TISSUE CONTACT DETECTION PRIOR TO AND DURING AN ABLATION PROCEDURE
The present invention provides systems and methods for radiometrically measuring temperature and detecting tissue contact during ablation. An interface module includes a first input/output (I/O) port for receiving radiometer and thermocouple signals from an integrated catheter tip (ICT) that includes a radiometer; a second I/O port for receiving ablative energy from an electrosurgical generator; a temperature display; a patient relay; a computer-readable medium storing radiometer and thermocouple parameters and instructions for causing the processor to: calculate a temperature adjacent to the ICT based on the radiometer and thermocouple signals and the parameters; causing the temperature display to display the calculated temperature; closing the patient relay to pass ablative energy from the second to the first I/O port; determining whether the ICT is in contact with tissue based on the radiometer signal. An output device indicates whether the ICT is determined to be in contact with the tissue.
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This application is a continuation application of U.S. patent application Ser. No. 14/274,438, filed May 9, 2014, which is a continuation application of U.S. patent application Ser. No. 13/486,889, filed on Jun. 1, 2012, the entirety of each of which is hereby incorporated by reference herein.
FIELDThis application generally relates to systems and methods for measuring temperature and detecting tissue contact prior to and during tissue ablation.
BACKGROUNDTissue ablation may be used to treat a variety of clinical disorders. For example, tissue ablation may be used to treat cardiac arrhythmias by destroying aberrant pathways that would otherwise conduct abnormal electrical signals to the heart muscle. Several ablation techniques have been developed, including cryoablation, microwave ablation, radio frequency (RF) ablation, and high frequency ultrasound ablation. For cardiac applications, such techniques are typically performed by a clinician who introduces a catheter having an ablative tip to the endocardium via the venous vasculature, positions the ablative tip adjacent to what the clinician believes to be an appropriate region of the endocardium based on tactile feedback, mapping electrocardiogram (ECG) signals, anatomy, and/or fluoroscopic imaging, actuates flow of an irrigant to cool the surface of the selected region, and then actuates the ablative tip for a period of time and at a power believed sufficient to destroy tissue in the selected region.
Although commercially available ablative tips may include thermocouples for providing temperature feedback via a digital display, such thermocouples typically do not provide meaningful temperature feedback during irrigated ablation. For example, the thermocouple only measures surface temperature, whereas the heating or cooling of the tissue that results in tissue ablation may occur at some depth below the tissue surface. Moreover, for procedures in which the surface of the tissue is cooled with an irrigant, the thermocouple will measure the temperature of the irrigant, thus further obscuring any useful information about the temperature of the tissue, particularly at depth. As such, the clinician has no useful feedback regarding the temperature of the tissue as it is being ablated or whether the time period of the ablation is sufficient.
Moreover, during an ablation procedure it is important that the clinician position the ablative tip directly against the cardiac surface (e.g., makes good contact) before activating the ablation energy source and attempting to ablate the tissue. If the clinician does not have good tissue contact, ablation energy may heat the blood instead of the tissue, leading to the formation of an edema, e.g., a fluid-filled pocket or blister on the tissue surface. Such an edema may inhibit adequate destruction of aberrant nerve pathways in the tissue. For example, edemas may physically interfere with the clinician's ability to contact a desired region of tissue with the ablative tip, and thus may interfere with destruction of a desired nerve pathway. Additionally, partial lesions or lesions in undesired locations have been found after the clinician completes the procedure and the edema dissipates. Formation of such partial or undesired lesions are thought to be caused by reduced contact between the ablative tip and the tissue, resulting in a tissue temperature insufficient to cause tissue necrosis. Edemas and partially formed lesions also may make it more difficult to create an effective lesion in the future, for example during a touch-up ablation within the same procedure or later on during a secondary procedure.
Accordingly, it may only be revealed after the procedure is completed—for example, if the patient continues to experience cardiac arrhythmias—that the targeted aberrant pathway was not adequately interrupted. In such a circumstance, the clinician may not know whether the procedure failed because the incorrect region of tissue was ablated, because the ablative tip was not actuated for a sufficient period of time to destroy the aberrant pathway, because the ablative tip was not touching or not sufficiently touching the tissue, because the power of the ablative energy was insufficient, or some combination of the above. Upon repeating the ablation procedure so as to again attempt to treat the arrhythmia, the clinician may have as little feedback as during the first procedure, and thus potentially may again fail to destroy the aberrant pathway. Additionally, there may be some risk that the clinician would re-treat a previously ablated region of the endocardium and not only ablate the conduction pathway, but damage adjacent tissues.
In some circumstances, to avoid having to repeat the ablation procedure as such, the clinician may ablate a series of regions of the endocardium along which the aberrant pathway is believed to lie, so as to improve the chance of interrupting conduction along that pathway. However, there is again insufficient feedback to assist the clinician in determining whether any of those ablated regions are sufficiently destroyed.
U.S. Pat. No. 4,190,053 to Sterzer describes a hyperthermia treatment apparatus in which a microwave source is used to deposit energy in living tissue to effect hyperthermia. The apparatus includes a radiometer for measuring temperature at depth within the tissue, and includes a controller that feeds back a control signal from the radiometer, corresponding to the measured temperature, to control the application of energy from the microwave source. The apparatus alternates between delivering microwave energy from the microwave source and measuring the radiant energy with the radiometer to measure the temperature. As a consequence of this time division multiplexing of energy application and temperature measurement, temperature values reported by the radiometer are not simultaneous with energy delivery.
