Patent Description:
During an ablation procedure on a heart, there may be local overheating of the heart surface being ablated, as well as of the heart tissue underlying the surface. The surface overheating may be manifested as charring, and the overheating of the underlying tissue may cause other damage to the tissue, even leading to penetration of the tissue causing additional problems. To monitor and control the temperature of the surface and the underlying tissue, as well as to estimate the temperature of the tissue, a temperature sensor may be positioned within a distal tip of the catheter, and the region being ablated may be irrigated with an irrigation fluid, typically saline, in order to prevent charring.

The research paper by Di Donna, Paolo, et al. "Efficacy of catheter ablation for atrial fibrillation in hypertrophic cardiomyopathy: impact of age, atrial remodeling, and disease progression. " Europace <NUM> (<NUM>), assessed the outcome of a multicenter hypertrophic cardiomyopathy cohort following radiofrequency catheter ablation for symptomatic atrial fibrillation refractory to medical therapy. This research paper describes using an irrigation rate of <NUM>-<NUM>/min in order to maintain, in a tip of an open irrigated-tip catheter, a temperature below <NUM>.

The research paper by <NPL>), evaluated electrode temperatures obtained using a radiofrequency ablation system that incorporates closed loop feedback control to achieve preset target electrode temperatures and to determine if closed loop temperature control results in a lower incidence of developing a coagulum. While automatically modulating the amount of power delivered (range, <NUM>. 5W - <NUM> W) so that the tip temperature approaches but does not exceed the selected target temperature (<NUM>° - <NUM>) by more than <NUM>, this research paper determined that successful ablation could be achieved with the electrode tip temperature being as low as <NUM>.

<CIT>, describes a method of targeting and ablating cardiac tissue. The method describes modulating the delivered ablation power between <NUM> - <NUM> W using feedback from a catheter-embedded thermocouple in order to attempt to achieve a selected target temperature of between <NUM> - <NUM>. The method also describes a mode of operation that achieves a tissue temperature below <NUM>, and preferably in the range of <NUM> - <NUM>.

<CIT>, describes systems and methods for ablating body tissue using an electrode for contacting tissue at a tissue-electrode interface to transmit ablation energy at a determinable power level. The method includes applying 30W of radiofrequency catheter ablation power in order to achieve ablation temperatures between <NUM> - <NUM>.

<CIT>, describes a cardiac ablation system and method that uses an ablation electrode having an energy emitting body. The system can maintain the temperature of the tissue undergoing ablation can also above a prescribed minimum temperature condition (e.g. <NUM>).

<CIT>describes methods and systems for ablating tissue within a body. The system includes a control that can be aimed so that a constant power to the electrode is maintained, or a constant temperature of the tip electrode is maintained.

<CIT> presents ablation systems and methods directed toward delivering pulsed radiofrequency (RF) energy to target tissue.

<CIT> discloses an apparatus, consisting of a probe configured to be inserted into contact with a myocardium, and an electrode attached to the probe. A temperature sensor, incorporated in the probe, is configured to output a temperature signal. A pump irrigates the myocardium, via the probe, with an irrigation fluid at a controllable rate, and a radiofrequency (RF) signal generator applies RF power via the electrode to the myocardium, so as to ablate the myocardium. The apparatus also has processing circuitry that measures a temperature of the probe, based on the temperature signal, while the RF power is applied and, when the measured temperature exceeds a preset target temperature, iteratively reduces the RF power applied by the signal generator and concurrently iteratively varies a rate of irrigation of the irrigation fluid provided by the pump, until the measured temperature is reduced to the preset target temperature.

There is provided, in accordance with an embodiment of the present disclosure, an irrigated ablation system including a medical probe including a flexible insertion tube having a distal end configured to be inserted into a chamber of a heart, an ablation electrode disposed at the distal end and configured to convey ablation energy to a region of myocardial tissue with which the electrode is in contact, a temperature sensor disposed at the distal end and configured to output a temperature signal indicative of a temperature of the region of myocardial tissue, a channel contained within the insertion tube and configured to deliver an irrigation fluid to the distal end, and one or more fluid ports coupled to the channel and disposed at the distal end. The irrigated ablation system also includes an ablation energy generator configured to apply a specified level of the ablation energy to the ablation electrode, a pump configured to force the irrigation fluid into the channel at a controllable pumping rate, and a processor configured to control the pumping rate responsively to the temperature signal so that a difference between a specified ablation temperature, which is no greater than <NUM>, and the indicated temperature is no greater than ±<NUM> while the ablation energy generator delivers a constant level of the ablation energy to the ablation electrode.

