Abstract:
Methods for delivering precise amounts of fluid into cardiac tissue for the purpose of facilitating ablation of the tissue along a desired lesion line. One method injects fluid through a hollow needle. The injected fluid can be a highly conductive fluid injected in conjunction with radiofrequency ablation to create an ablative virtual electrode. The injected conductive fluid can provide deeper and narrower conduction paths and resulting lesions. Radiofrequency ablation can be performed at the same time as the fluid injection, using the injection device as an electrode, or subsequent to the fluid injection, using a separate device. In some methods, the injected fluid is a protective fluid, injected to protect tissue adjacent to the desired lesion line. Fluid delivery can be endocardial, epicardial, and epicardial on a beating heart. The present methods find one use in performing maze procedures to treat atrial fibrillation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of U.S. patent application Ser. No. 10/356,868, filed on Feb. 3, 2003, now U.S. Pat. No. 7,294,143 which claims priority to U.S. provisional patent application Ser. No. 60/381,217, filed on May 16, 2002, titled DEVICE AND METHOD FOR ABLATION OF CARDIAC TISSUE, herein incorporated by reference in their entirety. The present invention is related to commonly assigned U.S. patent application Ser. No. 10/356,909, filed on Feb. 3, 2003, now U.S. Pat. No. 7,118,566, titled DEVICE AND METHOD FOR NEEDLE-LESS INTERSTITIAL INJECTION OF FLUID FOR ABLATION OF CARDIAC TISSUE. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of devices for cardiac surgery, and more specifically to devices for ablation of cardiac tissue. 
     BACKGROUND OF THE INVENTION 
     The present invention is directed toward treatment of tachyarrhythmias, which are heart rhythms in which a chamber or chambers of the heart exhibits an excessively fast rhythm. In particular, the present invention is directed toward treatment of tachycardias, which are due to the presence of ectopic foci within the cardiac tissue or due to the presence of aberrant condition pathways within the cardiac tissue. 
     There are many medical treatments that involve instances of cutting, ablating, coagulating, destroying, or otherwise changing the physiological properties of tissue. These techniques can be used beneficially to change the electrophysiological properties of tissue. For example, by ablation of cardiac tissue to cure various cardiac conditions. Normal sinus rhythm of the heart begins with the sinoatrial node (or “SA node”) generating a depolarization wave front. The impulse causes adjacent myocardial tissue cells in the atria to depolarize, which in turn causes adjacent myocardial tissue cells to depolarize. The depolarization propagates across the atria, causing the atria to contract and empty blood from the atria into the ventricles. The impulse is next delivered via the atrioventricular node (or “AV node”) and the bundle of HIS (or “HIS bundle”) to myocardial tissue cells of the ventricles. The depolarization of these cells propagates across the ventricles, causing the ventricles to contract. This conduction system results in the described, organized sequence of myocardial contraction leading to a normal heartbeat. 
     Sometimes aberrant conductive pathways develop in heart tissue, which disrupt the normal path of depolarization events. For example, anatomical obstacles in the atria or ventricles can disrupt the normal propagation of electrical impulses. 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 normal activation of the atria or ventricles. 
     The aberrant conductive pathways create abnormal; irregular, and sometimes life-threatening heart rhythms, called arrhythmias. An arrhythmia can take place in the atria, for example, as in atrial tachycardia, atrial fibrillation or atrial flutter. The arrhythmia can also take place in the ventricle, for example, as in ventricular tachycardia. 
