Method and system for radiofrequency ablation of cardiac tissue

What is claimed is:

1. A system for radiofrequency ablation of cardiac tissue, said system comprising:

a catheter having a proximal end, a distal end, an electrode near said distal end, and a temperature sensor near said distal end, said electrode being coupled to an electrode connection wire extending to said proximal end, and said temperature sensor being coupled to a temperature sensor connection wire extending to said proximal end; and

a radiofrequency power generator connectable to the proximal end of the catheter, said generator including:

(a) a power source which delivers radiofrequency power to the electrode based on a power output signal;

(b) means for measuring radiofrequency power from the power source to produce an actual power signal;

(c) an analog temperature controller which receives a temperature set point signal and an actual temperature signal from the temperature sensor and based on a difference therebetween produces power set point signal;

(d) an analog power controller coupled to the means for measuring radiofrequency Dower and to the analog temperature controller, wherein the analog power controller receives the power set point signal and the actual power signal and based on a difference therebetween produces the power output signal; and

means for connecting said power source to said electrode connection wire and for connecting said temperature controller to said temperature sensor connection wire.

2. A system as in claim 1, wherein the electrode is at the distal tip of the catheter.

3. A system as in claim 1, wherein the power source comprises a radiofrequency oscillator coupled to a power transformer.

4. A system as in claim 3, wherein the power transformer is coupled to the power controller to receive said power output signal.

5. A system as in claim 1, wherein the power set point signal is proportional to the difference between the actual temperature signal and the temperature set point signal.

6. A system as in claim 1, wherein the power output signal is proportional to the difference between the power set point signal and the actual power signal.

7. A system as in claim 1 further comprising means for optically isolating the temperature sensor from the radiofrequency power generator.

8. A system for radiofrequency ablation of tissue, said system comprising;

a catheter having a proximal end, a distal end, an electrode near said distal end, and a temperature sensor near said distal end, said electrode being coupled to an electrode connection wire extending to said proximal end, and said temperature sensor being coupled to a temperature sensor connection wire extending to said proximal end; and

a radiofrequency power generator connectable to the proximal end of the catheter, said generator including:

(a) power supply means for delivering radiofrequency power to the electrode based on a power output signal:

(b) means for controlling temperature at the temperature sensor, said means being connected to receive an actual temperature signal from the sensor and to modulate the power output signal based on the difference between said actual temperature signal and a temperature set point, wherein the means for controlling temperature comprise an analog temperature control circuit which produces a power set point signal based on the difference between said actual temperature signal and the temperature set point and an analog power control circuit which modulates the power output signal based on a difference between the actual power output from the power source and the power set point signal; and

(c) a battery connected to said power supply means and said means for controlling as the sole source of power for said radiofrequency power generator to reduce or eliminate spurious ground differential currents;

(d) means for connecting said power supply means to said electrode connection wire and for connecting said temperature control means to said temperature sensor connection wire.

9. A system for radiofrequency ablation of tissue, said system comprising:

a catheter having a proximal end, a distal end, an electrode near said distal end, and a temperature sensor near said distal end, said electrode being coupled to an electrode connection wire extending to said proximal end, and said temperature sensor being coupled to a temperature sensor connection wire extending to said proximal end; and

a radiofrequency power generator connectable to the proximal end of the catheter, said generator including

(a) power supply means for delivering radiofrequency power to the electrode based on a power output signal wherein the power output signal is proportional to the difference between the power set point signal and the actual power signal;

(b) means for controlling temperature at the temperature sensor, said means being connected to receive an actual temperature signal from the sensor and to modulate the power output signal based on the difference between said actual temperature signal and a temperature set point: and

(c) a battery connected to said power supply means and said means for controlling as the sole source of power for said radiofrequency power generator to reduce or eliminate spurious around differential currents:

(d) means for connecting said power supply means to said electrode connection wire and for connecting said temperature control means to said temperature sensor connection wire.

