially more narrow than the pouch. In this case, contraction of the appendage is essential to maintain an average absolute blood velocity high enough to eliminate potential stasis regions which may lead to thrombus formation.

In the maze procedure performed through open heart surgery, the typical access points into the interior of the atria are the atrial appendages. Therefore, at the conclusion of the surgical procedure, the region occupied by the atrial appendages is eliminated by surgically removing the appendages. This mitigates subsequent problems resulting from blood stasis in the atrial appendages as well as from electrical isolation of the appendages from the rest of the atria. However, as noted above, open heart surgery is very expensive and the incision based maze procedure is difficult to perform. Although catheter-based procedures do not admit themselves to surgical removal of the appendages, catheter-based procedures and apparatus have been recently developed which reposition the atrial appendages, affix them in an altered position and/or fuse the walls of the appendages to one another to isolate the appendages, reduce stasis regions and ultimately thrombus formation. Such procedures and apparatus are disclosed in commonly assigned U.S. application Ser. No. 08/880,711, filed Jun. 23, 1997, which is a File Wrapper Continuation of U.S. application Ser. No. 08/480,200, filed Jun. 7, 1995, entitled “Atrial Appendage Stasis Reduction Procedures and Devices” and incorporated herein by reference. One of these procedures involves the use of a catheter having a lasso which is tightened around the appendage. RF energy is then transmitted to the appendage by way of the lasso to thermally fuse the walls of the appendage to one another, thereby isolating the appendage.

It is believed the treatment of atrial fibrillation and flutter requires the formation of long, thin lesions of different lengths and curvilinear shapes in heart tissue. Such long, curvilinear lesion patterns require the deployment within the heart of flexible ablating elements having multiple ablating regions. The formation of these lesions by ablation can provide the same therapeutic benefits that the complex incision patterns that the surgical maze procedure presently provides, but without invasive, open heart surgery.

With larger and/or longer multiple electrode elements comes the demand for more precise control of the ablating process. The delivery of ablating energy must be governed to avoid incidences of tissue damage and coagulum formation. The delivery of ablating energy must also be carefully controlled to assure the formation of uniform and continuous lesions, without hot spots and gaps forming in the ablated tissue.

The task is made more difficult because heart chambers vary in size from individual to individual. They also vary according to the condition of the patient. One common effect of heart disease is the enlargement of the heart chambers. For example, in a heart experiencing atrial fibrillation, the size of the atrium can be up to three times that of a normal atrium.

Catheter-based ablation and atrial appendage isolation have proven to be a significant advance over the conventional open heart surgery based approaches. Nevertheless, the inventors herein have determined that further improvements are possible.

For example, and with respect to ablation procedures in particular, the inventors herein have determined that it can be quite difficult to accurately position an ablation electrode on the endocardium surface by manipulating the distal end of a relatively long catheter body from a remote handle. This is especially true with respect to left atrial sites. The present inventors have also determined that fluoroscopy is a somewhat inaccurate method of visualizing the ablation electrodes during positioning and when determining whether the electrodes are in proper contact with tissue.

Additionally, a primary goal of any ablation procedure is to create contiguous lesions (often long, curvilinear lesions) without over-heating tissue and causing coagulum and charring. Tissue ablation occurs at 50° C., while over-heating occurs at 100° C. The present inventors have further determined that it can be difficult to produce tissue contact that will accomplish this result with an electrode mounted on the distal end of a relatively long catheter. This is especially true in those procedures where an electrode on the distal tip of the catheter is dragged along the tissue. Such dragging also makes accurate placement of the electrode very difficult. Other shortcomings identified by the present inventors concern the convective cooling effects of the blood pool on the electrodes. For example, the system power requirements must be high enough to compensate for the heat losses due to convective cooling.

One proposed method of solving the over-heating problems associated with conventional ablation catheters is the so-called “cooled tip” approach. Here, the tissue surface is cooled with a saline solution. Although the saline is somewhat useful in keeping the surface temperature below the over-heating temperature, the sub-surface tissue temperature can still rise well above 100° C. Such temperatures will cause gas within the sub-surface tissue to expand. Ultimately, the tissue will tear or pop, which will result in perforations of the epicardial surface and/or the dislodging of chunks of tissue that can cause strokes.

Turning to atrial appendage isolation, the present inventors have determined that catheter-based procedures suffer from many of the same disadvantages discussed above, such as those concerning positioning and visualization. Additionally, the inventors herein have determined that the lasso can bunch up the tissue when the lasso is tightened and that tissue fusion would be improved if this bunching could be avoided.

With respect to energy control, conventional ablation devices include controls that are located either on the RF energy source, or on a foot pedal. The inventors herein have determined that such arrangements are inconvenient and can make it difficult to control power during a surgical procedure.

Turning to surgical procedures in general, one problem associated with many surgical procedures is excessive bleeding. For example, a high level of bleeding is often associated with the removal of liver lobes and certain cancerous tumors. The inventors herein have determined that present surgical methods could be improved in the area of blood loss.

SUMMARY OF THE INVENTIONS

Accordingly, the general object of the present inventions is to provide an apparatus for positioning an operative element (such as an ablation electrode) within the body which avoids, for practical purposes, the aforementioned problems. In particular, one object of the inventions is to provide tissue ablation systems and methods providing beneficial therapeutic results without requiring highly invasive surgical procedures. Another objective of the inventions is to provide systems and methods that simplify the creation of complex lesions patterns in soft tissue, such as myocardial tissue in the heart.

In order to accomplish these and other objectives, certain embodiments of one of the present inventions include an electrode support structure carried at the distal end of a guide body. The support structure includes a bendable stylet extending along an axis outside the distal end of the guide body. The structure also includes at least one flexible spline leg having a near end attached to the distal end of the guide body and a far end extending beyond the distal end of the guide body and attached to the bendable stylet. The spline leg is normally flexed between the distal guide body end and the bendable stylet in a first direction that extends along and radially outward of the axis of the stylet. At least one electrode element is on the flexible spline. The structure further includes a control element to apply tension to the stylet. The tension bends the stylet, thereby flexing the spline leg in a second direction.

The flexure of the spline leg in the first direction facilitates intimate contact between the electrode element and tissue. The additional flexure by the stylet of the spline leg in the second direction makes possible the creation of a diverse number of additional shapes and tissue contact forces.

In accordance with another embodiment of one of this invention, an electrode support structure is provided that, in addition to bending the stylet, includes another control element that moves the stylet along its axis to increase or decrease flexure of the spline leg in the first direction. This additional control over the flexure of the spline leg further enhances intimate contact against tissue, regardless of variations in the dimensions of the surrounding tissue region.

In accordance with another embodiment of this invention, an electrode support structure is provided that includes a malleable stylet. The physician imparts a desired flexure to the spline leg in the second direction by bending the malleable stylet. Alternatively, an electrode support structure is provided in which the spline leg itself is malleable.

Structures that embody the features of this invention make possible the creation of diverse number of shapes and contact forces to reliably achieve the type and degree of contact desired between electrode elements and targeted tissue areas, despite physiologic differences among patients.

Another aspect of this invention is associated with structures and methods for ablating tissue in a heart. The structures and methods include a probe for deployment within the heart. The probe carries at least one elongated flexible ablation element to which a bendable stylet is attached. The structures and method apply tension to bend the stylet. The bending of the stylet flexes the ablation element into a curvilinear shape along the contacted tissue region. By transmitting ablation energy to the ablation electrode while flexed in the curvilinear shape and in contact with the tissue region, the structures and methods make possible the formation of curvilinear lesion patterns in heart tissue.

In order to accomplish the above-described and other objectives, a surgical device in accordance with one embodiment of another one of the present inventions includes a relatively short shaft, a bendable spline assembly associated with the distal end of the shaft and having a predetermined configuration, the spline assembly being adapted to collapse in response to external forces and expand when the forces are removed, and an operative element associated with the bendable spline. Optionally, a substantially tubular member may be positioned around the shaft. Movement of the substantially tubular member over the spline assembly will cause the spline assembly to collapse, while the spline assembly will expand to the predetermined configuration in response to a retraction of the substantially tubular member.

In order to accomplish above-described and other objectives, an soft tissue coagulation probe in accordance with one embodiment of one of the inventions includes a relatively short shaft defining a distal end and a proximal end, a handle associated with the proximal end of the shaft, and at least one soft tissue coagulation electrode associated with the shaft and located in spaced relation to the handle.

In order to accomplish above-described and other objectives, a surgical device in accordance with another embodiment of this invention includes a relatively stiff shaft, a handle associated with the proximal end of the shaft, and a distal tip assembly associated with the distal end of the shaft, the distal tip assembly including a distal member, which is flexible and/or malleable, and an operative element carried by the distal member.

In order to accomplish this and other objectives, a surgical device in accordance with another embodiment of this invention includes a shaft, a relatively stiff tubular member positioned around a predetermined portion of the shaft and movable relative thereto, a distal tip assembly associated with the distal end of the shaft and including a flexible distal member and an operative element carried by the distal member, and a pivot assembly associated with the distal end of the tubular member and a distal portion of the tip assembly.

There are many advantages associated with these inventions. For example, the above-described embodiments of this invention may be used in a method of treating atrial fibrillation wherein access to the heart is obtained by way of a thoracostomy. Here, the operative element is an ablation electrode. Such a method may also be used to treat atrial fibrillation during mitral valve surgery wherein access to the heart is obtained through a thoracostomy, thoracotomy or median sternotomy.

The relatively short shaft and manner of insertion allows the ablation electrode to be easily inserted into the atrium and visually guided to the desired location. Thus, the ablation electrodes in the present device do not have to be guided by manipulating the relatively long shaft of an endovascular catheter. This makes the positioning of the electrodes within the heart easier and more accurate. Endocardial visualization is also improved because surgical methods employing the present device allow the endocardium to be viewed directly with the naked eye, a fiberoptic camera or other imaging modalities. This eliminates the need for fluoroscopic images and reduces the amount of radiation required, as compared to catheter-based procedures. Moreover, the shaft in the present device can be relatively stiff, as compared to a catheter shaft, because the present shaft does not have to travel through the tortuous vascular path to the heart. Along with the relatively short length of the present shaft, the additional stiffness enhances torque transmission and provides superior and more reliable electrode-endocardium contact force.

Surgical devices in accordance with this invention may also be used during procedures, such as valve replacement where the patient is on cardiopulmonary bypass, to create tissue lesions. During bypass, the electrodes elements will not be in contact with the blood pool and, accordingly, will not be affected by the convective cooling.

Patients can only be on bypass for a period of approximately four hours. Long bypass times are associated with increased morbidity and mortality. Thus, all procedures performed during bypass must be rapidly completed. Surgical devices in accordance with the present invention may include a series of temperature controlled electrodes that allow a long lesion to be created in rapid fashion, i.e. in approximately 30 to 120 seconds. The ability of the present surgical devices and techniques to create lesions rapidly allows procedures to be performed during bypass that, heretofore, could not due to the time constraints. For example, a conventional surgical maze procedure takes approximately 12 hours to complete (note that a portion of the procedure is performed while the patient is not on bypass), while such a procedure may be completed in approximately 5 to 15 minutes with the present devices and methods.

In accordance with another advantageous aspect of this invention, the shaft and/or sheath (if present) may be formed from a malleable material that a physician can bend into a desired configuration and remain in that configuration when released. Although malleable, the stiffness of such material must be at least such that the shaft and/or sheath (if present) will not bend under the forces applied thereto during a surgical procedure. Alternatively, or in addition, the distal end of the device may also be malleable, thereby allowing the physician to bend the distal end of the device into a shape corresponding to the bodily structure to be acted upon. This is particularly important in endocardial applications because the endocardial surface is typically non-uniform with ridges and trabeculae residing in the right and left atria. There are also dramatic differences between endocardial surface morphology from patient to patient and from lesion location to lesion location. To create contiguous lesions with a surgical approach, the device must either distend the atria to flatten out the non-uniformities, or the probe must be configured to conform to the atrial surface. There are, however, some regions where the atria cannot be distended to a flat state because of trabeculae, orifices, and ridges. A surgeon can observe the atrial surface and bend the present malleable device so as to conform thereto. The distal end may, instead, be spring-like or even rigid if the application so requires.

In order to accomplish the above-identified and other objectives, a surgical device in accordance with one embodiment of another one of the present inventions includes a handle having at least one movable handle member, first and second support members operably connected to the handle, at least one of the support members being movable with respect to the other support member in response to movement of the at least one movable handle member, and at least one ablation electrode associated with the first support member.

There are many advantages associated with this invention. By way of example, this invention is especially useful in a method of isolating an atrial appendage. Access to the atrium may be obtained by, for example, a thoracostomy and the appendage may be captured between the support members. RF energy is then applied to the captured portion of the appendage to thermally fuse the walls of the appendage to one another. This method provides better heating and fusing than the lasso catheter-based approach because the tissue is not bunched up when captured between the support members, as it is when the lasso is tightened. Additionally, the disadvantages associated with the use of catheters in general are also avoided.

A surgical clamp in accordance with one embodiment of another of the present inventions includes first and second clamp members, and at least one electrode associated with at least one of the clamp members. The clamp may be used to isolate an atrial appendage in a manner similar to that described in the preceding paragraph with the same advantageous results. Thereafter, the clamp may be either removed or left in place.

A surgical device in accordance one embodiment of another of the present inventions includes an energy source, at least one energy transmission device, and a handle including an energy control device coupled to the energy source and to the at least one energy transmission device. The energy control device is adapted to selectively control the transmission of energy from the energy source to the at least one energy transmission device. Because the energy control device is located on the handle, which is necessarily grasped by the physician during surgical procedures, the present surgical device provides more convenient energy control than that found in conventional devices.

Alternatively, and in accordance with one embodiment of another of the present inventions, energy control may be accomplished through the use of a remote energy control device that is connected to power unit, but located in close proximity to the patient or otherwise within the sterile zone of an operating room. Such an arrangement also provides more convenient energy control than that found in conventional devices.

Additionally, whether the power control interface is located on the handle of a surgical probe or on a remote control device, the power control aspect of the overall electrophysiological system can be more conveniently brought into the sterile zone because both the present surgical probe and remote control device are both readily sterilizable. Conventional power control interfaces, on the other hand, are part of a power control unit that is not readily sterilizable.

To further improve tissue contact, a pressure application probe in accordance with one embodiment of another of the present inventions may be used in conjunction with a probe having an energy transmission device on a support member. The pressure application probe includes an elongate main body portion and an engagement device adapted to releasably engage the support member. The pressure application probe can be used by the physician to insure that sufficient tissue contact is realized prior to energy transmission.

A coupling device in accordance with another of the present inventions can also be used in conjunction with a probe having an energy transmission device on a support member. One embodiment of the coupling device includes a base member adapted to be removably secured to a first portion of the probe's flexible support member and an engagement device connected to the base member and adapted to be removably secured to a second portion of the flexible support member. The coupling device enables a physician to form a distal loop in the support member when desired, thereby increasing the flexibility of the probe.

In order to reduce the blood loss associated certain surgical procedures, a surgical method in accordance with another of the present inventions includes the steps of coagulating soft tissue and then forming an incision is the coagulated tissue. If the incision is no deeper than the coagulation, the incision will not result in significant bleeding. This process can be repeated until an incision of the desired depth is achieved.

The above described and many other features and attendant advantages of the present invention will become apparent as the invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of the best presently known modes of carrying out the inventions. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the inventions.

The detailed description of the preferred embodiments is organized as follows:I. Bi-Directional Flexible StructuresII. Probe-Type ApparatusIII. Operative ElementsIV. Epicardial Applications of Probe-Type ApparatusV. Endocardial Applications of Probe-Type ApparatusVI. Other Surgical ApplicationsVII. Apparatus that Apply a Clamping ForceVIII. Applications of Apparatus that Apply a Clamping ForceIX. Power Control
The section titles and overall organization of the present detailed description are for the purpose of convenience only and are not intended to limit the present invention.