     The lesions used to treat atrial fibrillation, are typically long and thin and are carefully placed to interrupt the conduction routes of the most common reentry circuits. More specifically, the long thin lesions are used to create a maze pattern that creates a convoluted path for electrical propagation within the left and right atria. The lesions 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-lesions finally direct the impulse to the AV node to activate the ventricles, restoring normal atrioventricular synchrony. Several surgical approaches have been developed with the intention of treating atrial fibrillation. One particular example is known as the “maze procedure,” as is disclosed by Cox, J L et al. in “The surgical treatment of atrial fibrillation. I. Summary” Thoracic and Cardiovascular Surgery 101 (3), pp. 402-405 (1991); and also by Cox, J L in “The surgical treatment of atrial fibrillation. IV. Surgical Technique”, Thoracic and Cardiovascular Surgery 101 (4), pp. 584-592 (1991), both of which are incorporated by reference herein in their entireties. In general, the “maze” procedure is designed to relieve atrial arrhythmia by restoring effective atrial systole and sinus node control through a prescribed pattern of incisions about the tissue wall. In the early clinical experiences reported, the “maze” procedure included surgical incisions in both the right and the left atrial chambers. However, more recent reports predict that the surgical “maze” procedure may be substantially efficacious when performed only in the left atrium, such as is disclosed in Sueda et al., “Simple Left Atrial Procedure for Chronic Atrial Fibrillation Associated With Mitral Valve Disease” (1996), which is incorporated herein by reference in its entirety. 
     When modifying the electrophysiological properties of cardiac tissue by ablation, or by other means of destroying tissue to create lesions, physicians must carefully place the lesions. Otherwise, tissue will be unnecessarily destroyed. In addition, the heart is in close proximity to nerves and other nervous tissue and the destruction of this tissue will result in severe harm to the patient. Anatomical methods are used to locate the areas to be ablated or otherwise modified. In other words, the physician locates key structures such as the mitral valve annulus and the pulmonary veins. Lesions are typically formed that block propagations near these structures. Additional lesions are then formed which connect these lesions and complete the so-called “maze pattern.” However, the exact lesion pattern, and number of lesions created, can vary from patient to patient. 
     The surgical “maze procedure” as performed in the left atrium generally includes forming vertical incisions from the two superior pulmonary veins and terminating in the region of the mitral valve annulus, traversing the inferior pulmonary veins en route. An additional horizontal line also connects the superior ends of the two vertical incisions. Thus, the atrial wall region bordered by the pulmonary vein ostia is isolated from the other atrial tissue. In this process, the mechanical sectioning of atrial tissue eliminates the precipitating conduction to the atrial arrhythmia by creating conduction blocks within the aberrant electrical conduction pathways. 
     Although successful at treating AF, the surgical maze procedure is quite complex and is currently performed by only a few skilled cardiac surgeons in conjunction with other open heart procedures. Tools that could reliably duplicate the Maze incisions by other means (e.g. radiofrequency, laser, microwave, ultrasound energy) will reduce the time and invasiveness required for the maze procedure and make it more accessible to more surgeons. Problems faced by these methods, however, include (a) the creation of continuous, linear lesions in the atria for the prevention of atrial fibrillation, (b) minimization of clotting and thromboembolism, (c) the effect of heat loss due to circulating blood, (d) minimization of lesion width and minimization of atrial debulking, (e) conforming to an irregular myocardial thickness, (f) adaptability to a variety of lesion geometries and (g) usefulness from either the eridocardial surface of an open heart, or the epicardial surface of a beating heart. 
     Injection of alcohol into heart tissue has also been employed to ablate cardiac tissue. Alcohol may be delivered to blood vessels supplying the tissue to be ablated, as described in “Transcoronary Chemical Ablation of Arrhythmias”, by Nellens et al, Pace Vol. 15, pages 1368-1373, September 1992. Alternatively, alcohol can be delivered directly to the tissue to be ablated by means of a needle inserted through a catheter, as described in “Chemical Ablation by Subendocardial Injection of Ethanol via Catheter—Preliminary Results in the Pig Heart”, by Weismuller et al, European Heart Journal, Volume 12, pages 1234-1239, 1991. 
     SUMMARY OF THE INVENTION 
     This invention relates to a device and method for ablation of cardiac tissue in which a hand-held instrument having a hollow needle is used to deliver precise amounts of liquids into cardiac tissue for purposes of ablation of the tissue along a desired lesion line. 
