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United States Patent 6,645,202
Pless ,   et al. November 11, 2003
Apparatus and method for ablating tissue


Abstract

A control system alters one or more characteristics of an ablating element to ablate tissue. In one aspect, the control system delivers energy nearer to the surface of the tissue by changing the frequency or power. In another aspect, the ablating element delivers focused ultrasound which is focused in at least one dimension. The ablating device may also have a number of ablating elements with different characteristics such as focal length.

Inventors: Pless; Benjamin (Atherton, CA); Anderson; Scott C. (Sunnyvale, CA); Podmore; Jonathan L. (San Francisco, CA); Vaska; Matthias (Menlo park, CA); Crowe; John E. (Palo Alto, CA); Richman; Roxanne L. (Los Gatos, CA); Ciciarelli; Timothy (San Francisco, CA); Gallup; David A. (Alameda, CA); Ulstad, Jr.; Jack E. (Boulder Creek, CA)
Assignee: Epicor Medical, Inc. (Sunnyvale, CA)
Appl. No.: 09/699,215
Filed: October 27, 2000
Related U.S. Patent Documents
Application NumberFiling DatePatent NumberIssue Date
614991Jul., 2000
507336Feb., 2000
356476Jul., 19996311692
157824Sep., 19986237605
943683Oct., 19976161543
735036Oct., 1996

Current U.S. Class: 606/41 ; 600/439; 606/28
Field of Search: 606/27,28,41,169 604/22 600/437,439,459,462,466,472 601/2,3

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Primary Examiner: Peffley; Michael
Attorney, Agent or Firm: Hoekendijk; Jens E. Hoekendijk & Lynch, LLP
Parent Case Text


CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 09/614,991, filed Jul. 12, 2000, which is a continuation-in-part of application Ser. No. 09/507,336 filed Feb. 18, 2000 which is a continuation-in-part of application Ser. No. 09/356,476, filed Jul. 19, 1999, now U.S. Pat. No. 6,311,692, which is a continuation-in-part of application Ser. No. 09/157,824, filed Sep. 21, 1998, now U.S. Pat. No. 6,237,605, which is a continuation-in-part of application Ser. No. 08/943,683, filed Oct. 15, 1997, now U.S. Pat. No. 6,161,543, which is a continuation-in-part of application Ser. No. 08/735,036, filed Oct. 22, 1996, now abandoned, the complete disclosures of which are hereby incorporated herein by reference for all purposes.
Claims


What is claimed is:

1. A method of ablating cardiac tissue, comprising the steps of: providing an ablating device having an ultrasonic transducer, the device emitting focused ultrasound which is focused in at least one dimension; positioning the ablating device in contact with cardiac tissue; and activating the ultrasonic transducer to direct the focused ultrasound into the cardiac tissue, the activating step is carried out by activating the ultrasonic transducer for a first period of time at a first frequency and a second period of time at a second frequency which is different than the first frequency and occurs after the first period of time.

2. The method of claim 1, wherein: the activating step is carried out to electrically isolate one part of the heart from another part of the heart.

3. The method of claim 1, wherein: the providing and activating steps are carried out with the focused ultrasound being focused along a focal axis and diverging when viewed perpendicular to the focal axis.

4. The method of claim 1, further comprising the step of: moving a focus of the focused ultrasound relative to the cardiac tissue.

5. The method of claim 4, wherein: the moving step is carried out to move the focus closer to a near surface of the cardiac tissue.

6. The method of claim 1, wherein: the providing step is carried out so that at least 90% of the focused ultrasound passes within a focus area defined by a focal length of about 2 to 20 mm and an angle of about 10 to 170 degrees when viewed along a focal axis.

7. The method of claim 1, wherein: the providing step is carried out with the focused energy being emitted by a concave surface.

8. The method of claim 7, wherein: the providing step is carried out with the concave surface having a focal length of 2-20 mm.

9. The method of claim 8, wherein: the providing step is carried out with the focused energy having a focal length of 2 to 12 mm.

10. The method of claim 1, wherein: the activating step is carried out with the first frequency being lower than the second frequency.

11. The method of claim 1, wherein: the activating step is carried out with the first period of time being shorter than the second period of time.

12. The method of claim 11, wherein: the activating step is carried out with the first period of time being less than 1 second.

13. The method of claim 1, wherein: the activating step is carried out with the ultrasonic transducer being activated at the first frequency for a number of discrete time periods.

14. The method of claim 1, wherein: the activating step is carried out by changing the frequency to accumulate energy closer to a near surface of the tissue.

15. The method of claim 14, wherein: the activating step is carried out with the frequency being increased from a first frequency to a second frequency, the activating step being carried out at the first frequency for a number of discrete periods of time.

16. The method of claim 1, wherein: the providing step is carried out with the ultrasonic transducer producing the focused ultrasound having a focal length of 2-20 mm.

17. The method of claim 1, further comprising the step of: assessing contact between the ablating device and the tissue structure.

18. The method of claim 1, wherein: assessing contact between the ablating device and the tissue structure by measuring the electrical impedance.

19. The method of claim 1, further comprising the step of: measuring a tissue thickness using ultrasound energy delivered by the ablating device.

20. The method of claim 1, further comprising the step of: measuring a fat thickness using ultrasound energy delivered by the abating device.

21. The method of claim 1, wherein: the activating step is carried out with the ablating element being activated at the first frequency for a number of discrete time periods.

22. The method of claim 1, wherein: the activating step is carried out by activating the ultrasonic transducer at a third frequency different than the first and second.

23. The method of claim 1, wherein: the activating step is carried out with the first frequency being about 2-7 MHz and the second frequency being from 2-14 MHz.

24. The method of claim 1, further comprising the step of: measuring a blood flow velocity with the ultrasonic transducer.

25. The method of claim 1, further comprising the step of: determining a tissue layer thickness using the ultrasound transducer.

26. The method of claim 1, wherein: the determining step is carried out with the tissue layer being a tissue layer between a near surface and a far surface.

27. The method of claim 1, further comprising the step of: moving an ultrasonic beam emitted by the ultrasound transducer after the activating step.

28. The method of claim 27, further comprising the step of: tilting the ultrasonic beam.

29. A method of ablating cardiac tissue with ultrasound comprising the steps of: creating an opening in a patient's chest; providing an ablating device which emits focused ultrasound having a focus in at least one direction; introducing the ablating device through the opening in the patient's chest; positioning the ablating device in contact with a cardiac tissue structure to be ablated, the cardiac tissue structure having a near wall and a far wall; and operating the ablating device at a frequency and a power to direct the ultrasonic energy into the tissue structure for a number of discrete time periods; and changing at least one of the frequency and location of the focus relative to the tissue and activating the ablating device to ablate the cardiac tissue structure for another period of time.

30. The method of claim 29, wherein: the changing step is carried out with the frequency increasing.

31. The method of claim 29, wherein: the providing step is carried out with the ablating device producing focused ultrasound, wherein the focused ultrasound has a focal length of 2-20 mm.

32. The method of claim 29, further comprising the step of: assessing contact between the ablating device and the tissue structure.

33. The method of claim 29, further comprising the step of: assessing contact between the ablating device and the tissue structure by measuring the electrical impedance.

34. The method of claim 29, further comprising: measuring a tissue thickness using ultrasound energy delivered by the ablating device.