This specification discloses a number of electrode structures, mainly in the context of cardiac ablation, because the structures are well suited for use with myocardial tissue. Nevertheless, it should be appreciated that the structures are applicable for use in therapies involving other types of soft tissue. For example, various aspects of the present inventions have applications in procedures concerning other regions of the body such as the prostate, liver, brain, gall bladder, uterus and other solid organs.

The exemplary structures, systems, and techniques illustrated in this Section are discussed in the context of catheter-based cardiac ablation. Nevertheless, it should be appreciated that the structures, systems, and techniques are applicable for use in other tissue ablation applications, including those that are not necessarily catheter-based.

A. Loop Support Structures for Multiple Electrodes

FIG. 1shows a multiple electrode probe10that includes a loop structure20carrying multiple electrode elements28. Instead of, or in addition to the electrode elements, the loop structure can carry one or more of the other operative elements discussed in Section III below.

The probe10includes a flexible catheter tube12with a proximal end14and a distal end16. The proximal end14carries an attached handle18. The distal end16carries a loop structure20that supports multiple electrodes.

InFIG. 1, the loop support structure20comprises two flexible spline legs22spaced diametrically opposite each other. The dual leg loop structure20shown inFIG. 1will be called a “full-loop” structure.

The far ends of the spline legs22radiate from a distal hub24. The near ends of the spline legs22radiate from a base26attached to the distal end16of the catheter tube12. The multiple electrode elements28are arranged along each spline leg22.

In one implementation, the two spline legs22of the structure20are paired together in an integral loop body42(seeFIG. 2). Each body42includes a mid-section44from which the spline elements22extend as an opposed pair of legs. AsFIG. 2shows, the mid-section44includes a preformed notch or detent46, whose function will be described later.

The loop body42is preferably made from resilient, inert wire, like Nickel Titanium (commercially available as Nitinol material). However, resilient injection molded inert plastic or stainless steel can also be used. Preferably, the spline legs22comprise thin, rectilinear strips of resilient metal or plastic material. Still, other cross sectional configurations can be used.

In this implementation (seeFIGS. 3 and 4), the distal hub24has a generally cylindrical side wall50and a rounded end wall52. A longitudinal slot56extends through the hub24, diametrically across the center bore54.

In the illustrated embodiment, the hub24is made of an inert, machined metal, like stainless steel. The bore54and slot56can be formed by conventional EDM techniques. Still, inert molded plastic materials can be used to form the hub24and associated openings.

In this implementation, to assemble the structure20(seeFIGS. 4 and 5), a spline leg22of the hoop-like body42is inserted through the slot56until the mid-body section44enters the bore54. The detent46snaps into the bore54(seeFIG. 4) to lock the body42to the hub24, with the opposed pair of spline legs22on the body42radiating free of the slot56(seeFIG. 5).

In the illustrated embodiment (seeFIGS. 5 and 6a), the base26includes an anchor member62and a mating lock ring64. The anchor member62fits with an interference friction fit into the distal end16of the catheter tube12. The lock ring64includes a series of circumferentially spaced grooves66into which the free ends of the spline legs22fit. The lock ring64fits about the anchor member62to capture with an interference fit the free ends of the spline legs22between the interior surface of the grooves66and the outer surface of the anchor member62(seeFIG. 6). The anchor member62/lock ring64assembly holds the spline elements22in a desired flexed condition.

In an alternative construction (seeFIG. 6b), the base26can comprise a slotted anchor63carried by the distal end16of the catheter tube12. The slotted anchor63is made of an inert machined metal or molded plastic material. The slotted anchor63includes an outer ring65and a concentric slotted inner wall67. The interior of the anchor63defines an open lumen226to accommodate passage of wires and the like between the catheter tube bore36and the support structure20(as will be described in greater detail later).

The inner wall67includes horizontal and vertical slots69and71for receiving the free ends of the spline legs22. The free ends pass through the horizontal slots69and are doubled back upon themselves and wedged within the vertical slots71between the outer ring65and the inner wall67, thereby securing the spline legs22to the anchor63.

There are other alternative ways of securing the spline legs22to the distal end16of the catheter tube12, which will be described later.

Preferably, the full-loop structure20shown inFIG. 1does not include a hub24like that shown inFIGS. 1 and 3, and, in addition, does not incorporate a detented integral loop body42like that shown inFIG. 2. Any single full-loop structure without a center stiffener or stylet (as will be described later) preferably comprises a single length of resilient inert wire (like Nickel Titanium) bent back upon itself and preformed with resilient memory to form the desired full loop shape. Structure112inFIG. 29(which will be described in greater detail later) exemplifies the use of a preshaped doubled-back wire to form a loop, without the use of a hub24or detented loop body42.

FIG. 7shows an alternative loop structure20(1) that includes a single spline leg22(1) carrying multiple electrode elements28. This single leg loop structure will be called a “half-loop” structure, in contrast to the dual leg loop structure20(i.e., the “full-loop structure) shown inFIG. 1.

In assembling the half-loop structure20(1) shown inFIG. 7, the hoop-like body42shown inFIG. 2is cut on one side of the detent46to form the single spline leg22(1). The single spline leg22(1) is snap-fitted into the hub24and captured with an interference fit by the anchor member62/lock ring64assembly of the base26in the manner just described (shown inFIGS. 5 and 6a). Alternatively, the single spline leg22(1) can be wedged within the base anchor ring63shown inFIG. 6b. InFIG. 7, the half-loop structure20(1) also includes a center stiffener40passing through the base26and to the bore54of the hub24. The stiffener40can be made of a flexible plastic like PEEK, or from a hollow tube like hypo-tubing or braid plastic tubing.

It should be appreciated that other loop-type configurations besides the full-loop structure20and half-loop structure20(1) are possible. For example, two half-loop structures20(1), one or both carrying electrode elements28, can be situated in circumferentially spaced apart positions with a center stiffener40, asFIG. 8shows. As another example, four half-loop structures, or two full-loop structures can be assembled to form a three-dimensional, basket-like structure60(without using a center stiffener40), like that shown inFIG. 9.

Regardless of the configuration, the loop structure provides the resilient support necessary to establish and maintain contact between the electrode elements28and tissue within the body.

The electrode elements28can serve different purposes. For example, the electrode elements28can be used to sense electrical events in heart tissue. In the illustrated and preferred embodiments, the principal use of the electrode elements28is to emit electrical energy to ablate tissue. In the preferred embodiments, the electrode elements28are conditioned to emit electromagnetic radio frequency energy.

As described in greater detail in Section III below, the electrode elements28can be assembled in various ways.

In one preferred embodiment (seeFIG. 10), the elements comprise multiple, generally rigid ring electrode elements30arranged in a spaced apart, segmented relationship upon a flexible, electrically nonconductive sleeve32which surrounds the underlying spline leg22. The sleeve32is made a polymeric, electrically nonconductive material, like polyethylene or polyurethane. The electrode rings30are pressure fitted about the sleeve32. The flexible portions of the sleeve32between the rings30comprise electrically nonconductive regions. Alternatively, the electrode segments30can comprise a conductive material coated upon the sleeve32. The electrode coating can be applied either as discrete, closely spaced segments or in a single elongated section.

In a more preferred embodiment (seeFIGS. 11aand11b), spaced apart lengths of closely wound, spiral coils are wrapped about the sleeve32to form an array of segmented, generally flexible electrodes34. The inherent flexible nature of a coiled electrode structures34also makes possible the construction of a continuous flexible ablating element comprising an elongated, closely wound, spiral coil wrapped about all or a substantial length of the flexible sleeve32.

The electrode elements28can be present on all spline legs22, asFIG. 1shows, or merely on a selected number of the spline legs22, with the remaining spline legs serving to add structural strength and integrity to the structure.

Various access techniques can be used to introduce the probe10and its loop support structure20into the desired region of the heart. For example, to enter the right atrium, the physician can direct the probe10through a conventional vascular introducer through the femoral vein. For entry into the left atrium, the physician can direct the probe10through a conventional vascular introducer retrograde through the aortic and mitral valves.

Alternatively, the physician can use the delivery system shown in U.S. Pat. No. 5,636,634 entitled “Systems and Methods Using Guide Sheaths for Introducing, Deploying, and Stabilizing Cardiac Mapping and Ablation Probes.”

In the illustrated and preferred embodiments (seeFIGS. 10 and 11a/b), each flexible ablation element carries at least one and, preferably, at least two, temperature sensing elements68. The multiple temperature sensing elements68measure temperatures along the length of the electrode element28. The temperature sensing elements68, which can comprise thermistors or thermocouples, can be located on the ablation elements in the manner shown inFIGS. 10 and 11a/b. Preferably, the temperature sensing elements68can be located on one or both of the longitudinal end edges of the ablation elements, as shown in U.S. patent application Ser. No. 08/788,782, entitledmSystems and Methods for Controlling Ablation Using Multiple Temperature Sensing Elements,” which is incorporated herein by reference.

An external temperature processing element, such as that discussed below in Section IX, receives and analyses the signals from the multiple temperature sensing elements68in prescribed ways to govern the application of ablating energy to the flexible ablation element. The ablating energy is applied to maintain generally uniform temperature conditions along the length of the element. Additionally, further details of the use of multiple temperature sensing elements in tissue ablation can be found in co-pending U.S. application Ser. No. 08/638,989, filed Apr. 24, 1996, which is File Wrapper Continuation of U.S. application Ser. No. 08/286,930, filed Aug. 8, 1994, entitled “Systems and Methods for Controlling Tissue Ablation Using Multiple Temperature Sensing Elements.”

To aid in locating the structure20within the body, the handle16and catheter body12preferably carry a steering mechanism70(seeFIGS. 1 and 12) for selectively bending or flexing the distal end16of the catheter body12.

The steering mechanism18can vary. In the illustrated embodiment (seeFIG. 12), the steering mechanism70includes a rotating cam wheel72with an external steering lever74(seeFIG. 1). AsFIG. 12shows, the cam wheel72holds the proximal ends of right and left steering wires76. The steering wires76, like the signal wires58, pass through the catheter body lumen36. The steering wires76connect to the left and right sides of a resilient bendable wire or spring (not shown) enclosed within the distal end16of the catheter body12. Forward movement of the steering lever74flexes or curves the distal end16down. Rearward movement of the steering lever74flexes or curves the distal end16up.

Further details of this and other types of steering mechanisms are shown in Lundquist and Thompson U.S. Pat. No. 5,254,088, which is incorporated into this Specification by reference.

B. Variable Shape Loop Support Structures

To uniformly create long, thin lesions having the desired therapeutic effect, the loop support structure20or20(1) must make and maintain intimate contact between the electrode elements28and the endocardium. This invention provides loop support structures that the physician can adjust to adapt to differing physiologic environments.1. Distended Loop Structures

The adjustable loop structure78shown inFIG. 13is in many respects similar to the full-loop structure20shown inFIG. 1. The adjustable full-loop structure78includes the pair of diametrically opposite spline legs22that radiate from the base26and hub24.

In addition, the adjustable full-loop structure78includes a flexible stylet80attached at its distal end to the hub bore54. The stylet80can be made from a flexible plastic material, like PEEK, or from a hollow tube, like hypo-tubing or braid plastic tubing.

The stylet80extends along the axis of the structure78, through the base26and catheter body lumen36, and into the handle18. In this arrangement, the stylet80is free to slide fore and aft along the axis of the catheter body12.

The proximal end of the stylet80attaches to a control knob82in the handle18(asFIG. 13shows). The control knob82moves within a groove84(seeFIGS. 13 and 14) in the handle18to impart fore and aft movement to the stylet80. Stylet movement changes the flexure of the structure78.

Forward movement of the stylet80(i.e., toward the distal end16) pushes the hub24away from the base26(seeFIG. 15). The loop structure78elongates as the spline legs22straighten and move radially inward, to the extent permitted by the resilience of the spline legs22. With the spline legs22straightened, the loop structure78presents a relatively compact profile to facilitate vascular introduction.

Rearward movement of the stylet80(i.e., toward the distal end16) pulls the hub24toward the base26(seeFIG. 16). The spline legs22bend inward in the vicinity of the hub24, while the remainder of the splines, constrained by the base, distend. The loop structure78bows radially out to assume what can be called a “heart” shape.

When the structure78is positioned within the atrium88of a heart in the condition shown inFIG. 16, the stylet80compresses the spline legs22, making them expand or bow radially. The expansion presses the distended midportion of the spline legs22(and the electrode elements28they carry) symmetrically against opposite walls86of the atrium88. The symmetric expansion of the outwardly bowed spline legs22presses the opposite atrial walls86apart (asFIG. 16shows), as the radial dimension of the loop structure78expands to span the atrium88.

The symmetric expansion presses the electrode elements28into intimate surface contact against the endocardium. The symmetric expansion stabilizes the position of the loop structure78within the atrium88. The resilience of the spline legs22, further compressed by the pulled-back stylet80, maintains intimate contact between the electrode elements28and atrial tissue, without trauma, as the heart expands and contracts.

AsFIGS. 17 to 19show, the push-pull stylet80can also be used in association with a half-loop structure90, like that previously shown and discussed inFIG. 7.

In this arrangement, pushing the stylet80forward (asFIG. 18shows) elongates the half-loop structure90for vascular introduction. Pulling the stylet80rearward (asFIG. 19shows) bows the single spline leg22of the structure outward, expanding it so that more secure contact can be achieved against the atrial wall86, or wherever tissue contact is desired.2. Curvilinear Loop Structures

FIGS. 20 and 21show a full-loop structure92that includes a center stylet94, which can be flexed. The flexing of the center stylet94bends the spline legs22in a second direction different than the radial direction in which they are normally flexed. In the illustrated embodiment, this second direction is generally perpendicular to the axes of the spline legs22, asFIGS. 23a/band24show, although acute bends that are not generally perpendicular can also be made. The bending of the spline legs22in this fashion makes possible the formation of long, thin curvilinear lesions using a full-loop structure92, or (as will be described later) in a half-loop structure110, as well.

The stylet94itself can be either fixed in position between the hub24and the base26, or movable along the axis of the loop structure92to extend and distend the radial dimensions of the spline legs22in the manner already described (seeFIGS. 15 and 16). In the illustrated and preferred embodiment, the stylet94slides to alter the radial dimensions of the structure.

In one implementation, asFIG. 22best shows, the stylet94is made from a metal material, for example stainless steel 17-7, Elgiloy™ material, or Nickel Titanium material. A pair of left and right steering wires, respectively96(R) and96(L) is attached to opposite side surfaces of the stylet94near the hub24, by adhesive, soldering, or by suitable mechanical means. The steering wires96(R) and96(L) are attached to the stylet side surfaces in a diametric opposite orientation that is at right angles to the radial orientation of the spline legs22relative to the stylet94.

The steering wires96(R) and96(L) extend along the stylet94, through the base26and catheter body lumen36, and into the handle18(seeFIG. 25). Preferably, asFIG. 22best shows, a tube98surrounds the stylet94and steering wires96(R) and96(L), at least along the distal, exposed part of the stylet94within the structure92, keeping them in a close relationship. The tube98can be heat shrunk to fit closely about the stylet94and steering wires96(R) and96(L).

AsFIGS. 25 and 26show, a groove100in the handle carries a control assembly102. The stylet94is attached to the control assembly102, in the manner already described with respect to the control knob82inFIGS. 13 and 14. Sliding movement of the control assembly102within the groove100imparts fore and aft movement to the stylet94, thereby distending or extending the loop structure92.

The control assembly102further includes a cam wheel104(seeFIG. 26) rotatable about an axle on the control assembly102in response to force applied to an external steering lever108. The cam wheel104holds the proximal ends of the steering wires96(R) and96(L), in the manner disclosed in Lundquist and Thompson U.S. Pat. No. 5,254,088, already discussed, which is incorporated herein by reference.

Twisting the steering lever108counterclockwise applies tension to the left steering wire96(L), bending the loop structure92to the left (asFIG. 23ashows). The electrode elements28(which inFIGS. 20 to 27comprises a continuous coil electrode34, described earlier) likewise bend to the left.

Similarly, twisting the steering lever108clockwise applies tension to the right steering wire96(R), bending the loop structure92to the right (asFIGS. 23band24show). The electrode elements28likewise bend to the right.