10. A system for radiofrequency ablation, said system comprising:

a catheter having a proximal end including connecting means, a distal end, an electrode near the distal end, and a fuse, said electrode being coupled to an electrode connection wire extending to said proximal end and said fuse being coupled to first and second fuse connecting wires coupled to said connecting means;

a radiofrequency power generator connectable to the connecting means at the proximal end of the catheter for supplying radiofrequency power to said electrode through said electrode connection wire;

means in the generator coupled to said first and second fuse connecting wires, for (a) sensing the integrity of the fuse when the catheter is initially connected to the generator, (b) disabling operation of the generator if the fuse is initially broken, and (c) breaking the fuse if the fuse is initially intact, whereby the catheter cannot be reused; and

means for connecting the radiofrequency power generator to the electrode connection wire and for connecting said sensing, disabling and breaking means to said fuse.

11. A system as in claim 10, wherein the electrode is at the distal tip of the catheter.

12. A system as in claim 10, wherein the means for sensing is a voltage sensor coupled to a microprocessor and coupled to said connecting means.

13. A system as in claim 10, wherein the means for disabling operation of the generator is a relay coupled to a microprocessor and coupled to said connecting means for electrically decoupling the electrode connection wire from the generator.

14. A system as in claim 10, wherein the means for breaking the fuse is a current source coupled to said connecting means and monitored by a microprocessor for applying a current to the fuse.

15. A system as in claim 10, wherein the fuse is disposed in the proximal end of the catheter and coupled between a pair of conductors for coupling to said connecting means.

16. A system for radiofrequency ablation of tissue, said system comprising:

a catheter having a proximal end, a distal end, an electrode near said distal end, and a temperature sensor near said distal end, said electrode being coupled to an electrode connection wire extending to said proximal end, and said temperature sensor being coupled to a temperature sensor connection wire extending to said proximal end;

a radiofrequency power generator connectable to the proximal end of the catheter, said generator including

(a) a power source which delivers radiofrequency power to the electrode based on a power output signal;

(b) means for controlling temperature at the temperature sensor, said means being connected to receive a actual temperature signal from the sensor and to modulate the power output signal based on a control signal having a magnitude indicating the difference between said actual temperature signal and a temperature set point;

(c) means for connecting said power source to said electrode connection wire and for connecting said temperature control means to said temperature sensor connection wire; and

(d) means for providing an alternative control signal having a magnitude indicating a selected power level;

(e) means, coupled to said means for providing said alternative control signal for limiting the radiofrequency power delivered to said electrode according to the magnitude of said alternative control signal and irrespective of said actual temperature signal or said temperature set point:

first means for disabling said operation of said radiofrequency power generator comprising a microprocessor coupled to said power source, said microprocessor controlled by software program programmed to disable said radiofrequency power generator based on a first parameter selected from the group including impedance of said electrode, radiofrequency power delivered to said electrode, and said actual temperature signal if at least one of said first parameters exceeds a first limit; and

second means for disabling operation of said radiofrequency power generator based on a second parameter selected from the group including radiofrequency power delivered to said electrode and said actual temperature signal.

17. A system as in claim 16 wherein said second disabling means comprises at least one comparator coupled to the radiofrequency power source and the connecting means to disable said radiofrequency power source if at least one of said second parameters exceeds a second limit.

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of electrophysiology. More particularly, this invention relates to methods and apparatus for treating cardiac arrhythmias.

Symptoms of abnormal heart rhythm are generally referred to as cardiac arrhythmias, with an abnormally slow rhythm being classified as a bradycardia and an abnormally rapid rhythm being referred to a tachycardia. The present invention is concerned with the treatment of tachycardias which are frequently caused by the presence of an "arrhythmogenic site" or "accessory atrioventricular pathway" close to the inner surface of one of the chambers of the heart. The heart includes a number of normal pathways which are responsible for the propagation of signals necessary for the normal electrical function. The presence of arrhythmogenic sites or accessory pathways can bypass or short circuit the normal pathways, potentially resulting in very rapid heart contractions, referred to as tachycardias. Tachycardias may be defined as ventricular tachycardias (VT's) and supraventricular tachycardias (SVT's). VT's originate in the left or right ventricle and are typically caused by arrhythmogenic sites associated with a prior myocardial infarction. SVTt's originate in the atria and are typically caused by an accessory pathway.

