HK1065733A - System for operating an ablation generator with dual energy source - Google Patents

Description

System for operating an ablation generator with dual energy sources

Technical Field

The present invention relates to medical device systems for use in intracardiac mapping and ablation. In particular, the present invention relates to an ablation generator capable of delivering both radiofrequency energy and ultrasound energy to a catheter for the treatment of various forms of cardiac arrhythmias.

Background

The symptoms of abnormal heart rhythm are collectively referred to as arrhythmias, and abnormal tachyarrhythmias are referred to as tachycardias. The presence of proarrhythmic regions or side channels in the atria can bypass or short circuit the normal pathways, possibly leading to very rapid cardiac contraction, referred to herein as atrial flutter. Atrial flutter is generally characterized by a sawtooth pattern with negative deviations of the lower wall leads of the ECG, while atrial rates range from 240 to 340 beats per minute. Atrial fibrillation is a more complex condition of multiple atrial flutters that causes irregular and chaotic heart rhythms. Abnormal fast heart rhythms may also occur in the ventricles, a condition more commonly referred to as ventricular tachycardia.

Treatment of atrial flutter and atrial fibrillation (AFib) can be performed in a variety of ways, including drug, surgery, implantation of pacemakers/defibrillators, and catheter ablation. Although drug treatment can be selected for many patients, it only masks symptoms, does not cure the underlying cause, and also causes side effects. In addition, the implanted device can only correct after an arrhythmia has occurred. On the other hand, surgery and catheter-based treatments can in fact cure the condition, usually by ablating abnormal arrhythmogenic tissue or side-channels that cause tachycardia.

Atrial fibrillation is considered to be a condition in which electrical signals within the atrium conduct abnormally, causing a disorder in the propagation of electrical activity that causes atrial fibrillation to contract. AFib has been considered a benign disorder but is now widely recognized as an important pathogenic and lethal cause. The most dangerous consequences of AFib are thromboembolism, which causes blood stasis, and stroke, which is caused by disorganized contractions of the atria. This in turn can lead to clot formation and possibly to embolic stroke. According to the american society of cardiac medicine, approximately 75,000 strokes are associated with AFib each year.

With current catheter designs, known catheters typically have only one large ablation electrode, although Radio Frequency (RF) catheter ablation has produced promising results. The RF energy delivered to the catheter tip electrode causes the tissue temperature to drop rapidly within milliseconds, thus satisfying most of the treatment of the side channels and the treatment of atrioventricular nodal reentry tachycardia.

However, RF energy is not always suitable. For example, most ventricular arrhythmias associated with coronary ischemic heart disease require more tissue penetration for successful ablation. Left side ablation can cause stroke, while RF ablation at AFib originating in the pulmonary vein can cause stenosis. In AFib patients, because of the multiple microwaves of the reentry electrical pulses that occur simultaneously in the atria, it is necessary to block the multiple reentry pulses simultaneously or sequentially by creating a straight line lesion in the heart.

The use of Ultrasound (US) energy has been proposed, which may be promising in creating deeper lesions in thicker myocardium, and circumferential lesions in the ostia of the pulmonary veins. Ultrasonic waves are a form of vibrational energy (18,000 cycles per second or more) that propagates as mechanical waves through the motion of particles within a medium. This causes the particles to thicken and thin, thereby propagating pressure waves associated with the mechanical motion of the particles. In an absorptive medium, ultrasonic energy is continuously absorbed and converted to heat within the medium. Tissue damage can occur if the temperature rises high enough and is maintained for a specific time. This thermal effect is similar to that obtained using other heating systems with the same thermal exposure.

Disclosure of Invention

It is therefore an object of the present invention to provide an improved catheter-based ablation system having dual energy sources (RF and US) in a single generator unit for treating various arrhythmogenic clinical indications, such as supraventricular tachycardia, atrial flutter, atrial fibrillation, and ventricular tachycardia.

In order to achieve the object of the present invention, the present invention provides a catheter system having: an RF catheter, an ultrasonic catheter, and an ablation generator connected to the RF generator and the ultrasonic generator. The ablation generator is capable of generating RF energy and ultrasonic energy.

Drawings

Fig. 1 is a system diagram illustrating components of a catheter-based ablation system according to the present invention.