35. The method of claim 29, further comprising the step of: measuring a fat thickness using ultrasound energy delivered by the ablating device.

36. The method of claim 29, wherein: the activating step is carried out with the ablating device being activated at a first frequency for a number of discrete time periods.

37. The method of claim 29, wherein: the changing step is carried out by activating the ablating device at a frequency of 2-14 MHz.

38. The method of claim 29, wherein: the activating step is carried out at a first frequency of 2-7 MHz; and the changing step is carried out at a second frequency of 2-14 MHz.

39. The method of claim 29, further comprising the step of: measuring a blood flow velocity with ultrasound energy delivered by the ablating device.

40. The method of claim 29, further comprising the step of: determining a tissue layer thickness using ultrasound energy delivered by the ablating device.

41. The method of claim 29, further comprising the step of: moving an ultrasonic beam emitted by the ablating device after the activating step.

42. The method of claim 29, further comprising the step of: tilting an ultrasonic beam emitted by the ablating device after the activating step.

43. A method of ablating cardiac tissue to form an elongate lesion to treat a cardiac arrhythmia, comprising the steps of: providing an ablating device having a plurality of ablating elements, the plurality of ablating elements each emitting focused ultrasound, the focused ultrasound being focused in at least one direction and having a focal length of 2-20 mm; forming an opening in a patient's chest; introducing the ablating device through the opening in the patient's chest; positioning the ablating device against an epicardial surface overlying a cardiac tissue structure to be ablated, the cardiac structure having a near wall and a far wall; and activating the plurality of ablating elements each for a number of discrete periods of time, the ablating element emitting focused ultrasound into the cardiac tissue structure to ablate the cardiac tissue structure to treat the cardiac arrhythmia.

44. The method of claim 43, wherein: the positioning step is carried out with the plurality of ablating elements extending around the pulmonary veins on the epicardial surface.

45. The method of claim 43, wherein: the positioning step is carried out with the plurality of ablating elements being angled relative to the epicardial surface to at least partially direct the focused ultrasound toward an adjacent ablating element.

46. The method of claim 43, wherein: changing a characteristic of the ablating device and activating the ablating device to produce focused ultrasound which accumulates energy closer to the near wall as compared to the activating step.

47. The method of claim 46, wherein: the changing step is carried out with the frequency increasing.

48. The method of claim 43, further comprising the step of: assessing contact between the ablating device and the tissue structure.

49. The method of claim 43, wherein: assessing contact between the ablating device and the tissue structure by measuring the electrical impedance.

50. The method of claim 43, further comprising: measuring a tissue thickness using ultrasound energy delivered by the ablating device.

51. The method of claim 43, further comprising the step of: measuring a fat thickness using ultrasound energy delivered by the ablating device.

52. The method of claim 43, wherein: the activating step is carried out with at least one of the ablating elements being activated at a first frequency for a number of discrete time periods.

53. The method of claim 52, wherein: the activating step is carried out with the at least one ablating element being activated at a second frequency different than the first frequency.

54. The method of claim 53, wherein: the activating step is carried out with the first frequency being about 2-7 MHz and the second frequency being from 2-14 MHz.

55. The method of claim 43, further comprising the step of: moving an ultrasonic beam emitted by the ablating device after the activating step.

56. The method of claim 43, further comprising the step of: tilting an ultrasonic beam emitted by the ablating device after the activating step.
Description


FIELD OF THE INVENTION

This invention relates generally to devices and methods for ablating tissue. The diagnosis and treatment of electrophysiological diseases of the heart, and more specifically to devices and methods for epicardial mapping and ablation for the treatment of atrial fibrillation, are described in connection with the devices and methods of the present invention.

BACKGROUND OF THE INVENTION

Atrial fibrillation results from disorganized electrical activity in the heart muscle, or myocardium. The surgical maze procedure has been developed for treating atrial fibrillation and involves the creation of a series of surgical incisions through the atrial myocardium in a preselected pattern so as to create conductive corridors of viable tissue bounded by scar tissue.

As an alternative to the surgical incisions used in the maze procedure, transmural ablation of the heart wall has been proposed. Such ablation may be performed either from within the chambers of the heart (endocardial ablation) using endovascular devices (e.g. catheters) introduced through arteries or veins, or from outside the heart (epicardial ablation) using devices introduced into the chest. Various ablation technologies have been proposed, including cryogenic, radiofrequency (RF), laser and microwave. The ablation devices are used to create elongated transmural lesions--that is, lesions extending through a sufficient thickness of the myocardium to block electrical conduction--which form the boundaries of the conductive corridors in the atrial myocardium. Perhaps most advantageous about the use of transmural ablation rather than surgical incisions is the ability to perform the procedure on the beating heart without the use of cardiopulmonary bypass.

In performing the maze procedure and its variants, whether using ablation or surgical incisions, it is generally considered most efficacious to include a transmural incision or lesion that isolates the pulmonary veins from the surrounding myocardium. The pulmonary veins connect the lungs to the left atrium of the heart, and join the left atrial wall on the posterior side of the heart. This location creates significant difficulties for endocardial ablation devices for several reasons. First, while many of the other lesions created in the maze procedure can be created from within the right atrium, the pulmonary venous lesions must be created in the left atrium, requiring either a separate arterial access point or a transeptal puncture from the right atrium. Second, the elongated and flexible endovascular ablation devices are difficult to manipulate into the complex geometries required for forming the pulmonary venous lesions and to maintain in such positions against the wall of the beating heart. This is very time-consuming and can result in lesions which do not completely encircle the pulmonary veins or which contain gaps and discontinuities. Third, visualization of endocardial anatomy and endovascular devices is often inadequate and knowing the precise position of such devices in the heart can be difficult, resulting in misplaced lesions. Fourth, ablation within the blood inside the heart can create thrombus which, in the right chambers, is generally filtered out by the lungs rather than entering the bloodstream. However, on the left side of the heart where the pulmonary venous lesions are formed, thrombus can be carried by the bloodstream into the coronary arteries or the vessels of the head and neck, potentially resulting in myocardial infarction, stroke or other neurologic sequelae. Finally, the heat generated by endocardial devices which flows outward through the myocardium cannot be precisely controlled and can damage extracardiac tissues such as the pericardium, the phrenic nerve and other structures.

What are needed, therefore, are devices and methods for forming lesions that isolate the pulmonary veins from the surrounding myocardium which overcome these problems. The devices and methods will preferably be utilized epicardially to avoid the need for access into the left chambers of the heart and to minimize the risk of producing thrombus.

Additional aspects of the present invention are directed to devices and methods for ablating tissue. Ablation of heart tissue and, specifically, ablation of tissue for treatment of atrial fibrillation is developed as a particular use of these other aspects of the present invention.

SUMMARY OF THE INVENTION

The present invention meets these and other objectives by providing epicardial ablation devices and methods useful for creating transmural lesions that electrically isolate the pulmonary veins for the treatment of atrial fibrillation.

In a first embodiment, a method of forming a transmural lesion in a wall of the heart adjacent to the pulmonary veins comprises the steps of placing at least one ablation device through a thoracic incision and through a pericardial penetration so that at least one ablation device is disposed in contact with an epicardial surface of the heart wall; positioning at least one ablation device adjacent to the pulmonary veins on a posterior aspect of the heart while leaving the pericardial reflections intact; and ablating the heart wall with at least one ablating device to create at least one transmural lesion adjacent to the pulmonary veins. While the method may be performed with the heart stopped and circulation supported with cardiopulmonary bypass, the method is preferably performed with the heart beating so as to minimize morbidity, mortality, complexity and cost.

