Abstract:
Cardiac ablation is carried out by introducing a catheter into the left atrium, extending a lasso guide through the lumen of the catheter to engage the wall of a pulmonary vein, and deploying a balloon over the lasso guide. The balloon has an electrode assembly disposed its exterior. The electrode assembly includes a plurality of ablation electrodes circumferentially arranged about the longitudinal axis of the catheter. The inflated balloon is positioned against the pulmonary vein ostium, so that the ablation electrodes are in galvanic contact with the pulmonary vein, and electrical energy is conducted through the ablation electrodes to produce a circumferential lesion that circumscribes the pulmonary vein.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to medical devices. More particularly, this invention relates to improvements in cardiac catheterization. 
         [0003]    2. Description of the Related Art 
         [0004]    Cardiac arrhythmias, such as atrial fibrillation, occur when regions of cardiac tissue abnormally conduct electric signals to adjacent tissue, thereby disrupting the normal cardiac cycle and causing asynchronous rhythm. 
         [0005]    Procedures for treating arrhythmia include surgically disrupting the origin of the signals causing the arrhythmia, as well as disrupting the conducting pathway for such signals. By selectively ablating cardiac tissue by application of energy via a catheter, it is sometimes possible to cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions. 
         [0006]    Circumferential lesions at or near the ostia of the pulmonary veins have been created to treat atrial arrhythmias. U.S. Pat. Nos. 6,012,457 and 6,024,740, both to Lesh, disclose a radially expandable ablation device, which includes a radiofrequency electrode. Using this device, it is proposed to deliver radiofrequency energy to the pulmonary veins in order to establish a circumferential conduction block, thereby electrically isolating the pulmonary veins from the left atrium. 
         [0007]    U.S. Pat. No. 6,814,733 to Schwartz et al., which is commonly assigned herewith and herein incorporated by reference, describes a catheter introduction apparatus having a radially expandable helical coil as a radiofrequency emitter. In one application the emitter is introduced percutaneously, and transseptally advanced to the ostium of a pulmonary vein. The emitter is radially expanded, which can be accomplished by inflating an anchoring balloon about which the emitter is wrapped, in order to cause the emitter to make circumferential contact with the inner wall of the pulmonary vein. The coil is energized by a radiofrequency generator, and a circumferential ablation lesion is produced in the myocardial sleeve of the pulmonary vein, which effectively blocks electrical propagation between the pulmonary vein and the left atrium. 
         [0008]    Another example is found in U.S. Pat. No. 7,340,307 to Maguire, et al., which proposes a tissue ablation system and method that treats atrial arrhythmia by ablating a circumferential region of tissue at a location where a pulmonary vein extends from an atrium. The system includes a circumferential ablation member with an ablation element and includes a delivery assembly for delivering the ablation member to the location. The circumferential ablation member is generally adjustable between different configurations to allow both the delivery through a delivery sheath into the atrium and the ablative coupling between the ablation element and the circumferential region of tissue. 
       SUMMARY OF THE INVENTION 
       [0009]    Embodiments of the present invention provide a catheter that enables delivery of an ablation balloon to the ostium of a pulmonary vein. The balloon and the method of delivery simplify the procedure for the physician. 
         [0010]    There is provided according to embodiments of the invention a method of ablation, which is carried out by introducing a catheter into a left atrium of a heart, extending a lasso guide through the lumen of the catheter to engage an interior wall of a pulmonary vein, deploying an inflated balloon over a portion of the lasso guide, the balloon having an electrode assembly disposed on an exterior wall thereof. The electrode assembly includes a plurality of ablation electrodes circumferentially arranged about the longitudinal axis. The method is further carried out by positioning the balloon against the pulmonary vein ostium, so that the ablation electrodes are in galvanic contact with the pulmonary vein, and conducting electrical energy through the ablation electrodes to produce a circumferential lesion that circumscribes the pulmonary vein. 
         [0011]    One aspect of the method includes injecting a contrast agent through the catheter into the pulmonary vein after inflating and positioning the balloon. 
         [0012]    A further aspect of the method includes injecting a contrast agent through the catheter into the balloon after positioning the balloon. 