In some exemplary embodiments, the medical probe includes an intracardiac catheter.

In additional exemplary embodiments, the irrigation fluid includes a saline solution.

In further exemplary embodiments, the specified ablation temperature is at least <NUM>.

In supplementary exemplary embodiments, the temperature sensor includes a thermocouple.

In one exemplary embodiment, the irrigated ablation system may also include a temperature module configured to receive the temperature signal from the temperature sensor, to compute, based on the temperature signal, a temperature value, and wherein the processor is configured to control the pumping rate responsively to the temperature signal by controlling the pumping rate responsively to the temperature value. In some exemplary embodiments, the processor is configured to control the pumping rate responsively to the temperature signal by applying a proportional-integral-derivative controller (PID) algorithm to the indicated temperature.

In additional exemplary embodiments, the ablation energy can be selected from a list consisting of radio-frequency (RF) energy, high-intensity focused ultrasound (HIFU) energy and pulsed field ablation (PFA) energy.

There is also provided, in embodiments of the present disclosure, an unclaimed method including applying a specified level of ablation energy to an ablation electrode disposed at a distal end of a medical probe inserted into a chamber of a heart and in contact with a region of myocardial tissue, receiving, by a processor from a temperature sensor disposed at the distal end, a signal indicative of a temperature of the region of myocardial tissue, and controlling a pumping rate of irrigation fluid to one or more fluid ports disposed at the distal end distal end responsively to the temperature signal so that a difference between a specified ablation temperature, which is no greater than <NUM>° C, and the indicated temperature is no greater than ±<NUM>° C while delivering a constant level of the ablation energy to the ablation electrode.

There is also provided, in embodiments of the present disclosure, a computer software product, operated in conjunction with an intracardiac catheter having a distal end inserted into a chamber of a heart, a channel contained within the insertion tube and configured to deliver an irrigation fluid to the distal end, and one or more fluid ports coupled to the channel and disposed at the distal end, the product including a non-transitory computer-readable medium, in which program instructions are stored, which instructions, when read by a computer, cause the computer to apply a specified level of ablation energy to an ablation electrode disposed at the distal end and configured to convey ablation energy to a region of myocardial tissue with which the electrode is in contact to receive, from a temperature sensor disposed at the distal end, a temperature signal indicative of a temperature of the region of myocardial tissue, and to control a pumping rate of irrigation fluid to the one or more fluid ports end responsively to the temperature signal so that a difference between a specified ablation temperature, which is no greater than <NUM>° C, and the indicated temperature is no greater than ±<NUM>° C while delivering a constant level of the ablation energy to the ablation electrode.

The disclosure is herein described, by way of example only, with reference to the accompanying drawings, wherein:.

Embodiments of the present disclosure describe systems and unclaimed methods for maintaining the temperature of myocardial tissue within a specified range during an ablation procedure. As described hereinbelow, the system comprises a medical probe, an ablation energy generator, a pump, and a processor.

The medical probe comprises a flexible insertion tube having a distal end configured to be inserted into a chamber of a heart, and an electrode disposed at the distal end and configured to convey ablation energy to a region of myocardial tissue with which the electrode is in contact. The medical probe also comprises a temperature sensor disposed at the distal end and configured to output a temperature signal indicative of a temperature of the region of myocardial tissue. The medical probe further comprises a channel contained within the insertion tube and configured to deliver an irrigation fluid to the distal end. The medical probe additionally includes one or more fluid ports coupled to the channel and disposed at the distal end.

As described hereinbelow, the ablation energy generator is configured to apply a specified level of the ablation energy to the ablation electrode, and the pump is configured to force the irrigation fluid into the channel at a controllable pumping rate. In exemplary embodiments of the present invention, the processor is configured to control the pumping rate responsively to the temperature signal so that a difference between a specified ablation temperature, which is typically no greater than <NUM>, and an indicated or target temperature, is no greater than ±<NUM> while the ablation signal generator delivers a constant level of the ablation energy to the ablation electrode.

By keeping the temperature variation of the myocardial tissue to a narrow range (e.g., ±<NUM>), and by keeping the mean temperature at a relatively low value (e.g., below about <NUM>), systems implementing exemplary embodiments of the invention can help reduce the risk of heat-based complications (e.g., steam-pops) during ablation procedures.