U.S. Pat. No. 7,769,469 to Carr et al. describes an integrated heating and sensing catheter apparatus for treating arrhythmias, tumors and the like, having a diplexer that permits near simultaneous heating and temperature measurement. This patent too describes that temperature measured by the radiometer may be used to control the application of energy, e.g., to maintain a selected heating profile.
Despite the promise of precise temperature measurement sensitivity and control offered by the use of radiometry, there have been few successful commercial medical applications of this technology. One drawback of previously-known systems has been an inability to obtain highly reproducible results due to slight variations in the construction of the microwave antenna used in the radiometer, which can lead to significant differences in measured temperature from one catheter to another. Problems also have arisen with respect to orienting the radiometer antenna on the catheter to adequately capture the radiant energy emitted by the tissue, and with respect to shielding high frequency microwave components in the surgical environment so as to prevent interference between the radiometer components and other devices in the surgical field.
Acceptance of microwave-based hyperthermia treatments and temperature measurement techniques also has been impeded by the capital costs associated with implementing radiometric temperature control schemes. Radiofrequency ablation techniques have developed a substantial following in the medical community, even though such systems can have severe limitations, such as the inability to accurately measure tissue temperature at depth, e.g., where irrigation is employed. However, the widespread acceptance of RF ablation systems, extensive knowledge base of the medical community with such systems, and the significant cost required to changeover to, and train for, newer technologies has dramatically retarded the widespread adoption of radiometry.
In view of the foregoing, it would be desirable to provide apparatus and methods that permit radiometric measurement of temperature at depth in tissue, and permit use of such measurements to control the application of ablation energy in an ablation treatment, e.g., a hyperthermia or hypothermia treatment, particularly in which contact between the ablative tip and the tissue readily may be assessed.
It further would be desirable to provide apparatus and methods that employ microwave radiometer components that can be readily constructed and calibrated to provide a high degree of measurement reproducibility and reliability.
It also would be desirable to provide apparatus and methods that permit radiometric temperature measurement and control techniques to be introduced in a manner that is readily accessible to clinicians trained in the use of previously-known RF ablation catheters, with a minimum of retraining, and that provide readily understandable signals to the clinicians as to whether the ablative tip is in contact with tissue.
It still further would be desirable to provide apparatus and methods that permit radiometric temperature measurement and control techniques to be readily employed with previously-known RF electrosurgical generators, thereby reducing the capital costs needed to implement such new techniques.
SUMMARYIn view of the foregoing, it would be desirable to provide apparatus and methods for treating living tissue that employs a radiometer for temperature measurement and control. In accordance with one aspect of the invention, systems and methods are provided for radiometrically measuring temperature and detecting tissue contact prior to and during RF ablation, i.e., calculating temperature and detecting tissue contact based on signal(s) from a radiometer. Unlike standard thermocouple techniques used in existing commercial ablation systems, a radiometer may provide useful information about tissue temperature at depth—where the tissue ablation occurs—and thus provide feedback to the clinician about the extent of tissue damage as the clinician ablates a selected region of the tissue. Additionally, the radiometer may provide useful information about whether an ablative tip is in contact with tissue, and thus provide feedback to assist the clinician in properly contacting and ablating the tissue.
In one embodiment, the present invention comprises an interface module (system) that may be coupled to a previously-known commercially available ablation energy generator, e.g., an electrosurgical generator, thereby enabling radiometric techniques to be employed with reduced capital outlay. In this manner, the conventional electrosurgical generator can be used to supply ablative energy to an “integrated catheter tip” (ICT) that includes an ablative tip, a thermocouple, and a radiometer for detecting the volumetric temperature of tissue subjected to ablation. The interface module is configured to be coupled between the conventional electrosurgical generator and the ICT, and to coordinate signals therebetween. The interface module thereby provides the electrosurgical generator with the information required for operation, transmits ablative energy to the ICT under the control of the clinician, displays via a temperature display the temperature at depth of tissue as it is being ablated, and outputs a visible or audible indication of tissue contact for use by the clinician. The displayed temperature and determination of tissue contact may be calculated based on signal(s) measured by the radiometer using algorithms such as discussed further below.
In an exemplary embodiment, the interface module includes a first input/output (I/O) port that is configured to receive a digital radiometer signal and a digital thermocouple signal from the ICT, and a second I/O port that is configured to receive ablative energy from the electrosurgical generator. The interface module also includes a processor, a patient relay in communication with the processor and the first and second I/O ports, and a persistent computer-readable medium. The computer-readable medium stores operation parameters for the radiometer and the thermocouple, as well as instructions for the processor to use in coordinating operation of the ICT and the electrosurgical generator.