The bent electrode elements28, conforming to the bent spline legs22, assume different curvilinear shapes, depending upon amount of tension applied by the steering wires96(R) and96(L). When contacting tissue, the bent electrode elements28form long, thin lesions in curvilinear patterns.

In an altemative implementation, the stylet94is instead made of a malleable metal material, like annealed stainless steel. In this arrangement, before deployment in the body, the physician applies external pressure to manually bend the stylet94into a desired shape, thereby imparting a desired curvilinear shape to the electrode elements of the associated loop structure. The malleable material of the stylet94retains the preformed shape, until the associated loop structure is withdrawn from the body and sufficient external pressure is again applied by the physician to alter the stylet shape.

In addition to having a malleable stylet94, the splines22themselves can also be made of a malleable material, like annealed stainless steel, or untreated stainless steel 17-7, or untreated Nickel Titanium. In one implementation, the most distal parts of the malleable splines22are heat treated to maintain their shape and not collapse during introduction and deployment in the vascular system. This will also give the overall structure greater stiffness for better contact with the tissue. It also gives the physician the opportunity to bend the structure to form long, thin, lesions in prescribed curvilinear patterns set by the malleable splines.

Whether flexible and remotely flexed during deployment, or malleable and manually flexed before deployment, by further adjusting the fore-and-aft position of the stylet94, the physician can also control the radial dimensions of the loop structure94in concert with controlling the curvilinear shape of the loop structure92, asFIG. 27shows. A diverse array of radial sizes and curvilinear shapes is thereby available.

AsFIG. 28shows, a half-loop structure110can also include a fixed or movable stylet94with steering wires96(R) and96(L). The use of the same handle-mounted control assembly102/rotatable cam104assembly shown inFIGS. 25 and 26in association with the half-loop structure110makes possible the creation of diverse curvilinear shapes of variable radii. Alternatively, a malleable stylet94and malleable splines can be used.3. Loop Structures with Movable Spline Legs

FIGS. 29 to 35show a full-loop structure112in which only one spline leg114is attached to the base26. The fixed spline leg114is preformed with resilient memory to assume a curve of a selected maximum radius (shown inFIG. 33). The other spline leg116, located diametrically opposed to the fixed spline leg114, extends through the base26and catheter body lumen36(seeFIGS. 30aand30b) into the handle18. The spline leg116slides fore and aft with respect to the base26. Movement of the spline leg116changes the flexure of the structure112.

The full-loop structure112shown inFIGS. 29 to 35need not include a hub24like that shown inFIGS. 1 and 3, and, in addition, need not incorporate a detented integral loop body42like that shown inFIG. 2. Any single full-loop structure without a center stiffener or stylet, like the structure112inFIG. 29, can comprise a single length of wire bent back upon itself and preformed with resilient memory to form the desired full loop shape. For the same reason, the single full-loop structure20shown inFIG. 1can, in an alternative construction, be made without a hub24and a detented loop body42, and instead employ a preshaped doubled-back wire to form a loop, like the structure20.

FIG. 30bshows an alternative way of securing the fixed spline leg114to the distal end16of the catheter tube12, without using a base26. In this embodiment, the free end of the fixed spline leg114lies against the interior of the tube12. The leg114passes through a slit115formed in the catheter tube12. The leg114is bent back upon itself in a u-shape to lie against the exterior of the tube12, wedging the tube12within the u-shape bend117. A sleeve119is heat shrunk about the exterior of the tube12over the region where the u-shape bend117of the spline leg114lies, securing it to the tube12. Alternatively, a metallic ring (not shown) can be used to secure the spline leg114to the tube12. The movable spline leg116and wires58pass through the interior bore36of the catheter tube12, as before described.

The proximal end of the spline leg116(seeFIG. 29) is attached to a movable control knob82carried in a groove84on the handle18, like that shown inFIG. 13. Movement of the control knob82within the groove84thereby imparts fore-and-aft movement to the spline leg116.

In the illustrated embodiment, the fixed spline leg114carries electrode elements28in the manner already described. The movable spline leg116is free of electrode elements28. Still, it should be appreciated that the movable spline leg116could carry one or more electrode elements28, too.

AsFIGS. 31 to 33show, moving the control knob82forward slides the movable spline leg116outward, and vice versa. The movable spline leg116applies a counter force against the resilient memory of the fixed spline leg114, changing the flexure and shape of the loop structure112for vascular introduction and deployment in contact with tissue. By pulling the movable spline leg116inward (asFIG. 31shows), the counter force contracts the radius of curvature of the fixed spline leg114against its resilient memory. Pushing the movable spline leg116outward (asFIGS. 32 and 33show) allows the resilient memory of the fixed spline leg114to expand the radius of curvature until the selected maximum radius is achieved. The counter force applied changes the flexure and shapes the fixed spline leg114and the electrode elements28it carries to establish and maintain more secure, intimate contact against atrial tissue.

The magnitude (designated V inFIGS. 31 to 33) of the counter force, and the resulting flexure and shape of the loop structure112, varies according to extent of outward extension of the movable spline leg116. Pulling the movable spline leg116progressively inward (thereby shortening its exposed length) (asFIG. 31shows) contracts the loop structure112, lessening its diameter and directing the counter force progressively toward the distal end of the structure. Pushing the movable spline leg116progressively outward (thereby lengthening its exposed length) (asFIGS. 32 and 33show) progressively expands the loop structure112in response to the resilient memory of the fixed spline leg114, increasing its diameter and directing the counter force progressively away from the distal end of the structure.

AsFIGS. 34 and 35show, by manipulating the movable spline leg116, the physician can adjust the flexure and shape of the loop structure112within the atrium88from one that fails to make sufficient surface contact between the electrode element28and the atrial wall86(asFIG. 34shows) to one that creates an extended region of surface contact with the atrial wall86(asFIG. 35shows).

FIGS. 36 to 38show a full-loop structure118in which each spline leg120and122is independently movable fore and aft with respect to the base26. In the illustrated embodiment, both spline legs120and122carry electrode elements28in the manner already described.

In this arrangement, the handle18includes two independently operable, sliding control knobs124and126(shown diagrammatically inFIGS. 36 to 38), each one attached to a movable spline leg120/122, to impart independent movement to the spline legs120/122(as shown by arrows inFIGS. 36 to 38). Each spline leg120/122is preformed with resilient memory to achieve a desired radius of curvature, thereby imparting a resilient curvature or shape to the full-loop structure118itself. Coordinated opposed movement of both spline legs120/122(asFIGS. 37 and 38show) using the control knobs124/126allows the physician to elongate the curvature of the loop structure118into more of an oval shape, compared to more circular loop structures112formed using a single movable leg116, asFIGS. 31 to 33show.

FIGS. 39aand39bshow an alternative full-loop structure128having one spline leg130that is fixed to the base26and another spline leg132, located diametrically opposed to the fixed spline130, that is movable fore and aft with respect to the base26in the manner already described. The movable spline leg132can carry electrode elements28(asFIG. 39ashows), or be free of electrode elements, depending upon the preference of the physician.

In the structure shown inFIGS. 39aand39b, the fixed spline leg130branches in its midportion to form a smaller, secondary full-loop structure134that carries electrode elements28. In the embodiment shown inFIGS. 39aand39b, the secondary loop structure134lies in a plane that is generally perpendicular to the plane of the main full-loop structure128.

The smaller, secondary full-loop structure134makes possible the formation of annular or circumferential lesion patterns encircling, for example, accessory pathways, atrial appendages, and the pulmonary vein within the heart. In the illustrated embodiment, the movable spline leg132compresses the secondary full-loop structure134, urging and maintaining it in intimate contact with the targeted tissue area.

FIGS. 39aand39btherefore show a compound flexible support for electrode elements. While the primary support structure128and the secondary support structure134are shown as full loops, it should be appreciated that other arcuate or non-arcuate shapes can be incorporated into a compound structure. The compound primary structure128integrated with a secondary structure134need not include a movable spline leg, or, if desired, both spline legs can be movable. Furthermore, a center stylet to contract and distend the main structure128can also be incorporated, with or without a stylet steering mechanism.

FIGS. 40aand40bshow a modified full-loop structure216having an odd number of spline legs218,220, and222. The structure216includes two spline legs218and220that, in the illustrated embodiment, are fixed to the base26about 120° apart from each other. AsFIG. 40bshows, the base26is generally like that shown inFIG. 6b, with the slotted anchor63in which the near ends of the legs218and220are doubled back and wedged. The structure216also includes a third spline leg222that, in the illustrated embodiment, is spaced about 120° from the fixed spline legs218/220. AsFIG. 40bshows, the near end of the third spline leg222is not attached to the base26, but passes through the inner lumen226into the lumen36of the catheter tube12. The third spline leg222is thereby movable fore and aft with respect to the base26in the manner already described. Alternatively, all spline legs218,220, and222can be fixed to the base26, or more than one spline leg can be made moveable.

A hub24like that shown inFIGS. 3 and 4includes circumferentially spaced slots56to accommodate the attachment of the three splines218,220, and222.

The fixed splines218and220carry electrode elements28(asFIG. 40ashows), while the movable spline22is free of electrode elements. AsFIG. 40bshow, the wires58coupled to the electrode elements28pass through the anchor lumen226for transit through the catheter tube bore36. The orientation of the fixed splines218and220relative to the movable spline222thereby presents an ablation loop224, like the secondary loop structure134shown inFIGS. 39a/b, that lies in a plane that is generally transverse of the plane of the movable spline222. Of course, other orientations of an odd number of three or more spline legs can be used.

The movable spline leg222extends and compresses the secondary structure134to urge and maintain it in intimate contact with the targeted tissue area. Of course, a center stylet to further contract and distend the ablation loop224can also be incorporated, with or without a stylet steering mechanism.4. Bifurcated Loop Structures

FIGS. 41,42, and43show a variation of a loop structure, which will be called a bifurcated full-loop structure136. The structure136(seeFIG. 41) includes two oppositely spaced splines legs138and140, each carrying one or more electrode elements28. The near end of each spline leg138/140is attached to the base26. The far end of each spline leg138/140is attached a stylet142and144. Each spline leg138/140is preformed with resilient memory to achieve a desired maximum radius of curvature (whichFIG. 41shows).

The spline leg stylets142/144are joined through a junction146to a common control stylet148. The common control stylet148passes through the catheter body lumen36to a suitable slidable control knob150in the handle18, as already described. By sliding, the control knob150moves the control stylet148to change the flexure of the spline legs138/140.

When the control stylet148is fully withdrawn, asFIG. 41shows, the junction146is located near the base26of the structure136, and the spline legs138/140assume their preformed maximum radii of curvatures. The spline legs138/140form individual half-loop structures (like shown inFIG. 7) that together emulate a full-loop structure (like that shown inFIG. 1), except for the presence of a connecting, distal hub24.

Forward movement of the control stylet148first moves the junction146within the confines of the structure136, asFIG. 42shows. The forward movement of the control stylet148is translated by the spline leg stylets142/144to urge the spline legs138/140apart. The distal end of the bifurcated structure136opens like a clam shell.

As the spline legs138/140separate, they distend. The control stylet150thus compresses the splines legs138/140to press them into contact with the tissue area along opposite sides of the structure136. In this way, the bifurcated structure136emulates the full-loop structure78, when distended (asFIG. 16shows).

Continued forward movement of the control stylet150(asFIG. 43shows) moves the junction146and attached spline leg stylets142/146out beyond the confines of the structure136. This continued forward movement extends the spline legs136/140, while moving them radially inward. This, in effect, collapses the bifurcated structure136into a relatively low profile configuration for vascular introduction. In this way, the bifurcated structure136emulates the full-loop structure78, when elongated (asFIG. 15shows).

FIGS. 44 and 45show an alternative embodiment of a bifurcated full-loop structure152. The structure152includes two oppositely spaced spline legs154/156, each carrying one or more electrode elements28, like the structure136shown inFIGS. 41 to 43. Each spline leg154/156is preformed with a resilient memory to assume a desired maximum radius of curvature (whichFIG. 44shows).

Unlike the structure136shown inFIGS. 41 to 43, the structure152shown inFIGS. 44 and 45fixes both ends of the spline legs154/156to the base26. The spline legs154/156thereby form stationary, side-by-side half-loop structures, each with an inner portion158and an outer portion160. Together, the stationary half-loop structures create the bifurcated full-loop structure152.

In this arrangement, a center stylet162is attached to a ring164that commonly encircles the inner portions158of the spline legs154/156along the center of the structure152. Movement of the stylet162slides the ring164along the inner leg portions158. The stylet162passes through the catheter body lumen36to a suitable control in the handle (not shown), as already described.

Forward movement of the ring164(asFIG. 45shows) jointly extends the spline legs154/156, creating a low profile for vascular introduction. Rearward movement of the ring164(asFIG. 44shows) allows the resilient memory of the preformed spline legs154/156to bow the legs154/156outward into the desired loop shape.

FIG. 46shows another alternative embodiment of a bifurcated full-loop structure166. This structure166has two oppositely spaced spline legs168and170, each carrying one or more electrode elements28. Each spline leg168/170is preformed with a resilient memory to assume a maximum radius of curvature (whichFIG. 46shows).

The near end of each spline leg168/170is attached to the base26. The far end of each spline leg168/170is individually attached to its own stylet172/174. Instead of joining a common junction (as in the structure136shown inFIGS. 41 to 43), the spline stylets172/174of the structure166individually pass through the catheter body lumen36to suitable control knobs (not shown) in the handle18. Like the embodiment shown inFIGS. 44 and 45, a third stylet176is attached to a ring178that encircles the spline stylets172and174. The third stylet176passes through the guide tube lumen36to its own suitable control knob (not shown) in the handle18.

The embodiment shown inFIG. 46allows the physician to move the ring178up and down along the spline stylets172and174to shape and change the flexure of the structure166in the manner shown inFIGS. 44 and 45. Independent of this, the physician can also individually move the spline stylets172and174to further shape and change the flexure of each spline leg168and170, as in the case of the movable spline legs120/122shown inFIGS. 36 to 38. This structure166thus gives the physician latitude in shaping the loop structure to achieve the desired contact with the atrial wall.

Another alternative embodiment of a bifurcated full-loop structure180is shown inFIGS. 47 to 49. In this embodiment, the structure180includes two oppositely spaced spline legs182and184, each carrying one or more electrode elements28. Each spline leg182/184is preformed with a resilient memory to assume a desired maximum radius of curvature (whichFIG. 49shows).

The inner portion186of each spline leg182/184is attached to the base26. A stationary ring190encircles the inner portions186near the distal end of the structure180, holding them together.

The outer portion188of each spline leg182/184is free of attachment to the base26and is resiliently biased away from the base26. Each outer portion188is individually attached to its own stylet192and194. The spline stylets192and194individually pass through the catheter body lumen36to suitable control knobs (not shown) in the handle18.

Pulling the spline legs stylets192/194rearward pulls the outer portion188of the attached spline leg182/184radially toward the base26, against their resilient memories, creating a low profile suitable for vascular access (asFIG. 47shows). Pushing the spline stylets192/194forward pushes the outer portion188of the attached spline leg182/184, aided by the resilient memory of the spline leg182/184, outward (asFIGS. 48 and 49show). The spline stylets192/194can be manipulated together or individually to achieve the shape and flexure desired.5. Loop Support Structures for Movable Electrodes

FIGS. 50 and 51show a full-loop structure196which supports a movable ablation element198. The structure196includes a pair of spline legs200secured at their distal ends to the hub24and at their proximal ends to the base26, in the manner described in association with the structure shown inFIG. 1. A center stiffener202extends between the base26and the hub24to lend further strength.

The ablation element198(seeFIG. 52) comprises a core body204made of an electrically insulating material. The body204includes a central lumen206, through which one of the spline legs200passes. The core body204slides along the spline leg200(as shown by arrows inFIGS. 50 to 52).

In the illustrated and preferred embodiment (seeFIG. 52), a coil electrode element34(as already described) is wound about the core body204. Alternatively, the core body204can be coated with an electrically conducting material or have an electrically conducting metal band fastened to ft. As shown inFIG. 53, the ablation element can also comprise a composite structure198(1) (seeFIG. 53) of two bi-polar electrodes208separated by an electrically insulating material210. The core body204of the electrode can range in diameter from 3 Fr to 8 Fr and in length from 3 mm to 10 mm.