<FIG> is a schematic, pictorial illustration of a medical system <NUM> comprising a medical probe <NUM> and a control console <NUM>. Medical system <NUM> may be based, for example, on the CARTO® system, produced by Biosense Webster Inc. (Diamond Bar, California, U. In embodiments described hereinbelow, medical probe <NUM> comprises an intracardiac catheter that can be used for diagnostic or therapeutic treatment, such as for ablating tissue in a heart <NUM> of a patient <NUM>. Medical probe <NUM> may also be referred to as an ablation catheter.

Medical probe <NUM> comprises an insertion tube <NUM> and a handle <NUM> coupled to a proximal end of the insertion tube. By manipulating handle <NUM>, a medical professional <NUM> can insert a distal end <NUM> of medical probe <NUM> into a body cavity in patient <NUM>. For example, medical professional <NUM> can insert medical probe <NUM> through the vascular system of patient <NUM> so that distal end <NUM> enters a chamber of heart <NUM> and engages myocardial tissue at a desired location or locations.

Control console <NUM> is connected, by a cable <NUM> to body surface electrodes, which typically comprise adhesive skin patches <NUM> that are affixed to patient <NUM>. Control console <NUM> comprises a processor <NUM> that, in conjunction with a current tracking module <NUM>, determines position coordinates of distal end <NUM> inside heart <NUM> based on impedances measured between adhesive skin patches <NUM> and a location electrode <NUM> that is disposed at distal end <NUM>, as described in the description referencing <FIG> hereinbelow. Location electrode <NUM> is connected to control console <NUM> by wires (not shown) running through medical probe <NUM>.

Processor <NUM> may comprise real-time noise reduction circuitry <NUM> typically configured as a field programmable gate array (FPGA), followed by an analog-to-digital (A/D) ECG (electrocardiograph) signal conversion integrated circuit <NUM>. The processor can pass the signal from A/D ECG circuit <NUM> to another processor and/or can be programmed to perform one or more algorithms disclosed herein, each of the one or more algorithms comprising steps described hereinbelow. The processor uses noise reduction circuitry <NUM> and A/D ECG circuit <NUM> as well as features of modules which are described in more detail below, in order to perform the one or more algorithms presented in exemplary embodiments described herein.

The medical system shown in <FIG> uses impedance-based sensing to measure a location of distal end <NUM>; however, other position tracking techniques may be used (e.g., techniques using magnetic-based sensors). Impedance-based position tracking techniques are described, for example, in <CIT>, <CIT> and <CIT>. The methods of position sensing described hereinabove are implemented in the above-mentioned CARTO® system and are described in detail in the patents cited above.

Control console <NUM> also comprises an input/output (I/O) communications interface <NUM> that enables the control console to transfer signals from, and/or transfer signals to electrode <NUM> and adhesive skin patches <NUM>. Based on signals received from electrode <NUM> and/or adhesive skin patches <NUM>, processor <NUM> can generate can generate a map <NUM> that shows the position of distal end <NUM> in the patient's body.

During a procedure, processor <NUM> can present map <NUM> to medical professional <NUM> on a display <NUM>, and store data representing the electroanatomical LAT map in a memory <NUM>. Memory <NUM> may comprise any suitable volatile and/or non-volatile memory, such as random access memory or a hard disk drive.

In some exemplary embodiments, medical professional <NUM> can manipulate map <NUM> using one or more input devices <NUM>. In alternative exemplary embodiments, display <NUM> may comprise a touchscreen that can be configured to accept inputs from medical professional <NUM>, in addition to presenting map <NUM>.

Control console <NUM> also comprises an ablation energy generator such as a radio-frequency (RF) signal generator <NUM>. While exemplary embodiments herein describe using RF energy from RF signal generator <NUM> to ablate tissue in heart <NUM>, using other types of ablation energy is considered to be within the scope of the present invention. For example, the ablation energy generator may be configured to generate other types of ablation energy such as high-intensity focused ultrasound (HIFU) energy and pulsed field ablation (PFA) energy. Pulsed field ablation can also be referred to as irreversible electroporation (IRE).

In the configuration shown in <FIG>, control console <NUM> additionally comprises a pump <NUM> and a temperature module <NUM>. The respective functionalities of RF signal generator <NUM>, pump <NUM> and temperature module <NUM> are described in the description referencing <FIG> hereinbelow.

<FIG> is a schematic cross-sectional longitudinal view of distal end <NUM>. In the configuration shown in <FIG>, medical probe <NUM> comprises location electrode <NUM> and an ablation electrode <NUM> disposed at distal end <NUM>. Ablation electrode <NUM> typically comprises a thin metal layer formed over distal end <NUM>. Ablation electrode <NUM> is connected to RF signal generator <NUM> by conductors (not shown) in insertion tube <NUM>.