     In one aspect of the invention, a reciprocating needle device like that disclosed in U.S. Pat. No. 4,204,438, which is incorporated by reference in its entirety, is used to repeatedly penetrate cardiac tissue and deliver a cytotoxic agent to the cardiac tissue. The cytotoxic agent is used to “draw” a lesion on the myocardium by the repeated introduction of the needle and injection of cytotoxic fluid while moving the tip of the device along the desired lesion pattern. Because of the motor-driven reciprocating action of the device, the lesion pattern can be completed rapidly by the surgeon. A manually operated switch on the housing of the device is capable of energizing and de-energizing the device as desired by the operator and an eccentric drive advances and retracts the needle from the housing. The depth of needle penetration can be adjusted to control the depth at which the cytotoxic fluid is delivered to the tissue but preferably the depth of needle penetration enables the cytotoxic fluid to be injected into the tissue so that it extends through the entire thickness of the tissue. The hollow needle is filled with the cytotoxic agent. The cytotoxic fluid can be loaded into the needle a little at a time or it can be filled by means of a fluid reservoir. The delivery of the fluid can occur passively as the needle is inserted into the tissue or it can be actively injected into the tissue according to needle position. The fluid delivery can be performed endocardially, epicardially, and epicardially on a beating heart. 
     In yet another aspect of the invention, a non-reciprocating metering needle assembly like that disclosed in U.S. Pat. No. 4,719,825, which is incorporated by reference in its entirety, is use to repeatedly penetrate cardiac tissue and deliver a cytotoxic agent to the cardiac tissue. After the hollow needle has been inserted into the myocardial tissue, the device is activated by the operator to deliver a predetermined, metered amount of the cytotoxic agent into the myocardium. The needle is then withdrawn from the cardiac tissue and advanced to a second location along the desired lesion pattern where it is inserted into the myocardium and another predetermined metered amount of cytotoxic agent is dispensed into the myocardial tissue. In this manner, the device is advanced stepwise along the desired lesion line by the operator in order to complete the lesion. 
     In yet another aspect of the invention, a device as described above is utilized in combination with radiofrequency ablation. The needle can be connected to one pole of a radiofrequency generator while the other pole of the generator is connected to a large indifferent electrode. Rather than a cytotoxic agent, the needle delivers a conductive liquid such as a saline solution that creates an ablative virtual electrode when delivered into the tissue through the needle. The device is advanced along a desired lesion line on the tissue as the needle is advanced into and retracted from the tissue. Delivery of the conductive liquid and the ablative radiofrequency energy is synchronized to form the virtual electrode and ablate the tissue along the desired lesion line. 
     In yet another aspect of the invention, a device as described above is utilized in combination with a conventional radiofrequency ablation device such as the Cardioblate® pen sold by Medtronic., Inc. Rather than a cytotoxic agent, the needle delivers a conductive liquid such as a hypertonic saline solution to the tissue. The device is advanced along a desired lesion line on the tissue as the needle is advanced into and retracted from the tissue. Delivery of the conductive liquid is made into the tissue along the desired lesion line. The conductive tip of the Cardioblate pen is then drawn along the desired lesion line while applying radiofrequency energy to the tissue. The hypertonic saline solution that creates a low impedance electrical pathway to ground such that the resultant lesion is deeper and narrower than would normally result from the use of the conventional radiofrequency ablation device. 
     In yet another aspect of the invention, a device as described above is utilized in order to deliver a protective fluid in order to protect certain areas of cardiac tissue, such as tissue near vessels and valves. For example, a hypotonic fluid can be used as a protective fluid in order to increase the electrical impedance of the tissue to be protected relative to the surrounding tissues, essentially insulating the protected tissue from the electrical current of the radiofrequency ablation device. This aspect of the invention can be combined with one or more of the other aspects of the invention in which a conductive liquid is delivered to a first portion of cardiac tissue along a desired lesion line and a protective fluid is delivered to a second portion of cardiac tissue spaced apart from the desired lesion line. This can be readily accomplished by a device having a plurality of spaced-apart needles with centrally located needles delivering the conductive liquid and other needles on one or both sides of the centrally located needles which deliver the protective fluid. As the radiofrequency ablation device, such as the Cardioblate pen, is advanced along the desired lesion line a narrower and deeper lesion would result with this technique. 