A guide sire212is attached to at least one end of the ablation electrode198(seeFIGS. 50 and 52). The guide wire212extends from the handle18through the catheter body lumen36, along the center stiffener202and through the hub24for attachment to the ablation element198. A signal wire214also extends in common along the guide wire212(seeFIG. 52) to supply ablation energy to the electrode198. The proximal end of the guide wire212is attached to a suitable control knob (not shown) in the handle18. Movement of the guide wire212forward pushes the ablation element198along the spline leg200from the distal end of the structure196to the proximal end.

Two guide wires (212and213) may be used (asFIG. 52shows), which are attached to opposite ends of the ablation element198. Pulling on one guide wire212advances the electrode198toward the distal end of the structure196, while pulling on the other guide wire213advances the electrode198in the opposite direction toward the proximal end of the structure196. In an alternative implementation (not shown), the distal tip of a second catheter body can be detachably coupled either magnetically or mechanically to the movable electrode198. In this implementation, the physician manipulates the distal end of the second catheter body into attachment with the electrode198, and then uses the second catheter body to drag the electrode198along the structure196.

In use (asFIG. 54shows), once satisfactory contact has been established with the atrial wall86, sliding the ablation electrode198along the spline leg200while applying ablation energy creates a long and thin lesion pattern. The ablation can be accomplished by either moving the electrode198sequentially to closely spaced locations and making a single lesion at each location, or by making one continuous lesion by dragging the electrode198along the tissue while ablating.

One or both spline legs200can also be movable with respect to the base, as before described, to assure intimate contact between the ablation element198and the endocardium.6. Bundled Loop Structures

The assembly of bundled, independently adjustable loop structures to form a dynamic three dimensional electrode support structure228, like that shown inFIGS. 55 to 58, are also possible.

The structure228shown inFIGS. 55 to 58comprises four spline legs (designated L1, L2, L3, and L4) circumferentially spaced ninety degrees apart. Each spline leg L1, L2, L3, and L4is generally like that shown inFIG. 29. Each leg L1, L2, L3, and L4is preformed with resilient memory to assume a curve of selected maximum radius. In the illustrated embodiment, each leg L1to L4carries at least one electrode element28, although one or more of the legs L1to L4could be free of electrode elements28.

The outer portions230of each spline leg L1to L4are attached to the structure base26. AsFIG. 61shows, the base26is similar to that shown inFIG. 30b, having an outer ring236and a concentric slotted inner element238, through which the near ends of the outer spline leg portions230extend. The near ends are doubled back upon themselves and wedged in the space240between the outer ring236and inner element238, as earlier shown inFIG. 6b.

The inner portions232of each spline leg L1, L2, L3, and L4are not attached to the base26. They pass through lumens242in the inner element238of the base26(seeFIG. 61) and into catheter body lumen36for individual attachment to control knobs234on the handle18(seeFIG. 55). Wires58associated with the electrode elements28carried by each leg L1to L4pass through other lumens244in the inner element238(seeFIG. 61).

The inner portion232of each spline leg L1to L4is independently movable, in the same way as the spline leg shown inFIGS. 31 to 35. By manipulating the control knobs234, the physician can change the normal flexure of the structure228(whichFIGS. 55 and 56show) to a new flexure (whichFIGS. 57 and 58show), by altering the shape each spline leg L1to L4independent of each other. AsFIGS. 57 and 58show, the inner portion232of leg L4has been pulled aft, compressing the associated loop. The inner portion232of leg L2has been pushed forward, expanding the associated loop.

AsFIGS. 59a/band60a/bshow, by selective manipulation of the movable inner portions232of the spline legs L1to L4, the physician can adjust the shape of the three dimensional loop structure228within the atrium88from one that fails to make sufficient surface contact between the electrode element28and the atrial wall86(asFIGS. 59a/bshow) to one that expands the atrium88and creates an extended region of surface contact with the atrial wall86(asFIGS. 60a/60bshow). The physician can thereby tailor the shape of the three dimensional structure228to the particular physiology of the patient.

In an alternative arrangement, the inner portions232of the spline legs L1to L4can be fixed to the base26and the outer portions230made free to move in the manner shown inFIGS. 47 to 49.

It should be now be apparent that one or more movable spline legs can be used in association with a movable center stylet to provide control of the shape and flexure of the ablation element. The further inclusion of steering wires on the movable stylet, or the use of a malleable stylet and/or malleable spline legs adds the ability to form curvilinear lesion patterns.

It is thereby possible to combine in a single loop support structure one or more movable spline legs (asFIGS. 31 to 38show), a movable center stylet (asFIGS. 13 to 19show), and a stylet steering assembly or malleable stylet/splines (asFIGS. 20 to 28show). Such a structure is capable of creating a diverse number of shapes and contact forces to reliably achieve the type and degree of contact desired between the ablation elements and the targeted tissue area, despite physiologic differences among patients.

It should also be appreciated that the inventions discussed in this section are applicable for use in tissue ablation applications that are not catheter-based. For example, any of the loop structures like those described herein can be mounted at the end of hand-held probe for direct placement by the physician in contact with a targeted tissue area. For example, a hand held loop structure carrying multiple electrodes can be manipulated by a physician to ablate tissue during open heart surgery for mitral valve replacement.

As illustrated for example inFIGS. 62 and 63, a surgical device (or “probe”)250for positioning an operative element252within a patient includes a relatively short shaft254and a bendable spline assembly256, associated with the distal end of the shaft, for supporting the operative element. Here, the operative element252is in the form of a plurality of electrode elements294, as discussed in greater detail in Section III below. Preferably, the relatively short shaft may be between approximately 4 and 18 inches in length, and is preferably 8 inches in long, while the outer diameter of the shaft is preferably between approximately 6 and 24 French. The spline assembly256has a predetermined use configuration. In the exemplary embodiment shown inFIGS. 62 and 63, the spline assembly includes a pair of spline legs258and260and an annular member262which supports the operative element252. The surgical device also includes a tubular member264(a cylindrically shaped sheath in the exemplary embodiment) which covers a portion of the shaft254and is also slidable relative thereto. The spline assembly256is adapted to collapse (the insertion configuration) in response to movement of the substantially tubular member264in the distal direction and to expand to the predetermined use configuration when the substantially tubular member is moved in the proximal direction. A handle266may be provided on the proximal end of the shaft254. The tubular member264preferably includes a raised gripping surface268.

Another exemplary surgical device (or “probe”) for positioning an operative element within a patient, which is generally represented by reference numeral270, is illustrated inFIGS. 64a-65. Here, the surgical device includes a substantially triangularly shaped spline assembly272that consists of first and second side legs274and276and a distal leg278. The distal leg278, which is preferably non-linear from end to end and approximately 10 to 12 cm in length, includes first and second linear portions280and282and a bent portion284located mid-way between the ends. This spline configuration provides a spring force against the selected bodily surface during use (such as the atrium wall in a cardiac procedure) and the bend in the distal leg278optimizes the contact between the operative element252and the selected surface. The spline assembly272will collapse in the manner shown inFIG. 65when the tubular member264is advanced thereover and will return to the orientation shown inFIG. 64awhen the tubular member is retracted. The surgical device270also includes a second handle267.

During use of the exemplary surgical device shown inFIGS. 62–65, the handle266(FIG. 62) or267(FIG. 64a) is grasped by the physician and force is applied through the shaft254and side legs258and260(FIG. 62) or274and276(FIG. 64a) to the operative element supporting annular member262(FIG. 62) or distal leg278(FIG. 64a). Thus, the shaft and side legs (including the area where the side legs meet) should be sufficiently strong to prevent collapse when the force is applied. The fact that the present devices are not passed through a tortured vascular path to the site of interest allows the shaft and spline legs to be stiffer than a conventional catheter shaft. This aspect of the invention is discussed in greater detail below. Alternatively, the shaft254and side legs274and276in the embodiment shown inFIGS. 64aand65may be configured such that they collapse and form a semicircle with the distal leg278when force is applied to the shaft (noteFIG. 64b). Here, the operative element should be appropriately masked in one of the manners described below to limit contact of the operative element to the intended bodily structure.

As shown by way of example inFIG. 66, a guidewire286may be used to direct and/or anchor the distal leg278of the exemplary spline assembly272in an anatomical anchor site (such as one of the pulmonary veins shown inFIG. 66). The guidewire286passes through a lumen in the shaft254. The distal end of the guidewire286passes through a lumen288formed in one of the spline assembly side legs274and276, while the proximal end is secured to a handle290. Alternatively, two guide wires (one passing through each of the side legs) may be used to anchor the spline assembly272in two anatomical anchor sites. Both wires would extend to the same handle.

The exemplary embodiments illustrated inFIGS. 62–66may also be provided without the tubular member264. Such devices are especially useful in surgical procedures associated with a thoracotomy or a median sternotomy, where the spline assemblies can be easily collapsed and advanced to the desired location, or advanced into the desired location without being collapsed. Here, the spline assemblies can be malleable, if desired, as opposed to simply being bendable.

Turning toFIGS. 67aand67b, an endoscope292may be passed through one lumen in a tubular member264′ that has a pair of lumens. Alternatively, the shaft254and endoscope292can pass through a common lumen.

The spline assemblies illustrated inFIGS. 62–66are preferably made from resilient, inert wire, like nickel titanium (commercially available as Nitinol material) or 17-7 stainless steel. However, resilient injection molded inert plastic can also be used. The wire or molded plastic is covered by suitable biocompatible thermoplastic or elastomeric material such as PEBAX® or Pellethane®. Preferably, the various portions of the spline assemblies comprises a thin, rectilinear strips of resilient metal or plastic material. Still, other cross-sectional and longitudinal configurations can be used. For example, the spline legs can decrease in cross-sectional area in a distal direction, by varying, e.g., thickness or width or diameter (if round), to provide variable stiffness along its length. Variable stiffness can also be imparted by composition changes in materials or by different material processing techniques. Referring more specifically to the embodiments illustrated inFIGS. 64a–66, the distal leg278may be configured such that the leg is flat at the distal end, but becomes more semicircular in cross-section as the leg becomes more proximal in order to taper the stiffness profile and prevent lateral movement of the spline assembly. The curvature of the spline legs may also be varied and the lateral ends of the distal leg may be reinforced in order to provide more lateral stability.

As shown by way of example inFIGS. 70a–70e, the spline assembly of the probe shown inFIGS. 64aand65may be replaced by a curved spline assembly300. Here, the spline assembly includes a flat, inert wire302(preferably formed from Nitinol) that acts as a spring and an outer portion304(preferably formed from PEBAX® or Pellethane®). Viewed in cross-section, the flat wire302has a long side and a short side. The short sides lie in planes that are parallel to the plane shown inFIG. 70d. As such, the spline assembly300will deflect in the manner shown inFIGS. 70band70cwhen “in plane” forces F are applied to the spline assembly. Conversely, the assembly will resist bending when “out of plane” forces are applied in the manner shown inFIG. 70d. As such, it may be used to form an arcuate lesion during, for example, a procedure where a lesion is formed around the pulmonary vein.

It should be noted here that the wire302does not have to be rectangular in cross-section as shown. Other cross-sectional shapes where the length is greater than the width can also be used. The wire302can also be made from a malleable material such as partially or fully annealed stainless steel instead of the spring-like material discussed above. The malleable embodiments will enable the operator to form fit the ablation element support structure to irregular anatomical structures.

As shown inFIG. 70f, exemplary spline assembly300′ includes first and second steering wires301aand301bthat are secured to the spring-like flat wire302by, for example, welding, mechanical crimping or adhesive bonding. The proximal ends of the steering wires301aand301bare operably connected to a knob303on a handle266′ by way of a cam (not shown). The handle266′ is substantially similar to the handle266shown inFIG. 62, but for the knob303, cam and provisions for the steering wires301aand301b. Rotation of the knob303will cause the spline assembly to move side to side in, for example, the manner illustrated inFIG. 70c. Thus, in addition to simply moving the handle, the physician will be able to move the operative element252within the patient by rotating the knob303. Such movement is useful when the physician is attempting to precisely locate the operative element within the patient and/or control the contact force between the operative element and the tissue surface. This is especially true when the handle and or shaft254cannot be moved, due to anatomical or surgical constraints.

In the exemplary embodiment, the steering wires301aand301bare both secured at about the midpoint of the flat wire loop. Other configurations are possible depending on the configuration of the loop that is desired after the knob303is rotated. For example, one wire could be secured closer to the top of the loop than the other. The shape of the cam may also be varied. More detailed discussions of the use of steering wires, albeit in conventional catheter settings, can be found in commonly assigned U.S. Pat. Nos. 5,195,968, 5,257,451, and 5,582,609, which are incorporated herein by reference.

The shaft254is preferably relatively stiff. As used herein the phrase “relatively stiff” means that the shaft (or other structural element) is either rigid, malleable, or somewhat flexible. A rigid shaft cannot be bent. A malleable shaft is a shaft that can be readily bent by the physician to a desired shape, without springing back when released, so that it will remain in that shape during the surgical procedure. Thus, the stiffness of a malleable shaft must be low enough to allow the shaft to be bent, but high enough to resist bending when the forces associated with a surgical procedure are applied to the shaft. A somewhat flexible shaft will bend and spring back when released. However, the force required to bend the shaft must be substantial. Rigid and somewhat flexible shafts are preferably formed from stainless steel, while malleable shafts are formed from annealed stainless steel.

One method of quantifying the flexibility of a shaft, be it shafts in accordance with the present inventions or the shafts of conventional catheters, is to look at the deflection of the shaft when one end is fixed in cantilever fashion and a force normal to the longitudinal axis of the shaft is applied somewhere between the ends. Such deflection (σ) is expressed as follows:
σ=WX2(3L−X)/6EI
where:

W is the force applied normal to the longitudinal axis of the shaft,

L is the length of the shaft,

X is the distance between the fixed end of the shaft and the applied force,

E is the modulous of elasticity, and

I is the moment of inertia of the shaft.

When the force is applied to the free end of the shaft, deflection can be expressed as follows:
σ=WL3/3EI
Assuming that W and L are equal when comparing different shafts, the respective E and I values will determine how much the shafts will bend. In other words, the stiffness of a shaft is a function of the product of E and I. This product is referred to herein as the “bending modulus.” E is a property of the material that forms the shaft, while I is a function of shaft geometry, wall thickness, etc. Therefore, a shaft formed from relatively soft material can have the same bending modulus as a shaft formed from relatively hard material, if the moment of inertia of the softer shaft is sufficiently greater than that of the harder shaft.

For example, a relatively stiff 2 inch shaft (either malleable or somewhat flexible) would have a bending modulus of at least approximately 1 lb.-in.2Preferably, a relatively stiff 2 inch shaft will have a bending modulus of between approximately 3 lb.-in.2and approximately 50 lb.-in.2. By comparison, 2 inch piece of a conventional catheter shaft, which must be flexible enough to travel through veins, typically has bending modulus between approximately 0.1 lb.-in.2and approximately 0.3 lb.-in.2. It should be noted that the bending modulus ranges discussed here are primarily associated with initial deflection. In other words, the bending modulus ranges are based on the amount of force, applied at and normal to the free end of the longitudinal axis of the cantilevered shaft, that is needed to produce 1 inch of deflection from an at rest (or no deflection) position.

As noted above, the deflection of a shaft depends on the composition of the shaft as well as its moment of inertia. The shaft could be made of elastic material, plastic material, elasto-plastic material or a combination thereof. By designing the shaft254to be relatively stiff (and preferably malleable), the surgical tool is better adapted to the constraints encountered during the surgical procedure. The force required to bend a relatively stiff 2 inch long shaft should be in the range of approximately 1.5 lbs. to approximately 12 lbs. By comparison, the force required to bend a 2 inch piece of conventional catheter shaft should be between approximately 0.2 lb. to 0.25 lb. Again, such force values concern the amount of force, applied at and normal to the free end of the longitudinal axis of the cantilevered shaft, that is needed to produce 1 inch of deflection from an at rest (or no deflection) position.

