WO1999017671A1

WO1999017671A1 - Transmyocardial revascularization using radiofrequency energy

Info

Publication number: WO1999017671A1
Application number: PCT/US1998/020799
Authority: WO
Inventors: Michael Aita; Carl J. Simpson; Randy J. Kesten
Original assignee: Cardiogenesis Corporation
Priority date: 1997-10-02
Filing date: 1998-10-02
Publication date: 1999-04-15
Also published as: AU9680398A; JP2001518345A; WO1999017671A9; CA2305333A1; EP1018961A1

Abstract

The invention is directed to a system and method for revascularization of a patient's heart tissue by at least one burst of RF energy over an interval of about 1 to about 500 msec, preferably about 30 to about 130 msec. The device preferably has an elongated insulated, electrical conducting shaft with an uninsulated distal tip which is configured to emit RF energy. A method is described for myocardial revascularization of a human heart in which an elongated flexible device is used which includes a radiofrequency ablation device. In some embodiments, the device is configured to be introduced percutaneously, on other embodiments, the device is configured to be introduced intraoperatively. The RF energy emitter is advanced to a position adjacent a desired area of the heart wall. The device is activated, moving tissue to form a revascularization channel.

Description

TRANSMYOCARDIAL REVASCULARIZATION USING RADIOFREQUENCY ENERGY

RELATED APPLICATIONS

This application is a continuation-in-part of copending application Serial No.

08/942,874, filed October 2, 1997, and application Serial No. 08/968,184, filed

November 12, 1997, which are both continuations of application Serial No.

08/517,499, filed August 9, 1995. All of the above-referenced applications are

hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

This invention is directed to the ablation or disruption of tissue in the wall of a

patient's heart and particularly to form channels within the heart wall in order to

perform transmyocardial revascularization (TMR), to deliver therapeutic or

diagnostic agents to various locations in the patient's heart wall or for a variety of

other utilities.

As presently used, TMR involves forming a plurality of channels in a

ventricular wall of a patient's heart by means of laser energy. The first clinical trials

of the TMR procedure using laser energy were performed by Mirhoseini et al. See

for example the discussions in Lasers in General Surgery (Williams & Wilkins;

1989), pp. 216-223. Other early disclosures of the TMR procedure are found in an

article by Okada et al. in Kobe J. Med. Sci 32, 151-161 , October 1986 and in U.S.

Patent 4,658,817 (Hardy). These early references describe intraoperative TMR

procedures which require an opening in the chest wall and include formation of

channels completely through the heart wall starting from the epicardium. U.S. Patent NO. 5,554,152 which issued on December 20, 1994 (Aita et al.),

which is incorporated herein in its entirety, describes a system for TMR which is

introduced through the chest wall either as an intraoperative procedure where the

chest is opened up or as a minimally invasive procedure where the system is

introduced into the patient's chest cavity through small openings in the chest by

means of a thoroscope.

In U.S. Patent No. 5,389,096 (Aita et al.) a percutaneous TMR procedure is

described wherein an elongated flexible laser based optical fiber device is

introduced through the patient's peripheral arterial system, e.g., the femoral artery,

and advanced through the aorta until the distal end of the device extends into the

patient's left ventricle. Within the left ventricle, the distal end of the optical fiber

device is directed toward a desired location on the patient's endocardium and urged

against the endocardial surface while a laser beam is emitted from its distal end to

form the channel.

Copending application Serial No. 08/078,443, filed on June 15, 1993 (Aita et

al.), which is incorporated herein in its entirety, describes an intravascular system

for myocardial revascularization which is percutaneously introduced and advanced

into the left ventricle of the patient's heart where laser energy initiates

revascularization through the endocardium and into the myocardium. This

procedure eliminates the need of the prior procedures to open the chest cavity and

to penetrate the epicardium in order to form the channel through the endocardium

into the myocardium.

The laser based revascularization procedure has been shown to be clinically

beneficial to a variety of patients, particularly patients who were, for the most part, not suitable candidates for by-pass surgery or for minimally invasive procedures

such as angioplasty or atherectomy. However, to date the equipment for laser

based systems has been quite expensive. What has been needed is a system

which is less expensive than but as clinically effective as laser based systems. The

present invention satisfies these and other needs.