     In yet another aspect of the invention, a device as described above is utilized in order to deliver an ink or dye to the cardiac tissue in order to identify the position of the lesion line on the cardiac tissue and to identify portions of tissue along the lesion line where the lesion has been completed. For example, the ink or dye can be added to the cytotoxic fluid in order to identify portions of tissue which have received the cytotoxic fluid and that those portions create a complete lesion along the desired lesion line. Alternatively, the ink or dye can be added to the conductive liquid in order to identify the portions of tissue which has been ablated by the radiofrequency energy of a virtual electrode. Again the completeness of the lesion line is indicated by the presence of the ink or dye. Alternatively, the ink or dye can be added to the conductive liquid in order to identify the position of the desired lesion line so that the Cardioblate pen or other radiofrequency ablation device can be guided along the line that has been established by the delivery of the conductive fluid. In yet another aspect, the ink or dye can be thermochromic such that it changes color when heated to a temperature which indicates that a lesion has been formed by the application of radiofrequency energy. Typically, temperatures above about 50 to 55 degrees C. are required to cause cell death in an ablative lesion made by radiofrequency ablation and the photochromic material would preferably change color in that temperature range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a prior art device suitable for use in the present invention 
         FIG. 2  is a perspective view of a prior art device suitable for use in the present invention. 
         FIG. 3  is a schematic view of a device with a reciprocating needle operating according to the invention. 
         FIG. 4  is a side sectional view of a needle delivering a fluid into tissue according to the invention. 
         FIG. 5  is a side sectional view of fluid delivered according to the invention that has diffused into tissue near its point of delivery. 
         FIG. 6  is a side sectional view showing needles delivering fluid according to the invention into tissue at varying depths. 
         FIG. 7  is a side sectional view of a needle delivering fluid according to the invention during reciprocation of the needle. 
         FIG. 8  is a side view of a distal portion of a needle showing multiple fluid openings for delivery of fluid according to the present invention. 
         FIG. 9  is a side sectional view of a lesion created by the application of radiofrequency energy according to the invention. 
         FIG. 10  is a fragmentary, schematic, side sectional view of a linear array of needles which can be used for delivering protective fluid about a delivered cytotoxic and/or conductive fluid. 
         FIG. 11  is a schematic view of the heart showing various maze lesions that can be formed according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered identically. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Several forms of the invention have been shown and described, and other forms will now be apparent to those skilled in art. It will be understood that embodiments shown in drawings and described below are merely for illustrative purposes, and are not intended to limit the scope of the invention as defined in the claims which follow. 
     This invention relates to a device and method for ablation of cardiac tissue in which a hand-held instrument having a hollow needle is used to deliver precise amounts of liquids into cardiac tissue for purposes of ablation of the tissue along a desired lesion line.  FIGS. 1 and 2  show prior art devices suitable for the practice of the present invention.  FIG. 1  shows a reciprocating needle device  1  as disclosed in U.S. Pat. No. 4,204,438. The reciprocating needle device  1  includes a motor housing  10  and a needle housing  12 . The needle housing  12  has an opening  14  through which a needle reciprocates. The device  1  may be held by hand by a surgeon and used to repeatedly penetrate cardiac tissue by a reciprocating action of the needle and deliver a cytotoxic agent to the cardiac tissue.  FIG. 2  shows a non-reciprocating metering needle device  20  like that disclosed in U.S. Pat. No. 4,719,825. The metering needle device  20  has a barrel portion  22  that can be held by hand, a tip portion  24  through which a needle  26  extends and a switch  28 . A surgeon can advance the needle  26  into myocardial tissue and then deliver a metered amount of a cytotoxic agent from the needle  26  by activating the switch  28  on the metering needle device  20 . Some tattoo pens are also believed suitable for practicing the present invention. The tattoo pens preferably provide a longer than conventional needle travel path and also provide a stronger than conventional driving force for driving the needle or needles through the longer path. 