Ductile materials are preferable in many applications because such materials can deform plastically before failure due to fracturing. Materials are classified as either ductile or brittle, based upon the percentage of elongation when the fracture occurs. A material with more than 5 percent elongation prior to fracture is generally considered ductile, while a material with less than 5 percent elongation prior to fracture is generally considered brittle. Material ductility can be based on a comparison of the cross sectional area at fracture relative to the original cross area. This characteristic is not dependent on the elastic properties of the material.

Alternatively, the shaft could be a mechanical component similar to shielded (metal spiral wind jacket) conduit or flexible Loc-Line®, which is a linear set of interlocking ball and socket linkages that can have a center lumen. These would be hinge-like segmented sections linearly assembled to make the shaft.

The exemplary tubular member264illustrated inFIGS. 62–67bis preferably in the form of a relatively thin cylindrical sheath (e.g., with a wall thickness of about 0.005 inch) and has an outer diameter which is preferably less than 0.180 inch. The sheath material is preferably also lubricious, to reduce friction during movement of the sheath relative to the shaft254and spline assemblies256and272. For example, materials made from polytetrafluoroethylene (PTFE) can be used for the sheath. The distal end of the sheath should be relatively flexible to prevent injury. If necessary, additional stiffness can be imparted to the remaining portion of the sheath by lining the sheath with a braided material coated with PEBAX® material (comprising polyethel block amide related to nylon). Other compositions made from PTFE braided with a stiff outer layer and other lubricious materials can be used.

Alternatively, the tubular member264may be relatively stiff and formed from the materials described above with respect to the shaft254.

As shown by way of example inFIG. 71a, a surgical probe308in accordance with another embodiment of this invention includes a relatively stiff shaft310, a handle312and a distal section314. The shaft310consists of a hypo-tube316, which is either rigid or relatively stiff, and an outer polymer tubing318over the hypo-tube. A relatively stiff tube, either malleable or somewhat flexible, will preferably have a bending modulus of between approximately 3 lb.-in.2and approximately 50 lb.-in.2. The handle312is similar to the handle266discussed above in that it includes a PC board320for connecting the operative elements on the distal portion of the probe to a power source. The handle312preferably consists of two molded handle halves and is also provided with strain relief element322. An operative element254(here, in the form of a plurality of electrode elements294) is provided on the distal section314. This embodiment is particularly useful because it can be easily inserted into the patient through an introducing port such as a trocar.

The handle312shown inFIG. 71ais intended to be used in a conventional power supply configuration, wherein power transmission from an RF generator (or other energy source) to the electrodes294is controlled by a foot switch. As shown by way of example inFIG. 71d, and in accordance with one embodiment of a present invention, a handle312′ is provided with a manually operable on-off switch313. On-off switch313allows the physician to selectively enable and disable the supply of RF ablation energy (and other types of power) to the electrode(s) on the distal portion of the probe.

In addition to the global on-off switch313, the exemplary handle312″ shown inFIG. 71ealso includes a plurality of individual on-off switches315for each of the electrodes. The individual on-off switches315allow the physician to selectively control the supply of power to individual electrodes. The exemplary handle312″, which has seven individual on-off switches315, is preferably used in a probe having seven electrodes. If for example, the physician intends to ablate tissue with only three of the electrodes, then the three chosen electrodes may be enabled by way of the corresponding switches315prior to placing the global on-off switch313in the “on” position.

A plurality of indicator elements317are also provided on the exemplary handle312″ shown inFIG. 71e. Preferably, there is one indicator element317for each of the on-off switches315. In the illustrated embodiment, the indicator elements317are in the form of buttons that are raised when a corresponding on-off switch315is depressed. This provides the physician with a tactile as well as visual indication of the on-off status of the switches315. The indicator elements317may also be in the form of indicator lights. Sound-based indications of the on-off status of the switches315may also be used. For example, a speaker on the handle or the power supply device may be employed to periodically indicate which of the switches315are in the “on” position.

In accordance with another aspect of the present inventions, a probe may be configured such that the handle is re-usable and the remaining portions of the probe are disposable or separately re-usable. Turning toFIGS. 71fand71g, exemplary handle312″ includes an edge-type connector having a first portion319on the handle and a second portion321on the remaining portion of the probe. In the illustrated embodiment, the remaining portion is primarily the shaft310which, as described above, supports a plurality of electrode elements (not shown).

The first and second connector portions319and321have elements that will mechanically couple the handle to the remaining portion of the probe and release the two when desired. The first and second connector portions will also connect signal wires from the electrodes (or other operative elements) and temperature sensors to the energy source. A locking mechanism (not shown) may be used to maintain the integrity of the connection between the two connector portions. A cable323may be provided to connect the handle to an energy source.

The handles shown inFIGS. 71e–71gmay be used with any of the probes disclosed herein and the features of such handles may be incorporated into any of the other handles disclosed herein.

As shown by way of example inFIGS. 71hand71i, and in accordance with one embodiment of a present invention, a remote power control unit325may be used in conjunction with a surgical probe308or a catheter (not shown). The remote power control unit325includes a main body327aand a plurality of on/off switches327b. Preferably, there is one on/off switch327bfor each electrode and, in the illustrated embodiment, there are seven electrodes and seven on/off switches. The remote power control unit can also include a global power on/off switch (not shown). Alternatively, a foot pedal (not shown) may be provided to perform the same function.

The size and shape of the remote power control unit325allow it to be easily grasped in one hand by the physician or other member of the operating room staff. Preferably, the remote power control unit325is about 8 inches in length, about 1.5 inches in width and about 0.5 inches in thickness. Of course, the size and shape can be adjusted to suit particular needs.

The remote power control unit325may be used in conjunction with conventional electrophysiology power control units, such as that shown in U.S. Pat. No. 5,545,193, that are connected to a source of energy (such as ablation energy) and provide individual electrode control. To facilitate such use, the remote control device includes a connection apparatus which, in the illustrated embodiment, consists of a cable329aand a connector329b. The cable329ashould be relatively long, i.e. between about 6 feet and about 15 feet in length and is preferably 10 feet. The connection apparatus can also be in the form of a wireless transmitter/receiver arrangement or any other suitable device. The surgical probe308is also connected to the electrophysiology power control unit. When a foot pedal is used, it too is connected to the electrophysiology power control unit.

The exemplary remote power control unit325includes indicia333in the shape of the distal portion of a surgical probe, indicator lights335, and numbers corresponding to the respective electrodes on the probe. The combination of indicia, lights and numbers allows the physician to readily determine which electrodes are enabled and which electrodes are disabled.

The surgical probe308(as well as the other probes disclosed herein) and the remote power control unit325are sterilizable. To that end, these devices are either entirely hermetically sealed or selected portions, such as those enclosing electronic components, are sealed. Those components which are not sealed are penetrable by a gas sterilant, such as ethylene oxide (EtO). The surgical probes and remote power control units should also be splash-proof.

In those instances where a malleable shaft310is desired, the hypo-tube316may be the heat treated malleable hypo-tube316shown inFIGS. 71a,73and74. By selectively heat treating certain portions of the hypo-tube, one section of the hypo-tube (preferably the distal section) can be made more malleable than the other. This will alleviate any discontinuity between the distal section314and the shaft310when the distal section is malleable.

A plurality of temperature sensing elements (such as thermocouples which are not shown) may be located on, under, abutting the longitudinal end edger of, or in between, the electrode elements294in any of the exemplary devices disclosed herein. Additionally, a reference temperature sensing element may be provided. For example, a reference temperature sensing324may be located in the handle so that room temperature will be used as the reference as shown inFIG. 71a. The reference temperature sensor may, alternatively, be provided on or near the distal tip of the device. Another alternative is to use an electronic circuit to function as the reference temperature sensor. A reference temperature sensor can also be placed on the patient or in the operating room and the physician can simply input the reference temperature into the power control device. It should be noted that the accuracy of the reference temperature sensor is less important in applications where the patient is on bypass because the convective cooling effects of blood flowing past the electrodes is substantially reduced. Also, the present surgical devices provide better tissue contact than conventional catheter-based devices, which provides more accurate temperature monitoring.

The distal section314can be either somewhat flexible, in that it will conform to a surface against which it is pressed and then spring back to its original shape when removed from the surface or, as noted above, malleable. A bending modulus of between 3 lb.-in.2and 50 lb.-in.2is preferred. As shown by way of example inFIG. 72a, a somewhat flexible distal section314may include a spring member330, which is preferably either a solid flat wire spring (as shown), a round wire, or a three leaf flat wire Nitinol spring, that is connected to the distal end of the hypo-tube316. Other spring members, formed from materials such as 17-7 or carpenter's steel, may also be used. A series of lead wires332and334connect the electrode elements294and temperature sensor elements, respectively, to the PC board320. The spring member330and leads wires332and334are enclosed in a flexible body336, preferably formed from PEBAX® material, polyurethane, or other suitable materials. The spring member330may also be pre-stressed so that the distal tip is pre-bent in the manner shown inFIG. 71a. Also, an insulating sleeve331may be placed between the spring member330and the lead wires332and334.

In those instances where a malleable distal portion314is desired, the spring member330may be replaced by a mandrel337made of suitably malleable material such as annealed stainless steel or beryllium copper, as illustrated for example inFIG. 72b. The mandrel will ideally be fixed to the distal tip of the device (by, for example, soldering, spot welding or adhesives) and run through the shaft into the handle where it will also be fixed to insure good torque transmission and stability of the distal tip. Alternatively, the malleable mandrel may be fixed directly within the distal end of the shaft's hypo-tube316and secured by, for example, soldering, spot welding or adhesives.

Alternatively, and as shown by way of example inFIG. 72c, a slot339may be formed in the hypotube316′. The malleable mandrel337is inserted into the slot339and then held in place by spot welds341(shown), solder or adhesive. The slot339includes an opening341at one end thereof through which the mandrel337extends. The slot339could also include another opening at the other end. The slot339is located in spaced relation to the proximal end of the hypotube316′ to create additional support for the mandrel337when it is bent and formed into various shapes. By shortening the length of the mandrel337, the torque of the shaped distal assembly is increased relative to the embodiment described above wherein the mandrel is anchored within the handle.

The distal portion314may also be formed by a hypo-tube that is simply a continuation of the shaft hypo-tube316. However, the distal end hypo-tube can be a separate element connected to the shaft hypo-tube316, if it is desired that the distal end hypo-tube have different stiffness (or bending) properties than the shaft hypo-tube.

The shaft310may be from 4 inches to 18 inches in length and is preferably 6 to 8 inches. The distal portion314may be from 1 inch to 10 inches in length and is preferably 2 to 3 inches. To facilitate the formation of long continuous lesions, the distal portion314preferably includes six spaced electrode elements294that are approximately 12 mm in length. The number and length of the electrode elements294can, of course, be varied to suit particular applications.

In accordance with some embodiments of this invention, and as shown by way of example inFIGS. 71band71c, the distal section314may be provided with a distal (or tip) electrode. Referring first toFIG. 71b, the distal electrode326may be a solid electrode with a through hole for one or more temperature sensors. Another exemplary electrode is the shell electrode328shown inFIG. 71c, which could also have one or more temperature sensors inside. The distal electrodes have a variety of applications. For example, a distal electrode may be dragged along an anatomical surface to create a long lesion. The distal electrode may also be used to touch up lesions (straight or curvilinear) created by electrode elements294if, for example, the distal section314does not exactly conform to the anatomical surface, and to continue lesions formed by the electrode elements. The distal electrode may also be used to create lesions in anatomical ridges that are shaped such that the integrity of the surgical device would be compromised if the distal section314were bent to conform to the ridge.

As shown by way of example inFIG. 74, an exemplary surgical probe340is provided with a pull wire342that allows the physician to adjust the curvature of the distal portion314from no curve, to a slight curve, an extreme curve, or even a loop, as desired. The pull wire distal portion344is connected to the distal tip of distal section314. The distal portion of the pull wire enters the shaft proximal to the ablation electrodes, and the proximal portion346exits through an aperture formed in the handle312. But for the pull wire342, the probe340is substantially the same as the spring tip probe version shown inFIGS. 71aand72a. Alternatively, the proximal portion of the pull wire342may be associated with a handle/knob arrangement such as that shown inFIG. 70f.

In accordance with another embodiment of this invention, and as illustrated for example inFIGS. 75 and 76, a surgical probe348is provided with a distal loop structure350that includes an operative element252in the form of a plurality of electrodes294. The distal loop structure350, which extends through an opening352in a sheath354, is connected to a shaft356. The shaft is, in turn, connected to the handle312. The proximal portion of the sheath354includes a handle358that allows the sheath to be moved distally and proximally. The stiffness of the loop structure350is less than that of the sheath354. As such, when the sheath354is pulled in the proximal direction, the loop structure350will bulge out of the sheath opening352in the manner shown inFIG. 75. When the sheath354is returned to its distal most position, the loop structure350will slide back into the sheath such that the sheath and the loop structure are coaxial.

The exemplary loop structure350is similar to the distal portion314of the probe shown inFIGS. 71aand72ain that it includes a spring member (not shown), such as a leaf spring or a flat wire spring (preferably formed from Nitinol), which is covered by a flexible material such as a PEBAX® tube359. In addition to allowing the distal portion350to bulge outwardly, the spring member can be flat so that it also provides resilience which helps the distal portion conform to the anatomical surface of interest and prevents “out of plane bending.”

In the exemplary embodiment illustrated inFIGS. 75 and 76, a pivot assembly360is provided on the distal end of the sheath354. The pivot assembly360includes a base member362and a pivot member364which is secured to the base member by a pivot pin366. Referring more specifically toFIG. 76, the pivot member364pivots within a slot368that is formed in the base member362. The size and shape of the slot368, and the location of the pivot member364therein, may be adjusted to adjust the shape of the loop. For example, the location of the pivot member364and the shape and size of the slot368may be varied such that the pivot member can only rotate 30, 60, 90 or 180°. However, up to 270° of rotation is possible. The pivot member364includes a connector372(such as the illustrated threaded or barbed connector) for securing the distal end of the loop structure350to the pivot member.

The rigidity, malleability, or flexibility of the probe348may be provided in a number of ways. For example, the sheath354may be formed from a rigid stainless steel hypo-tube, a relatively stiff somewhat flexible stainless steel hypotube, or a relatively stiff malleable annealed stainless steel hypo-tube. Additionally, or alternatively, the shaft356may be a rigid (or somewhat flexible) stainless steel hypo-tube or a malleable annealed stainless steel hypo-tube. In either case, the distal end374of the shaft356will abut the flexible portion of the loop structure350. Other materials can, of course, be used in place of stainless steel. A rigid high durometer plastic tube, for example, may be substituted for the stainless steel hypo-tube in the sheath or shaft.

Once the sheath354and shaft356are positioned relative to one another such that the desired loop is produced, the sheath may be secured to the shaft by a touhy borst connector376that is secured to the distal end of the sheath354between the handle358and the handle312.

An ablation probe378in accordance with another aspect of this invention is illustrated, for example, inFIG. 77. The probe includes a shaft380(similar to shafts254,310or356described above) on which one or more ablation electrodes294are mounted. As described in greater detail in Section III below, masking296may be used to control the focus of the ablation energy and/or prevent convective cooling when the probe is in the blood pool. A handle266is also provided. The shaft380is preferably between approximately 4 and 16 inches in length, between approximately 3 and 8 mm in diameter. Additionally, the shaft may either be rigid or relatively stiff and, if relatively stiff, can be either malleable or somewhat flexible. The ablation probe378may be used for a variety of procedures. For example, the shaft may be inserted into the heart to perform ablation procedures.

Turning toFIGS. 95 and 96, a pressure application probe650may be used to apply pressure to the distal section of a probe, such as the probe308shown inFIG. 71a, or any other operative element supporting device. The application of pressure with the probe650can improve the level of contact between tissue and, for example, the distal section314of the probe308. The pressure application probe650includes an elongate main body portion652and at least one engagement device654. The exemplary pressure application probe shown inFIGS. 95 and 96also includes a second engagement device658. As discussed in detail below, the second engagement device658has a slightly different shape than the engagement device654.