In another aspect of the invention, an apparatus for forming a transmural lesion in the heart wall adjacent to the pulmonary veins comprises, in a preferred embodiment, an elongated flexible shaft having a working end and a control end; an ablation device attached to the working end for creating a transmural lesion in the heart wall; a control mechanism at the control end for manipulating the working end; and a locating device near the working end configured to engage one or more of the pulmonary veins, or a nearby anatomical structure such as a pericardial reflection, for positioning the working end adjacent to the pulmonary veins. The locating device may comprise a catch, branch, notch or other structure at the working end configured to engage one or more of the pulmonary veins or other anatomical structure such as the inferior vena cava, superior vena cava, aorta, pulmonary artery, left atrial appendage, right atrial appendage, or one of the pericardial reflections. The ablation device 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 transmural lesions. Preferably, 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 or on the pulmonary veins.

The working end may additionally include one or more movable elements that are manipulated from the control end and which may be moved into a desired position after the working end has been located near the pulmonary veins. Slidable, rotatable, articulated, pivotable, bendable, pre-shaped or steerable elements may be used. Additional ablation devices may be mounted to these movable elements to facilitate formation of transmural lesions. The movable elements may be deployed to positions around the pulmonary veins to create a continuous transmural lesion which electrically isolates the pulmonary veins from the surrounding myocardium.

In addition, a mechanism may be provided for urging all or part of the working end against the epicardium to ensure adequate contact with the ablation devices. This mechanism may be, for example, one or more suction holes in the working end through which suction may be applied to draw the working end against the epicardium, or an inflatable balloon mounted to the outer side of the working end such that, upon inflation, the balloon engages the inner wall of the pericardium and forces the working end against the epicardium. This also functions to protect extracardiac tissues such as the pericardium from injury by retracting such tissues away from the epicardial region which is being ablated, and, in the case of the balloon, providing an insulated barrier between the electrodes of the ablation probe and the extracardiac tissues.

The apparatus may be either a single integrated device or two or more devices which work in tandem. In either case, the apparatus may have two or more tips at the working end which are positioned on opposing sides of a tissue layer such as a pericardial reflection. A device may be provided for approximating the two free ends on opposing sides of the tissue layer, such as an electromagnet mounted to one or both of the free ends. In this way, a continuous lesion may be created in the myocardium from one side of the pericardial reflection to the other without puncturing or cutting away the pericardial reflection.

The apparatus may further include a working channel through which supplemental devices may be placed to facilitate visualization, tissue manipulation, supplementary ablation, suction, irrigation and the like.

The apparatus and methods of the invention are further useful for mapping conduction pathways in the heart (local electrograms) for the diagnosis of electrophysiological diseases. Any of the electrodes on the apparatus may be individually selected and the voltage may be monitored to determine the location of conduction pathways. Alternatively, the apparatus of the invention may be used for pacing the heart by delivering current through one or more selected electrodes at levels sufficient to stimulate heart contractions.

Additionally, although the ablation apparatus and methods of the invention are preferably configured for epicardial use, the principles of the invention are equally applicable to endocardial ablation catheters and devices. For example, an endocardial ablation apparatus according to the invention would include a locating device configured to engage an anatomical structure accessible from within the chambers of the heart such as the coronary sinus (from the right atrium), pulmonary artery (from the right ventricle), or the pulmonary veins (from the left atrium), and the ablation device would be positionable in a predetermined location relative to the locating device. The endocardial apparatus could further include suction holes, expandable balloons, or other mechanisms for maintaining contact between the ablation device and the interior surface of the heart wall.

In another aspect of the present invention, an anchor is used to hold part of the device while displacing another part of the device. The anchor is preferably a balloon but may also be tines, a suction port or a mechanically actuated device. After actuating the anchor, a proximal portion of the device may be moved by simply manipulating the device or by advancement or withdrawal of a stylet.

The present invention is also related to a method of creating a continuous ablation lesion in tissue underlying a pericardial reflection without penetrating the pericardial reflection. First and second ablating devices are introduced into the space between the pericardium and the epicardium. The first ablating device is positioned on one side of the pericardial reflection and the second ablating device is positioned on the other side of the pericardial reflection. Tissue beneath the pericardial reflection is then ablated with one or both of the devices to create a continuous lesion beneath the pericardial reflection. The devices may be aligned across the pericardial reflection by any suitable method such as with magnetic force, use of an emitter and sensor, or by marking the pericardial reflection on one side and locating the mark from the other side of the pericardial reflection. The emitter and sensor may work with electromagnetic radiation such as light, ultrasound, magnetic field, and radiation.

In yet another aspect of the invention, the ablating device may have a guide portion which aligns the device between the pericardium and epicardium. The guide portion may be a continuous strap or a number of discrete guide portions. The guide portions may be fins, wings or one or more laterally extending elements such as balloons. The guide portions may be individually actuated to align the device and ablate discrete locations of the tissue along the ablating device.

The ablating device may also be advanced into position over a guide. The guide is preferably a guidewire but may be any other suitable structure. The guide may also lock into position with a coaxial cable or locking arm. The guide is advanced ahead of the ablation device and positioned along the desired ablation path. The ablating device is then advanced or retracted along the guide. The ablating device preferably includes a device for locating previously formed lesions so that subsequent lesions will merge with a previously formed lesion to create a continuous, transmural lesion. The device for locating previously created lesions may be pacing and sensing electrodes or electrodes which simply measure electrical impedance.

Although cutting through the pericardial reflections has certain risks, the methods and devices of the present invention may, of course, be practiced while cutting through the pericardial reflections. After penetrating through the pericardial reflection, the ablating device may interlock with another part of the same device or with a separate device.

In another method and device of the present invention, another ablating device is provided which may be used to ablate any type of tissue including heart tissue for the reasons described herein. The ablating device has a suction well and an ablating element. The suction well adheres the device to the tissue to be ablated. The device is preferably used to ablate cardiac tissue from an epicardial location to form a transmural lesion. The device preferably includes a number of cells which each have a suction well and at least one ablating element. The cells are coupled together with flexible sections which permit the cells to displace and distort relative to one another. The device preferably has about 5-30 cells, more preferably about 10-25 cells and most preferably about 16 cells. The suction well has an inner lip and an outer lip. The inner lip forms a closed wall around the ablating element.

The device also has a fluid inlet and a fluid outlet for delivering and withdrawing fluid from within the closed wall formed by the inner lip. The fluid is preferably a conductive fluid, such as hypertonic saline, which conducts energy from the ablating element, such as an RF electrode, to the tissue. The fluid is preferably delivered along a short axis of the ablating element so that the temperature change across the ablating element is minimized.

The ablating elements are preferably controlled by a control system. One or more temperature sensors on the device are coupled to the control system for use as now described. The control system may control ablation in a number of different ways. For example, the control system may activate one or more pairs of adjacent cells to form continuous lesions between the adjacent cells. After ablation at the one or more adjacent cells, another pair of adjacent cells is activated to form another continuous ablation segment. This process is continued until a continuous lesion of the desired geometry is produced. In another mode of operation, the control system may activate every other or every third cell. Still another mode of operation is to activate only the ablating elements which have low temperatures by using a multiplexer coupled to the temperature sensors.

