Patent Description:
Techniques for controlling RF ablation were previously proposed in patent literature. For example, <CIT> describes an integrated multiple energy ablation system that allows for a variety of ablation procedures to be performed without the interchanging of catheters. A console is provided that is connected to one or more energy treatment devices such as catheters or probes, via an energy-delivering umbilical system. The integrated ablation station is designed to be compatible with commercial catheters and allows for sequential or simultaneous ablation and mapping procedures to be performed when a deeper and wider lesion capability and/or a broader temperature ablation spectrum is desired. Incorporating a closed system of fluid circulation allows circulating fluid to cool an RF catheter ablation electrode during delivery of radiofrequency energy.

As another example, <CIT> describes a method, including selecting a first maximum radiofrequency (RF) power to be delivered by an electrode within a range of 70W-100W, and selecting a second maximum RF power to be delivered by the electrode within a range of 20W-60W. The method also includes selecting an allowable force on the electrode within a range of <NUM>-<NUM>, selecting a maximum allowable temperature, of tissue to be ablated, within a range of <NUM>-<NUM>, and selecting an irrigation rate for providing irrigation fluid to the electrode within a range of <NUM>-<NUM>/min. The method further includes performing an ablation of tissue using the selected values by initially using the first power, switching to the second power after a predefined time between <NUM> and <NUM>, and terminating the ablation after a total time for the ablation between <NUM> and <NUM>.

<CIT> describes body tissue ablation that is carried out by inserting a probe into a body of a living subject, urging the probe into contact with a tissue in the body, generating energy at a power output level, and transmitting the generated energy into the tissue via the probe. While transmitting the generated energy the ablation is further carried out by determining a measured temperature of the tissue and a measured power level of the transmitted energy, and controlling the power output level responsively to a function of the measured temperature and the measured power level. Related apparatus for carrying out the ablation is also described.

European Patent Application Publication <CIT> describes a high-frequency ablation of tissue in the body using a cooled high-frequency electrode connected to a high frequency generator including a computer graphic control system and an automatic controller for control the signal output from the generator, and adapted to display on real time graphic display a measure parameter related to the ablation process and visually monitor the variation of the parameter of the signal output that is controlled by the controller during the ablation process. In one example, one or more measured parameters are displayed simultaneously to visually interpret the relation of their variation and values. In one example, the displayed one or more parameters can be taken from the list of measured voltage, current, power, impedance, electrode temperature and tissue temperature related to the ablation process. The graphic display gives the clinician an instantaneous and intuitive feeling for the dynamics and stability of the ablation process for safety and control. This invention relates to monitoring and controlling multiple ground pads to optimally carry and return currents during high-frequency tissue ablation, and to prevent of grand-pad skin burns. This invention relates to the use of ultrasound imaging to intraoperatively during a tissue ablation procedure. This invention relates to the use of nerve stimulation and blocking during a tissue ablation procedure.

European Patent Application Publication <CIT> describes 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.

The invention is defined by appended claim <NUM>. Embodiments are disclosed in the dependent claims.

Cardiac radiofrequency (RF) ablation systems may vary the amount of ablative energy and a corresponding lesion depth. To accomplish this, such systems may vary both the irrigation rate and the RF power input, as well as the duration of ablation, while ensuring that the temperature of the ablated tissue does not exceed a maximum value. However, during the ablation, for example with thin tissues, the tissue may sometimes a poor temperature response (e.g., the temperature may rise/fall unexpectedly). The amount of energy, which varies correspondingly, may cause uncontrolled lesion depth.

Embodiments of the present invention that are described hereinafter operate an ablation system in a constant energy mode, wherein, within constraints, a preset amount of ablating RF energy is applied to tissue within the shortest possible time to achieve a preplanned lesion depth. (The short ablation time assists in concentrating the energy in the desired lesion area, i.e., reduces the amount of energy that escapes the desired area. ) A maximal RF power level is set, yielding a nominal time for ablation. During the ablation the temperature is monitored to maintain temperature within an allowable temperature range comprising high and low temperature limits.

During the ablation the irrigation flow rate and the power output level are adjusted to maintain maximal possible RF power, while keeping the temperature within its allowed range. In some embodiments, when the applied RF power level is lowered, ablation time is extended so that the preset amount of ablating RF energy target is met.

A processor running an algorithm for the ablation commands an increased irrigation flow rate within the allowable flow rate range, so that the ablation power can be maintained at the highest possible level allowed by the preset upper power limit and temperature range. In other words, lowering power is reverted to only as a last resort, when it is impossible to stay below the maximum temperature limit using irrigation alone.

In some embodiments, a non-claimed method includes the steps of (a) defining a target amount of ablation energy needed to create a specified lesion in tissue in a body of a patient, (b) making contact between an ablation probe and the tissue, and (c) using the ablation probe, applying to the tissue an ablation signal, which delivers the target amount of ablation energy during a smallest time duration permitted within a defined maximum-power constraint.