SUMMARY OF THE INVENTION

The present invention is directed to a method and system for the

revascularization of a region of a patient's heart by ablating or disrupting tissue in

said region with emissions of radiofrequency (RF) energy and is particularly

directed to the methods and systems to ablate or disrupt tissue in the patient's heart

wall to form channels therein by means of such RF energy.

One method includes the step of inserting an elongated shaft having an RF

energy emitter into a patient's vasculature. Preferably, a system for guiding the

device is also provided. The RF energy emitter is guided to the interior of the left

ventricle and positioned against a desired portion of the ventricle's inner wall.

Then, the RF energy emitter is activated to remove or otherwise injure tissue. The

RF energy emitter may be advanced so as to remove tissue until a channel or

disrupted area is formed to the desired depth. Methods for controlling the depth of

channel formation include fluoroscopic or ultrasonic visualization or advancing the

revascularization means a fixed distance. In addition, penetration limitation can be

achieved with mechanical penetration limiters such as those taught in copending

U.S. Application Ser. No. 08/486,978, which is hereby incorporated by reference in

its entirety. The RF energy emitter is repositioned against another portion of the heart wall and the process is repeated until enough channels or regions of ablated

tissue are formed to provide the desired revascularization.

In accordance with one embodiment of the invention, tissue is ablated within

a patient's heart wall by means of one or more bursts of RF emissions over

intervals of about one to about 500 msec and preferably about 30 to about 130

msec. A radiofrequency burst may comprise a continuous emission or

discontinuous emission, i.e. be pulsatile, and, if pulsatile, may involve a plurality or

train of pulses which may or may not be of the same width (duration), frequency or

amplitude.

The RF emissions are preferably controlled so that heart tissue is exposed to

the RF energy over a desired period and particularly over a period which will avoid

interfering with the patient's heart beat, e.g., just after the R wave but before the T

wave. One to about 10 bursts of RF energy may be required to effectively form the

desired channel within the patient's heart wall and preferably one burst of RF

emission is delivered per heart cycle. The RF energy source generally should have

a peak power output of about 150 to about 500 watts, preferably about 200 to about

300 watts.

It also may be desirable to operate the RF energy emitter at more than one

energy level. Initially, the channel formation or tissue disruption may be performed

at a relatively high energy level to position and anchor the RF ablation device. For

greater control, the remainder of the procedure may be performed at a lower energy

level.

One presently preferred system for revascularizing a patient's heart wall

includes an RF energy transmitting member which has a proximal end, and an uninsulated distal tip configured to emit RF energy. The system is introduced into

the patient and advanced within the patient until the uninsulated distal tip thereof is

disposed adjacent to a surface of the patient's heart wall. At least one burst of RF

energy from an RF energy source is transmitted through the RF energy transmitting

member to the uninsulated distal tip thereof. The RF energy is then emitted from

the distal tip and into the heart wall in contact with said distal tip. In preferred

embodiments, the channel formed in the heart wall preferably has an aspect ratio,

i.e., depth to width, of at least 1 , preferably at least 2.

Any particles of tissue produced by the RF energy emitter have the potential

to create emboli if allowed to escape into the patient's circulatory system.

Accordingly, in a number of these embodiments, the RF energy emitter includes

lumens for perfusion and aspiration to remove the particles from the patient's body.

Alternatively, the RF energy emitter is configured to produce particles small enough

to safely propagate through the smallest branches of the patient's vasculature,

approximately 6-10 μm in diameter.

One embodiment of the invention utilizes a percutaneous approach in which

a flexible RF energy emitter is advanced through the patient's vasculature until a

distal portion of the system enters a heart chamber such as the left ventricle. The

RF energy transmitting member is advanced so that the uninsulated distal tip which

emits RF energy contacts the interior surface of the heart wall which defines in part

the heart chamber. At least one burst of RF energy is emitted from the uninsulated

distal tip of the system into the patient's heart wall wherein tissue is ablated or

otherwise disrupted, resulting in the revascularization of the heart wall region.