         [0013]    In still another aspect of the method, the lasso guide has a mapping electrode disposed thereon. The method is further carried out by obtaining a pre-ablation electrogram with the mapping electrode prior to performing conducting electrical energy through the ablation electrodes. 
         [0014]    In another aspect of the method, the lasso guide has a mapping electrode disposed thereon. The method is further carried out by obtaining a post-ablation electrogram with the mapping electrode after performing conducting electrical energy through the ablation electrodes. 
         [0015]    There is further provided according to embodiments of the invention an ablation apparatus including a probe, a lasso guide that assumes a collapsed state for delivery through the lumen of the probe and assumes an expanded state after delivery through the probe. The lasso guide has a plurality of mapping electrodes that are connectable to electrocardiographic circuitry. The apparatus further includes an inflatable balloon deployable through the lumen over the lasso guide, the balloon having a plurality of ablation electrodes arranged circumferentially about the longitudinal axis on its exterior wall. The balloon is fenestrated by a plurality of irrigation pores and is connected to a source of fluid for passage of the fluid through the pores. 
         [0016]    In an additional aspect of the apparatus, a subassembly has a plurality of strips radiating outwardly from the longitudinal axis of the balloon, wherein the ablation electrodes are disposed on the strips. 
         [0017]    According to another aspect of the apparatus, the subassembly has apertures formed therethrough that are in fluid communication with the pores of the balloon. 
         [0018]    In another aspect of the apparatus wires in the distal portion of the probe lead to the ablation electrodes, and the strips of the subassembly comprise pigtails extending over a surface of the balloon and overlying respective wires. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0019]    For a better understanding of the present invention, reference is made to the detailed description of the invention, by way of example, which is to be read in conjunction with the following drawings, wherein like elements are given like reference numerals, and wherein: 
           [0020]      FIG. 1  is a pictorial illustration of a system for performing catheterization procedures on a heart, in accordance with a disclosed embodiment of the invention; 
           [0021]      FIG. 2  is a view of the distal portion of the catheter shown in  FIG. 1  in accordance with an embodiment of the invention; 
           [0022]      FIG. 3  is another view of the distal portion of the catheter shown in  FIG. 1  in accordance with an embodiment of the invention; 
           [0023]      FIG. 4  is a view of the distal portion of the catheter shown in  FIG. 1  in an operating position for ablation in accordance with an embodiment of the invention; 
           [0024]      FIG. 5  is a bottom plan view of the catheter electrode assembly shown in  FIG. 4  in accordance with an embodiment of the invention; 
           [0025]      FIG. 6  is a top plan view of the catheter electrode assembly shown in  FIG. 4  in accordance with an embodiment of the invention; 
           [0026]      FIG. 7  is a side elevation of an embodiment of a balloon of the catheter shown in  FIG. 4  in accordance with an embodiment of the invention; 
           [0027]      FIG. 8  is a cut-away sectional view through line  8 - 8  of the balloon shown in  FIG. 7  in accordance with an embodiment of the invention; and 
           [0028]      FIG. 9  is a flow-chart of a method of pulmonary vein isolation in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of the various principles of the present invention. It will be apparent to one skilled in the art, however, that not all these details are necessarily needed for practicing the present invention. In this instance, well-known circuits, control logic, and the details of computer program instructions for conventional algorithms and processes have not been shown in detail in order not to obscure the general concepts unnecessarily. 
         [0030]    Turning now to the drawings, reference is initially made to  FIG. 1 , which is a pictorial illustration of a system  10  for evaluating electrical activity and performing ablative procedures on a heart  12  of a living subject, which is constructed and operative in accordance with a disclosed embodiment of the invention. The system comprises a catheter  14 , which is percutaneously inserted by an operator  16  through the patient&#39;s vascular system into a chamber or vascular structure of the heart  12 . The operator  16 , who is typically a physician, brings the catheter&#39;s distal tip  18  into contact with the heart wall, for example, at an ablation target site. Electrical activation maps may be prepared, according to the methods disclosed in U.S. Pat. Nos. 6,226,542, and 6,301,496, and in commonly assigned U.S. Pat. No. 6,892,091, whose disclosures are herein incorporated by reference. One commercial product embodying elements of the system  10  is available as the CARTO® 3 System, available from Biosense Webster, Inc., 3333 Diamond Canyon Road, Diamond Bar, Calif. 91765. This system may be modified by those skilled in the art to embody the principles of the invention described herein. 