The computer-readable medium preferably stores instructions that cause the processor to execute the step of calculating a temperature adjacent to the ICT based on the digital radiometer signal, the digital thermocouple signal, and the operation parameters. This temperature is expected to provide significantly more accurate information about lesion quality and temperature at depth in the tissue than would a temperature based solely on a thermocouple readout. The computer-readable medium may further store instructions for causing the processor to cause the temperature display to display the calculated temperature, for example so that the clinician may control the time period for ablation responsive to the displayed temperature. The computer-readable medium may further store instructions for causing the processor to close the patient relay, such that the patient relay passes ablative energy received on the second I/O port, from the electrosurgical generator, to the first I/O port, to the ICT. Note that the instructions may cause the processor to maintain the patient relay in a normally closed state, and to open the patient relay upon detection of unsafe conditions.
The computer-readable medium preferably also stores instructions that cause the processor to execute the step of determining whether the ICT is in contact with tissue, based on the digital radiometer signal. For example, because blood and tissue have different dielectric constants, the digital radiometer signal may change when the ICT is brought into or out of contact with the tissue. The instructions may cause the processor to monitor the digital radiometer signal for changes. Any such changes may be compared to a predetermined threshold value (also stored on the computer-readable medium). If the change is determined to be greater than the threshold value, then the processor outputs a signal to an output device that, responsive to the signal, indicates whether the ICT is in contact with tissue. The output device may be, for example, a visual display device that visually represents the tissue contact, e.g., a light that illuminates when there is tissue contact, or an audio device that audibly represents the tissue contact, e.g., a speaker that generates a tone when there is tissue contact. Preferably, the processor determines whether the ICT is in contact with the tissue before passing ablation energy to the ICT.
Embodiments of the present invention provide systems and methods for radiometrically measuring temperature and detecting tissue contact prior to and during ablation, in particular cardiac ablation. As noted above, commercially available systems for cardiac ablation may include thermocouples for measuring temperature, but such thermocouples may not adequately provide the clinician with information about tissue temperature or tissue contact. Thus, the clinician may need to make an “educated guess” about whether an ablative tip is in contact with tissue, as well as whether a given region of tissue has been sufficiently ablated to achieve the desired effect. By comparison, calculating a temperature based on signal(s) from a radiometer is expected to provide accurate information to the clinician about the temperature of tissue at depth, even during an irrigated procedure. Moreover, the signal(s) from the radiometer may be used to determine whether the ablative tip is in sufficient contact with tissue before attempting to ablate the tissue, so as to reduce the likelihood of forming edemas such as described above and improve the likelihood of creating effective transmural lesions. The present invention provides a “retrofit” solution that includes an interface module that works with existing, commercially available ablation energy generators, such as electrosurgical generators. In accordance with one aspect of the present invention, the interface module displays a tissue temperature and provides an indication of tissue contact based on signal(s) measured by a radiometer, that a clinician may use to perform ablation procedures with significantly better accuracy than can be achieved using only a thermocouple for temperature measurement.
First, high level overviews of the interface module, including tissue contact indicator, and connections thereto are provided. Then, further detail on the internal components of the interface module, and exemplary methods of calculating radiometric temperature, determining tissue contact, and controlling an ablation procedure based on same, are provided. Data obtained during experimental procedures also is presented. Lastly, further detail on components that may be used with the interface module is provided.
In embodiments in which the ablation energy is radiofrequency (RF) energy, the ablative tip may include an irrigated ablation electrode, such as described in greater detail below with reference to
Front panel 111 includes tissue contact indicator 170, which is an output device configured to indicate whether ICT 122 is in contact with tissue, e.g., which interface module 110 determines based on signal(s) from the radiometer as described in greater detail below. Tissue contact indicator 170 may include a visual display device that visually represents interface module 110's determination of whether ICT 122 is in contact with tissue. For example, tissue contact indicator 170 may include a light that illuminates when interface module 110 determines that ICT 122 is in contact with tissue, and is dark when interface module 110 determines that ICT 122 is out of contact with tissue. Alternatively, tissue contact indicator 170 may be an audio device that audibly represents interface module 110's determination of whether ICT 122 is in contact with tissue. For example, tissue contact indicator 170 may include a speaker that generates a tone when interface module 110 determines that ICT 122 is in contact with tissue, and is silent when interface module 110 determines that ICT 122 is out of contact with tissue. Tissue contact indicator 170 may continuously generate a tone throughout the duration of the contact, and cease generating the tone when contact is lost, so as to facilitate the clinician's ability to determine whether tissue contact has been lost. Alternatively, tissue contact indicator 170 may generate a brief tone at a first frequency when contact is made, and may generate a second tone at a second frequency when contact is lost. Optionally, tissue contact indicator 170 includes a visual display device and an audio device for providing the clinician with both visible and audible indications of tissue contact.
Back panel 112 of interface module 110 may be connected via connection cable 135 to a commercially available previously-known ablation energy generator 130, for example an electrosurgical generator 130, such as a Stockert EP-Shuttle 100 Generator (Stockert GmbH, Freiburg Germany) or Stockert 70 RF Generator (Biosense Webster, Diamond Bar, Calif.). In embodiments where the electrosurgical generator 130 is a Stockert EP-Shuttle or 70 RF Generator, generator 130 includes display device 131 for displaying temperature and the impedance and time associated with application of a dose of RF ablation energy; power control knob 132 for allowing a clinician to manually adjust the power of RF ablative energy delivered to subject 101; and start/stop/mode input 133 for allowing a clinician to initiate or terminate the delivery of RF ablation energy. Start/stop/mode input 133 also may be configured to control the mode of energy delivery, e.g., whether the energy is to be cut off after a given period of time.