During application of the ablation signal, the disclosed method further includes applying irrigation fluid in a vicinity of the tissue and monitoring a temperature in the vicinity of the tissue. If the monitored temperature exceeds a defined maximum-temperature limit, the processor commands increasing a flow of the irrigation fluid.

If the monitored temperature exceeds the defined maximum-temperature limit but the flow of the irrigation fluid exceeds a defined maximum-flow limit, the processor commands reducing a power of the ablation signal and extending the time duration of the ablation signal.

The disclosed RF ablation technique, according to a target amount of RF energy to be disposed in tissue, allows maintaining maximal RF power level for a shorter duration and thus may improve the clinical outcome of a catheter-based RF ablation procedure.

<FIG> is a schematic, pictorial illustration of a system <NUM> for cardiac radiofrequency (RF) ablation therapy, in accordance with an embodiment of the present invention. Typically, a memory <NUM> of system <NUM> stores numerous ablation protocols for different clinical scenarios, such as the protocol described in <FIG>.

A physician <NUM> inserts a catheter <NUM> through a blood vessel into a chamber of a heart <NUM> of a subject <NUM>, and manipulates the catheter so that a distal end <NUM> of the catheter contacts the endocardium in an area that is to be treated. A tip electrode <NUM> of catheter <NUM>, seen in inset <NUM>, comprises one or more temperature sensors <NUM>, which measure the temperature of the electrode. In some embodiments this temperature is used as an estimate of the temperature in the vicinity of the ablated tissue.

After positioning distal end <NUM> at an ablation site, and ensuring that the tip is in contact with the endocardium, operator <NUM> actuates an RF energy generator <NUM> in a control console <NUM> to supply RF energy via a cable <NUM> to distal end <NUM>. Meanwhile, an irrigation pump <NUM> supplies a cooling fluid, such as normal saline solution, via a tube <NUM> and a lumen in catheter <NUM> to the distal end. Typically, both before and during the ablation, a display <NUM> displays values of the ablation parameters, such as those listed in Tables I-IV below, to physician <NUM>.

Operation of the RF energy generator and the irrigation pump may be coordinated in order to give the appropriate volume of irrigation during ablation, so as to cool the tip of the catheter and the tissue without overloading the heart with irrigation fluid. Each temperature sensor inside temperature sensors <NUM> provides feedback to console <NUM> for use, for example, in controlling the RF energy dosage and/or irrigation volume.

In order to operate system <NUM>, a processor <NUM> includes a number of modules used by the processor to operate the system. These modules comprise a temperature module <NUM>, a power control module <NUM>, and an irrigation module <NUM>, the functions of which are described below. In particular, processor <NUM> runs a dedicated algorithm as disclosed herein, included in <FIG>, that enables processor <NUM> to perform the disclosed steps, as further described below.

Although the pictured embodiment relates specifically to the use of a tip ablation device for ablation of heart tissue, the methods described herein may alternatively be applied in ablation devices comprising multiple ablation electrodes when the operation of each electrode is independently controlled by processor <NUM>.

<FIG> is a flow chart that schematically illustrates steps of an algorithm performed in operation of RF ablation system <NUM> of <FIG>, according to an embodiment of the present invention. The process begins at an ablation parameter presetting step <NUM>, in which physician <NUM> presets each of the variable ablation parameters referred to above, and in particular sets target amount of ablation energy. Such a step may involve generating many protocols for different clinical scenarios, where such protocols are saved, for example, in memory <NUM> of system <NUM>.

In some embodiments, the ablation parameters are set as shown in one of Tables I-IV. Typically, for the RF power, an operator of the system only sets the maximal RF power, while the minimal RF power is automatically set by the system to zero for safety reasons.

Tables I-IV provide four different settings that may be used for optimizing lesion depth while minimizing collateral damage, depending on the clinical need for example:.

Ablation parameter setting step <NUM> is implemented before physician <NUM> performs an ablation.

At the beginning of an ablation session, in a probe introduction step <NUM>, physician <NUM> inserts catheter <NUM> into a desired location in heart <NUM>, using a catheter position tracking system incorporated into system <NUM>. At that step, physician <NUM> brings catheter <NUM> into contact with target cardiac tissue.

At an impedance decision step <NUM>, processor <NUM> uses power control module <NUM> to check if the impedance of electrode <NUM> is more than a preset impedance value. If it is, the system halts the ablation procedure for electrode <NUM> in a termination step <NUM>. If step <NUM> returns a negative value, control of the algorithm continues to RF ablation step <NUM>.

At RF delivery step <NUM>, physician <NUM> operates system <NUM>, with a particular ablation protocol the physician selected, for which the parameter values were selected in step <NUM>. Physician <NUM> task is to perform the preset ablation protocol by applying (e.g., with electrode <NUM>) the target amount of energy during a smallest time duration permitted, as, for example, shown in table I. Display <NUM> of system <NUM> may be configured to display to the physician <NUM>, by methods which are known in the art, the progress of the RF delivery to the electrode. The display of the progress may be graphical, such as a simulation of the dimensions of a respective lesion as it is produced by the ablation, and/or by way of an alphanumeric display.