The control system may also conduct a thermal response analysis of the tissue to be ablated to determine the appropriate ablation technique. The tissue to be ablated is heated, or cooled, and the temperature response of the tissue over time is recorded. The temperature response is then analyzed to determine the appropriate ablation technique. The analysis may be a comparison of the temperature response against a database of temperature responses or may be a calculation which may require user input as described below.

In a further aspect of the invention, the ablating element preferably produces focused ultrasound in at least one dimension. An advantage of using focused ultrasound is that the energy can be concentrated within the tissue. Another advantage of using focused ultrasound is that the energy diverges after reaching the focus thereby reducing the possibility of damaging tissue beyond the target tissue as compared to collimated ultrasonic energy. When ablating epicardial tissue with collimated ultrasound, the collimated ultrasound energy not absorbed by the target tissue travels through blood and remains concentrated on a relatively small area when it reaches another surface such as the endocardial surface on the other side of a heart chamber. The present invention reduces the likelihood of damage to other structures since the ultrasonic energy diverges beyond the focus and is spread over a larger area. The focused ultrasound has a focal length of about 2 to 20 mm, more preferably about 2 to 12 mm and most preferably about 8 mm in at least one dimension. The focused ultrasound also forms an angle of 10 to 170 degrees, more preferably 30 to 90 degrees and most preferably about 60 degrees as defined relative to a focal axis. The focused ultrasound preferably emits over 90%, and more preferably over 99%, of the energy within the angles and focal lengths described above. The focused ultrasound may be produced in any manner and is preferably produced by a curved transducer with a curved layer attached thereto. The ultrasound is preferably not focused, and may even diverge, when viewed along an axis transverse to the focal axis.

The ultrasound transducers are preferably operated while varying one or more characteristics of the ablating technique such as the frequency, power, ablating time, and/or location of the focal axis relative to the tissue. In a first treatment method, the transducer is activated at a frequency of 2-7 MHz, preferably about 3.5 MHz, and a power of 80-140 watts. preferably about 110 watts, in short bursts. For example, the transducer may be activated for 0.01-1.0 second and preferably about 0.4 second. The transducer is inactive for 2-90 seconds, more preferably 5-80 seconds, and most preferably about 45 seconds between activations. Treatment at this frequency in relatively short bursts produces localized heating at the focus. Energy is not absorbed as quickly in tissue at this frequency as compared to higher frequencies so that heating at the focus is less affected by absorption in the tissue.

In a second treatment method, the transducer is operated for longer periods of time, preferably about 1-4 seconds and more preferably about 2 seconds, to distribute more ultrasound energy between the focus and the near surface. The frequency during this treatment is also 2-14 MHz, more preferably 3-7 MHz and preferably about 6 MHz. The transducer is operated for 0.7-4 seconds at a power of 20-60 watts, preferably about 40 watts. The transducer is inactive for at least 3 seconds, more preferably at least 5 seconds and most preferably at least 10 seconds between each activation.

In a third treatment method, the ultrasonic transducer is activated at a higher frequency to heat and ablate the near surface. The transducer is preferably operated at a frequency of at least 6 MHz and more preferably at least 10 MHz and most preferably about 16 MHz. The transducer is operated at lower power than the first and second treatment methods since ultrasound is rapidly absorbed by the tissue at these frequencies so that the near surface is heated quickly. In a preferred method, the transducer is operated at 2-10 watts and more preferably about 5 watts. The transducer is preferably operated until the near surface NS temperature reaches 70-85 degrees C.

In general, the treatment methods described above deliver energy closer and closer to the near surface NS with each subsequent treatment method. Such a treatment method may be practiced with other devices without departing from this aspect of the invention and, as mentioned below, may be automatically controlled by the control system.

The device preferably has a number of cells with each cell having at least one ablating element. After ablating tissue with all of the cells, gaps may exist between adjacent ablations. The tissue in the gaps is preferably ablated by moving at least one of the ablating elements. In one method, the entire device is shifted so that each cell is used a second time to ablate one of the adjacent gaps. Yet another method of ablating tissue in the gaps is to tilt one or more of the ablating elements to direct the ultrasound energy at the gaps between cells. The ablating element may be moved, tilted or pivoted in any suitable manner and is preferably tilted with an inflatable membrane. The transducer may also simply be configured to direct ultrasound energy to tissue lying beneath the gaps between adjacent transducers. In this manner, the device does not need to be moved or tilted.

The device may be adhered to tissue with suction although suction is not required. The device may also have a membrane filled with a substance which transmits the ultrasound energy to the tissue. The membrane conforms to the tissue and eliminates air gaps between the device and tissue to be ablated. Alternatively, the device may have a solid element which contacts the tissue and transmits the ultrasound energy to the tissue. The device may also be used with a gel applied to the tissue which transmits the ultrasound energy and eliminates air gaps.

The device may also have a number of ultrasound transducers with varying characteristics. For example, the device may have cells which provide focused ultrasound having different focal lengths or which are intended to operate at different frequencies or power. In this manner, the user may select the appropriate cell to ablate a particular tissue structure. For example, it may be desirable to select an ablating element with a small focal length and/or low power when ablating thin tissue.

An advantage of using ultrasound for ablating tissue is that the transducer may be used for other measurements. For example, the transducer may be used to provide temperature, tissue thickness, thickness of fat or muscle layers, and blood velocity data. The ultrasound transducer may also be used to assess the adequacy of contact between the device and the tissue to be ablated. These features find obvious use in the methods described herein and all uses of ultrasound mentioned here, such as temperature feedback control, may be accomplished using other methods and devices.

Other aspects and advantages of the invention are disclosed in the following detailed description and in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is side view of a left ablation probe according to the invention.

FIG. 1B is a side view of a right ablation probe according to the invention.

FIGS. 2A-2F are side views of a working end of the left ablation probe of FIG. 1A in various configurations thereof.

FIG. 3 is a side cross-section of the working end of the left ablation probe of FIG. 1A.

FIG. 4 is a transverse cross-section of the shaft of the left ablation probe of FIG. 1A.

FIGS. 5A-C are partial side cross-sections of the working end of the left ablation probe of FIG. 1A, showing the deployment of a superior sub-probe and inner probe thereof.

FIG. 6 is a side view of the left ablation probe of FIG. 1A.

FIG. 7 is a partial side cross-section of the handle of the left ablation probe of FIG. 1A.

FIG. 8 is an anterior view of the thorax of a patient illustrating the positioning of the left and right ablation probes according to the method of the invention.

FIG. 9 is a side view of the interior of a patient's thorax illustrating the positioning of the left and right ablation probes according to the method of the invention.

FIG. 10 is a posterior view of a patient's heart illustrating the use of the left and right ablation probes according to the method of the invention.

FIG. 11 is a posterior view of a patient's heart illustrating a transmural lesion formed according to the method of the invention.

FIGS. 12 and 13 are side views of the left ablation probe of the invention positioned on a patient's heart, showing a balloon and suction ports, respectively, on the inner probe.

FIG. 14A shows the ablating device having a pre-shaped distal portion.

FIG. 14B shows an alternative anchor.

FIG. 14C shows another anchor.

FIG. 14D shows still another anchor.

FIG. 15 shows the ablating device having a flexible distal portion which is shaped with a stylet.