         [0031]    Areas determined to be abnormal, for example by evaluation of the electrical activation maps, can be ablated by application of thermal energy, e.g., by passage of radiofrequency electrical current through wires in the catheter to one or more electrodes at the distal tip  18 , which apply the radiofrequency energy to the myocardium. The energy is absorbed in the tissue, heating it to a point (typically above 60° C.) at which it permanently loses its electrical excitability. When successful, this procedure creates non-conducting lesions in the cardiac tissue, which disrupt the abnormal electrical pathway causing the arrhythmia. The principles of the invention can be applied to different heart chambers to diagnose and treat many different cardiac arrhythmias. 
         [0032]    The catheter  14  typically comprises a handle  20 , having suitable controls on the handle to enable the operator  16  to steer, position and orient the distal end of the catheter as desired for the ablation. To aid the operator  16 , the distal portion of the catheter  14  contains position sensors (not shown) that provide signals to a processor  22 , located in a console  24 . The processor  22  may fulfill several processing functions as described below. 
         [0033]    Wire connections  35  link the console  24  with body surface electrodes  30  and other components of a positioning sub-system for measuring location and orientation coordinates of the catheter  14 . The processor  22  or another processor (not shown) may be an element of the positioning subsystem. Catheter electrodes (not shown) and the body surface electrodes  30  may be used to measure tissue impedance at the ablation site as taught in U.S. Pat. No. 7,536,218, issued to Govari et al., which is herein incorporated by reference. Temperature sensors (not shown), typically a thermocouple or thermistor, may be mounted on ablation surfaces on the distal portion of the catheter  14  as described below. 
         [0034]    The console  24  typically contains one or more ablation power generators  25 . The catheter  14  may be adapted to conduct ablative energy to the heart using any known ablation technique, e.g., radiofrequency energy, ultra-sound energy, and laser-produced light energy. Such methods are disclosed in commonly assigned U.S. Pat. Nos. 6,814,733, 6,997,924, and 7,156,816, which are herein incorporated by reference. 
         [0035]    In one embodiment, the positioning subsystem comprises a magnetic position tracking arrangement that determines the position and orientation of the catheter  14  by generating magnetic fields in a predefined working volume and sensing these fields at the catheter, using field generating coils  28 . The positioning subsystem is described in U.S. Pat. No. 7,756,576, which is hereby incorporated by reference, and in the above-noted U.S. Pat. No. 7,536,218. 
         [0036]    As noted above, the catheter  14  is coupled to the console  24 , which enables the operator  16  to observe and regulate the functions of the catheter  14 . Console  24  includes a processor, preferably a computer with appropriate signal processing circuits. The processor is coupled to drive a monitor  29 . The signal processing circuits typically receive, amplify, filter and digitize signals from the catheter  14 , including signals generated by sensors such as electrical, temperature and contact force sensors, and a plurality of location sensing electrodes (not shown) located distally in the catheter  14 . The digitized signals are received and used by the console  24  and the positioning system to compute the position and orientation of the catheter  14 , and to analyze the electrical signals from the electrodes. 
         [0037]    In order to generate electroanatomic maps, the processor  22  typically comprises an electroanatomic map generator, an image registration program, an image or data analysis program and a graphical user interface configured to present graphical information on the monitor  29 . 
         [0038]    Typically, the system  10  includes other elements, which are not shown in the figures for the sake of simplicity. For example, the system  10  may include an electrocardiogram (ECG) monitor, coupled to receive signals from one or more body surface electrodes, in order to provide an ECG synchronization signal to the console  24 . As mentioned above, the system  10  typically also includes a reference position sensor, either on an externally-applied reference patch attached to the exterior of the subject&#39;s body, or on an internally-placed catheter, which is inserted into the heart  12  maintained in a fixed position relative to the heart  12 . Conventional pumps and lines for circulating liquids through the catheter  14  for cooling the ablation site are provided. The system  10  may receive image data from an external imaging modality, such as an MRI unit or the like and includes image processors that can be incorporated in or invoked by the processor  22  for generating and displaying images. 