Another embodiment of the invention involves a minimally invasive approach where a small incision is made in the patient's chest and with or without the benefit

of a trocar sheath, an elongated RF energy transmitting member is advanced into

the patient's chest cavity until the uninsulated distal tip of the RF transmitting

member contacts the exterior of the patient's heart. One or more bursts of RF

energy are emitted from the uninsulated distal tip so as to ablate or disrupt tissue

within the patient's heart wall causing the revascularization thereof, as in the

previously discussed embodiments of the invention. A similar procedure may be

used in conjunction with an open chest procedure such as coronary by-pass

surgery or in other surgical procedures, as is the case with laser based

transmyocardial revascularization.

The RF energy emitter preferably includes an RF energy transmitting

member which is insulated along its length except for the distal tip thereof which is

uninsulated and which is configured to contact the surface of the heart wall and to

emit bursts of RF energy therefrom into adjacent tissue of the heart wall. The

uninsulated distal tip can have a diameter of about 0.025 to about 0.2 inch (0.64-5.1

mm), preferably about 0.04 to about 0.08 inch (1-2 mm) and a length of about 0.1 to

about 5 mm, preferably about 1.5 to about 3.5 mm. The distal tip may be solid or

hollow and may be relatively sharp or blunt. However, it should not be sharp

enough to penetrate the tissue of the heart wall when pressed against the wall to

maintain contact during the emission of RF energy bursts. The average power level

should be about 50 to about 500 watts, preferably about 100 to about 300 watts.

The frequency of the RF current should not be less than 100 kHz and preferably is

about 250 to about 500 kHz.

The method and system of the invention effectively ablates or disturbs tissue within the patient's heart wall to revascularize the ablated region and particularly can

be used to form channels within the heart wall. These and other advantages of the

invention will become more apparent from the following detailed description of the

invention and the accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a system for revascularizing heart tissue

which embodies features of the invention.

FIG. 2 is a transverse cross-section of the RF energy transmitting member of

the system shown in FIG. 1 taken along the lines 2-2.

FIG. 3 is a schematic illustration of the one shot shown in FIG. 1.

FIG. 4 is a schematic illustration of a system for generating trigger signals

based upon the patient's heart beat.

FIG. 5 is an elevational view of a delivery system for the RF energy emitter

for positioning the operative distal end thereof adjacent to the endocardium of a

patient's heart wall.

FIG. 6 is a schematic elevational view, partially in cross-section, of a human

heart showing revascularization of the myocardium according to the invention.

FIG. 7 is a schematic longitudinal cross-sectional view of the distal portion of

a deflectable elongated RF system which embodies features of the invention.

FIGS. 8 and 9 are schematic longitudinal cross-sectional views of RF

systems useful in the practice of this invention. DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 depict an RF system 10 embodying features of the invention

which includes an RF energy transmitting member 11 having a proximal end

configured for electrical connection to a source 12 of RF energy and an uninsulated

exposed distal end 13 which is configured to emit pulsed RF energy received from

the source and transmitted through the RF energy transmitting member. The RF

energy transmitting member 11 includes an electrical conductor 14 which may be

hollow or solid, a single or multiple strand and an insulating jacket 15 formed of

suitable insulating polymeric material. A suitable source of RF energy is the

Excaliber RF Generator from Aspen Laboratories (ConMed, Englewood, CO, USA).

The output from the RF energy source 12 is pulsed by pulse-trigger system

16 which includes a one-shot 17, such as CD4047 sold by National Semiconductor,

configured to receive trigger signals 18 through electrical conductor 19 and

generate in response a pulsed output signal 20 connected to a NPN transistor 21.

The pulsed output signal 20 from the one-shot 17 actuates the transistor 21 for the

duration of the output signal. The output of the transistor 21 is connected to reed

relay 22 which is configured to close upon receiving the output from the transistor

21. The output of the reed relay 22 is connected in series to the foot switch 23.

When the foot switch 23 is closed and reed relay 22 is closed, the RF energy

source is actuated to emit RF energy for the duration of the output of the reed

relay 22.

