Abstract:
A device and associated method for performing ablation procedures on anatomical structures accessible from within the chambers of the heart to form lesions that electrically isolate the tissue.

Description:
This application claims the benefit and priority of U.S. Provisional Patent Application Ser. No. 60/473,774, filed May 27, 2003, which is herein incorporated by reference for all purposes. 

   BACKGROUND 
   1. Field of the Invention 
   The invention generally relates to the treatment of electrophysiological disease, and more particularly to devices and methods for ablating tissue in treating atrial fibrillation. 
   2. Related Art 
   A procedure known as the surgical maze procedure has been developed for treating atrial fibrillation, a condition which results from, disorganized electrical activity in the heart muscle or myocardium. The surgical maze procedure involves the creation of a series of surgical incisions in a preselected pattern so as to create conductive corridors of viable tissue bounded by scar tissue. 
   Ablative procedures have been used as an alternative to the surgical incisions used in the maze procedure. Typically, the ablative techniques include endocardial or epicardial ablation, which create lesions extending through a sufficient thickness of the myocardium to block electrical conduction. 
   Unfortunately, the maze procedure, whether using surgical or ablative techniques, is often very time-consuming and can result in lesions which do not completely encircle the pulmonary veins or which contain gaps and discontinuities. Most procedures do not include means for visualization of endocardial anatomy and most endovascular devices are often inadequate in relaying the precise position of such devices in the heart. This may result in misplaced lesions. 
   SUMMARY 
   The present invention provides a device and associated method for performing ablation procedures on anatomical structures accessible from within the chambers of the heart to form lesions that electrically isolate the tissue. 
   The method includes placing at least one ablation device through the major vein or artery usually in the neck or groin area, and guided into the heart chambers; deploying an inflatable balloon at an orifice within the cardiac myocardium in which the balloon can be anchored; radially deploying at least one ablation element; and ablating the heart wall with at least one ablation element to create at least one lesion. 
   In another aspect of the invention, an apparatus for forming a lesion in the heart wall includes an ablation device including a catheter body concentrically formed with an outer sheath having a distal end and a proximal end; a balloon coupled at the distal end to perform a centering and anchoring function at an orifice within the cardiac myocardium; at least one ablation element positioned proximal to the balloon which can be radially deployed with respect to the central axis of the apparatus for creating a lesion in the heart wall. The apparatus may also include a control device at the proximal end for manipulating the ablation device. 
   The ablation element may be a radiofrequency electrode, microwave transmitter, cryogenic element, laser, ultrasonic transducer or any of the other known types of ablation devices suitable for forming lesions. The apparatus includes a plurality of such ablation devices arranged along the working end in a linear pattern suitable for forming a continuous, uninterrupted lesion around the orifice of heart vasculature or around the ostium of the pulmonary veins. 
   These and other features and advantages of the present invention will be more readily apparent from the detailed description of the preferred embodiments set forth below taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1A  is a simplified side view of an ablation device in accordance with an embodiment of the present invention. 
       FIG. 1B  is a simplified sectional view as indicated of a cross section of the embodiment of  FIG. 1A . 
       FIG. 1C  is a simplified side view of an ablation device shown with alternate ablating member within the sheath in accordance with an embodiment of the present invention. 
       FIG. 2  is a side cross sectional view of yet another embodiment of the present invention. 
       FIGS. 3A and 3B  are simplified illustrations of a deployed ablation device in accordance with an embodiment of the present invention. 
       FIG. 4  is a simplified cross sectional view of a balloon in accordance with an embodiment of the present invention. 
       FIG. 5  is a simplified view of an ablation element including protective sheath in accordance with an embodiment of the present invention. 
       FIG. 6  is a simplified view of a deployed ablation device in accordance with an embodiment of the present invention. 
       FIG. 7  is a simplified illustration of a display coupleable to the ablation device for showing the radially deployed ablation elements in accordance with an embodiment of the present invention. 
       FIG. 8  is a simplified illustration of an embodiment of the present invention. 
       FIGS. 9A and 9B  are a simplified illustration of an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1A  and  FIG. 1C  are simplified side cross-sectional views of an embodiment of ablation device  100  in accordance with the present invention. In this embodiment, ablation device  100  includes a catheter body  102  having a proximal end  104  and a distal end  106  with a balloon  114  formed at distal end  106 . Catheter body  102  includes an inflation/deflation lumen  108  surrounded by an outer sheath  111  formed concentric with lumen  108 . In one embodiment, outer sheath  111  can be made to translate over lumen  108  in a telescopic arrangement. 
   Catheter body  102  and balloon  114  of ablation device  100  are configured for insertion into a main vein or artery through a small percutaneous incision. The extreme proximal end of ablation device  100  is operably coupled to a control device (not shown) used for manipulating ablation device  100  from outside the vein or artery. In one embodiment, ablation device  100  is made to enter the left heart chamber and advanced to the pulmonary veins. Ablation device  100  is made flexible enough to allow advancement to the heart chambers and can be made to any suitable dimension to reach the desired location within the heart chamber. Ablation device  100  can be made of a flexible biocompatible polymer or polymer matrix with metal wire braids and can include radiopaque markers  118  or radiopaque filler such as bismuth or barium sulfate. 