Treatment of beth ventricular and supraventricular tachycardias may be accomplished by a variety of approaches, including drugs, surgery, implantable pacemakers/defibrillators, and catheter ablation. While drugs may be the treatment of choice for many patients, they only mask the symptoms and do not cure the underlying cause. Implantable devices only correct the arrhythmia after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem, usually by ablating the abnormal arrhythmogenic tissue or accessory pathway responsible for the tachycardia. The catheter-based treatments rely on the application of various destructive energy sources to the target tissue, including direct current electrical energy, radiofrequency electrical energy, laser energy, and the like.

Of particular interest to the present invention are radiofrequency ablation protocols which have proven to be highly effective in tachycardia treatment while exposing the patient to minimum side effects and risks.

Radiofrequency catheter ablation is generally performed after an initial mapping procedure where the location of the arrhythmogenic sites and accessory pathways are determined. After mapping, a catheter having a suitable electrode is introduced to the appropriate chamber and manipulated so that the electrode lies proximate the accessory pathway. Radiofrequency energy is then applied through the electrode to the cardiac tissue in order to ablate a region of the tissue which forms part of the accessory pathway. By successfully destroying that tissue, the accessory pathway or arrhythmogenic site is destroyed so that the abnormal signalling patterns responsible for the tachycardia will no longer occur.

While very promising, radiofrequency ablation suffers from certain disadvantages. The application of radiofrequency energy to the heart tissue can have complications, particularly if the directed energy has not been properly controlled. Many systems which have been used thus far for radiofrequency ablation have utilized radiofrequency power supplies originally intended for electrosurgery and electrocautery. While such power supplies are workable, they do not provide power control of a type which is best used with cardiac tissue ablation and can subject the patient to spurious ground potentials. Such ground potentials can be a problem when the heart is being treated. Such conventional radiofrequency power supplies are also usually bulky and relatively heavy because of the need to provide power supply transformers.

2. Description of the Background Art

The successful treatment of supraventricular and ventricular tachycardias by radiofrequency catheter ablation of accessory atrioventricular pathways is described in Kuck et al. (1991) Lancet 337:1557-61; Langberg et al. (1991) Am. J. Cardiol. 67:142-47; and Kuck et al. (1991) Circulation 84:2366-2375. Catheters useful for the intracardiac application of radiofrequency energy are described in U.S. Pat. Nos. 4,945,912; 4,940,064; and 4,641,649. A power supply and radiofrequency ablation catheter suitable for intracardiac tissue ablation are available from Dr. Osypka GMBH under the tradenames HAT 200 S and CERABLATE.RTM., respectively. The power supply and catheter together permit ablation to be performed under a digital temperature control mode. The present state of cardiac radiofrequency ablation treatment is summarized in Fackelmann (1991) Science News 140:42-43.

SUMMARY OF THE INVENTION

An improved method for radiofrequency ablation of cardiac tissue relies on the introduction of an electrode to a target site, typically the location of an accessory pathway, within an interior chamber of a patient's heart. Radiofrequency energy is applied to the target location through the electrode from an external power source, where the amount of radiofrequency energy delivered is controlled based on a particular temperature control protocol which has been found to provide very precise control of the ablation temperature. Such precise temperature control reduces the risk of unintended damage to the cardiac tissue and, in particular, provides for better localization of the treatment. That is, tissue necrosis is more accurately limited to within the target region than with non-temperature controlled protocols. The temperature control protocol also limits the total amount of energy delivered to achieve the desired tissue ablation by reducing the duty cycle of the power source. The reduced duty cycle is of particular advantage in that a more controlled ablation result is obtained. The use of a battery power source is advantageous since it reduces or eliminates the generation of spurious ground differential currents, which can be a particular problem in equipment used with the heart.