Although generator 130 may be configured to display temperature on display device 131, that temperature is based on readings from a standard thermocouple. As noted above, however, that reported temperature may be inaccurate while irrigant and ablative energy are being applied to tissue. Interface module 110 provides to generator 130, via connection cable 135, a thermocouple signal for use in displaying such a temperature, and signals from the ECG electrodes; and provides via indifferent electrode cable 134 a pass-through connection to indifferent electrode 140. Interface module 110 receives from generator 130, via connection cable 135, RF ablation energy that module 110 controllably provides to ICT 122 for use in ablating tissue of subject 101.
As will be familiar to those skilled in the art, for a monopolar RF ablation procedure, a clinician may position an indifferent electrode (IE) 140 on the back of subject 101 so as to provide a voltage differential that enables transmission of RF energy into the tissue of the subject. In the illustrated embodiment, IE 140 is connected to interface module 110 via first indifferent electrode cable 141. Interface module 110 passes through the IE signal to second indifferent electrode cable 134, which is connected to an indifferent electrode input port on electrosurgical generator 130. Alternatively, IE 140 may be connected directly to that port of the electrosurgical generator 130 via appropriate cabling (not shown).
It should be understood that electrosurgical generators other than the Stockert EP-Shuttle or 70 RF Generator suitably may be used, e.g., other makes or models of RF electrosurgical generators. Alternatively, generators that produce other types of ablation energy, such as microwave generators, cryosurgical sources, or high frequency ultrasound generators, may be used. Ablation energy generator 130 need not necessarily be commercially available, although as noted above it may be convenient to use one that is. It should also be appreciated that the connections described herein may be provided on any desired face or panel of interface module 110, and that the functionalities of different connectors and input/output (I/O) ports may be combined or otherwise suitably modified.
Front panel 111 of interface module 110 includes temperature display 113, e.g., a digital two or three-digit display device configured to display a temperature calculated by a processor internal to interface module 110, e.g., as described in greater detail below with reference to
Back panel 112 of interface module 110 includes connectors (not labeled) through which interface module 110 is connected to electrosurgical generator 130, via indifferent electrode cable 134 and connection cable 135. Back panel 112 of interface module 110 also includes data ports 114 configured to output one or more signals to a suitably programmed personal computer or other remote device, for example an EP monitoring/recording system such as the LABSYSTEM™ PRO EP Recording System (C.R. Bard, Inc., Lowell, Mass.). Such signals may, for example, include signals generated by the thermocouple, radiometer, and/or ECG electrodes of the ICT, the tissue temperature calculated by interface module 110, and the like.
Referring now to
Electrosurgical generator 130 optionally is in operable communication with electrophysiology (EP) monitoring/recording system 160 via appropriate cabling 161, or alternatively via data ports 114 of interface module 110 and appropriate cabling (not shown). EP monitoring/recording system 160 may include, for example, various monitors, processors, and the like that display pertinent information about an ablation procedure to a clinician, such as the subject's heart rate and blood pressure, the temperature recorded by the thermocouple on the catheter tip, the ablation power and time period over which it is applied, fluoroscopic images, and the like. EP monitoring/recording systems are commercially available, e.g., the MEDELEC™ Synergy T-EP-EMG/EP Monitoring System (CareFusion, San Diego, Calif.), or the LABSYSTEM™ PRO EP Recording System (C.R. Bard, Inc., Lowell, Mass.).
If ICT 122 includes irrigation port(s), then one convenient means of providing irrigant to such ports is irrigation pump 140 associated with electrosurgical generator 130, which pump is in operable communication with the generator and in fluidic communication with the ICT 122 via connector 151. For example, the Stockert 70 RF Generator is designed for use with a CoolFlow™ Irrigation pump, also manufactured by Biosense Webster. Specifically, the Stockert 70 RF Generator and the CoolFlow™ pump may be connected to one another by a commercially available interface cable, so as to operate as an integrated system that works in substantially the same way as it would with a standard, commercially available catheter tip. For example, prior to positioning ICT 122 in the body, the clinician instructs the pump to provide a low flow rate of irrigant to the ICT, as it would to a standard catheter tip; the ICT is then positioned in the body. Then, when the clinician presses the “start” button on the face of generator 130, the generator may instruct pump 150 to provide a high flow rate of irrigant for a predetermined period (e.g., 5 seconds) before providing RF ablation energy, again as it would for a standard catheter tip. After the RF ablation energy application is terminated, then pump 150 returns to a low flow rate until the clinician removes the ICT 122 from the body and manually turns off the pump.