FIG. 3 illustrates in more detail the one-shot shown in FIG. 1 which has 14

pins, identified as pins a-n in FIG. 3. The one-shot shown in FIG. 3 has the pins

designated with letters a-n to avoid confusion with other reference numbers used herein. The one-shot model number CD4047 has these pins numbered 1-14. The

trigger signal 18 from an ECG unit is received by pin h and upon receipt of the

trigger signal an on signal is emitted from pin j. The duration of the on signal from

pin j is controlled by the resistance R and capacitance C from the RC circuit

connected to pins a-c as shown. The resistance R can typically range from about

0.1 to about 1 meg ohm and the capacitance can typically range from about 0.08 to

about 0.12 microfarads to control the duration of the pulses of output signal 20 from

about 50 to about 300 msec.

FIG. 4 schematically illustrates a system of generating trigger signals 18

based upon the patient's heart cycle 30. The signals from the patient's heart 31 are

detected with a conventional ECG unit and the detected signals are transmitted to a

trigger generating system 32 which may also be contained in the ECG unit. The

trigger signal generating system 32 is preprogrammed to emit one or more trigger

signals 18 at a predetermined time between the R and the T wave of the heart cycle

30.

Reference is made to FIG. 5 which illustrates a system for the percutaneous

delivery of an RF system which has an outer catheter 40, a shaped distal end 41 , a

port 42 in the distal end of the outer catheter and an inner lumen extending within

the outer catheter to the port in the distal end. This system also includes an inner

catheter 44 which is slidably and rotatably disposed within the inner lumen of the

outer catheter 40 and which has a shaped distal section 45, a distal end 46, a port

47 in the distal end of the inner catheter and an inner lumen 48 extending therein to

the port in the distal end. An RF energy emitter 50 is slidably disposed within the

inner lumen of inner catheter 44. The distal section 45 of the inner catheter 44 is at an angle with respect to the main shaft section 51 of the inner catheter to orient the

RF energy emitter 50 extending out the distal end of the inner catheter. In this

manner the disposition of the distal end 52 of the RF energy emitter 50 can be

controlled by raising and lowering and rotation of the RF energy emitter within the

inner lumen of the inner catheter 44 and the inner catheter within the inner lumen of

the outer catheter 40. The distal end 52 of the RF energy emitter 50 is thus pointed

in a desired direction to the endocardium defining the left ventricle 53. Longitudinal

and rotational movement of the inner catheter 44 provides access to a large region

of the endocardium.

Referring to FIG. 6, the present invention also comprises a method for

revascularizing the myocardium 54 of a human heart 56. An RF system 10 including

an elongated shaft 60 with an RF energy emitter 50 disposed at the distal end is

inserted into the vasculature of a patient, generally through one of the major

vessels by the conventional Seldinger technique. The RF energy emitter 50 is

advanced into the left ventricle 53 and positioned against a desired portion of the

heart muscle 62 in need of increased blood circulation due to cardiovascular

disease. The RF energy emitter 50 is activated and urged against the muscle 62 to

effect removal of tissue, forming the revascularization channel 64. The tissue

region disturbed or ablated should extend a desired distance through the

endocardium 66 and into the myocardium 54 without perforating the epicardium 68.

The RF energy emitter 50 is deactivated, withdrawn from channel 64 and

repositioned against another portion of muscle 62.

In another method of the invention (not shown) an RF system 10 having an

RF energy emitter 50 on the distal end is introduced through a small opening in the patient's chest wall. RF system 10 is advanced until the RF energy emitter 50 is

positioned against the ischemic portion of the heart muscle 62. The RF energy

emitter 50 is activated and urged towards the muscle 62. Tissue is removed

sequentially from the epicardium 68, the myocardium 54 and the endocardium 66 to

form the revascularization channel 64 into the left ventricle 53. As above, the RF

energy emitter 50 is then deactivated, withdrawn from the muscle 62 and

repositioned. In either method, the operator repeats the process until a sufficient

number of channels 64 or similar revascularization sites are formed in muscle 62 to

treat the ischemic condition.

In operation, the RF energy emitter 50 may be maintained in position on the

heart muscle 62 by a controlled advance and gentle pressure, to insure that the RF

energy emitter 50 is not dislodged during formation of the channel. Alternatively,

the RF energy emitter 50 can be maintained in place by applying a vacuum at the

distal tip thereof.