FIG. 16 is a cross-sectional view of the ablating device of FIGS. 14 and 15 with three chambers of the balloon inflated.

FIG. 17 is a cross-sectional view of the ablating device of FIGS. 14 and 15 with two chambers of the balloon inflated.

FIG. 18 shows the ablating device advanced into the transverse pericardial sinus with the balloon deflated.

FIG. 19 shows the ablating device advanced into the transverse pericardial sinus with the balloon inflated.

FIG. 20 shows the ablating device extending between the left and right inferior pulmonary veins and another ablating device having an end superior to the right superior pulmonary vein.

FIG. 21 shows the ablating device moved toward the right superior and right inferior pulmonary veins.

FIG. 22 shows one of the ablating devices having an emitter and the other ablating device having a sensor for aligning the devices across a pericardial reflection.

FIG. 23 shows the ablating device having a needle to deliver a marker which is located on the other side of the pericardial reflection.

FIG. 24 shows the ablating device having a number of discrete guide portions.

FIG. 25 shows the guide portions being inflatable balloons.

FIG. 26 shows selective inflation of the balloons for selective ablation along the ablating device.

FIG. 27A shows the guide portions used when ablating around the pulmonary veins.

FIG. 27B shows the guide portions being inflatable when ablating around the pulmonary veins.

FIG. 28 is a bottom view of another ablating device which is advanced over a guide.

FIG. 29 is a top view of the ablating device of FIG. 28.

FIG. 30 is a cross-sectional view of the ablating device of FIGS. 28 and 29 along line A--A of FIG. 29.

FIG. 31 is another cross-sectional view of the ablating device of FIGS. 28 and 29 along line B--B of FIG. 29.

FIG. 32 shows the guide advanced to a desired location with the balloon deflated.

FIG. 33 shows the ablating device advanced over the guide and creating a first lesion.

FIG. 34 shows the ablating device creating a second lesion continuous with the first lesion.

FIG. 35 shows the ablating device creating a third lesion continuous with the second lesion.

FIG. 36 shows another ablating device having an expandable device movable thereon.

FIG. 37 is a cross-sectional view of the ablating device of FIG. 36.

FIG. 38 is an enlarged view of the cross-sectional view of FIG. 37.

FIG. 39 shows the ablating device with a piercing element in a retracted position.

FIG. 40 shows the ablating device aligned across the pericardial reflection.

FIG. 41 shows the ablating device interlocked with another ablating device on opposite sides of the pericardial reflection.

FIG. 42 shows a mechanism for locking the first and second ablating devices together.

FIG. 43 shows the piercing element engaging a lock on the other ablating device.

FIG. 44 shows the ablating device passing through the pericardial reflection and interlocking with itself.

FIG. 45 shows the ablating devices interlocked across the pericardial reflections.

FIG. 46 shows the ablating device adhered to a pericardial reflection with suction.

FIG. 47 shows the penetrating element penetrating the pericardial reflection.

FIG. 48 shows the ablating device passing through the pericardial reflection.

FIG. 49 shows another ablating device.

FIG. 50 shows a buckle for forming a closed loop with the ablating device.

FIG. 51 shows another buckle for forming the closed loop with the ablating device.

FIG. 52 shows a bottom side of the ablating device of FIG. 49.

FIG. 53A is a cross-sectional view of the ablating device along line C--C of FIG. 52.

FIG. 53B is an alternative cross-sectional view of the ablating device along line C--C of FIG. 52.

FIG. 54 is a cross-sectional view of the ablation device along line D--D of FIG. 53A showing a fluid inlet manifold.

FIG. 55 is a cross-sectional view of an alternative embodiment of the device.

FIG. 56 shows a system for controlling the ablation device of FIG. 55.

FIG. 57 shows the device having two sets of lumens extending from each end of the device toward the middle of the device.

FIG. 58 shows another ablating device.

FIG. 59 is an exploded view of a cell of the ablating device.

FIG. 60 is a cross-sectional view of the ablating device of FIG. 60.

FIG. 61 is a perspective view of a transducer with a layer attached thereto.

FIG. 62 is an end view of the transducer and layer.

FIG. 63 is a plan view of the transducer and layer.

FIG. 64 shows another ablating device with a membrane filled with a substance with transmits energy from the transducer to the tissue.

FIG. 65 shows the membrane inflated to move the focus relative to the tissue.

FIG. 66 shows another ablating device with a membrane which tilts the device when inflated.

FIG. 67 shows another ablating device.

FIG. 68 shows still another ablating device having at least two ablating elements which have different ablating characteristics.

FIG. 69 is an isometric view of another ablating element which diverges in at least one dimension to ablate tissue beneath gaps between ablating elements.

FIG. 70 is a side view of the ablating element of FIG. 69.

FIG. 71 shows still another device for ablating tissue.

FIG. 72 is a partial cross-sectional view showing three ablating elements which are movable within a body of the device.

FIG. 73 shows the ablating elements with the body removed.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

FIGS. 1A-1B illustrate a first embodiment of the apparatus of the invention. In this embodiment, the apparatus comprises a left ablation probe 20, shown in FIG. 1A. and a right ablation probe 22, shown in FIG. 1B, which work in tandem to form a transmural lesion isolating the pulmonary veins from the surrounding myocardium. Left ablation probe 20 has a flexible shaft 21 extending to a working end 24 configured for insertion into the chest cavity through a small incision, puncture or access port. Opposite working end 24, shaft 21 is attached to a control end 26 used for manipulating the working end 24 from outside the chest. Shaft 21 is dimensioned to allow introduction through a small incision in the chest, preferably in a subxiphoid location, and advanced to the pulmonary veins on the posterior side of the heart. Preferably, shaft 21 is configured to be flexible about a first transverse axis to allow anterior-posterior bending and torsional flexibility, but relatively stiff about a second transverse axis perpendicular to the first transverse axis to provide lateral bending stiffness. In an exemplary embodiment, shaft 21 has a length in the range of about 10-30 cm, and a guide portion 25 having a rectangular cross-section with a width-to-height ratio of about 2-5, the cross-sectional width being about 6-35 mm and the cross-sectional height being about 3-17 mm. The guide portion 25 aligns the device between the epicardium and pericardium to ablate tissues as described below. Shaft 21 is made of a flexible biocompatible polymer such as polyurethane or silicone, and preferably includes radiopaque markers or a radiopaque filler such as bismuth or barium sulfate.

Working end 24 includes a plurality of ablating elements 27. The ablating elements 27 are preferably a plurality of electrodes 28 for delivering radiofrequency (RF) current to the myocardium so as to create transmural lesions of sufficient depth to block electrical conduction. Electrodes 28 may be partially-insulated solid metal rings or cylinders, foil strips, wire coils or other suitable construction for producing elongated lesions. Electrodes 28 are spaced apart a distance selected so that the lesions created by adjacent electrodes contact or overlap one another, thereby creating a continuous, uninterrupted lesion in the tissue underlying the electrodes. In an exemplary embodiment, electrodes 28 are about 2-20 mm in length and are spaced apart a range of 1-6 mm. It is understood that the term electrodes 28 as used herein may refer to any suitable ablating element 27. For example, as an alternative to RF electrodes, the ablating elements 27 may be microwave transmitters, cryogenic element, laser, heated element, ultrasound, hot fluid or other types of ablation devices suitable for forming transmural lesions. The heated element may be a self-regulating heater to prevent overheating. Electrodes 28 are positioned so as to facilitate lesion formation on the three-dimensional topography of the left atrium. For example, lateral electrodes 28a face medially to permit ablation of the myocardium on the lateral side of the left inferior pulmonary vein and medial electrodes 28b face anteriorly to permit ablation of the posterior surface of the myocardium adjacent to the left inferior pulmonary vein.