Referring now to
Interface module 110 also includes processor 210 coupled to non-volatile (persistent) computer-readable memory 230, user interface 280, load relay 260, and patient relay 250. Memory 230 stores programming that causes processor 210 to perform steps described further below with respect to
As illustrated in
So as to inhibit potential degradations in the performance of processor 210, memory 230, or user interface 280 resulting from electrical contact with RF energy, interface module 110 may include opto-electronics 299 that communicate information to and from processor 210, but that substantially inhibit transmission of RF energy to processor 210, memory 230, or user interface 280. This isolation is designated by the dashed line in
With respect to
As illustrated in
Isolated main power supply 205 is coupled to internal ground A via a low resistance pathway. Isolated main power supply 205 is also coupled to, and provides power (e.g., ±12V) to, one or more internal isolated power supplies that in turn provide power to components internal to interface module 110. Such components include, but are not limited to components illustrated in
RF circuitry 290 may include patient and load relays 250, 260, as well as circuitry that receives the radiometer and thermocouple signals and provides such signals to the processor via optoelectronic coupling, and circuitry that generates a clock signal to be provided to the ICT as described further below with reference to
As shown in
As further illustrated in
Referring now to
In method 300 of
In method 300 of
In method 300 of
In method 300 of
In method 300 of
Tissue contact module 236 then may cause processor 210 of interface module 110 to compare the change in the radiometer signal to a predetermined threshold value, e.g., predetermined threshold value 235 stored in memory 230. The predetermined threshold value preferably is selected such that changes in the radiometer signal caused by non-contact sources such as noise fall below the threshold value, while changes in the radiometer caused by tissue contact fall above the threshold value. As such, threshold values may vary from system to system, depending on the particular noise characteristics and sensitivity of the radiometer. For example, at baseline, the radiometer signal may have a noise level of about ±0.1 V. It may be determined via calibration that the radiometer signal increases to about 0.3 V above baseline when ICT 122 is brought into contact with tissue. As such, predetermined threshold value 135 suitably may be set to an intermediate magnitude between the upper end of the noise level and the average value when ICT 122 is in contact with tissue, e.g., a value in the range of about 0.11-0.29 V in the above example, e.g., 0.15 V, 0.2 V, or 0.25 V. Alternatively, the noise level of the radiometer is ±10% of baseline, and it may be determined via calibration that the radiometer signal increases by about 30% when ICT 122 is brought into contact with tissue. As such, predetermined threshold value 135 suitably may be set to an intermediate percentage between the upper end of the noise level and the average value when ICT 122 is in contact with tissue, e.g., in the range of 11-29% in the above example, e.g., 15%, 20%, or 25% in the above example.
If processor 210 of interface module 110 determines that the change in the radiometer signal is greater than stored predetermined threshold value 235, then the processor causes tissue contact indicator 170 to indicate that there is contact between ICT 122 and the tissue. For example, processor 210 may transmit a signal to tissue contact indicator 170 that indicates that ICT 122 is in contact with tissue. Responsive to the signal, tissue contact indicator 170 generates an appropriate indicator that the clinician may perceive as meaning that ICT 122 has been brought into contact with tissue. For example, tissue contact indicator 170 may include a light that illuminates when there is tissue contact, and/or may include a speaker that generates a tone when there is tissue contact, or otherwise signal contact such as described above with reference to
In method 300 illustrated in
Interface module 110 also generates an analog version of the thermocouple signal, and provides the ECG and analog thermocouple signals to generator 130 (step 308). Preferably, step 308 is performed continuously by the interface module throughout steps 303 through 307, rather than just at the end of the ablation procedure. For example, as will be familiar to those skilled in the art, the Stockert EP-Shuttle or 70 RF Generator may “expect” certain signals to function properly, e.g., those signals that the generator would receive during a standard ablation procedure that did not include use of interface module 110. The Stockert EP-Shuttle or 70 RF generator requires as input an analog thermocouple signal, and optionally may accept analog ECG signal(s). The interface module 110 thus may pass through the ECG signal(s) generated by the ICT to the Stockert EP-shuttle or 70 RF generator via second I/O port 202. However, as described above with reference to
Turning to
In
Processor 210 then obtains via first I/O port 201 and opto-electronics 299 the raw digital signal from the thermocouple, TCRaw (step 352), and calculates the thermocouple temperature, TCT, based on TCRaw using the following equation (step 353):
Then, processor 210 causes temperature display 113 to display TCT until both of the following conditions are satisfied: TCT is in the range of 35° C. to 39° C., and ablation energy is being provided to the ICT (e.g., until step 307 of
As illustrated in
As illustrated in
Processor 210 also calculates the radiometric temperature Trad based on Vrad and Tref using the following equation (step 357):
During operation of interface module 110, processor 210 may continuously calculate TCT, and also may continuously calculate Tref and Trad during times when ablation power is provided to the ICT (which is subject to several conditions discussed further herein). Processor 210 may store in memory 230 these values at specific times and/or continuously, and use the stored values to perform further temperature calculations. For example, processor 210 may store in memory 230 TCT, Tref, and Trad at baseline, as the respective values TCBase, TrefBase, and TradBase. The processor then re-calculates the current radiometric temperature TradCurrent based on the current Vrad received on second I/O port 202, but instead with reference to the baseline reference temperature TrefBase, using the following equation (step 358):
Processor 210 then calculates and causes temperature display 113 to display a scaled radiometric temperature TSrad for use by the clinician based on the baseline thermocouple temperature TCBase, the baseline radiometer temperature TradBase, and the current radiometer temperature TradCurrent, using the following equation (step 359):
TSrad=TCBase+(TradCurrent−TradBase)×F
In this manner, interface module 110 displays for the clinician's use a temperature calculated based on signal(s) from the radiometer that is based not only on voltages generated by the radiometer and its internal reference, described further below with reference to
With respect to
In method 360 of
After confirming that the ICT is in contact with tissue based on an indication by tissue contact indicator 170 such as described above, the clinician presses a button on the generator to start the flow of ablation energy to the ICT; this may cause the generator to initiate a high flow of irrigant to the ICT and generation of ablation energy following a 5 second delay (step 362). The interface module passes the ablation energy to the ICT via the patient relay, as described above with respect to step 306 of
Based on the calculated and displayed radiometric temperature (see methods 300 and 350 described above with respect to
Interface module 110 may use the calculated radiometric temperature to determine whether the ablation procedure is being performed within safety parameters. For example, processor 210 may obtain safety parameters 232 from memory 230. Among other things, these safety parameters may include a cutoff temperature above which the ablation procedure is considered to be “unsafe” because it may result in perforation of the cardiac tissue being ablated, with potentially dire consequences. The cutoff temperature may be any suitable temperature below which one or more unsafe conditions may not occur, for example “popping” such as described below with respect to
The ablation procedure terminates (step 365), for example, when the clinician presses the appropriate button on generator 130, or when the generator 130 automatically cuts of ablation energy at the end of a predetermined period of time.