     The cytotoxic agent is an agent which has cytotoxic properties and can be delivered as an injectable liquid or a liquid suspension. Preferably the cytotoxic substance has potent cytotoxic properties that destroys cell function without affecting protein structure and scaffolding. Also preferably, the cytotoxic agent has limited and controllable diffusion properties through extracellular spaces. Also preferably the cytotoxic agent has a fleeting effect such that the compound washes out of the systemic circulation quickly. Alkylating agents such as cytotaxan or melphalan or their active metabolites are preferred. 
     The cytotoxic agent is used to “draw” a lesion on the myocardium by the repeated introduction of the needle and injection of cytotoxic fluid while moving the tip of the device along the desired lesion pattern.  FIG. 11  shows some possible generally linear lesion patterns  110  that are capable of interrupting conductive pathways  112  and  114 . 
     Referring now to  FIGS. 3-5 , a reciprocating needle device  30  can have a reservoir  32  and a hollow, reciprocating needle  34  through which the fluid  36  can be delivered into myocardial tissue  38 . The needle  34  may be tapered to allow for easy penetration of the tissue  38  and delivery of fluid  36  into the tissue  38 . Following delivery of the fluid, the needle is withdrawn and the fluid  36  diffuses into the tissue  38 . Needles  34   a - 34   c  also represent varying depth needles included within an array or linear array of needles. The needle array can be advanced along the desired lesion path and the needles inserted together, insuring multiple fluid delivery depths along the path. Such a phased linear array of needles also can reduce the force required to enter the myocardium, relative to a constant dept array, as the time of entry into the tougher outer layer occurs at different times. 
     Referring now to  FIGS. 6-8 , the depth of penetration for needles  34   a - c  can be adjusted to control the depth at which the cytotoxic fluid  36  is delivered to the tissue  38  through injection ports or orifices  37 . The needle  34   d  can also be adjusted to deliver the cytotoxic fluid as the needle  34   d  is inserted and/or withdrawn in order to provide delivery of fluid  36  at various depths. Also, the needle may be provided with injection ports or openings  42  which will deliver fluid from a plurality of side openings or ports along the length of the needle  34   e . The delivery of the fluid can therefore occur passively as the needle is inserted into the tissue or it can be actively injected into the tissue according to needle position. 
     Referring now to  FIG. 9 , the device can also be utilized in combination with radiofrequency ablation. An ablative lesion  44  can be created in tissue  48  by a needle connected to a radiofrequency generator (not shown) as a conductive fluid  46  is delivered through the needle  49  into the tissue  48 . Rather than a cytotoxic agent, the needle delivers a conductive liquid such as a saline solution that creates an ablative virtual electrode when delivered into the tissue through the needle. The device is advanced along a desired lesion line on the tissue as the needle is advanced into and retracted from the tissue. Delivery of the conductive liquid and the ablative radiofrequency energy can be synchronized to form the virtual electrode and ablate the tissue along the desired lesion line. 
       FIG. 10  illustrates a linear array of needles  50  including an injection manifold  52 . Linear array  50  includes outer needles  54 ,  56 ,  58 , and  60 , and inner needles  62  and  64 . Inner needles  62  and  64  are fed by a first fluid delivery lumen  66  while outer needles  54 - 60  are fed by a second fluid delivery lumen  68 . The inner needles can deliver a conductive and/or cytotoxic fluid, while the outer needles can deliver a protective fluid, described below. 