In embodiments where the RF energy emitter 50 allows rapid, intermittent

switching between active and inactive states, the operation may be synchronized

with the patient's heart cycle to avoid channel formation during the vulnerable

period of the heart cycle. Preferably, the RF energy emitter 50 is subject to

automatic control means which prevents operation during the T-wave portion of the

ECG, as known in the art.

Additionally, the RF energy emitter 50 may operate at two or more energy

levels. Preferably, the initial tissue removal to penetrate the endocardium 66 is

performed at a relatively high energy level. The rapid channel formation at this

energy level helps anchor the RF energy emitter 50 within the channel 64. The remainder of the tissue removal may be performed at a lower energy level to

provide slower channel formation and greater control.

In the embodiment depicted in FIG. 2, a plurality of control lines 70 are

connected at their distal ends to the distal end 72 of shaft 60 such as by adhesive

bonding. Adhesive bonding may utilize any of a variety of adhesives, including

cyanoacrylate. At least two, and preferably four, control lines 70 are thus axially,

and preferably symmetrically, disposed about shaft 60. Axial movement of control

lines 70 will thus change the angle of deflection of distal end 72 of shaft 60 with

respect to its proximal end. A mechanism (not shown) such as a ring or knob may

be attached to the proximal ends of control lines 70 to allow manipulation of control

lines 70. Control lines 70 are preferably approximately 3-mil stainless steel wire,

but may be similar filaments, such as nylon, or other suitable materials having

appropriate tensile strength.

In addition, an outer tubular member 74 preferably encloses control lines 70

and shaft 60, forming a protective covering. Outer tubular member 74 is secured at

its distal end to distal end 72 of shaft 60, rearward of RF energy emitter 50. In

order to facilitate precise control of the tip during the procedure, control lines 70 are

routed through spaced apart channels 76 that are attached to the outer surface of

shaft 60. Channels 76 are preferably constructed of 30 gauge polyamide tubing.

Control lines 70 are thus guided to remain both separated and within well controlled

areas on the exterior of shaft 60, thus allowing for the accurate guidance of the

RF system 10 through the remote manipulation of control lines 70.

Another means for guiding shaft 60 and RF energy emitter 50 into a proper

position within the heart is to place the shaft 60 within a deflectable guiding catheter having dual axis steerability, for an added degree of steerability and control. Co-

pending application, S.N. 08/438,743 filed May 10, 1995, entitled DELIVERY

SYSTEM AND METHOD FOR MYOCARDIAL REVASCULARIZATION discloses

such a system and is hereby incorporated in its entirety by reference thereto. In

practice, the positioning of the device may be viewed by esophageal ultrasound

imaging, trans-thoracic ultrasound imaging and trans-thoracic fluoroscopic imaging.

Accordingly, it may be desirable to add one or more radiopaque marker bands to

the distal end 72 of shaft 60, for fluoroscopic imaging. RF energy emitter 50 may

thereby be aimed and controlled for forming channels 64 in the myocardium 54 of

the ischemic heart muscle 62.

Alternative means of ablation are suitable, including thermal and other

radiation means. For example, FIG. 8 illustrates the distal portion of an RF system

100 which has a thermal ablator 78. The thermal ablator 78 has an electrode 80

wrapped around thermally-conductive probe 82 and extending the length of the

system 100. The diameter of probe 82 should be from about 1.0 to 5.0 mm. The

proximal ends of the electrode 80 is are connected to a radiofrequency generating

means (not shown). Applying radiofrequency energy at suitable frequency and

power through electrode 80 produces resistive heating transmitted through probe

82. Generally, energy from about 30 MHz to about 10 GHz is suitable to generate

sufficient heat at probe 82 to ablate heart tissue.

Radiofrequency energy may also provide inductive heating as shown in

FIG. 9. The distal portion of an RF system 10 has a ferrite probe 84 on the end. A

radiofrequency generating means (not shown) irradiates the patient's body with

energy at a frequency to which body tissue is relatively transparent but the ferrite Radiofrequency energy may also provide inductive heating as shown in FIG. 9. The

distal portion of an RF system 10 has a ferrite probe 84 on the end. A

radiofrequency generating means (not shown) irradiates the patient's body with

energy at a frequency to which body tissue is relatively transparent but the ferrite

probe readily absorbs, generating ablating heat.