Referring now to
As can be seen in
As can be seen from
A series of cardiac ablation procedures were also performed in living humans using the experimental setup described above with respect to
The results of the ablation procedures performed on the five individuals are summarized in the following table:
As can be seen from the above table, 44% of the ablation procedures did not reach the clinician's target tissue temperature of 55° C. As such, it is likely that this percentage of the procedures resulted in insufficient tissue heating to interrupt aberrant pathway(s). However, although many of the ablation procedures failed, the clinician repeated the ablation procedures a sufficient number of times to achieve 100% treatment of the individuals' atrial flutter. It is believed that displaying the calculated temperature to the clinician during ablation procedures would enable the clinician to far more accurately assess the quality of contact between the ablative tip of the ICT and the individual's cardiac tissue, and thus to sufficiently heat the tissue above the target temperature for a desired period of time, and thus reduce the clinicians' need to repeatedly perform numerous ablation procedures on the same subject so as to achieve the desired treatment.
As shown in the above table, 12% of the ablation procedures triggered the high temperature cutoff such as illustrated in
Additional components that may be used in conjunction with interface module 110 of the present invention, e.g., PIM 121 and ICT 122 of catheter 120, are now briefly described with reference to
In
PIM circuitry 502 receives on first I/O port 505 an analog thermocouple (TC) signal, raw analog radiometer signals, and analog ECG signals from catheter 120. PIM circuitry 502 includes TC signal analog-to-digital (A/D) converter 540 that is configured to convert the analog TC signal to a digital TC signal, and provide the digital TC signal to interface module 110 via second I/O port 506. PIM circuitry 502 includes a series of components configured to convert the raw analog radiometer signals into a usable digital form. For example, PIM circuitry may include radiometric signal filter 510 configured to filter residual RF energy from the raw analog radiometer signals; radiometric signal decoder 520 configured to decode the filtered signals into analog versions of the Vref and Vrad signals mentioned above with reference to
On second I/O port 506, PIM circuitry 502 receives RF ablation energy from generator 130 (e.g., a Stockert EP-Shuttle or 70 RF Generator) via interface module 110. PIM circuitry 502 passes that RF ablation energy through to catheter 120 via first I/O port 505. PIM circuitry 502 also receives on second I/O port 506 a clock signal generated by RF circuitry within interface module 110, as described further above with reference to
Referring now to
As described in the Carr publication and as depicted in
Center conductor 103 may be fixed coaxially within passage 106 by means of an electrically insulating collar or bushing 109, e.g. of PTFE, press fit into passage 106 at distal end segment 104b of the carrier and by a weld to the passage wall or by an electrically conductive collar or bushing (not shown) at the carrier proximal segment 104c. This causes a short circuit between conductor 103 and carrier 104 at the proximal end of the carrier, while an open circuit may be present therebetween at the distal end of the carrier. In the carrier center segment 104a, the walls 106a of passage 106 may be spaced from center conductor 103. This forms a quarter wave stub S, as described in greater detail in U.S. Pat. No. 7,769,469 and U.S. Patent Publication No. 2010/0076424. Conductor 103 includes distal end segment 103a which extends beyond the distal end of carrier 104 a selected distance, and a proximal end segment 103b which extends from the proximal end of ICT 122 and connects to the center conductor of cable 105 configured to connect to PIM 121.
As illustrated in
When the ICT is being assembled, plate 115a may be seated on the upper flat 108a of carrier 104 and the lower plate 115b is likewise seated on the lower flat 108b so that the center conductor 103 is contacted from above and below by the conductive strips 117 of the upper and lower plates and the layer 118 side edges of those plates contact carrier segment 104a. A suitable conductive epoxy or cement may be applied between those contacting surfaces to secure the plates in place.