In the configuration shown in <FIG>, RF signal generator <NUM> is configured to apply RF energy to ablation electrode <NUM>. In operation, ablation electrode <NUM> conveys applied RF energy to a region <NUM> of myocardial tissue <NUM> that is in contact with the ablation electrode <NUM>, thereby ablating the myocardial tissue <NUM>. In exemplary embodiments of the present invention, RF signal generator <NUM> can, in response to instructions (i.e., power signals) from processor <NUM>, monitor and control ablation parameters such as the level, the frequency and the duration of RF energy applied to ablation electrode <NUM>.

Ablation electrode <NUM> comprises a plurality of fluid ports <NUM>. In the configuration shown in <FIG>, fluid ports <NUM> are disposed at distal end <NUM> within ablation electrode <NUM>. Medical probe <NUM> also comprises a channel <NUM> (e.g., tubing) that is contained within insertion tube <NUM>. A first end of channel <NUM> is coupled to fluid ports <NUM>, and a second end of the channel is coupled to pump <NUM>.

Pump <NUM> forces irrigation fluid <NUM> (e.g., a saline solution) into channel <NUM>, and fluid ports <NUM> convey the pumped irrigation fluid to myocardial tissue <NUM> in order to irrigate and thereby control the temperature of the myocardial tissue during an ablation procedure. In exemplary embodiments, pump <NUM> can, in response to instructions received from processor <NUM>, control a rate of flow of irrigation fluid <NUM> from the pump <NUM>.

Medical probe <NUM> further comprises a temperature sensor <NUM> (e.g., a thermocouple) disposed at distal end <NUM> of probe <NUM>. Temperature sensor <NUM> generates a temperature signal indicating a temperature of myocardial tissue <NUM> in contact with ablation electrode <NUM>. Temperature sensor <NUM> is connected to temperature module <NUM> by conductors (not shown) in insertion tube <NUM>. In operation, temperature module <NUM> analyzes the temperature signal received from temperature sensor <NUM> located at the distal end <NUM> of the probe <NUM> so as to determine the temperature indicated by the temperature signal.

While the configuration of medical probe <NUM> in <FIG> shows distal end <NUM> comprising a single ablation electrode <NUM> and a single temperature sensor <NUM>, configurations of the medical probe with the distal end comprising multiple ablation electrodes <NUM> and/or multiple temperature sensors <NUM> are considered to be within the scope of the present invention.

<FIG> is a flow diagram that schematically illustrates a method for maintaining the temperature of region <NUM> of myocardial tissue <NUM> within a specified range during an ablation procedure. In a positioning step <NUM>, medical professional <NUM> inserts distal end <NUM> into a chamber of heart <NUM> and manipulates handle <NUM> so that ablation electrode <NUM> engages a targeted region <NUM> of myocardial tissue <NUM>.

In a specification step <NUM>, processor <NUM> specifies ablation procedure parameters comprising a target ablation temperature, a temperature difference threshold, a level or radio-frequency (RF) energy for ablation and a plurality of pumping rates for irrigation fluid <NUM>. In one exemplary embodiment, processor <NUM> can retrieve one or more of the ablation procedure parameters from memory <NUM>. In another exemplary embodiment, processor <NUM> can receive inputs from medical professional <NUM> (e.g., via input devices <NUM>) specifying one or more of the ablation procedure parameters.

The following are examples for the ablation procedure parameters:.

In an initialization step <NUM>, processor <NUM> sets the pumping rate for pump <NUM> to one of the specified pumping rates. For example, processor <NUM> can convey a pump signal to pump <NUM> instructing the pump to initially set the pumping rate to the intermediate pumping rate of <NUM>/minute.

In an application step <NUM>, processor <NUM> conveys a power signal to RF signal generator <NUM> instructing the RF signal generator to generate a specific level of RF energy and to apply (i.e. convey) the generated RF energy to ablation electrode <NUM>.

In a delivery step <NUM>, pump <NUM> forces irrigation fluid <NUM> into channel <NUM> at the set pumping rate, and the irrigation fluid exits distal end <NUM> via fluid ports <NUM>, thereby irrigating the region of myocardial tissue <NUM>.

In a receive step <NUM>, processor <NUM> receives, from temperature sensor <NUM>, a temperature signal indicative of a temperature of the engaged region of myocardial tissue <NUM>. In some exemplary embodiments, temperature module <NUM> can receive the temperature signal from temperature sensor <NUM>, compute, based on the temperature signal, a temperature value, and convey, to processor <NUM>, the computed temperature value (also referred to herein as the indicated temperature).