EXAMPLE

Eighteen channels were made in the heart of a live, anesthetized medium

size dog by means of pulsed RF energy. The wattage and the size and type of

distal tip of the RF delivery system were varied to determine the nature of the

channels formed which result from such variations. The results are set forth

e table below.

Those skilled in the art will recognize that various changes can be made to

the invention without departing from the scope thereof. There has been described

herein various systems and methods for myocardial revascularization employing an

elongated revascularization device. The revascularization may be performed from

within the left ventricle or from the exterior of the heart. Various modifications to the

present invention will become apparent to those skilled in the art from the foregoing

description and accompanying drawings. Accordingly, the present invention is to

be limited solely by the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. An RF system for performing TMR, comprising:

a) an elongated shaft having a proximal end and a distal end

configured to access a patient's heart; and

b) an RF energy emitter disposed at the distal end of the

elongated shaft configured to emit RF energy to surrounding tissue.

2. The RF system of claim 1 further comprising an elongated RF energy

transmitting member having a distal end electrically coupled to the RF energy

emitter.

3. The RF system of claim 1 wherein the RF energy transmitting member

further comprises an insulating sheath having a distal end disposed about at least a

portion thereof.

4. The RF system of claim 3 wherein the RF energy emitter is comprised

of an uninsulated distal tip portion of the elongated RF energy transmitting member

which extends distally beyond the distal end of the insulating sheath.

5. The RF system of claim 4 wherein the uninsulated distal tip has a

diameter of about 0.025 to about 0.20 inch configured to emit pulses of RF energy.

6. The RF system of claim 4 wherein the uninsulated distal tip has a

length of about 0.1 to about 5 mm.

7. The RF system of claim 4 wherein the uninsulated distal tip has a

length of about 1.5 to about 3.5 mm.

8. The RF system of claim 4 wherein the uninsulated distal tip has a

diameter of about 0.04 to about 0.08 inch.

9. A system for ablating tissue in a wall of a patient's heart with one or

more bursts of RF energy, comprising:

a) a source for RF energy;

b) a trigger signal generator operatively coupled to electrical

signals generated by a patient's heart;

c) a control unit which is operatively coupled to the trigger signal

generator and the source for RF energy, and which operates the source of

RF energy upon receipt of trigger signals from the trigger signal generator so

as to emit at least one burst of RF energy in response to a received trigger

signal; and

d) an RF energy transmitting member having a proximal end

which is configured to receive RF energy from the source, an elongated

shaft configured to transmit RF energy received from said source and an

uninsulated distal tip which is configured to emit transmitted RF energy to a

patient's heart wall to ablate tissue therein.

10. The system of claim 9 wherein control unit controls the duration of the

burst of RF energy.

11. The system of claim 9 wherein the trigger generator emits at least one

trigger signal during a desired portion of the patient's heart cycle.

12. A method of forming a channel in a patient's heart wall, comprising:

a) providing an elongated RF energy transmitting device having

proximal and distal ends and which includes an elongated insulated electrical

conductor and an uninsulated distal tip configured to emit RF energy;

b) introducing the elongated RF energy transmitting device into

the patient and advancing the elongated RF energy transmitting device

therein until the uninsulated distal tip thereof is disposed adjacent to a

surface of the patient's heart wall; and

c) emitting one or more bursts of RF energy from the uninsulated

distal tip of the RF energy transmitting device over at least one interval from

about 1 to about 500 msec to form a channel within the heart wall by ablating

tissue therein.

13. The method of claim 12 wherein one or more bursts of RF energy are

emitted from the distal tip over an interval of about 30 to about 130 msec.

14. The method of claim 12 wherein the channel is formed during a single

interval.

15. The method of claim 12 wherein at least one burst of RF energy

emitted from the uninsulated distal tip comprises a plurality of pulses of RF energy.

16. The method of claim 15 wherein the individual pulses have durations

of at least about one msec.