At least one of the plates, e.g. plate 115a, functions also as a support surface for one or more monolithic integrated circuit chips (M_MICs), e.g. chips 122 and 124. The chip(s) may include a coupling capacitor connected by a lead (not shown) to center conductor 103 and the usual components of a radiometer such as a Dicke switch, a noise source to provide a reference temperature, amplifier stages, a band pass filter to establish the radiometer bandwidth, additional gain stages if needed, a detector and buffer amplifier. Due to the relatively small profile of the present ICT 122, the above circuit components may be arranged in a string of four chips. The chip(s) may be secured to the metal layer 118 of plate 115a by a suitable conductive adhesive so that that layer which, as described above, is grounded to the insert 104 may function as a ground plane for those chips. The plates also conduct heat away from the chips to conductor 103 and carrier 104. Various leads (not shown) connect the chips to each other and other leads 125b extend through carrier slot 107 and connect the last chip 124 in the string, i.e. the radiometer output, to corresponding conductors of cable 105 leading to PIM 121.
A tubular outer conductor 126 may be slid onto carrier 104 from an end thereof so that it snugly engages around the carrier with its proximal and distal ends coinciding with the corresponding ends of the carrier (not shown). The conductor 126 may be fixed in place by a conductive epoxy or cement applied around the carrier segments 104b and 104c.
ICT 122 also may include an annular dielectric spacer 137, e.g. of PTFE, which is centered on the distal end of carrier 104 and surrounds the conductor segment 103a. The spacer may have a slit 137a enabling it to be engaged around that conductor segment from the side thereof. The spacer 137 may be held in place by a conductive collar 136 which encircles the spacer and is long enough to slidably engage over a distal end segment of outer conductor 126. The collar 136 may be press fit around that conductor and carrier segment 104b to hold it in place and to electrically connect all those elements.
The distal end of the ICT 122 may be closed off by conductive tip 142 which, in axial section, may be T shaped. That is, the tip 142 may have discoid head 142a that forms the distal end of the ICT and an axially extending tubular neck 142b. The conductor segment 103a is sufficiently long to extend beyond the distal end of the spacer 137 into the axial passage in neck 104b. The tip may be secured in place by conductive adhesive applied around the distal end of conductor segment 103a and at the distal end or edge of collar 136. When the tip is in place, the conductor segment 103a and tip 104 form a radiometric receiving antenna, as described in greater detail in U.S. Pat. No. 7,769,469 and U.S. Patent Publication No. 2010/0076424.
ICT 122 may further include dielectric sheath 144 which may be engaged over the rear end of outer conductor 126 and slid forwardly until its distal end 144a is spaced a selected distance behind the distal end of tip 142. The conductors 103 and 126 of ICT 122 form an RF transmission line terminated by the tip 104. When the ICT 122 is operative, the transmission line may radiate energy for heating tissue only from the uninsulated segment of the probe between tip 104 and the distal end 144a of the sheath 144. That segment thus constitutes an RF ablation antenna.
The proximal ends of the center conductor segment 103b, outer conductor 126 and sheath 144 may be connected, respectively, to the inner and outer conductors and outer sheath of cable 105 that leads to PIM 121. Alternatively, those elements may be extensions of the corresponding components of cable 105. In any event, that cable 105 connects the center conductor 103 to the output of a transmitter which transmits a RF heating signal at a selected heating frequency, e.g. 500 GHz, to the RF ablation antenna.
As illustrated in
If desired, cable 105 further may include probe steering wire 145 whose leading end 145a may be secured to the wall of a passage 146 in carrier segment 104c.
Preferably, helical through slot 147 is provided in collar 136 as shown in
The inner or center conductor 103 may be a solid wire, or preferably is formed as a tube that enables conductor 103 to carry an irrigation fluid or coolant to the interior of probe tip 142 for distribution therefrom through radial passages 155 in tip head 142a that communicate with the distal end of the axial passage in tip neck 142b.
When plates 115a and 115b are seated on and secured to the upper and lower flats 108a and 108b, respectively, of carrier 104, conductive strips 117, 117 of those members may be electrically connected to center conductor 103 at the top and bottom thereof so that conductor 103 forms the center conducts for of a slab-type transmission line whose ground plane includes layers 118, 118.
When ablation energy is provided to ICT 122, a microwave field exists within the substrate 116 and is concentrated between the center conductor 103 and layers 118, 118. Preferably, as noted here, conductive epoxy is applied between conductor 103 and strips 117 to ensure that no air gaps exist there because such a gap would have a significant effect on the impedance of the transmission line as the highest field parts are closest to conductor 103.
Plates 115a, 115b and conductor 103 segment together with carrier 104 form a quarter wave (λR/4) stub S that may be tuned to the frequency of radiometer circuit 124, e.g. 4 GHz. The quarter wave stub S may be tuned to the center frequency of the radiometer circuit along with components in chips 122, 124 to form a low pass filter in the signal transmitting path to the RF ablation antenna, while other components of the chips form a high pass or band pass filter in the signal receiving path from the antenna to the radiometer. The combination forms a passive diplexer D which prevents the lower frequency transmitter signals on the signal transmitting path from antenna T from reaching the radiometer, while isolating the path to the transmitter from the higher frequency signals on the signal receiving path from the antenna.
The impedance of the quarter wave stub S depends upon the K value and thickness t of substrates 116 of the two plates 115a, 115b and the spacing of center conductor 103 from the walls 106a, 106a of passage 106 in the carrier center segment 104a. Because the center conductor 103 is not surrounded by a ceramic sleeve, those walls can be moved closer to the center conductor, enabling accurate tuning of the suspended substrate transmission line impedance while minimizing the overall diameter of the ICT 122. As noted above, the length of the stub S may also be reduced by making substrate 116 of a dielectric material which has a relatively high K value.