During the RF delivery procedure, processor <NUM> uses temperature module <NUM> to perform a number of checks on the progress of the procedure, as shown in the flow chart by decision steps <NUM>, <NUM>, and <NUM>. Irrigation module <NUM> and power control module <NUM> perform modifications, as shown in the flowchart, by modification steps <NUM> and <NUM>.

In alternative embodiments, not claimed, temperature is checked, and if the temperature reaches a prespecified target, the processor instructs the generator to decrease power to keep the temperature in the range of the prespecified temperature target. If the system identifies that power is decreased by more than a given power (for example by 1W) the irrigation flow is increased to prevent the power from decreasing. Increasing the flow enables increasing the power while keeping the temperature on target.

At a first temperature decision step <NUM>, the processor uses temperature module <NUM> to check if the measured tissue temperature deviated from the allowable preset temperature range selected in step <NUM>. If temperature decision step <NUM> returns a positive answer, irrigation control module <NUM> modifies the flow rate of irrigation to bring temperature into the allowable range, at an irrigation modification step <NUM>.

At a second temperature decision step <NUM>, the processor uses temperature module <NUM> to recheck if the measured tissue temperature deviated from the allowable preset temperature range selected in step <NUM>. If temperature decision step <NUM> returns a positive answer, power control module <NUM> modifies the power to electrode <NUM> to bring temperature into the allowable range, at a power modification step <NUM>.

If modifications of steps <NUM> and <NUM> were unsuccessful in controlling tissue temperature according to Table I, the system halts the ablation procedure for the electrode <NUM> at a termination step <NUM>.

If any of decision steps <NUM>, <NUM>, or <NUM> returns a negative answer, control continues to ablation decision step <NUM>.

At ablation decision step <NUM>, processor <NUM> checks if the amount of ablative energy deposited by the given electrode, set in step <NUM>, has been reached. If it has, then the process ends. If the energy has not been reached or was exceeded, control passes to a duration decision step <NUM>, in which processor <NUM> checks if the maximal time of ablation, set in step <NUM>, has been reached or exceeded. If the maximal preset time has been reached the system halts the procedure for the electrode <NUM> in termination step <NUM>. Otherwise the process loops back to decision step <NUM>.

Decision steps <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> have been presented sequentially in the flowchart for simplicity and clarity. Typically, however, the system uses the power control module to perform these steps in parallel.

The example flow chart shown in <FIG> is chosen purely for the sake of conceptual clarity. The present embodiment also comprises additional steps of the algorithm, such as checking a level of contact force of electrode <NUM> with tissue, which have been omitted from the disclosure herein purposely on order to provide a more simplified flow chart.

In an embodiment, not claimed, the disclosed method further includes, during application of the ablation signal, the steps of applying irrigation fluid in a vicinity of the tissue, monitoring a temperature in the vicinity of the tissue, and if the monitored temperature exceeds a defined maximum-temperature limit, decreasing a power of the ablation signal to keep the temperature at the maximum-temperature limit up to a given tolerance.

In another embodiment, not claimed, the disclosed method further includes, during application of the ablation signal, the step of, if the power of the ablation signal is decreasing, increasing an irrigation flow to reduce the temperature below the maximum-temperature limit and subsequently increasing a power of the ablation signal to the maximum-power target.

In yet another embodiment, the disclosed method further includes, during application of the ablation signal, if the target amount of ablation energy is not met during the time duration permitted, stopping the ablation signal.

Although the embodiments described herein mainly address cardiac applications, the methods and systems described herein can also be used, for example, in ablating other organs of the body.

Claim 1:
A system (<NUM>) for body tissue ablation, the system comprising:
a memory (<NUM>), which is configured to store a value of target amount of ablation energy needed to create a specified lesion in tissue in a body of a patient;
an ablation probe (<NUM>), which is configured to make contact with tissue;
a generator (<NUM>), which is configured to generate an ablation signal; and
a processor (<NUM>), which is configured to;
control the generator and the ablation probe to apply the ablation signal to the tissue with the target amount of ablation energy during a smallest time duration permitted within a defined maximum-power constraint; and
control the probe, during application of the ablation signal, to:
apply irrigation fluid in a vicinity of the tissue;
monitor a temperature in the vicinity of the tissue;
if the monitored temperature exceeds a defined maximum-temperature limit, increase a flow of the irrigation fluid; and
if the monitored temperature exceeds the defined maximum-temperature limit, but the flow of the irrigation fluid exceeds a defined maximum-flow limit, the processor is further configured to control the generator to reduce a power of the ablation signal and extend the time duration of the ablation signal.