17. The method of claim 12 wherein from about 2 to about 10 bursts of RF

energy are emitted from the uninsulated distal tip to form the channel.

18. A method of revascularizing a desired region of a patient's heart wall,

comprising:

a) providing an elongated flexible RF energy transmitting device

having proximal and distal ends and which includes an uninsulated distal tip

configured to emit RF energy;

b) introducing the elongated flexible RF energy transmitting

device into the patient's vasculature and advancing the elongated flexible RF

energy transmitting device therein until the uninsulated distal tip thereof is

disposed adjacent to and in contact with a surface of the patient's heart wall;

and

c) delivering RF energy from a source thereof through the RF

energy transmitting member to said uninsulated distal tip; and

d) emitting at least one burst of RF energy from the uninsulated

distal tip of the elongated flexible RF energy transmitting device over an

interval of about 1 to about 500 msec to ablate tissue in the desired region of

the patient's heart wall.

19. The method of claim 16 wherein the RF energy source has a peak

power output of about 200 to about 500 watts.

20. A percutaneous method of revascularizing a desired region of a

patient's heart wall, comprising:

a) providing an elongated flexible RF energy transmitting device

having proximal and distal ends and which includes an elongated insulated

electrical conducting member and an uninsulated distal tip configured to emit

RF energy;

b) introducing the elongated flexible RF energy transmitting

device into the patient's vasculature and advancing said device therein until

the uninsulated distal tip thereof is disposed adjacent to and in contact with a

surface of the patient's heart wall;

c) delivering at least one burst of RF energy over an interval of

about 1 to about 500 msec from a source thereof through the RF energy

transmitting device to the uninsulated distal tip thereof; and

d) emitting at least one transmitted burst of RF energy from the

uninsulated distal tip to ablate tissue in the desired region of the patient's

heart wall.

21. The method of claim 20 wherein a channel is formed by said tissue

ablation.

22. The method of claim 20 wherein at least one burst of RF energy

comprises a plurality of pulses of RF energy.

23. The method of claim 22 wherein each individual pulse of RF energy

has a duration of at least one msec.

24. The method of claim 20 wherein the RF energy source has a peak

power output of about 200 to about 500 watts.

25. A method of revascularizing a desired region of a patient's heart wall,

comprising:

a) providing an RF energy transmitting member having proximal

end, an elongated insulated shaft and an uninsulated distal tip configured to

emit RF energy;

b) introducing at least a distal portion of the RF energy

transmitting member into the patient and advancing said member until the

uninsulated distal tip thereof is disposed adjacent to and in contact with a

surface of the patient's heart wall; and

c) during a desired period of the patient's heart cycle, emitting at

least one burst of RF energy from the uninsulated distal tip of the elongated

flexible RF energy transmitting member to ablate tissue in the desired region

of the patient's heart wall to revascularize the desired region.

26. The method of claim 25 wherein the RF energy emission is

continuous during at least one of said bursts.

27. The method of claim 25 wherein the RF energy emission is

discontinuous during at least one of said bursts.

28. The method of claim 27 wherein the discontinuous emission of RF

energy is pulsatile during at least one of said bursts.

29. The method of claim 28 wherein the pulsatile RF energy emission is a

train of pulses.

30. The method of claim 25 wherein at least one burst of RF energy is

emitted from said uninsulated distal tip over an interval of about 1 to about 500

msec.

31. The method of claim 25 wherein at least one burst of RF energy is

emitted from said uninsulated distal tip over an interval of about 30 to about 150

msec.

32. A method of forming a channel in a desired region of a patient's heart

wall, comprising:

a) providing an RF energy transmitting member having a proximal

end, an elongated insulated shaft and an uninsulated distal tip configured to

emit RF energy;

b) introducing at least a distal portion of the elongated RF energy

transmitting member into the patient until the uninsulated distal tip thereof is

disposed adjacent to and in contact with a surface of the patient's heart wall;

and c) emitting at least one burst of RF energy from the uninsulated

distal tip over an interval of about 1 to about 500 msec to form a channel in

the desired region of the patient's heart wall by ablating tissue therein.