Working end 24 further includes a locating mechanism which locates the working end at one of the pulmonary veins and helps to maintain it in position once located. In a preferred embodiment, working end 24 is bifurcated into two branches 30, 32, and the locating mechanism is a notch 34 disposed between the two branches. Notch 34 tapers into a concave surface 36 so as to receive one of the pulmonary veins between branches 30, 32 and to atraumatically engage the pulmonary vein against concave surface 36. In an exemplary embodiment, notch 34 is about 10 to 30 mm in width at its widest point between branches 30, 32 and tapers toward concave surface 36 which has a radius of curvature of about 4 to 15 mm, so as to conform to the outer curvature of the pulmonary vein. Preferably, notch 34 is sized and positioned for placement against the left inferior pulmonary vein, as described more fully below. Alternatively, the locating mechanism may be configured to engage another anatomic structure such as the inferior vena cava, superior vena cava, pericardial reflections, pulmonary vein, aorta, pulmonary artery, atrial appendage, or other structure in the space between the pericardium and the myocardium. The various shapes of the ablating devices described and shown herein are, of course, useful in locating various structures to position the ablating elements against predetermined tissues to be ablated.

Working end 24 further includes a superior sub-probe 38 and an inferior subprobe 40 which are slidably extendable from working end 24, as further described below.

Control end 26 includes a handle 42 and a plurality of slidable actuators 44A-44E, which are used to extend superior sub-probe 38 and inferior sub-probe 40 from working end 24, and to perform other functions as described below. An electrical connector 46 suitable for connection to an RF generator is mounted to handle 42 and is electrically coupled to electrodes 28 at working end 24. Also mounted to handle 42 are a working port 48 in communication with a working channel 92, described below, and a connector 50 for connection to a source of inflation fluid or suction, used for purposes described below.

Right ablation probe 22 has a flexible shaft 52 extending from a control end 54 to a working end 56. Working end 56 has a cross-member 58 to which are mounted a plurality of electrodes 60. Cross member 58 preferably has tips 59 which are pre-shaped or deflectable into a curve so as to conform to the right lateral walls of the right pulmonary veins, and which are separated by a distance selected so that the two right pulmonary veins may be positioned between them, usually a distance of about 20-50 mm. Electrodes 60 are sized and positioned so as to create a continuous lesion along the right side (from the patient's perspective) of the pulmonary veins as described more fully below. In an exemplary embodiment, electrodes 60 are about 2-20 mm in length, and are spaced apart about 1-6 mm. Shaft 52 is dimensioned to allow introduction through a small incision in the chest, preferably in a subxiphoid location, and advanced to the pulmonary veins on the posterior side of the heart. Shaft 52 will have dimensions, geometry and materials like those of shaft 21 of left ablation probe 20, described above.

Control end 54 includes a handle 62. An electrical connector 64 adapted for connection to an RF generator is attached to handle 62 and is electrically coupled to electrodes 60 at working end 56. An inflation or suction connector 65 is mounted to handle 62 and adapted for connection to a source of inflation fluid or suction, for purposes described below. Handle 62 may further include a working port (not shown) like working port 48 described above in connection with left ablation probe 20.

FIGS. 2A-2E illustrate the deployment of the various components of working end 24 of left ablation probe 20. Superior sub-probe 38 is slidably extendable from working end 24 as shown in FIG. 2B. A plurality of electrodes 66 are mounted to superior sub-probe 38 and are sized and positioned to create a continuous lesion along the left side of the pulmonary veins. Superior sub-probe 38 has an articulated or steerable section 68 which can be selectively shaped into the position shown in FIG. 2C, with its distal tip 70 pointing in a lateral direction relative to the more straight proximal portion 72.

As shown in FIG. 2D, an inner probe 74 is slidably extendable from superior sub-probe 38 and is directed by steerable section 68 in a lateral direction opposite notch 34. Inner probe 74 is separated from notch 34 by a distance selected such that inner probe 74 may be positioned along the superior side of the pulmonary veins when the left inferior pulmonary vein is positioned in notch 34. In an exemplary embodiment, the maximum distance from concave surface 36 to inner probe 74 is about 20-50 mm. A plurality of electrodes 76 are mounted to inner probe 74 and positioned to enable the creation of a continuous transmural lesion along the superior side of the pulmonary veins as described more fully below.

Referring to FIG. 2E, inferior sub-probe 40 is slidably extendable from working end 24. Its distal tip 78 is attached to a tether 80 extending through a lumen in shaft 21. Tether 80 may be selectively tensioned to draw distal tip 78 away from inner probe 74 (toward control end 26), imparting a curvature to inferior sub-probe 40. Inferior sub-probe 40 is constructed of a resilient, bendable plastic which is biased into a straight configuration. When inferior sub-probe 40 has been advanced sufficiently, tether 80 may be released, whereby the resiliency of inferior sub-probe 40 causes it to conform to the pericardial reflection and the medial and/or inferior sides of the four pulmonary veins. Inferior sub-probe 40 further includes a plurality of electrodes 82 sized and positioned to produce a continuous transmural lesion in the myocardium along the inferior side of the pulmonary veins, as described more fully below.

Referring to FIGS. 3 and 4, superior sub-probe 38 is slidably disposed in a first lumen 84 and inferior sub-probe 40 is slidably disposed in a second lumen 86 in shaft 21. Electrodes 28 along notch 34 are coupled to wires 88 disposed in a wire channel 90 running beneath electrodes 28 and extending through shaft 21. Each electrode is coupled to a separate wire to allow any electrode or combination of electrodes to be selectively activated. Shaft 21 also includes a working channel 92 extending to an opening 94 in working end 24 through which instruments such as endoscopes, suction/irrigation devices, mapping and ablation devices, tissue retraction devices, temperature probes and the like may be inserted. Superior sub-probe 38 has an inner lumen 96 in which inner probe 74 is slidably disposed. Electrodes 76 on inner probe 74 are coupled to wires 98 extending through inner probe 74 to connector 46 on handle 42, shown in FIG. 1A. Similarly, electrodes 66 on superior sub-probe 38 are coupled to wires 99 (FIG. 4) and electrodes 82 on inferior sub-probe 40 are coupled to wires 100, both sets of wires extending to connector 46 on handle 42. Tether 80 slidably extends through tether lumen 102 in shaft 21.