     FIG. 1B  is a sectional view as indicated of a cross section of catheter body  102  of  FIG. 1A . As shown in  FIG. 1B , outer sheath  111  can include one to a plurality of smaller element housing lumens  116  configured to receive an ablation element  110 . The one to a plurality of ablation elements  110  are used to form lesions isolating the pulmonary veins from the surrounding myocardium. 
   In one embodiment, each ablation element  110  disposed in lumens  116  includes a pre-shaped wire. In one embodiment, ablation elements  110  may include an energy tip  112  formed at the most distal end of the element. As described in detail below, energy tip  110  may include, for example, an RF electrode or other type of energy source capable of performing ablation of tissue. Thermocouples  113  can also be positioned proximate to energy tip  112 , or may be welded or bonded to the energy tips themselves, to monitor the amount of heat generated at the ablation site and to facilitate temperature measurement of the target tissue during ablation and thus, prevent overheating. Thermocouples  113  can be coupled to wires which extend to proximal end  104  of ablation device  100  and ultimately to temperature monitoring equipment or electrical monitoring equipment as to facilitate mapping of electrical activity at the target sites. 
   As shown in  FIG. 2 , the pre-shaped wire can be received within lumens  116  and aligned parallel to a central axis A of catheter body  102 . Openings  202  are formed along outer sheath  111  to allow ablation elements  110  to exit from lumen  116 . In one embodiment, ablation elements  110  exit lumens  116  in a direction toward proximal end  104  through openings  202  while in one embodiment, ablation elements  110  can be made to exit lumens  116  in direction toward distal end  106  as shown in  FIG. 1C . As the ablation elements  110  exit lumens  116  the pre-shaped wires radially expand away from central axis A, while at the same time the pre-shaped wire begins to regain its arcuate shape causing energy tip  112  to translate toward distal  106  ( FIG. 1A ). Generally, as described in greater detail below, the bend in arcuate shaped ablation element  110  causes energy tip  112  to advance toward the ablation site. 
   Ablation elements  110  include electrodes  112  formed at the distal end of ablation elements  110  for delivering current to the myocardium so as to create lesions of sufficient depth to block electrical conduction. Electrodes  112  may be solid metal rings or cylinders, foil strips, wire coils or other suitable construction for producing elongated lesions. It is understood that the term electrodes  112  as used herein may refer to any suitable ablating element  112 , such as microwave transmitters, cryogenic elements, lasers, heated elements, ultrasound, hot fluid or other types of ablation devices suitable for forming lesions. 
   Referring again to  FIG. 1B , ablation elements  110  are disposed in outer sheath  111  spaced apart a distance d about the circumference of sheath  111 . The number of ablation elements  110  disposed in outer sheath  111  is variable and depends on the desired procedure. In one embodiment, each ablation element  110  is positioned a distance r from the central axis A. In one embodiment, ablation elements  110  are positioned so as to facilitate lesion formation on the three-dimensional topography of the myocardium. Ablation elements  110  can be made of any flexibly resilient material that possess a spring quality and can be pre-shaped, such as Nitinol and other memory shape metals, stainless steel, and steel alloys, and the like. 
   Proximal end  104  of ablation device  100  further includes a control handle (not shown) which locates distal end  106  at one of the pulmonary veins. The control end includes a handle and one to a plurality of slidable actuators, which are used to extend each ablation element  110  from lumens  116 . An electrical connector suitable for connection to an energy source can be mounted to the handle. 
   As shown in  FIG. 2 , electrical wires, disposed in electric conduits  204 , can be used to electrically couple the energy source to ablation elements  110  and ultimately electrodes  112 . Each electrode  112  can be coupled to a separate wire to allow any electrode  112  or combination of electrodes to be selectively activated. The thermocouples mounted near the electrodes can be coupled to temperature or electrical monitoring equipment to control temperature of selected electrode  112  and monitor electrical activity at the target site. Also mounted to the handle can be a connector for connection to a source of inflation fluid or suction, used for the inflation/deflation of balloon  114 . 
   In one embodiment, the actuators in the handle are coupled to the proximal end of each ablation element  110 , and may be advanced forward to deploy each ablation element  110  from a non-deployed or retracted orientation, as shown in  FIG. 2  to a deployed or radially expanded orientation, as shown in  FIG. 1A . 
   The ablating element captured within the outer sheath  111  is free to transverse and rotate relative to the inner lumen  108 . This allows the positioning of the radially expanded ablating element and its electrode  112  to vary in distance relative to the location of the anchoring balloon  114  and rotate along the central axis of the anchored balloon  114 . Alternatively, outer sheath  111  and inner lumen  108  are coupled in a slidable relationship while the ablating element is captured in between the outer sheath  111  and inner lumen  108  and not part of the outer sheath  111 . In this alternative embodiment, outer sheath  111  can be pulled back relative to inner lumen  108  which causes ablation elements to become exposed, which allows ablation elements to radially expand due to their shaped memory and be directed to the tissues to be ablated. 