The main body portion652is preferably either rigid, malleable or somewhat flexible and about 4 inches to about 18 inches in length, although the length may be adjusted to suit particular applications. When a malleable main body portion is desired, the main body portion652may be formed in the manner described above with respect to the shaft254, and preferably consists of a soft metal rod or tube, or a settable plastic rod or tube. For example, the shaft254may be formed from a nickel titanium rod or tube, which is ductile at room temperature and which will straighten out at elevated temperatures such as those used during autoclave sterilization. Regardless of stiffness, the outer surface of the main body portion652should be covered with insulating material such as PEBAX® or urethane. The engagement device654is preferably formed from insulating material such as polycarbonate, urethane, glass filled thermoplastic or ABS.

The engagement device may have any of a variety of configurations. In the exemplary embodiment illustrated inFIGS. 95 and 96, the engagement devices654and658are generally c-shaped, with engagement device658having a more open shape. In use, the c-shape helps maintain the engagement devices at the desired location on the distal portion of the surgical probe308so that pressure can be applied to the desired location. The open shape of the engagement device658allows the engagement device to be readily repositioned along the distal portion of the surgical probe without disturbing the position of the surgical probe relative to the tissue.

The c-shaped engagement device654can be coupled to the distal section314of the probe308as shown inFIG. 95, or any other probe, by either inserting the distal tip of the probe through the opening656or by snap-fitting the engagement device654over the distal section. When snap-fitting is desired, the engagement device should be somewhat flexible. This arrangement allows the pressure application probe650to be rotated relative to the probe308when the two are engaged. As a result, the pressure application probe650can be reoriented without moving the probe308. The pressure application probe650may also be used to move the probe308within the patient when the two are engaged.

As shown by way of example inFIG. 97, an exemplary pressure application probe660is provided with an engagement device662having a relatively narrow profile. The narrow profile allows the probe660to engage the distal section of an operative element supporting device, such as the distal section314of probe308, even when the two devices are oriented at severe angles relative to one another. Of course, the engagement device is not limited to the shapes shown inFIGS. 95–97. Any shape that is capable of engaging the distal portion of a probe may be used.

Although not limited to such a use, the pressure application probes shown inFIGS. 95–97are especially useful in thoroscopic procedures. Here, the pressure application probe may be inserted into a patient through one port, while the electrode supporting probe is inserted through another port and connected to the pressure application probe.

Another device which may be used in conjunction with probes such as the probe308shown inFIG. 71ais illustrated, for example, inFIG. 98. The exemplary coupling device664includes a base member666, a generally c-shaped engagement device668(similar to that described above) and, in the illustrated embodiment, a connecting member670. The base member666and engagement device668can also be directly connected to one another.

The coupling device664has a wide range of uses. For example, the coupling device may part of a pressure application probe672, as shown inFIG. 99. Another exemplary use of the coupling device664is shown inFIG. 100. Here, the coupling device664is placed on a probe such as probe308and used to create a distal loop. The coupling device can be located at different points along the length of the probe and arranged at different rotational orientations relative to the probe (note arrows674aand674b) in order to control the shape of the loop. To that end, the base member666and a portion of the distal section314can include respective sets of teeth that allow the rotational orientation of the coupling device664to be fixed relative to the probe308. Note teeth676inFIG. 101.

In order to increase the number of coupling device applications, the connecting member670may be configured in a variety of ways. For example, the connecting member670can be rigid, flexible, somewhat flexible, or malleable. The connecting member670can also be in the form of a swivel or pivot. The base member666and engagement device668can also be fixed at various angles relative to one another (note, for example,FIG. 99).

III. The Operative Elements

A. Exemplary Operative Elements

In the exemplary embodiments illustrated inFIGS. 62–77, the operative element252is made up of a plurality of electrode elements294. Electrode elements294can serve a variety of different purposes, as can electrode elements28and30(FIGS. 1–61). The operative elements252may also be lumens for chemical ablation, laser arrays, ultrasonic transducers, microwave electrodes, and D.C. hot wires, and such devices may be substituted for the electrode elements28and30.

In the illustrated embodiments, the principal use of the electrode elements is to transmit electrical energy and, more particularly, RF energy, to ablate heart tissue. However, the electrode elements can also be used to sense electrical events in heart tissue. Alternatively, or in addition, the electrode elements can serve to transmit electrical pulses to measure the impedance of heart tissue, to pace heart tissue, or to assess tissue contact using conventional pacing and sensing techniques. Once the physician establishes contact with tissue in the desired heart region, the physician applies ablating energy to the electrode elements.

In the exemplary embodiments shown inFIGS. 1–61, the electrode elements28are electrically coupled to individual wires58(seeFIG. 11a) to conduct ablating energy to them. The wires58extend along the associated spline leg22(asFIG. 11ashows), through a suitable access opening provided in the base24(for example, the anchor lumen226shown inFIG. 6b) into and through the catheter body lumen36(as generally shown inFIG. 1andFIGS. 30a/b), and into the handle18, where they are electrically coupled to external connectors38(seeFIG. 1). The connectors38plug into a source of RF ablation energy (not shown).

Turning to the exemplary embodiments illustrated inFIGS. 62–77, the electrode elements294are electrically coupled to individual wires (see reference numeral295FIGS. 69band70eand reference numeral332inFIGS. 72a,72band73) to conduct ablating energy to them. The wires are passed in conventional fashion through a lumen extending through one of the spline legs and the shaft254into a PC board in the handle266, where they are electrically coupled to a connector296which is received in a port298(seeFIG. 62). The connector296plugs into a source of RF ablation energy. A plurality of temperature sensing elements (not shown), such as theremocouples or thermistors, may also be provided on the spline assemblies shown herein. Such temperature sensing elements may be located on, under, abutting the longitudinal end edges of, or in between, the electrode elements294. For temperature control purposes, signals from the temperature sensor elements are transmitted to the source of ablation energy by way of wires (see reference numeral297inFIGS. 69band70eand reference numeral334inFIGS. 72a,72band73) which are also connected to the PC board. Suitable temperature sensor elements and controllers which control power to an electrode based on a sensed temperature are disclosed in U.S. Pat. Nos. 5,456,682 and 5,582,609, which are incorporated herein by reference. The respective numbers of wires will, of course, depend on the numbers of sensors and electrodes used in a particular application. A suitable temperature control system is described below with reference toFIGS. 89–92.

The electrode elements can be assembled in various ways. They can, for example, comprise multiple, generally rigid electrode elements arranged in a spaced apart, segmented relationship. The segmented electrodes can each comprise solid rings of conductive material, like platinum, which makes an interference fit about the annular spline member. Alternatively, the electrode segments can comprise a conductive material, like platinum-iridium or gold, coated upon the device using conventional coating techniques or an ion beam assisted deposition (IBAD) process. For better adherence, an undercoating of nickel or titanium can be applied. The electrodes can also be in the form of helical ribbons.

Alternatively, the electrode elements can comprise spaced apart lengths of closely wound, spiral coils wrapped about the device to form an array of generally flexible electrode elements. The coils are made of electrically conducting material, like copper alloy, platinum, or stainless steel, or compositions such as drawn-filled tubing (e.g. a copper core with a platinum jacket). The electrically conducting material of the coils can be further coated with platinum-iridium or gold to improve its conduction properties and biocompatibility.

Electrode elements can be formed with a conductive ink compound that is pad printed onto a non-conductive tubular body. A preferred conductive ink compound is a silver-based flexible adhesive conductive ink (polyurethane binder), however other metal-based adhesive conductive inks such as platinum-based, gold-based, copper-based, etc., may also be used to form electrodes. Such inks are more flexible than epoxy-based inks.

As illustrated for example inFIG. 68, the electrode elements can also include a porous material coating299, which transmits ablation energy through an electrified ionic medium. For example, as disclosed in U.S. application Ser. No. 08/879,343, filed Jun. 20, 1997, entitled “Surface Coatings For Catheters, Direct Contacting Diagnostic and Therapeutic Devices,” which is incorporated herein by reference, electrode elements and temperature sensor elements may be coated with regenerated cellulose, hydrogel or plastic having electrically conductive components. With respect to regenerated cellulose, the coating acts as a mechanical barrier between the surgical device components, such as electrodes, preventing ingress of blood cells, infectious agents, such as viruses and bacteria, and large biological molecules such as proteins, while providing electrical contact to the human body. The regenerated cellulose coating also acts as a biocompatible barrier between the device components and the human body, whereby the components can now be made from materials that are somewhat toxic (such as silver or copper).

For applications in which the ablation electrode is in contact with flowing blood as well as tissue, such as when the patient is not on bypass, coating electrodes with regenerated cellulose decreases the effect of convective cooling on the electrode because regenerated cellulose is a poor thermal conductor as compared to metal. Thus, the effect of convective cooling by blood flowing past the regenerated cellulose coated electrodes is diminished. This provides better control for a lesion-generating process because the hottest tissue temperature is closer to the ablation electrode.

Furthermore, the regenerated cellulose coating decreases the edge effects attributed to delivering RF energy to an electrode having a sharp transition between the conductive electrode and insulating material. The current density along the electrode and power density within tissue are more uniform, which reduces the incidence and severity of char and/or coagulum formation. The more uniform current density along the axis of the device also results in a more uniform temperature distribution at the electrode, which decreases the requirement for precise placements of the temperature sensors at the ablation electrodes. Additionally, by coating a device with regenerated cellulose to create the outer surface, less labor-intensive methods of forming electrodes and bonding wires to electrode surfaces can be used.

During the coating process, a device such as the one of the above-described distal spline assemblies is coated with a viscose solution. The viscose solution is preferably cellulose xanthate, which is a form of solubilized cellulose derivative that is dissolved in a sodium hydroxide solution. The viscose solution is dip-coated onto the distal end assembly, which includes the electrodes, signal wires, temperature sensors, etc. The coated device is then regenerated by contacting it with an acid, such as sulfuric acid, which converts the xanthate back into the cellulose structure. The term regenerated cellulose refers to cellulose which has been converted from a solubilized cellulose derivative back into a pure cellulose structure. This regeneration process creates large enough micro size pores in the coating allowing ionic transport yet small enough to prevent ingress of blood cells, infectious agents, such as viruses and bacteria, and large biological molecules such as proteins.

Once the cellulose is regenerated, it is rinsed with water to remove acid residuals and sulfur compounds. An oxidizing agent (bleach, etc.) may be added to the rinse water to accelerate the removal of sulfur compounds. After the cellulose is regenerated, it is fully cured in an environmental chamber at a low humidity. Thereafter, it is preferable to make the regenerated cellulose flexible when dry, and to do so moisture is reintroduced into the cellulose coating material by setting the environmental chamber to a higher humidity. Alternatively, a small quantity of a material such as glycerol may be applied to the coating, and the hydroscopic nature of the glycerol will hydrate the cellulose coating to create sufficient flexibility. An overall thickness range for operable regenerated cellulose coatings is from 0.001 inches to 0.015 inches, with a preferable thickness range being from 0.001 inches to 0.003 inches; a preferred thickness being approximately 0.002 inches.

Materials other than regenerated cellulose that are mechanically robust and that have suitable characteristics could be used for the coating material. Hydrophilic materials that have effective pore sizes from 500 to 500,000 Daltons with a porosity of 1–10% and which are biocompatible could be effective. Some types of hydrogels, such as those used for disposable contact lenses are good candidate materials. Plastic materials that have additives to make them semiconductive could also be used. The loaded plastic would need to have a resistivity in the range of about 200–2,000 ohm-cm, and would need to be applicable in very thin films to the device.

The thickness of the cellulose coating is controlled by the viscosity of the coating solution and the dipping rate, and a different viscosity of the coating solution can be achieved by diluting it with the sodium hydroxide solution. A variable wall thickness can be achieved by varying the extraction rate during the dipping process. The slower the extraction rate, the thinner the wall thickness, and the faster the extraction rate, the thicker the wall thickness. An increased coating wall thickness can also be obtained by multiple layers of coating. To ensure proper lamination between such layers, each layer is coagulated with a salt solution (sodium sulfate, etc.) before applying another layer. In addition, spraying and co-extruding the viscose solution over the electrodes and the distal section can also be used to achieve a variable wall thickness cellulose coating.

In another method for covering a distal electrode assembly, a tubular casing of regenerated cellulose material is created on a mandrel. The regenerated cellulose casing is then shrunk onto the distal assembly.

The regenerated cellulose coating may also be applied over a “wet” electrode element. The moisture from the wet electrode element prevents the electrode elements from sticking to tissue during an ablation procedure. A wet electrode element is formed by a material that has high absorption capacity for liquids, such as an open cell sponge, hydrogel or cloth. Alternatively, the regenerated cellulose coating may simply be wet prior to the procedure, such as an ablation procedure.

The electrode elements may be operated in a uni-polar mode, in which the ablation energy emitted by the electrode elements is returned through an indifferent patch electrode (not shown) externally attached to the skin of the patient. Alternatively, the elements may be operated in a bi-polar mode, in which ablation energy emitted by one or more electrode elements is returned through other electrode elements. The amount of power required to ablate tissue ranges from 5 to 150 w.

The electrode elements are preferably about 4 mm to about 20 mm in length. For example, the size and spacing of the electrode elements28shown inFIGS. 10 and 11a/bare well suited for creating continuous, long and curvilinear lesion patterns in tissue when ablation energy is applied simultaneously to adjacent emitting electrode elements. Continuous lesion patterns uniformly result when adjacent electrode elements are spaced no farther than about 2.5 times the electrode segment diameter apart. Further details of the formation of continuous, long and thin lesion patterns are found in co-pending U.S. application Ser. No. 08/763,169, filed Dec. 10, 1996, which is a File Wrapper Continuation of U.S. application Ser. No. 08/287,192, filed Aug. 8, 1994, entitled “Systems and Methods for Forming Elongated Lesion Patterns in Body Tissue Using Straight or Curvilinear Electrode Elements,” which is incorporated herein by reference. Similar sizing and spacing may be used in conjunction with the other embodiments illustrated herein.

Using rigid electrode segments, the length of the each electrode segment can vary from about 2 mm to about 10 mm. Using multiple rigid electrode segments longer than about 10 mm each adversely effects the overall flexibility of the element. Generally speaking, adjacent rigid electrode segments having lengths of less than about 2 mm do not consistently form the desired continuous lesion patterns.

When flexible electrode segments are used, electrode segments longer that about 10 mm in length can be used. Flexible electrode segments can be as long as 50 mm. If desired, the flexible electrode structure can extend uninterrupted along the entire length of a support spline.

The diameter of the electrode segments30or34(FIGS. 1-61) and underlying spline leg22(including the flexible sleeve32) can vary from about 2 French to about 10 French.

B. Operative Element Considerations in a Non-Convective Cooling Environment

In the exemplary embodiments shown in, for example,FIGS. 15–20,62–67a,68,70a–f,71,74and75, the electrode elements are not masked. Such embodiments are particularly useful when little to no fluid flow will be present, such as when the heart is on bypass and there is no blood flow within the heart. Here, air acts as an insulator and produces only modest convective cooling effects, as compared to a flowing blood pool that has a higher convection coefficient than virtually static air. Energy transmission is, therefore, essentially limited to the RF energy that is transmitted from the portion of the electrode surface that is in contact with the tissue to either a ground electrode, or another electrode within the group of electrode elements. The overall impedance of the system will increase (as compared to a situation where blood is present) due to the smaller effective surface area between the electrode and tissue.

Both of these conditions, focused RF energy and low heat dissipation into the air, will impact the ablation because they result in a high current density with high local desposition of heat without the heat sinking that convective cooling provides. When creating long lesions with a conventional catheter, char can be created as the tip is dragged because of the high current density and the difficulty in monitoring tissue temperature and controlling power that is inherent in the dragging process. The present invention, however, can take advantage of the high current density because the electrodes are not being dragged. For example, a number of electrodes can be used to ablate simultaneously because the effective (tissue contacting) surface area between all of the ablating electrodes is smaller and the convective cooling effects are reduced, as compared to situations where blood is present. This reduces the power requirements of the system. In addition, by using electrodes with lower thermal mass (as compared to a conventional solid tip electrode), less heat will be retained by the electrode and better temperature sensing can be made at the tissue surface. This will speed up the creation of the lesions and enable better lesion creation control.