33. The method of claim 32 including the step of detecting a desired

period of the patient's heart cycle; and emitting said burst of RF energy from the

uninsulated distal tip during the detected desired period.

34. The method of claim 33 wherein the desired period of the patient's

heart cycle is between the R wave and the T wave of the patient's heart cycle.

35. A method of performing transmyocardial revascularization in a desired

region of a wall of a patient's heart, comprising:

a) providing an elongated device having proximal and distal ends

and a thermal ablator located at the distal end;

b) introducing the device into the body of the patient and directing

the distal end of the device to the desired region of the patient's heart wall

wherein the transmyocardial revascularization procedure is to be performed;

and

c) supplying energy to the thermal ablator to form a

revascularization channel in the myocardium layer.

36. The method of claim 35 wherein the elongated device is a flexible

intravascular device, further comprising the steps of:

a) introducing the device into the patient's body by advancing the

device through the patient's vasculature until a distal portion thereof is

disposed within a chamber of the patient's heart defined by the wall;

b) directing the distal end of the device to the desired region of

the patient's heart wall; and c) supplying energy to the thermal ablator to first ablate tissue

while performing the transmyocardial revascularization.

37. The method of claim 35 wherein the elongated device is configured to

be introduced through the patient's chest wall, further comprising the steps of:

a) directing the distal end of the device to the epicardium layer of

the desired region of the wall; and

b) supplying energy to the thermal ablator to remove tissue

sequentially from the epicardium layer, the myocardium layer and the

endocardium layer to form the revascularization channel.

38. The method of claim 36 wherein the thermal ablator is advanced

through the endocardium layer at a first energy level and within the myocardium

layer at a second energy level lower than the first energy level.

39. The method of claim 35 wherein the elongate device includes lumens

for perfusing and aspirating the desired region of the heart wall, further comprising

the step of clearing the ablated tissue from the patient's heart.

40. The method of claim 35 further comprising the step of forming the

revascularization channel with the thermal ablator at a temperature between about

60 to about 600┬░ C.

41. The method of claim 35 wherein the thermal ablator comprises a

ferrite probe, further comprising the step of irradiating the probe with radiofrequency

energy to form the revascularization channel.

42. The method of claim 41 wherein the revascularization channel are

formed by irradiating the ferrite probe with radiofrequency energy at a frequency

between about 30 MHZ to about 10 GHz.

43. A method of forming a revascularization channel in a desired region of

a wall of a patient's heart, comprising:

a) providing an elongated shaft having proximal and distal ends

and an RF energy emitter located at the distal end;

b) introducing the shaft into the body of the patient and directing

the distal end of the device to the desired region of the wall wherein the

revascularization channel is to be formed; and

c) supplying RF energy to the RF energy emitter to form a

revascularization channel in the myocardial layer.

44. The method of claim 43 wherein the elongated shaft is a flexible

intravascular shaft, further comprising the steps of:

a) introducing the shaft into the patient's body by advancing the

shaft through the patient's vasculature until a distal portion thereof is

disposed within a chamber of the patient's heart defined by the wall;

b) directing the distal end of the shaft to the endocardial layer of

the desired region of the wall; and

c) supplying RF energy to the RF energy emitter to first remove

tissue from the endocardial layer when forming the revascularization

channel.

45. The method of claim 43 wherein the elongated shaft is configured to

a) directing the distal end of the shaft to the epicardial layer of the

desired region of the wall; and

b) supplying RF energy to the RF energy emitter to remove tissue

sequentially from the epicardial layer, the myocardial layer and the

endocardial layer to form the revascularization channel.

46. The method of claim 44 wherein the RF energy emitter is advanced

through the endocardial layer at a first energy level and within the myocardial layer

at a second energy level lower than the first energy level.

47. The method of claim 43 wherein the elongated shaft includes means

the step of clearing the removed tissue from the patient's heart.

48. The method of claim 43 wherein the RF energy emitter comprises a

probe connected to a first and second electrode which extend the length of the

device, further comprising the step of supplying RF energy across the electrodes to

form the revascularization channel.

49. The method of claim 48 wherein the revascularization channel is

formed by supplying RF energy between about 30 MHZ to about 10 GHz across the

electrodes.