Fig. 2 is a block diagram of an ablation generator of the system shown in fig. 1.

Fig. 3 is a flow chart showing the operation of the system shown in fig. 1.

Fig. 4 illustrates how the system of fig. 1 delivers ultrasonic energy during ablation.

Fig. 5 illustrates how the system of fig. 1 delivers RF energy during ablation.

Detailed Description

The following detailed description is of the best modes contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention. The scope of the invention is best defined by the appended claims.

Fig. 1 illustrates components of a catheter-based ablation system 10 of the present invention. The system 10 includes a first catheter device 12, the catheter device 12 being used to provide RF energy to a treatment site where ablation is performed. The system 10 further includes a second catheter device 14, the catheter device 14 being for providing ultrasonic energy to a treatment site where ablation is to be performed. Devices 12 and 14 may be provided using catheter structures known in the RF catheter and ultrasound catheter arts, respectively, and may operate using RF and ultrasound principles known in the art, and therefore, their structure and operation will not be described in detail herein.

The system 10 also includes an ablation generator 16. The ablation generator 16 has an indifferent electrode 18 connected to a patient return electrode pad 20, which return electrode pad 20 is attached to the back of the patient to complete the RF circuit, but is not required when using the ultrasound catheter 14. The ablation generator 16 also includes an RF patient connector 22 that connects to the RF catheter 12 to provide ultrasound energy to the catheter 12. The ablation generator 16 further includes an ultrasound patient connector 24, the ultrasound patient connector 24 being connected to the ultrasound catheter 14 to provide ultrasound energy to the ultrasound catheter 14. The ultrasound catheter 14 has an ultrasound transducer enclosed in a balloon provided at the distal end portion of the catheter. A plurality of electrodes are disposed on the distal portion of the RF catheter 2, and a guidewire extending through the lumen of the RF catheter 12 connects each separate electrode to a connector pin at the proximal end of the catheter shaft.

Fig. 2 is a block diagram showing the major components of ablation generator 16. The ablation generator 16 has an AC power inlet 30 that receives an AC input. The output of the AC power inlet 30 is connected to the input of an isolation transformer 32 which serves to isolate the patient from the circuitry of the system 10. The output of the transformer 32 is connected to a DC power supply 34 and an RF circuit board 36. The DC power supply 34 converts the AC voltage into a DC voltage. The output of the DC power supply 34 is provided to the input of the color LCD display and microcontroller 38, the input of the RF circuit board 36, the input of the thermocouple and thermistor circuit board 48, and the input of the ultrasonic circuit board 50. The color LCD display and microcontroller 38 controls the display of information on a display screen 42 (see fig. 1) and controls the power, temperature and impedance of the generator 16. The inputs and outputs of the color LCD display and microcontroller 38, the output of the transformer 32 and one output of the DC power supply 34 are connected to the RF circuit board 36. The RF circuit board 36 also receives the output of the indifferent electrode 18. The RF circuit board 36 generates a power signal of about 500kHz and about 150 watts and provides an output to an input of the RF splitter circuit board 40. The RF splitter circuit board 40 splits the power signal from the RF circuit board 36 into four tank circuits. The RF splitter circuit board 40 has an input connected to the RF isolated patient connector 22 and the output is also connected to an input of a low pass filter 44. The other input to the low pass filter 44 is from the ultrasound patient connector 24.

The output of the low pass filter 44 is connected to the input of an Electrocardiogram (ECG) connector 46. The color LCD display and inputs and outputs of the microcontroller 38 are provided to the ultrasound circuit board 50, while the outputs of the ultrasound circuit board 50 are provided to the ultrasound patient connector 24. The ultrasonic circuit board 50 generates ultrasonic energy of about 7-8MHz and about 50 watts. A phase-locked loop circuit provided in the ultrasonic circuit board 50 maximizes the acoustic energy transmitted through the ultrasonic transducer. A phase detector is provided in the phase locked loop circuit and detects the impedance of the ultrasonic transducer in the ultrasonic catheter 14 to enable the generator 16 to provide the appropriate ultrasonic ablation frequency. In particular, the phase detector sweeps the appropriate current and voltage phases and adjusts them to zero phase and sweep the minimum transducer impedance. The minimum transducer impedance allows the ultrasonic transducer to vibrate at its eigenfrequency or resonant frequency, which is the maximum vibration energy.