It is also noteworthy that the masking described in the following section can be useful during bypass because tissue can partially wrap around the electrodes when the distal end of the device is pressed against the tissue. Such masking can also be used to control lesion thickness.

C. Operative Element Considerations in a Convective Cooling Environment

In instances where the patient will not be on bypass and blood will be flowing past the electrodes, or in other situations when fluid flow is present, the portion of the electrode elements (or other operative elements) not intended to contact tissue may be masked through a variety of techniques with a material that is preferably electrically and thermally insulating. For example, a layer of UV adhesive (or another adhesive) may be painted on preselected portions of the electrode elements to insulate the portions of the elements not intended to contact tissue. Alternatively, a slotted sheath may be positioned over the portion of the electrode elements not intended to contact tissue. Deposition techniques may also be implemented to position a conductive surface only on those portions of the spline assembly intended to contact tissue. A coating may be formed by dipping the electrode elements in polytetrafluoroethylene (PTFE) material.

For example, asFIGS. 10 and 11bshow, the side of the ablation elements28that, in use, is exposed to the blood pool may be covered with a coating48of an electrically and thermally insulating material. The coating48prevents the transmission of ablating energy directly into the blood pool. Instead, the coating48directs the applied ablating energy directly toward and into the tissue.

As shown by way of example inFIG. 69a, a polymer layer296may be thermally fused over the electrodes294to mask desired portions of the electrodes. An exemplary process for applying the polymer layer is as follows. A segment of shaft tubing is cut long enough to cover the desired electrodes, and is then split in half (or other desired angle) along the axis. One half is placed over the assembled distal section so that it covers the side of the electrodes that are to be masked. A piece of polymeric shrink tubing, preferably RNF-100 or irradiated LDPE, is then carefully slid over the catheter distal end, so that the mask tubing is not moved from its placement over the electrodes and so that it stops approximately 2 cm beyond the end of the tubing half. The distal end is then heated in a controlled heat source at approximately 400° F. so that the mask tubing fuses into the distal shaft tubing along its length, and so that all of its edges are well fused into the shaft tubing, but not fused so much that the covered electrodes begin to poke through. Finally, the polymeric shrink tubing is split on one end and the assembly is heated at approximately 225° F. while the polymeric shrink tubing is slowly peeled off of the fused catheter shaft.

Additionally, as illustrated inFIG. 69b, the shape of an electrode294′ may be such that the metallic material in the region not intended to contact tissue is eliminated.

The masking techniques described in the preceding paragraphs improve the efficiency of, for example, an ablation procedure by decreasing the surface area of the electrodes and, therefore, the energy required to heat tissue. The masking can be used to form a narrow electrode which is sometimes desirable, even when the patient will be on bypass. The convective cooling effects of blood flowing by the electrode are also reduced. In addition, the transmission of RF energy to unintended anatomic structures is prevented. This is especially important in epicardial applications when the ablation electrode elements may be sandwiched between multiple anatomic structures including, for example, the aorta and pulmonary artery. The masking techniques also focus the application of ablating energy to helps to control the characteristics of the lesion.

IV. Epicardial Applications of Probe-Type Apparatus

The inventions described above (primarily those discussed above with reference toFIGS. 71a–75) may be used in a variety of epicardial procedures. One such procedure is a maze-like ablation procedure to prevent atrial fibrillation. A thoracostomy, which is a surgical procedure that is less invasive than a thoracotomy or median sternotomy, may be used to gain access to the atrium. Here, relatively small incisions are created in the intercostal space. At each of the incisions, a trocar may be used to provide a port to access the thoracic cavity. These ports may be used for visualization with fiberoptic cameras, ultrasound, or other visualization devices, as well as for the surgical devices that ablate tissue. The surgical devices may be, for example, inserted through the ports located on the left side of the patient which provide direct access to the left atrium. The devices may then be used to create long, thin, curvilinear lesions or annular lesions on the epicardial surface. If necessary, lung lobes may be deflated during the procedure by inserting an endotracheal tube that inflates the right lung only. The left lung will collapse when the chest is opened.

There is also a high prevalence of atrial fibrillation substrates proximate to the pulmonary veins. Lesions may be created on the epicardial surface around pulmonary veins or between pulmonary veins. There is, however, some difficulty associated with epicardial access due to the presence of fatty deposits in the pulmonary vein region. The devices described above can create lesions on the epicardial surface proximate to the pulmonary veins because they can penetrate through fatty deposits and exert enough force against the epicardial surface to compress the remaining fat to such an extent that the ablation electrodes contact the epicardium. It is, however, very difficult to achieve suitable contact between the tissue and the electrodes. Thus, it is preferable to perform endocardial ablation around or between pulmonary veins in the manner described below.

V. Endocardial Applications of Probe-Type Apparatus

The inventions described above may be used in a variety of endocardial procedures. To create lesions on the endocardial surface, access to the interior of the left atrium must also be obtained. To obtain thoracoscopic access to the left atrium via a thoracostomy, a cannula may be inserted through the left atrial appendage or the left atrial free wall. The preferred access point is the left atrial appendage, especially if the physician intends to isolate the left atrial appendage at the end of the procedure. More specifically, and as shown by way of example inFIGS. 93 and 94, a grabbing catheter642having movable grasping prongs644, which is described in U.S. application Ser. No. 08/880,711, filed Jun. 23, 1995, entitled “Atrial Appendage Stasis Reduction Procedures and Devices” may be used to capture, pull and stretch the appendage AP. Next, a lasso catheter646having a lasso648, which is also described in U.S. application Ser. No. 08/880,711, may be used to encircle the left atrial appendage near the base of the appendage. The grabbing catheter facilitates the positioning of the lasso at the base of the appendage by pulling the appendage through the lasso. A needle is then used to puncture the appendage wall and gain access to the left atrium. A guidewire is advanced through the needle into the left atrium. The needle is then removed, leaving the guidewire in place. An introducer/dilator combination is then advanced over the guidewire into the left atrium. Next, the lasso is then tightened around the introducer to prevent blood flow past the introducer into the distal region of the atrial appendage. The dilator is then removed, leaving the introducer as the access to the interior of the left atrium.

Instead of the lasso technique, a purse string technique may be employed wherein sutures are used to tighten the atrial appendage around the introducer.

One of the exemplary devices described above, such as those described with reference toFIGS. 1–70f, may then be inserted into the atrium with its spline collapsed. Once inside, the sheath is retracted such that the spline returns to its predetermined configuration and the ablation procedure is performed. The sheath is pushed over the spline when the ablation procedure is complete and the device is removed from the atrium. Similarly, the devices described above with reference toFIGS. 75–76may be inserted with the loop in its retracted state, while the device shown inFIG. 74may be inserted prior to pulling the wire attached to the distal tip. These devices may then be manipulated to cause the loops to form. The ablation procedure can then be performed. The devices described above with reference toFIGS. 71a–c,73and77need only be inserted to perform the procedure. The same is also true for malleable versions of the exemplary devices shown inFIGS. 62–70e.

Upon completion, the introducer is removed and the lasso tightened to isolate the left atrial appendage. The lasso may be detached from the probe and left in place to keep the appendage isolated. Where the aforementioned purse string technique is employed, the sutures may be tightened isolate the appendage. Alternatively, the appendage may be isolated in the manner described below with reference toFIG. 87.

In addition to thoracoscopic procedures, another area of cardiac treatment which will benefit from the present invention is the repair and replacement of mitral valves (which typically involves a thoracotomy, median sternotomy, or thoracostomy) because atrial fibrillation can be a complication of mitral disease which occurs prior to or subsequent to mitral valve surgery. More specifically, incisional reentry can develop subsequent to surgical procedures (such as mitral valve and thoracoscopic procedures) where an incision is made in the atrial wall that is subsequently closed by either sutures, mechanical closures, or other similar devices. Creating a lesion from the incision to the mitral valve annulus (or other anatomic barrier) will reduce the potential for reentrant propagation around the incision and, therefore, will terminate atrial fibrillation and/or prevent atrial fibrillation from developing. For example, if the left atrial appendage is used to access the interior of the left atrium for devices that create lesions on the endocardial surface, an additional lesion should be created from this access site to the mitral valve annulus so that incisional reentry will not develop when the incision is closed. This additional procedure is also applicable for right atrial procedures using incisions to access the interior of the atrium.

There is also a high prevalence of atrial fibrillation substrates proximate to the pulmonary veins. The creation of long, curvilinear lesions between pulmonary veins, around single pulmonary veins, and/or from pulmonary veins to the mitral valve annulus will prevent atrial fibrillation. The exemplary device illustratedFIGS. 62 and 63, which has an annular electrode assembly, is especially well suited for positioning ablation electrodes around the inside of a pulmonary vein. Alternatively, lesions may be created on the epicardial surface around pulmonary veins or between pulmonary veins. There is, however, some difficulty associated with epicardial access due to the presence of fatty deposits in the pulmonary vein region.

VI. Other Surgical Applications

A surgical method in accordance with a present invention may be used to reduce the level of bleeding during surgical procedures. The method generally comprises the steps of coagulating (or ablating) tissue to a predetermined depth and then forming an incision in the coagulated tissue. The coagulation can be accomplished by applying RF energy with, for example, the probe shown inFIG. 71a. Because the tissue is coagulated, the incision will not result in bleeding.

One exemplary procedure employing the present method is the removal of a diseased liver lobe. This a relatively time consuming procedure and, using conventional surgical techniques, there is a significant risk of serious bleeding. In accordance with one embodiment of the present invention, tissue in the lobe is coagulated to a depth of approximately 3 mm to 7 mm using RF energy. The coagulated tissue is then cut and separated with a scalpel, electro-surgical device, or other suitable instrument. To avoid bleeding, the depth of the cut should not exceed the depth of the coagulated tissue. The process of coagulating tissue and then forming an incision in the coagulated tissue can be repeated until the incision reaches the desired depth. Here, each coagulation and incision cycle will take approximately 90 seconds, 60 seconds to perform the coagulation and 30 seconds to perform the incision.

The present surgical technique is, of course, applicable to surgical procedures in addition to the removal of a liver lobe. Such procedures may, for example, involve the spleen, the kidneys, other areas of the liver, the heart, skeletal muscle, the lungs (such as a pulmonary lobotomy) and the brain. The present technique is also useful in oncological surgical procedures because cancerous tumors tend to be highly vascularized. One exemplary oncological procedure is the de-bulking of a cancerous tumor.

A surgical tool set in accordance with a present invention includes, among the other tools needed for a particular procedure, a device for coagulating soft tissue and a cutting the tissue. Suitable devices for coagulating soft tissue are illustrated for example, inFIGS. 62–88and95–101with respect to the probe shown inFIGS. 71fand71g, the portion of the probe which includes the second connector portion321, the shaft310and a plurality of electrode elements can be included in the tool set with or without the handle312″. As noted above, scalpels, electro-surgical devices and other suitable instruments may be used to cut tissue. Preferably, the tool set is housed in a sterile package that has a flat rigid bottom portion and a top transparent top cover that provides recesses for the tools, thereby providing a ready to use surgical kit. The bottom portion may be formed from Tyvek® spun bonded plastic fibers, or other suitable materials, which allow the contents of the package to be sterilized after the tools are sealed within the package.

VlI. Apparatus that Apply a Clamping Force

In accordance with another of the present inventions, and as shown by way of example inFIGS. 78–80, a clamp382includes a pair of clamp members384and386, which are pivotably secured to one another by a pin388, and an operative element252that may be of the type discussed above in Section III. Here, the operative element consists of a plurality of ablation electrodes294. The clamp382also includes a pair of locking members390and392and an electrical connector394that may be used to, for example, connect the electrodes294to a source RF energy. Referring more specifically toFIG. 80, the clamp382may also, if desired, be curved over its length. Of course, the overall shape of the clamp will depend upon the procedure for which it is intended.

Certain procedures require the application of a clamping force to the bodily structure of interest in addition to the operation performed by the operative element. One such procedure is the isolation of an atrial appendage, which is discussed in greater detail below with reference toFIG. 87. As illustrated for example inFIG. 81, a suitable surgical device396for use in such a procedure includes a handle398having a pair of handle members400and402which are movable relative to one another. In the exemplary embodiment, the handle members are pivotably secured to one another by a pin404and include respective openings406and408. The handle398, which is actuated in a manner similar to scissors, is operably connected to a pair of support members410and412by, for example, a suitable mechanical linkage located within a housing414. Actuation of the handle398causes the support members410and412to move relative to one another to create a clamping force. Of course, other types of handles that can cause movement of the support members may also be used.

An operative element252, is associated with one or both (as shown) of the support members410and412. Preferably, the operative element consists of one or more electrode elements294suitable for ablation (such as those discussed in detail in Section III above and operable in either the uni-polar or bi-polar mode) on each of the support members410and412. Of course, the operative element252may also consist in whole or in part of other types of electrodes, such as a hot tip to cauterize appendage walls. The electrode elements294(or other operative element) may be connected to a control/power source surgical device by way of a connector416. Wires extend from the electrode elements294through lumens in the support members410and412and handle398to the connector416.

Turning toFIG. 82, surgical device418is similar to that shown inFIG. 81except that handle398is not connected to the operative element support members410and412by a mechanical linkage. Instead, the handle member420and support member422form an integral unit as do the handle member424and support member426. The integral units are pivotably secured to one another by a pin428. Thus, while the embodiment shown inFIG. 81is especially useful in situations where thoracostomy is used, the embodiment shown inFIG. 82is especially useful for thoracotomy or median sternotomy access. In either case, the atrial appendage (or other bodily structure) is captured (or clamped) such that it is perpendicular to the surgical device.

As shown by way of example inFIGS. 83 and 84, the operative element support members432and434in exemplary surgical device430are secured to the distal ends of the handle members436and438, respectively, such that the support members are perpendicular to the handle members. Although the handle members436and438are respectively secured to the middle portion of the support members432and434(viewed longitudinally as shown inFIG. 84), the support members may be offset in one direction or the other to suit particular needs (noteFIG. 84a). Additionally, as illustrated for example inFIGS. 85aand85b, the support members (432′ and432″) may also be curved, or L-shaped with the angle θ between about 90° and about 180°. The preferred embodiments shown inFIGS. 83–85bhold the bodily structure such that it is parallel to the surgical device.

The exemplary embodiments shown inFIGS. 83–85bmay be provided with a holding device that is used to grasp a bodily structure and pull the structure in the proximal direction. As illustrated for example inFIG. 86, the holding device440includes a cylindrical member442that is biased in the proximal direction by a spring444. A pair of clamping jaws446extend outwardly from the distal end of the cylindrical member442. The clamping jaws446, which pivot relative to one another, are connected to a rod448which passes through the cylindrical member442and slides relative thereto. The rod448is biased in the proximal direction by a spring450which, in turn, biases the clamping jaws446in the proximal direction against the distal end of the cylindrical member442. As such, the clamping jaws446are biased to their closed position and the jaws may be loosened by pushing the rod448in the distal direction.

VII. Applications of Apparatus that Apply a Clamping Force

The exemplary clamp382shown inFIGS. 78–80can both isolate a bodily structure and deliver the therapeutic and/or diagnostic effects of the operative element252. In an atrial appendage isolation procedure, for example, the clamp382may be used to capture the atrial appendage and isolate it from the interior of the atrium. RF energy may then be delivered via the electrodes294(in either the uni-polar mode or the bi-polar mode) to fuse the walls of the atrial appendage to one another. Thereafter, the clamp may either be removed, or disconnected from the RF energy source and left in place.