   Referring again to  FIGS. 1A and 2 , balloon  114  is positioned at the distal end  106  of ablation device  100  just distal to ablation elements  110 . Balloon  114  is used to position and manipulate ablation elements  110 . In operation, inner lumen  108  is configured to carry a gas or fluid through opening  120 , to or away from balloon  114 , to cause the balloon to inflate or deflate as desired. As shown in  FIGS. 3A and 3B , the size of the inflated balloon  114  controls the range of the ablation site along the axis of the vasculature. For example, balloon  114  can be used to anchor ablation device  100  at the opening of the vasculature ( FIG. 3A ). Alternatively, ablation device  100  can be allowed to enter into the vasculature and expanded to anchor ablation device  100  upstream of the vascular opening. In any embodiment, the inflated balloon is used to position and manipulate the ablation element  110 . 
     FIG. 1C  is a simplified illustration of an alternative embodiment of ablation device  100 . In this alternative embodiment, ablation elements  110  are deployed forward toward distal end  106 . Upon exiting outer sheath  111 , ablation elements  110  take a pre-shaped form which causes them to bend around balloon  114  and avoid contact therewith. 
   As shown in  FIG. 4 , in one embodiment, balloon  402  is formed of multi-chambers in a shape other than a sphere. Inner lumen  108  can include multiple openings  120 , to feed gas or liquid into each chamber of balloon  402 . For example, balloon  402  can be made with a clove-like shape. The clover like shaped balloon can anchor ablation device  100  within an orifice at the highest points of the clover-like shape, while allowing blood to flow between the recessed spaces formed between the multi-chamber sections. 
   In situations where the ostium is not normal to the axis of the vascular opening, ablation element  110  can be manipulated to contact the high and low points of the ostium by the use of balloon  114  having multi-chambers and independently controlled inflation chambers. For example, filling one of the chambers more or less against the other chambers can be used to bias ablation elements  110  to only contact specific quadrants of the circumferential pattern. Alternatively, the biasing of the elements to specific areas can be accomplished using a single chamber balloon and independent and selectively deploying the abating element. This may be controlled by the user at the handle. 
   The radially expanding ablation elements  110  can be made flexible enough to account for the varying topography of the opening. 
     FIG. 5  is a simplified illustration of ablation element  110  including a protective sheath  502  which provides a more efficient energy delivery. Protective sheath  502  can be a non-conductive compliant polymer. The differential stiffness between the ablation element  110  and the protective sheath  502  pushes back the sheath relative to the tip of the ablation element to form an expanded lip portion or petal  504 . Petal  504  provides increased impedance and provides minimal heating of blood surrounding electrode  112 . 
   Protective sheath  502  can be made to seal against the tissue wall before electrode  112  is energized to minimize the contact with blood and to maximize the contact with the tissue. A soft suction within the sheath  502  can be used to cause the sheath  502  to seal against the soft tissue. 
   As shown in  FIG. 6 , petal  504  at the end of sheath  502  can also provide a self-aligning footing for the un-even contours of the tissue wall by directing electrode  112  of ablation element  110  to contact the tissue perpendicular to the surface of the tissue. The flexible ablation element  110  can adjust to align the petal  504  perpendicular to the contact surface, since petal  504  will naturally try to bias ablation element  110  into such an orientation. 
   Ablation elements  110  can accomplish focal, segmented, or circumferential ablation concentric to balloon  114 , which is deployed in an orifice of the vasculature, such as the pulmonary vein near its ostium. 
   In one embodiment, outer sheath  111  which houses ablation elements  110  is free to rotate with respect to inner lumen  108 . Where a circumferential pattern is desired, the radially expanding ablation elements  110  can be indexed while the inner lumen  108  coupled to balloon  114  is anchored and remains stationary to complete the ablation concentric with a central axis of balloon  114 . 
     FIGS. 9A and 9B  show that outer sheath  111  can be made to traverse along the central axis A to provide flexible positioning of ablation elements  110 . The traversed position as well as the amount of radial deployment of ablation element  110  determines the size of the circumferential pattern and the precise location of the segmented focal lesion site ( FIG. 8 ). For example, outer sheath  111  can be positioned such that ablation elements  110  deploy to form a circumferential pattern C 1  or positioned closer to balloon  114  to form circumferential pattern C 2 . 
     FIG. 7  is a simplified illustration of a display feature  702  to show when contact has been made between ablation element  110  and the tissue. A visual display can be used with energy delivery equipment to show when optimum contact has been achieved (impedance). Display  702  shows a location of each radially deployed ablation element  110  that has made good contact with the target tissue. 
   In one embodiment, the LEDs  704  light up a pattern that corresponds to the contact points of the ablation elements  110  on the target tissue based on an impedance measurement at each electrode  112 . Sensitivity setting can be adjusted to show whether the contact made is optimal or not or how close to optimal the contact has become. 
   Having thus described embodiments of the present invention, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. Thus the invention is limited only by the following claims.