In addition, the color LCD display and microcontroller 38 is connected to the thermocouple and thermistor circuit board 48 via a two-way connector. The thermocouple and thermistor circuit board 48, which functions as a temperature amplifier, also has inputs that receive outputs from the DC power supply 34, the RF isolated patient connector 22 and the ultrasound patient connector 24.

Temperature sensors (not shown) are also provided at the proximal end of each electrode of the RF catheter 12, and on the balloon of the ultrasound catheter 14 or near the ultrasound transducer. The sensor constantly monitors the temperature of the body tissue and forwards the temperature to the color LCD display and microcontroller 38.

The DC power supply 34 thus provides the required power to the RF circuit board 36 and the ultrasonic circuit board 50. RF circuit board 36 provides RF energy to RF catheter 12, while ultrasound circuit board 50 provides ultrasound energy to ultrasound catheter 14, all under the control of color LCD display and microcontroller 38. Software programs or algorithms are provided in the color LCD display and microcontroller 38 to control the supply of RF or ultrasonic energy. In particular, microcontroller 38 provides signals to a current divider circuit board 40, which is used to control the RF energy output of each electrode over a predetermined temperature range. The microcontroller 38 also provides signals to the ultrasonic circuit board 50 to control the voltage and current that the microcontroller sends from the microcontroller 38 to maximize the ultrasonic energy output of the ultrasonic transducer. The sum of the total duration of RF and ultrasonic energy output sent to each electrode or ultrasonic transducer and within a predetermined temperature range is individually preset.

An RF energy density is provided to each of the four electrodes, and when acoustic energy is selected for delivery, is also provided to the ultrasound transducer on the catheter. "RF energy fluence" is defined herein as the RF energy delivered per unit of tissue contact surface area. The generator 16 additionally includes a closed loop control (provided in the microcontroller 38) for each electrode with a temperature sensor (which may be the same as the temperature sensor described above). To better control the desired lesion properties, more RF energy may be provided to an electrode when the tissue contact temperature detected from that electrode is relatively low. On the other hand, RF energy may be reduced when the measured tissue contact temperature is relatively high. The generator 16 also has a programmed control device for independently selecting and controlling the ablation electrodes of the RF catheter 12 via the RF splitter circuit board 40. In this case the number of electrodes used for ablation can be selected and controlled in one of the following ways: simultaneous mode, sequential mode, individual mode, or a combination thereof.

More ultrasonic energy is provided when the measured tissue contact temperature is relatively low for better control of the lesion properties. Conversely, less ultrasonic energy is provided when the detected tissue contact temperature is relatively high.

Fig. 3 is a flow chart illustrating operation of the ablation generator 16 shown in fig. 2. As shown in fig. 3, the generator 16 first determines whether the ultrasound catheter 14 or the RF catheter 12 is used. Once the nature or type of catheter is determined, the mode, power and temperature of ablation are set, and ablation is then initiated by providing the selected energy (RF or ultrasound) to the catheter 12 or 14. The generator 16 will also check whether the temperature, impedance, phase and power (as applicable) are within preselected limits and stop ablation if any of the parameters are outside of preselected ranges. On the other hand, ablation continues as long as these parameters are within preselected limits.

Fig. 4 illustrates how the system of fig. 1 delivers ultrasonic energy during ablation. The ultrasound catheter 14 is connected to an ultrasound patient connector 24 and the catheter 14 is percutaneously advanced in a minimally invasive manner into a treatment area within the patient's heart. Fig. 5 illustrates how the system of fig. 1 delivers RF energy during ablation. The RF catheter 12 is connected to an RF patient connector 22 and the catheter 12 is percutaneously advanced in a minimally invasive manner into a treatment area within the patient's heart. Patient return electrode pad 20 is connected to indifferent electrode 18 and attached to the back of the patient to complete the RF circuit.

While the above has been described with reference to specific implementations of the invention, it will be appreciated that many modifications may be made without departing from the spirit of the invention. It is intended that the appended claims cover all such modifications as fall within the scope and spirit of the invention.

Claims (1)

1. A catheter system, comprising:

an RF catheter;

an ultrasonic waveguide; and

an ablation generator connected to the RF generator and the ultrasound generator and having means for generating RF energy and ultrasound energy.