Turning toFIG. 87, one exemplary use of the surgical device396shown inFIG. 81is the isolation of an atrial appendage. Here, the device is inserted into an opening of the chest wall. The atrial appendage is captured between the support members410and412by actuating the handle398. RF energy is then transmitted, either from the electrodes294on one support member to the electrodes on the other (bi-polar mode) or from the electrodes to an indifferent reference electrode on, for example, a patch (uni-polar mode) to thermally fuse the walls of the atrial appendage together and isolate the atrial appendage. The surgical device shown inFIGS. 82–87may be used in similar fashion.

As shown by way of example inFIG. 88, the operative element (such as, for example, electrodes294) may be offset from one side or the other of the support members452and454. This offset configuration, which may be used in conjunction with any of the exemplary devices shown inFIGS. 81–86, is especially useful in an atrial appendage isolation procedure. Here, the electrodes294are offset from the side of the support members452and454that is proximate to the interior of the left atrium. By making the portions of the support members that do not support the electrodes insulative, and by directing the RF energy towards the side of the appendage (or other structure) isolated by the clamping force, coagulum or thrombus due to heating static blood will develop in the portion of the appendage that will be isolated from the blood pool when the side walls fuse to one another. Of course, when the patient is in bypass, such masking is unnecessary unless it is being used to create lesions of a certain shape.

IX. Power Control

FIG. 89shows, in schematic form, a representative system500for applying ablating energy by multiple emitters based, at least in part, upon local temperature conditions sensed by multiple sensing elements.

InFIG. 89, the multiple sensing elements comprise thermocouples508,509, and510individually associated with the multiple emitters of ablating energy, which comprise electrode regions501,502, and503. The system500also includes a common reference thermocouple511carried within the coupler element for exposure to the blood pool. Alternatively, other kinds of temperature sensing elements can be used, like, for example, thermistors, fluoroptic sensors, and resistive temperature sensors, in which case the reference thermocouple511would typically not be required.

The system500further includes an indifferent electrode519for operation in a uni-polar mode.

The ablating energy emitters501,502,503can comprise the rigid electrode segments previously described. Alternatively, the electrode regions501,502,503can comprise a continuous or segmented flexible electrode of wrapped wire or ribbon. It should be appreciated that the system500can be used in association with any ablating element that employs multiple, independently actuated ablating elements.

The system500includes a source517of ablating energy. InFIG. 89, the source517generates radio frequency (RF) energy. The source517is connected (through a conventional isolated output stage516) to an array of power switches514, one for each electrode region501,502, and503. A connector512(carried by the probe handle) electrically couples each electrode region501,503,503to its own power switch514and to other parts of the system500.

The system500also includes a microcontroller531coupled via an interface530to each power switch514. The microcontroller531turns a given power switch514on or off to deliver RF power from the source517individually to the electrode regions501,502, and503. The delivered RF energy flows from the respective electrode region501,502, and503, through tissue, to the indifferent electrode519, which is connected to the return path of the isolated output stage516.

The power switch514and interface530configuration can vary according to the type of ablating energy being applied.FIG. 90shows a representative implementation for applying RF ablating energy.

In this implementation, each power switch514includes an N-MOS power transistor535and a P-MOS power transistor536coupled in between the respective electrode region501,502, and503and the isolated output stage516of the power source517.

A diode533conveys the positive phase of RF ablating energy to the electrode region. A diode534conveys the negative phase of the RF ablating energy to the electrode region. Resistors537and538bias the N-MOS and P-MOS power transistors535and536in conventional fashion.

The interface530for each power switch514includes two NPN transistors539and540. The emitter of the NPN transistor539is coupled to the gate of the N-MOS power transistor535. The collector of the NPN transistor540is coupled to the gate of the P-MOS power transistor534.

The interface for each power switch514also includes a control bus543coupled to the microcontroller531. The control bus543connects each power switch514to digital ground (DGND) of the microcontroller531. The control bus543also includes a (+) power line (+5V) connected to the collector of the NPN transistor539and a (−) power line (−5V) connected to the emitter of the NPN interface transistor540.

The control bus543for each power switch514further includes an ESELline. The base of the NPN transistor539is coupled to the ESELline of the control bus543. The base of the NPN transistor540is also coupled to the ESELline of the control bus543via the Zener diode541and a resistor532. The ESELline connects to the cathode of the Zener diode541through the resistor532. The Zener diode541is selected so that the NPN transistor540turns on when ESELexceeds about 3 volts (which, for the particular embodiment shown, is logic 1).

It should be appreciated that the interface530can be designed to handle other logic level standards. In the particular embodiment, it is designed to handle conventional UTL (transistor transfer logic) levels.

The microcontroller531sets ESELof the control bus543either at logic 1 or at logic 0. At logic 1 the gate of the N-MOS transistor535is connected to (+) 5 volt line through the NPN transistors539. Similarly, the gate of the P-MOS transistor536is connected to the (−) 5 volt line through the NPN transistor540. This conditions the power transistors535and536to conduct RF voltage from the source517to the associated electrode region. The power switch514is “on.”

When the microcontroller531sets ESELat logic 0, no current flows through the NPN transistors539and540. This conditions the power transistors535and536to block the conduction of RF voltage to the associated electrode region. The power switch514is “off.”

The system500(seeFIG. 89) further includes two analog multiplexers (MUX)524and525. The multiplexers524and525receive voltage input from each thermocouple508,509,510, and511. The microcontroller531controls both multiplexers524and525to select voltage inputs from the multiple temperature sensing thermocouples508,509,510, and511.

The voltage inputs from the thermocouples508,509,510, and511are sent to front end signal conditioning electronics. The inputs are amplified by differential amplifier526, which reads the voltage differences between the copper wires of the thermocouples508/509/510and the reference thermocouple511. The voltage differences are conditioned by element527and converted to digital codes by the analog-to-digital converter528. The look-up table529converts the digital codes to temperature codes. The temperature codes are read by the microcontroller531.

The microcontroller531compares the temperature codes for each thermocouple508,509, and510to preselected criteria to generate feedback signals. The preselected criteria are inputted through a user interface532. These feedback signals control the interface power switches514via the interface530, turning the electrodes501,502, and503off and on.

The other multiplexer525connects the thermocouples508,509,510, and511selected by the microcontroller531to a temperature controller515. The temperature controller515also includes front end signal conditioning electronics, as already described with reference to elements526,527,528, and529. These electronics convert the voltage differences between the copper wires of the thermocouples508/509/510and the reference thermocouple511to temperature codes. The temperature codes are read by the controller and compared to preselected criteria to generate feedback signals. These feedback signals control the amplitude of the voltage (or current) generated by the source517for delivery to the electrodes501,502, and503.

Based upon the feedback signals of the microcontroller531and the temperature controller515, the system500distributes power to the multiple electrode regions501,502, and503to establish and maintain a uniform distribution of temperatures along the ablating element. In this way, the system500obtains safe and efficacious lesion formation using multiple emitters of ablating energy.

The system500can control the delivery of ablating energy in different ways. Representative modes will now be described.

The electrode regions501,502, and503will be symbolically designated E(J), where J represents a given electrode region (J=1 to N).

As before described, each electrode region E(J) has at least one temperature sensing element508,509, and510, which will be designated S(J,K), where J represents the electrode region and K represents the number of temperature sensing elements on each electrode region (K=1 to M).

In this mode (seeFIG. 91), the microcontroller516operates the power switch interface530to deliver RF power from the source517in multiple pulses of duty cycle 1/N.

With pulsed power delivery, the amount of power (PE(J)) conveyed to each individual electrode is as follows:
PE(J)˜AMPE(J)2×DUTYCYCLEE(J)
where:

AMPE(J)is the amplitude of the RF voltage conveyed to the electrode region E(J), and

DUTYCYCLEE(J)is the duty cycle of the pulse, expressed as follows:
DUTYCYCLEE(J)=TONE(J)/[TONE(J)+TOFFE(J)]
where:

TONE(J)is the time that the electrode region E(J) emits energy during each pulse period,

TOFFE(J)is the time that the electrode region E(J) does not emit energy during each pulse period.

The expression TONE(J)+TOFFE(J)represents the period of the pulse for each electrode region E(J).

In this mode, the microcontroller531collectively establishes duty cycle (DUTYCYCLEE(J)) of 1/N for each electrode region (N being equal to the number of electrode regions).

The microcontroller531may sequence successive power pulses to adjacent electrode regions so that the end of the duty cycle for the preceding pulse overlaps slightly with the beginning of the duty cycle for the next pulse. This overlap in pulse duty cycles assures that the source517applies power continuously, with no periods of interruption caused by open circuits during pulse switching between successive electrode regions.

In this mode, the temperature controller515makes individual adjustments to the amplitude of the RF voltage for each electrode region (AMPE(J)), thereby individually changing the power PE(J)of ablating energy conveyed during the duty cycle to each electrode region, as controlled by the microcontroller531.

In this mode, the microcontroller531cycles in successive data acquisition sample periods. During each sample period, the microcontroller531selects individual sensors S(J,K), and voltage differences are read by the controller515(through MUX525) and converted to temperature codes TEMP(J).

When there is more than one sensing element associated with a given electrode region, the controller515registers all sensed temperatures for the given electrode region and selects among these the highest sensed temperature, which constitutes TEMP(J).

In this mode, the controller515compares the temperature TEMP(J) locally sensed at each electrode E(J) during each data acquisition period to a set point temperature TEMPSETestablished by the physician. Based upon this comparison, the controller515varies the amplitude AMPE(J)of the RF voltage delivered to the electrode region E(J), while the microcontroller531maintains the DUTYCYCLEE(J)for that electrode region and all other electrode regions, to establish and maintain TEMP(J) at the set point temperature TEMPSET.

The set point temperature TEMPSETcan vary according to the judgment of the physician and empirical data. A representative set point temperature for cardiac ablation is believed to lie in the range of 40° C. to 95° C., with 70° C. being a representative preferred value.

The manner in which the controller515governs AMPE(J)can incorporate proportional control methods, proportional integral derivative (PID) control methods, or fuzzy logic control methods.

For example, using proportional control methods, if the temperature sensed by the first sensing element TEMP(1)>TEMPSET, the control signal generated by the controller515individually reduces the amplitude AMPE(1)of the RF voltage applied to the first electrode region E(1), while the microcontroller531keeps the collective duty cycle DUTYCYCLEE(1)for the first electrode region E(1) the same. If the temperature sensed by the second sensing element TEMP(2)<TEMPSET, the control signal of the controller515increases the amplitude AMPE(2)of the pulse applied to the second electrode region E(2), while the microcontroller531keeps the collective duty cycle DUTYCYCLEE(2)for the second electrode region E(2) the same as DUTYCYCLEE(1), and so on. If the temperature sensed by a given sensing element is at the set point temperature TEMPSET, no change in RF voltage amplitude is made for the associated electrode region.

The controller515continuously processes voltage difference inputs during successive data acquisition periods to individually adjust AMPE(J)at each electrode region E(J), while the microcontroller531keeps the collective duty cycle the same for all electrode regions E(J). In this way, the mode maintains a desired uniformity of temperature along the length of the ablating element.

Using a proportional integral differential (PID) control technique, the controller515takes into account not only instantaneous changes that occur in a given sample period, but also changes that have occurred in previous sample periods and the rate at which these changes are varying over time. Thus, using a PID control technique, the controller515will respond differently to a given proportionally large instantaneous difference between TEMP (J) and TEMPSET, depending upon whether the difference is getting larger or smaller, compared to previous instantaneous differences, and whether the rate at which the difference is changing since previous sample periods is increasing or decreasing.

C. Deriving Predicted Hottest Temperature

Because of the heat exchange between the tissue and the electrode region, the temperature sensing elements may not measure exactly the maximum temperature at the region. This is because the region of hottest temperature occurs beneath the surface of the tissue at a depth of about 0.5 to 2.0 mm from where the energy emitting electrode region (and the associated sensing element) contacts the tissue. If the power is applied to heat the tissue too quickly, the actual maximum tissue temperature in this subsurface region may exceed 100° C. and lead to tissue desiccation and/or micro-explosion.

FIG. 92shows an implementation of a neural network predictor600, which receives as input the temperatures sensed by multiple sensing elements S(J,K) at each electrode region, where J represents a given electrode region (J=1 to N) and K represents the number of temperature sensing elements on each electrode region (K=1 to M). The predictor600outputs a predicted temperature of the hottest tissue region TMAXPRED(t). The controller515and microcontroller531derive the amplitude and duty cycle control signals based upon TMAXPRED(t), in the same manners already described using TEMP(J).

The predictor600uses a two-layer neural network, although more hidden layers could be used. As shown inFIG. 91, the predictor600includes first and second hidden layers and four neurons, designated N(L,x), where L identifies the layer1or2and X identifies a neuron on that layer. The first layer (L=1) has three neurons (X=1 to 3), as follows N(1,1); N(1,2); and N(1,3). The second layer (L=2) comprising one output neuron (X=1), designated N(2,1).

Temperature readings from the multiple sensing elements, only two of which—TS1(n) and TS2(n)—are shown for purposes of illustration, are weighed and inputted to each neuron N(1,1); N(1,2); and N(1,3) of the first layer.FIG. 31represents the weights as WL(k,N), where L=1; k is the input sensor order; and N is the input neuron number1,2, or3of the first layer.

The output neuron N(2,1) of the second layer receives as inputs the weighted outputs of the neurons N(1,1); N(1,2); and N(1,3).FIG. 91represents the output weights as WL(O,X), where L=2; ◯ is the output neuron1,2, or3of the first layer; and X is the input neuron number of the second layer. Based upon these weighted inputs, the output neuron N(2,1) predicts TMAXPRED(t). Alternatively, a sequence of past reading samples from each sensor could be used as input. By doing this, a history term would contribute to the prediction of the hottest tissue temperature.

The predictor600must be trained on a known set of data containing the temperature of the sensing elements TS1and TS2and the temperature of the hottest region, which have been previously acquired experimentally. For example, using a back-propagation model, the predictor600can be trained to predict the known hottest temperature of the data set with the least mean square error. Once the training phase is completed the predictor600can be used to predict TMAXPRED(t).

Other types of data processing techniques can be used to derive TMAXPRED(t). See, e.g., co-pending U.S. application Ser. No. 08/801,484, filed Feb. 18, 1997, which is a File Wrapper Continuation of U.S. application Ser. No. 08/503,736, filed Jul. 18, 1995, which is a File Wrapper Continuation of U.S. application Ser. No. 08/266,934, filed Jun. 27, 1994, and entitled “Tissue Heating and Ablation Systems and Methods Using Predicted Temperature for Monitoring and Control.”

It should be noted that there are certain considerations which should be taken into account when ablation/coagulation procedures are performed with little or no fluid present. Such procedures include, for example, procedures performed during cardiac bypass. These considerations stem from the fact that the convective cooling effects associated with air are far less than that associated with blood and other fluids. In addition, the intimate physical (and thermal) contact between the electrodes and tissue will allow heat to be exchanged relatively freely therebetween.

Because the electrodes which transmit RF energy have high conductivity, they will be subjected to much less ohmic heating. However, heat will be drawn from the tissue to the electrode as RF power is applied to the tissue, which results in a time lag between hottest tissue temperature and the temperature of the electrode as well as a temperature gradient within the tissue near the tissue surface. The electrode temperature will eventually approach the tissue temperature. At this point, there will be a relatively small temperature gradient between the hottest tissue temperature and the electrode temperature, as well as relatively little heat transfer between the tissue and the electrode. Accordingly, the temperature control algorithm should take into account the time lag between the sub-surface tissue temperature and the temperature sensed at the electrode. However, the difference between the plateau tissue temperatures and the sensed temperatures can typically be disregarded.

In addition to the control considerations, the user interface should also allow the physician to indicated whether convective cooling is going to be present, thereby allowing the physician to select the proper temperature control algorithm.

The illustrated and preferred embodiments used digital processing controlled by a computer to analyze information and generate feedback signals. It should be appreciated that other logic control circuits using micro-switches, AND/OR gates, invertors, analog circuits, and the like are equivalent to the micro-processor controlled techniques shown in the preferred embodiment.

Although the present inventions have been described in terms of the preferred embodiments above, numerous modifications and/or additions to the above-described preferred embodiments would be readily apparent to one skilled in the art. It is intended that the scope of the present invention extends to all such modifications and/or additions.