The distal end of inner probe 74 has a tip electrode 104 for extending the transmural lesion produced by electrodes 76. Preferably, inner probe 74 further includes a device for approximating the tip of inner probe 74 with the superior tip 106 of right ablation probe 22 (FIG. 1B) when the two are separated by a pericardial reflection. In a preferred embodiment, a first electromagnet 108 is mounted to the distal end of inner probe 74 adjacent to tip electrode 104. First electromagnet 108 is coupled to a wire 110 extending to handle 42, where it is coupled to a power source and a switch (not shown) via connector 46 or a separate connector. Similarly, a second electromagnet 112 is mounted to distal tip 78 of inferior subprobe 40, adjacent to a tip electrode 114, which are coupled to wires 116, 118 extending to a connector on handle 42. As shown in FIG. 1B, a third electromagnet 120 is mounted to superior tip 106 of right ablation probe 22, and a fourth electromagnet 122 is mounted to inferior tip 124 of right ablation probe 22. Electromagnets 120, 122 are coupled to wires (not shown) extending to a connector on handle 62 for coupling to a power source and switch. In this way, superior tip 106 and inferior tip 124 may be approximated with inner probe 74 and inferior sub-probe 40 across a pericardial reflection by activating electromagnets 108, 112, 120, 122.

It should be noted that thermocouples, thermistors or other temperature monitoring devices may be mounted to the working ends of either left or right ablation probes 20, 22 to facilitate temperature measurement of the epicardium during ablation. The thermocouples may be mounted adjacent to any of the electrodes described above, or may be welded or bonded to the electrodes themselves. The thermocouples will be coupled to wires which extend through shafts 21, 52 alongside the electrode wires to connectors 46, 64 or to separate connectors on handles 42, 62, facilitating connection to a temperature monitoring device.

FIGS. 5A-5C illustrate the operation of superior sub-probe 38. Superior subprobe 38 has a pull wire 126 movably disposed in a wire channel 128 in a sidewall adjacent to inner lumen 96. Pull wire 126 is fixed at its distal end 130 to steerable section 68 of superior sub-probe 38. Steerable section 68 is constructed of a flexible, resilient plastic such that by tensioning pull wire 126, steerable section 68 may be deformed into a curved shape to direct inner probe 74 in a transverse direction relative to the straight proximal portion 72, as shown in FIG. 5B. Once in this curved configuration, inner probe 74 may be slidably advanced from superior sub-probe 38 as shown in FIG. 5C.

Referring to FIG. 6, actuator 44D is slidably disposed in a longitudinal slot 132 in handle 42 and is coupled to the proximal end of inferior sub-probe 40. Actuator 44E is slidably disposed in a longitudinal slot 134 in handle 42 and is coupled to the proximal end of tether 80. When sub-probe 40 is to be deployed, actuator 44D is slid forward, advancing inferior sub-probe 40 distally. Actuator 44E may be allowed to slide forward as well, or it may be held in position to maintain tension on tether 80, thereby bending sub-probe 40 into the curved shape shown in FIG. 2E. When sub-probe 40 has been fully advanced, actuator 44E may be released, allowing distal end 78 of sub-probe 40 to engage the pericardial reflection along the inferior surfaces of the pulmonary veins, as further described below.

Actuators 44A-C are slidably disposed in a longitudinal slot 136 in handle 42, as more clearly shown in FIG. 7. Actuator 44A is attached to the proximal end of superior sub-probe 38, and may be advanced forward to deploy the sub-probe from working end 24 as shown in FIG. 2A. Actuator 44B is attached to inner probe 74, which is frictionally retained in inner lumen 96 such that it is drawn forward with superior sub-probe 38. Actuator 44C is attached to pull wire 126 which is also drawn forward with superior sub-probe 38. In order to deflect the steerable section 68 of superior sub-probe 38, actuator 44C is drawn proximally, tensioning pull wire 126 and bending steerable section 68 into the configuration of FIG. 2C. Finally, to deploy inner probe 74, actuator 44B is pushed forward relative to actuators 44A and 44C, advancing inner probe 74 from superior sub-probe 38 as shown in FIG. 2D.

The slidable relationship between the shafts and probes 74, 40, 38 helps to guide and direct the probes to the tissues to be ablated. The shafts have various features, including the ablating elements 27, however, the shafts may be simple sheaths which locate structures and/or direct the probes into various regions of the pericardial space.

Referring now to FIGS. 8-11, a preferred embodiment of the method of the invention will be described. Initially, left ablation probe 20 and right ablation probe 22 are connected to an RF generator 140. RF generator 140 will preferably provide up to 150 watts of power at about 500 kHz, and will have capability for both temperature monitoring and impedance monitoring. A suitable generator would be, for example, a Model No. EPT-1000 available from the EP Technologies Division of Boston Scientific Corp. of Natick, Mass. Retraction, visualization, temperature monitoring, suction, irrigation, mapping or ablation devices may be inserted through working port 142. Left ablation probe 20 may further be connected to a source of suction or inflation fluid 144, for reasons described below. If electromagnets are provided on left and right ablation probes 20, 22 as described above, an additional connection may be made to a power supply and switch for operating the electromagnets, or power may be supplied by RF generator 140 through connectors 46, 64.

A subxiphoid incision (inferior to the xiphoid process of the sternum) is made about 2-5 cm in length. Under direct vision through such incision or by visualization with an endoscope, a second small incision is made in the pericardium P (FIG. 9). Left ablation probe 20 is introduced through these two incisions and advanced around the inferior wall of the heart H to its posterior side under fluoroscopic guidance using fluoroscope 146. Alternative methods of visualization include echocardiography, endoscopy, transillumination, and magnetic resonance imaging. Left ablation probe 20 is positioned such that left inferior pulmonary vein LI is disposed in notch 34 as shown in the posterior view of the heart in FIG. 10.

Superior sub-probe 38 is then advanced distally from working end 24 until its steerable section 68 is beyond the superior side of the left superior pulmonary vein LS. Steerable section 68 is then deflected into the curved configuration shown in FIG. 10 such that its distal end 70 is superior to the left superior pulmonary vein LS and pointing rightward toward the right superior pulmonary vein RS. Inner probe 74 is then advanced toward the right until its distal tip is very close to or contacting the pericardial reflection PR superior to the right superior pulmonary vein RS.

Inferior sub-probe 40 is next advanced from working end 24 while maintaining tension on tether 80 such that the inferior sub-probe engages and conforms to the shape of the pericardial reflection PR between the left inferior and right inferior pulmonary veins. When inferior sub-probe 40 has been fully advanced, tension is released on tether 80 so that distal tip 78 moves superiorly into engagement with the right inferior pulmonary vein RI adjacent to pericardial reflection PR inferior thereto.

Right ablation probe 22 is-placed through the subxiphoid incision and pericardial incision and advanced around the right side of the heart as shown in FIG. 8. Under fluoroscopic guidance, right ablation probe 22 is positioned such that cross-member 58 engages the right superior and inferior pulmonary veins, as shown in FIG. 10. In this position, superior tip 106 and inferior tip 124 should be generally in opposition to distal tip 75 of inner probe 74 and distal tip 78 of inferior sub-probe 40, respectively, separated by pericardial reflections PR. In order to ensure close approximation of the two tip pairs, electromagnets 108, 120, 114, 122 may be energized, thereby attracting the tips to each other across the pericardial reflections RS.

It should be noted that the pericardium P attaches to the heart at the pericardial reflections PR shown in FIGS. 10-11. Because of the posterior location of the pulmonary veins and the limited access and visualization available, cutting or puncturing the pericardial reflections in the vicinity of the pulmonary veins poses a risk of serious injury to the heart or pulmonary veins themselves. The apparatus and method of the present invention avoid this risk by allowing the pericardial reflections to remain intact, without any cutting or puncturing thereof, although the pericardial reflections may also be cut without departing from the scope of the invention.