     Referring now to  FIG. 11 , some possible generally linear lesion patterns  110  are shown that are capable of interrupting conductive pathways  112  and  114 . The lesion patterns can be made as described above or in combination with a conventional radiofrequency ablation device such as the Cardioblate pen sold by Medtronic, Inc. (not shown). Rather than a cytotoxic agent, the needle delivers a conductive liquid such as a hypertonic saline solution to the tissue. The device is advanced along a desired lesion line  110  on the tissue as the needle is advanced into and retracted from the tissue. Delivery of the conductive liquid is made into the tissue along the desired lesion line  110 . The conductive tip of the Cardioblate pen is then drawn along the desired lesion line  110  while applying radiofrequency energy to the tissue. The hypertonic saline solution that creates a low impedance electrical pathway to ground such that the resultant lesion is deeper and narrower than would normally result from the use of the conventional radiofrequency ablation device. 
     A protective fluid can also be used when making the linear lesions  110  in order to protect certain areas of cardiac tissue, such as tissue near vessels and valves like the pulmonary veins  116 . For example, a hypotonic fluid can be used as a protective fluid in order to increase the electrical impedance of the tissue to be protected relative to the surrounding tissues, essentially insulating the protected tissue from the electrical current of the radiofrequency ablation device. Alternatively, the protective fluid can be a thermally protective fluid such as a chilled fluid which protects tissue adjacent to the intended lesion from being overheated. This aspect of the invention can be combined with one or more of the other aspects of the invention in which a conductive liquid is delivered to a first portion of cardiac tissue along a desired lesion line and a protective fluid is delivered to a second portion of cardiac tissue spaced apart from the desired lesion line. This can be readily accomplished by a device having a plurality of spaced-apart needles with centrally located needles delivering the conductive liquid and other needles on one or both sides of the centrally located needles which deliver the protective fluid, as discussed with respect to  FIG. 10 . As the radiofrequency ablation device, such as the Cardioblate pen, is advanced along the desired lesion line a narrower and deeper lesion would result with this technique. 
     Also, the device as described above can be utilized in order to deliver an ink or dye to the cardiac tissue in order to identify the position of the lesion line  110  on the cardiac tissue and to identify portions of tissue along the lesion line  110  where the lesion has been completed. For example, the ink or dye can be added to the cytotoxic fluid in order to identify portions of tissue which have received the cytotoxic fluid and that those portions create a complete lesion along the desired lesion line. Alternatively, the ink or dye can be added to the conductive liquid in order to identify the portions of tissue which has been ablated by the radiofrequency energy of a virtual electrode. Again the completeness of the lesion line is indicated by the presence of the ink or dye. Alternatively, the ink or dye can be added to the conductive liquid in order to identify the position of the desired lesion line so that the Cardioblate pen or other radiofrequency ablation device can be guided along the line that has been established by the delivery of the conductive fluid. Dyes such as those used for tattoos are believed suitable, as are some tissue dyes. Toluene blue and methylene blue are examples of dyes believed suitable for use in the present invention. 
     In yet another aspect, the ink or dye can be thermochromic such that it changes color when heated to a temperature which indicates that a lesion has been formed by the application of radiofrequency energy. Typically, temperatures above about 50 to 55 degrees C. are required to cause cell death in an ablative lesion made by radiofrequency ablation and the photochromic material would preferably change color in that temperature range. 
     In still another aspect, the injected fluid can include a viscous enhancing agent or fluid added to reduce or retard fluid diffusion after delivery. Reducing the diffusion of a cytotoxic and/or conductive fluid can reduce the width of the resulting lesion. Reducing the diffusion of a protective fluid can maintain the protective fluid in a desired position adjacent the cytotoxic and/or conductive fluid, to serve its protective function. Viscous fluids such as dextrose or glycerol may be added to increase the viscosity of a delivered fluid. The viscous fluids or agents can provide a fluid viscosity of at least about twice that of water. 
     It will be appreciated by those skilled in the art that while the invention has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto. The entire disclosure of each patent and publication cited herein is incorporated by reference, as if each such patent or publication were individually incorporated by reference herein.