         [0039]    Reference is now made to  FIG. 2 , which is a view of the distal portion of the catheter  14  ( FIG. 1 ) in accordance with an embodiment of the invention. The distal tip  18  of the catheter is within the left atrium of the heart  12  ( FIG. 1 ). Pulmonary vein ostia  37 ,  39  are visible. A lasso guide  41  has been partially deployed beyond the distal tip  18 . The lasso guide  41  may have a shape memory, and when extended through the distal tip  18  of the catheter  14 , the distal portion of the lasso guide  41  configures itself into a ring or spiral. Multiple ring electrodes  43  may be disposed on the lasso guide  41 . The electrodes  43  are useful for obtaining electrograms to confirm electrical isolation of the pulmonary vein following ablation while the lasso guide  41  is still engaged with the wall of the pulmonary vein. Other types of electrodes and sensors may be mounted on the lasso guide  41 , for example contact force sensors and magnetic location sensors. 
         [0040]    Reference is now made to  FIG. 3 , which is a view of the distal portion of the catheter  14  ( FIG. 1 ) in accordance with an embodiment of the invention. The lasso guide  41  has been deployed and is engaged with the wall of pulmonary vein  45 . A balloon  47  has been inflated, aided by the stability provided by the lasso guide  41  that is anchored against the vessel wall. Correct placement of the balloon  47  can be verified by injecting a contrast agent through the catheter  14 . Additionally or alternatively the contrast agent may be injected into the balloon  47 . 
         [0041]    Reference is now made to  FIG. 4 , which is a pictorial side view of distal segment of the catheter  14  ( FIG. 1 ) shown in an operating position at ostium  49  of pulmonary vein  45  in accordance with an embodiment of the invention. The lasso guide  41  has been fully extended through the distal tip  18 . Once the guide is positioned in the vein, the balloon  47 , which is mounted on a shaft  51 , extends beyond the distal tip  18  of the catheter  14 . The balloon  47  is inflated by injection with saline solution, in order to close off the vein at the ostium  49 . The balloon  47  is fenestrated. Apertures or pores (best seen in  FIG. 6 ) allow the saline to irrigate the ostium  49 . The balloon  47  has an electrode assembly  53  disposed on its eternal surface. Multiple ablation electrodes are disposed on the electrode assembly  53 , as best seen in  FIG. 5 . The components of the electrode assembly  53  are elongate, and directed longitudinally in respective planes that are normal to the shaft  51  in order to maximize galvanic contact between its electrodes  55  ( FIG. 5 ) and the wall of the ostium  49 . Pigtails  57  prevent the electrode assembly  53  from delaminating when the balloon  47  is retracted into the shaft of the catheter  14  and protect wires (not shown) leading to the electrodes of the electrode assembly  53 . Other geometric configurations for the electrode assembly  53  are possible, for example a spiral arrangement, or concentric rings. Passage of electrical energy through the electrodes  55  ( FIG. 5 ) creates a circumferential lesion  59  at the ostium  49  that blocks electrical propagation and isolates the pulmonary vein from the heart. The ablation site is cooled by flow of a cooling fluid  61  through pores formed in the balloon  47  and the electrode assembly  53 . Alternatively, a portion of the electrodes  55  may be configured for electrical mapping. 
         [0042]    Reference is now made to  FIG. 5 , which is a bottom plan view of the electrode assembly  53  in accordance with an embodiment of the invention. The electrode assembly  53  is shown detached from the balloon  47 . The bottom surface of the electrode assembly  53  is adapted to be adhered to the external surface of the balloon  47  ( FIG. 4 ) The electrode assembly  53  comprises a central aperture  63  through which the shaft  51  ( FIG. 4 ) extends. This arrangement permits injection of contrast material or sampling through the shaft  51  as may be required by the medical procedure. The electrode assembly  53  comprises a substrate of radiating strips  65  that extend about the balloon  47  and are brought into contact with a pulmonary vein ostium when the balloon is inflated and navigated to the pulmonary vein. Electrodes  55  are disposed on each of the strips  65 , and come into galvanic contact with the ostium during an ablation operation, during which electrical current flows through the electrodes  55  and the ostium. Ten strips  65  are shown in the example of  FIG. 5  and are evenly distributed about of central axis the aperture  63 . Other numbers of strips are possible. However, there should be a sufficiently small angle between adjacent strips  65  such that at least one continuous circumferential lesion is produced in the pulmonary vein when the electrodes  55  are activated for ablation. 