RF generator 140 is then activated to deliver RF energy to electrodes 28. 60, 66, 76, 82, 104, and 112 on left and right ablation probes 20, 22, producing the transmural lesion L shown in FIG. 11. Preferably, power in the range of 20-150 watts is delivered at a frequency of about 500 kHz for a duration of about 30-180 seconds, resulting in localized myocardial temperatures in the range of 45-95.degree. C. Ultrasound visualization may be used to detect the length, location and/or depth of the lesion created. Lesion L forms a continuous electrically-insulated boundary encircling the pulmonary veins thereby electrically isolating the pulmonary veins from the myocardium outside of lesion L.

Ablation probes 20, 22 may further be used for mapping conduction pathways in the heart (local electrocardiograms) for the diagnosis of electrophysiological abnormalities. This is accomplished by selecting any of the electrodes on the ablation probes and monitoring the voltage. A commercially available electrophysiology monitoring system is utilized, which can select any electrode on the ablation probes and monitor the voltage. Various electrodes and various locations on the heart wall may be selected to develop a map of potential conduction pathways in the heart wall. If ablation treatment is then required, the steps outlined above may be performed to create transmural lesions at the desired epicardial locations.

During any of the preceding steps, devices may be placed through working port 142 and working channel 92 to assist and supplement the procedure. For example, a flexible endoscope may be introduced for visualization to assist positioning. Ultrasound probes may be introduced to enhance visualization and for measuring the location and/or depth of transmural lesions. Suction or irrigation devices may be introduced to clear the field and remove fluid and debris. Tissue manipulation and retraction devices may be introduced to move and hold tissue out of the way. Cardiac mapping and ablation devices may also be introduced to identify conduction pathways and to supplement the ablation performed by left and right ablation probes 20, 22.

Furthermore, mapping and ablation catheters, temperature monitoring catheters, and other endovascular devices may be used in conjunction with the left and right ablation probes of the invention by introducing such devices into the right atrium or left atrium either through the arterial system or through the venous system via the right atrium and a transeptal puncture. For example, an ablation catheter may be introduced into the left atrium to ablate any region of the myocardium not sufficiently ablated by left and right ablation probes 20, 22 in order to ensure complete isolation of the pulmonary veins. Additionally, ablation catheters may be introduced into the right chambers of the heart or epicardial ablation devices may be introduced through incisions in the chest to create other transmural lesions.

In some cases, it may be desirable to actively ensure adequate contact between the epicardium and the electrodes of left and right ablation probes 20, 22. For this purpose. left ablation probe 20 and/or right ablation probe 22 may include one or more expandable devices such as balloons which are inflated in the space between the heart and the pericardium to urge the ablation probe against the epicardial surface. An exemplary embodiment is shown in FIG. 12, in which a balloon 150 is mounted to the outer surface of inner probe 74 opposite electrodes 76 on left ablation probe 20. Inner probe 74 further includes an inflation lumen 152 in communication with an opening 154 within balloon 150 and extending proximally to inflation fitting 50 on handle 42, through which an inflation fluid such as liquid saline or gaseous carbon-dioxide may be delivered. When inflated, balloon 150 engages the inner surface of the pericardium P and urges inner probe 74 against the epicardial surface of heart H. This ensures close contact between electrodes 76 and the epicardium, and protects extracardiac tissue such as the pericardium and phrenic nerve from injury caused by the ablation probes. Balloons or other expandable devices may similarly be mounted to superior sub-probe 38, inferior sub-probe 40, or right ablation probe 22 to ensure sufficient contact between the epicardium and the electrodes on those components.

Alternatively or additionally, suction ports may be provided in the ablation probes of the invention to draw the electrodes against the epicardium, as shown in FIG. 13. In an exemplary embodiment, suction ports 156 are disposed in inner probe 74 between or adjacent to electrodes 76. Suction ports 156 are in communication with a suction lumen 158 which extends proximally to suction fitting 48 on handle 42. In this way, when suction is applied through suction port 156, inner probe 74 is drawn tightly against the heart, ensuring good contact between electrodes 76 and the epicardium. In a similar manner, superior subprobe 38, inferior sub-probe 40 and right ablation probe 22 may include suction ports adjacent to the electrodes on those components to enhance contact with the epicardium.

Referring to FIGS. 14A, 15, 16 and 17, the ablating device 20 is shown with various features described above. The embodiments are specifically referred to as ablating device 20A and like or similar reference numbers refer to like or similar structure. The ablating device 20A may have any of the features of the ablating devices 20, 22 described above and all discussion of the ablating devices 20, 22 or any other ablating device described herein is incorporated here. As mentioned above, the ablating device 20A may have a preshaped portion 160 or a flexible or bendable portion 162 as shown in FIGS. 14 and 15, respectively. A stylet 164 or sheath (not shown) is used to shape the ablating device 20A as described below. The stylet 164 passes through a working channel 166 which may receive other devices as described above. The working channel 166 may also be coupled to a source of fluid 169, such as fluoroscopic contrast, which may be used for visualization. The contrast may be any suitable contrast including barium, iodine or even air. The fluoroscopic contrast may be introduced into the pericardial space to visualize structures in the pericardial space.

Referring to FIG. 14A, the pre-shaped portion 160 has a curved or L-shape in an unbiased position. The distal portion of the device 20A may have any other shape such as a hook or C-shape to pass the device 20A around a structure. The stylet 164 holds the preshaped portion 160 in any other suitable geometry, such as dotted-line 167, for introduction and advancement of the ablating device 20A. The stylet 164 may also be malleable. When the ablating device 20A is at the appropriate position, the stylet 164 is withdrawn thereby allowing the distal end 160 to regain the angled or curved shape. The device 20A may also be shaped with a sheath (not shown) through which the device 20A passes in a manner similar to the manner of FIGS. 2 and 5.

Referring to FIG. 15, the ablating device 20A has the flexible distal portion 162 which is shaped by the stylet 164 into the dotted line 168 position. The pre-shaped portion 160 may be used to position or advance the ablating device 20A between the epicardium and pericardium. FIG. 18 shows the pre-shaped portion positioned around the left superior pulmonary vein as described below. A number of different stylets 164 may be used to shape the flexible portion 162 around various structures.

The ablating device 20A also has an anchor 170 to anchor a portion of the device 20A while moving another part of the device 20A. When the anchor 170 is the balloon 150, the balloon may have a number of chambers 171, preferably three, which can be inflated as necessary to position the device as shown in FIGS. 16 and 17. The chambers 171 are coupled to a source of inflation fluid 173 via inflation lumens 175. The anchor 170 is preferably an expandable element 172 such as the balloon 150, but may also be tines which grab the epicardium, pericardium or pericardial reflection. The anchor 170 may also be one or more suction ports 156, as described above (see FIG. 13). The suction ports 156 may be used to anchor the device to the pericardium, epicardium, pericardial reflection or any other structure in the space between the pericardium and epicardium. Although only one anchor 170 is located at the distal end, the anchor 170 may be positioned at any other location and more than one anchor 170 may be provided without departing from the scope of the invention.

Referring to FIGS. 18-21, a specific use of the ablating device 20A is now described. The ablating devices described herein may, of course, be used to ablate other tissues when positioned in the space between the epicardium and pericardium. The ablating device 20A is preferably introduced in the same manner as the ablating device 20 or in any other suitable manner. When the ablating device