The temperature control protocol comprises measuring temperature at the target location, typically using a temperature sensor within the treatment electrode. The resulting actual temperature signal is amplified and then compared with a temperature set point signal, and a power set point signal is produced based on the deviation between the actual temperature and temperature set point. Power output from the power source (typically an output power oscillator connected to a battery) is measured to produce an actual power signal, and the actual power signal is compared with the power set point to produce a power output signal based on the difference between the set point and the actual power. Power from the power source is then controlled based on the power output signal. Usually, both the temperature control and power control loops will be based on proportional control schemes.

In a particular aspect, the present invention provides a method for connecting an intravascular catheter, such as a radiofrequency ablation catheter, to a power source. After connecting a proximal end of the catheter to the power source, the status of a fuse within the catheter is sensed. If the fuse is found to be broken at the time of connection, the power source is disabled, i.e. further use of the catheter is prevented. If the fuse is found to be intact at the time of connection, the fuse will then be broken (typically by passing excess current therethrough) and use of the catheter permitted for so long as it remains connected to the power source. Once the catheter is removed from the power source, the connection method will be repeated to prevent reconnection of used catheter, i.e., those catheters which have been previously connected to the power source and which as a result have broken the internal fuse.

The present invention further provides a radiofrequency power generator which comprises a power source for producing radiofrequency power based on a power output signal. The generator comprises circuitry for measuring the amount of radiofrequency power produced by the power source to produce an actual power signal. An analog temperature controller receives both a temperature set point and an actual temperature signal and, based on the different therebetween, produces a power set point signal. A separate analog power controller receives the power set point signal from the temperature controller and the actual power signal from the power measurement circuitry, and, based on the difference therebetween, produces the power output signal which controls the power source. The generator further comprises an interface for connecting a catheter to the radiofrequency power source and for connecting an external temperature sensor in the catheter to the temperature controller in the generator.

In yet another aspect, the present invention provides a system for radiofrequency ablation of cardiac tissue which comprises both a catheter and a radiofrequency power generator. The catheter includes both an electrode and a temperature sensor near its distal end, and the radiofrequency power generator includes both a power source to deliver radiofrequency power to the electrode and a battery connected to the power source. A temperature controller is further provided for modulating the power to the catheter from the power source. In this way, the total power delivered and power duty cycle can be limited in order to reduce the demand on the battery for the power source.

In a still further embodiment, the present invention provides a radiofrequency ablation system comprising a catheter and a radiofrequency generator connectable to the catheter. A catheter includes electrode near its distal end and a fuse within its body. Circuitry within the generator is capable of sensing the integrity of the fuse when the catheter is initially connected to the generator. Operation of the generator, including the delivery of power to the electrode, is disabled if it is sensed that the fuse is initially broken. Conversely, if it is sensed that the fuse is initially intact, the fuse will be broken by the generator and subsequent operation of the generator, including power delivery to the electrode, will be permitted.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a system for radiofrequency ablation of cardiac tissue constructed in accordance with the principles of the present invention, comprising a catheter connected to a radiofrequency generator.

FIG. 2 is an enlarged view of the catheter of FIG. 1, with a curved tip shown in broken line.

FIG. 3 is a detailed view of the catheter of FIGS. 1 and 2, shown in section.

FIG. 4 is a block diagram of the circuitry of a radiofrequency generator constructed in accordance with the principles of the present invention.

FIG. 5 illustrates the exterior of a power supply system constructed in accordance with the principles of the present invention.

FIGS. 6A and 6B illustrate a flow chart of the operating program of the microprocessor-controlled power system of the present invention.

FIGS. 7,7a-7f, 8,8a-8d, 9,9a-9d, 10,10a-10d, 11,11a-11c, 12,12a-12c are schematics illustrating the circuitry of the radiofrequency generator of FIG. 4.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The method and apparatus of the present invention are intended for delivering radiofrequency energy to a target location within an interior chamber within a patient's heart, usuall