         [0043]    Numerous pores  67  (typically 25-100 microns in diameter) are formed through each of the strips  65  and perforate the underlying balloon  47  as well. The pores  67  conduct a flow of cooling irrigation fluid from the interior of the balloon  47  onto and near the ablation site. The flow rate may be varied by a pump control (not shown) from an idle rate of about 4 mL/min to the ablation flow rate of 60 mL/min. 
         [0044]    Reference is now made to  FIG. 6 , which is a top plan view of the electrode assembly  53  in accordance with an embodiment of the invention. Electrodes  55  are shown. In operation they come into contact with the wall of the pulmonary vein. 
         [0045]    Reference is now made to  FIG. 7 , which is a side elevation of an embodiment of a balloon  69  having a proximal end  71  and a distal end  73  in accordance with an embodiment of the invention. An electrode assembly  75  is adhered to the exterior of the outer wall  77  of the balloon  69 . At its proximal end  71 , the balloon  69  is narrowed and configured to adapt to a connecting tube, which provides mechanical support and a supply of fluid. The distal end  73  is narrowed to permit fluid continuity between the interior of the balloon  69  and the lumen of a vessel. 
         [0046]    Reference is now made to  FIG. 8 , which is a cut-away sectional view through line  8 - 8  of the balloon  69  ( FIG. 7 ) in accordance with an embodiment of the invention. A rim  79  seals the balloon  69  to a support (not shown), and prevents escape of fluid used for inflation of the balloon and irrigation fluid. An inner passage  81  permits fluid communication between a vessel and a location outside the body. For example contrast material may be transmitted through the passage  81 . 
         [0047]    Reference is now made to  FIG. 9 , which is a flow-chart of a method of pulmonary vein isolation in accordance with an embodiment of the invention. At initial step  83  a cardiac catheter is conventionally introduced into the left atrium of a heart. 
         [0048]    Next, at step  85  the lasso guide  41  is deployed and positioned to engage the interior wall of a pulmonary vein. Pre-ablation electrograms may be acquired once the lasso guide  41  is in position. 
         [0049]    Next, at step  87  the balloon  47  is extended over the lasso guide  41  and inflated. 
         [0050]    Next, at step  89  the balloon  47  is navigated into circumferential contact with a pulmonary vein ostium in order to occlude the ostium. 
         [0051]    Next, at step  91  a radio-opaque contrast agent is injected through the lumen of the catheter, The contrast agent passes through a gap between the lasso guide  41  and the wall of the lumen in order to confirm that the balloon  47  is in a correct position against the pulmonary vein ostium. The contrast agent does not enter the balloon. 
         [0052]    Control now proceeds to decision step  93 , where it is determined if the balloon  47  is correctly positioned. If the determination at decision step  93  is negative, then control returns to step  89  and another attempt is made to position the balloon. 
         [0053]    If the determination at decision step  93  is affirmative, then control proceeds to step  95  where ablation is performed using the ablation electrodes of the electrode assembly  53  ( FIG. 4 ). A circumferential lesion is created in a region of tissue that circumscribes the pulmonary vein. The lesion blocks electrical propagation and effectively electrically isolates the pulmonary vein from the heart. Post-ablation electrograms may be obtained from the electrodes  43  of the lasso guide  41  ( FIG. 2 ) in order to confirm functional isolation of the pulmonary vein. 
         [0054]    After completion of the ablation, the procedure may be iterated using another pulmonary vein ostium by withdrawal of the balloon  47  and the lasso guide  41 . Control may then return to step  85 . Alternatively, the procedure may end by removal of the catheter  14  at final step  97 . 
         [0055]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description.