In one working embodiment of the ICT 122, which is only about 0.43 in. long and about 0.08 in. in diameter, the components of the ICT have the following dimensions:
Thus, the overall length and diameter of the ICT 122 may be relatively small, which is a useful feature for devices configured for percutaneous use.
While various illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made herein without departing from the invention. For example, although the interface module has primarily been described with reference for use with an RF electrosurgical generator and the PIM and ICT illustrated in
Claims
1. A method of using an interface module with an ablation energy generator and an integrated catheter tip (ICT), the ICT including a radiometer, an ablative tip, and a thermocouple, the method of using the interface module comprising the steps of:
- (a) receiving at a first I/O port of the interface module a radiometer signal and a thermocouple signal from the ICT;
- (b) receiving at a second I/O port of the interface module ablative energy from the ablation energy generator;
- (c) calculating at the interface module a temperature adjacent to the ICT based on the radiometer signal, the thermocouple signal, and the operation parameters;
- (d) determining at the interface module whether the ICT is in contact with tissue based on the radiometer signal;
- (e) outputting with an output device an indication of the interface module's determination of whether the ICT is in contact with the tissue;
- (f) displaying on a temperature display of the interface module the calculated temperature; and
- (g) after step (e), passing ablative energy received on the second I/O port to the first I/O port by closing a patient relay of the ablation module.
2. The method of claim 1, wherein step (d) comprises:
- (i) identifying a change in the radiometer signal;
- (ii) comparing the change in the radiometer signal to a threshold value;
- (iii) if the change is greater than the threshold value, transmitting a signal to the output device.
3. The method of claim 2, wherein the output device comprises a visual display device configured to visually represent tissue contact responsive to the signal.
4. The method of claim 2, wherein the output device comprises an audio device configured to audibly represent tissue contact responsive to the signal.
5. The method of claim 1, further comprising the steps of:
- (h) storing at the interface module a safety cutoff temperature;
- (i) at the interface module, comparing the calculated temperature to the safety cutoff temperature while the patient relay is closes; and
- (j) if the calculated temperature exceeds the safety cutoff temperature, opening the patient relay and closing a load relay of the ablation module such that the load relay passes ablative energy received on the second I/O port to a dummy load of the ablation module.
6. The method of claim 1, wherein the patient relay is maintained in a normally closed state and opened upon detection of an unsafe condition.
7. The method of claim 1, further comprising the steps of:
- (h) initially calculating at the interface module a temperature adjacent to the ICT based on the thermocouple signal and the operation parameters but not the radiometer signal;
- (i) displaying on the temperature display the initially calculated temperature; and
- (j) if the temperature calculated in step (h) is in the range of 35° C. to 39° C., and if the second I/O port is receiving ablative energy from the ablation energy generator, then performing steps (c)-(g).
8. The method of claim 1, further comprising the steps of:
- (h) receiving at a third I/O port of the ablation energy generator a signal from an indifferent electrode; and
- (i) providing at a fourth I/O port the signal from the indifferent electrode to the ablation energy generator.
9. The method of claim 1, wherein the ablative energy is selected from the group consisting of RF energy, microwave energy, cryoablation energy, and high frequency ultrasound energy.
10. The method of claim 1, wherein the ablative energy is RF energy.
11. A system for facilitating detection of contact with a target region of a subject, comprising:
- a processor,
- wherein the processor is configured to receive a signal from a radiometer carried by a medical instrument and to provide an output indicative of contact between a portion of the medical instrument and a target region of a subject based upon, at least in part, properties determined from the signal received from the radiometer.
12. The system of claim 11, wherein the processor is configured to regulate operation of an energy delivery member of the medical instrument based on the output indicative of the contact between the portion of the medical instrument and the target region of the subject.
13. The system of claim 11, wherein the system is configured to provide to a user of the system confirmation of contact between the portion of the medical instrument and the target region of the subject.
14. The system of claim 11, wherein the medical instrument comprises a catheter comprising an irrigation pump in fluid communication with a fluid passage of the catheter, wherein the irrigation pump is configured to selectively deliver irrigation fluid through the fluid passage of the catheter and at least one irrigation fluid port of the catheter in fluid communication with the fluid passage of the catheter during use.
15. The system of claim 11, further comprising the medical instrument, wherein the medical instrument comprises an ablation catheter configured to deliver energy sufficient to ablate the target region upon being activated by an ablation energy source after the output indicative of contact is provided by the processor.
16. The system of claim 11, further comprising the medical instrument, wherein the medical instrument comprises an energy delivery catheter configured to deliver energy to the target region upon being activated by an energy source after the output indicative of contact is provided by the processor.
Type: Application
Filed: Apr 17, 2015
Publication Date: Feb 11, 2016
Applicants: Advanced Cardiac Therapeutics, Inc. (Santa Clara, CA), Meridian Medical Systems, LLC (Portland, ME)
Inventors: John F. McCarthy (Newbury, NH), Timothy J. Lenihan (Hradec Kralove), Eric R. Kanowsky (Santa Barbara, CA), Robert C. Allison (Rancho Palos Verdes, CA)
Application Number: 14/689,373