In a computation step <NUM>, processor <NUM> computes a difference "D" between the target ablation temperature "T" and the indicated temperature "I" using the formula <MAT>.

In a first comparison step <NUM>, if D=<NUM>, then in a first adjustment step <NUM>, processor <NUM> conveys a pump signal to pump <NUM> instructing the pump to set the pumping rate to the intermediate pumping rate. In some exemplary embodiments, processor <NUM> may allow for noise so that the condition D=<NUM> is true if D=<NUM>±<NUM>.

In a second comparison step <NUM>, if the ablation procedure is not complete, then the method continues with step <NUM>. If the ablation procedure is complete, then in a halt step <NUM>, processor <NUM> conveys a power signal instructing RF signal generator <NUM> to halt generation and application of the specified level of RF energy, and the method ends.

Returning to step <NUM>, if D><NUM>, then in a second adjustment step <NUM>, processor <NUM> conveys a pump signal to pump <NUM> instructing the pump to increase the pumping rate. In one embodiment, processor <NUM> can increase the pumping rate by conveying a pump signal to pump <NUM> that instructs the pump to set the pumping rate to the high pumping rate. In another embodiment, processor <NUM> can increase the pumping rate by conveying a pump signal to pump <NUM> that instructs the pump to increase the pumping rate by a specified value (e.g., increase by <NUM>/minute).

In an additional exemplary embodiment, processor <NUM> can apply an algorithm such as a proportional-integral-derivative controller (PID) algorithm to analyze the indicated temperature in order to control a continuously variable flow of irrigation fluid <NUM>. In this additional exemplary embodiment, if pump <NUM> forces irrigation fluid <NUM> into channel <NUM> at the high pumping rate while the indicated temperature exceeds a specified maximum temperature (e.g., <NUM>) for longer than a specified time period (e.g., <NUM> seconds), processor <NUM> can use a variation of the PID algorithm that is configured to instruct RF signal generator <NUM> to reduce the level of RF energy applied to ablation electrode <NUM>.

Returning to step <NUM>, if D<<NUM>, then in a third adjustment step <NUM>, processor <NUM> conveys a pump signal to pump <NUM> instructing the pump to decrease the pumping rate. In one exemplary embodiment, processor <NUM> can decrease the pumping rate by conveying a pump signal to pump <NUM> that instructs the pump to set the pumping rate to the low pumping rate. In another exemplary embodiment, processor <NUM> can decrease the pumping rate by conveying a pump signal to pump <NUM> that instructs the pump to decrease the pumping rate by a specified value (e.g., decrease by <NUM>/minute). In embodiments of the present invention, processor <NUM> conveys, in response to the indicated temperature, pump signals instructing pump <NUM> to adjust the pumping rate while RF signal generator generates a constant specific level of RF energy. In other words, while continuously generating the specific level of RF energy, medical console <NUM> adjusts the pumping rate for irrigation fluid <NUM> in order to maintain the temperature of the myocardial tissue being treated at or near the target ablation temperature.

Claim 1:
An irrigated ablation system, comprising:
a medical probe (<NUM>) comprising:
a flexible insertion tube (<NUM>) having a distal end (<NUM>) configured to be inserted into a chamber of a heart (<NUM>);
an ablation electrode (<NUM>) disposed at the distal end (<NUM>) and configured to convey ablation energy to a region of myocardial tissue (<NUM>) with which the ablation electrode (<NUM>) is in contact;
a temperature sensor (<NUM>) disposed at the distal end (<NUM>) and configured to output a temperature signal indicative of a temperature of the region of myocardial tissue (<NUM>);
a channel (<NUM>) contained within the insertion tube and configured to deliver an irrigation fluid (<NUM>) to the distal end (<NUM>); and
one or more fluid ports (<NUM>) coupled to the channel (<NUM>) and disposed at the distal end (<NUM>);
an ablation energy generator (<NUM>) configured to apply a specified level of the ablation energy to the ablation electrode;
a pump (<NUM>) configured to force the irrigation fluid (<NUM>) into the channel (<NUM>) at a controllable pumping rate; and
a processor (<NUM>) configured to control the pumping rate responsively to the temperature signal so that a difference between a specified ablation temperature, which is no greater than <NUM>° C, and the indicated temperature is no greater than ±<NUM> while the ablation energy generator (<NUM>) delivers a constant level of the ablation energy to the ablation electrode (<NUM>).