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The present invention relates to a method and system for performing a cardiac ablation procedure, such as a procedure used for treating atrial fibrillation, without injuring the phrenic nerves.
Cardiac arrhythmia, a condition in which the heart's normal rhythm is disrupted, includes many different forms. For example, cardiac arrhythmia includes premature atrial contractions (PACs), atrial flutter, accessory pathway tachycardias, atrial fibrillation, atrioventricular (AV) nodal reentrant tachycardia (AVNRT), premature ventricular contractions (PVCs), ventricular tachycardia (VT), ventricular fibrillation, long QT syndrome, and bradyarrhythmias.
Certain types of cardiac arrhythmias, including atrial fibrillation (AF), may be treated by ablation (for example, radiofrequency (RF) ablation, cryoablation, ultrasound ablation, laser ablation, and the like), either endocardially or epicardially. However, one of the possible complications of this procedure is damage to the phrenic nerves, which are involved in breathing and both receive and transmit nerve signals to the diaphragm. Phrenic nerve injury (PNI) can cause dyspnea, cough, hiccup, and/or sudden diaphragmatic elevation. The majority of patients with PNI recover over time, such as within days or months, but PNI may be persistent in a minority of patients.
The main function of the phrenic nerves is to control breathing by acting on the diaphragm. As such, it is possible to monitor phrenic nerve viability by stimulating the phrenic nerves electrically and detecting the corresponding physiologic response. Means for detecting physiologic response may include electromyography (the detection of electromyograms, or electrical potential generated by muscle cells when the cells are electrically or neurologically activated), mechanomyography (the detection of mechanomyograms, or mechanical signals observable from the surface of a muscle when the muscle is contracted), and kinemyography (the detection of electrical currents generated after deformation of a mechanosensor). However, these physiologic indices have drawbacks. Namely, electromyography is prone to noise and electromagnetic interference, whereas mechanomyography and kinemyography have limited sensitivity to sharp thoracic contractions.
It is therefore desired to provide a method and system for monitoring and/or preventing phrenic nerve injury during a medical procedure such as ablation.
The present invention advantageously provides a method and system for preventing phrenic nerve injury during a cardiac ablation procedure. In a first embodiment, the method may generally include activating a pacing electrode proximate a phrenic nerve to transmit stimulation energy to the phrenic nerve, obtaining an audio signal from the patient's thoracic region while stimulation energy is transmitted to the phrenic nerve, determining whether phrenic nerve stimulation is present based on a comparison between an amplitude of the obtained audio signal and a predetermined threshold audio signal amplitude, and ablating tissue within the patient's heart proximate the phrenic nerve while phrenic nerve stimulation is present. Ablating tissue within the patient's heart may be by a medical device having a treatment element that delivers ablation energy to the tissue at a treatment location, and the method may further include adjusting at least one of the ablation energy delivered by the treatment element, an output of the pacing electrode, and a location of the treatment element relative to the phrenic nerve when phrenic nerve stimulation is determined to be absent. For example, the ablation energy delivered by the treatment element may be reduced and/or the output of the pacing electrode may be increased when phrenic stimulation is determined to be absent. Additionally or alternatively, the ablation energy delivered by the treatment element may be maintained or increased when phrenic nerve stimulation is determined to be present. Alternatively, ablating tissue within the patient's heart may be by a medical device having a treatment element that withdraws energy from tissue at the treatment location, and at least one of the ablation energy delivered by the treatment element, an output of the pacing electrode, and a location of the treatment element relative to the phrenic nerve may be adjusted when phrenic nerve stimulation is determined to be absent. For example, energy withdrawn from the tissue at the treatment location by the treatment element may be reduced when phrenic nerve stimulation is determined to be absent and the energy withdrawn from the tissue, and the energy withdrawn may be maintained or increased when phrenic nerve stimulation is determined to be present. Phrenic nerve injury may be determined to be present when phrenic nerve stimulation is determined to be absent. Stimulation energy may have a frequency, and the method may further include determining a patient-specific threshold audio signal amplitude, comparing the amplitude of the audio signal received from the audio sensor to the threshold audio signal amplitude at the frequency of the stimulation energy. For example, phrenic nerve stimulation may be determined to be present when the amplitude of the audio signal received from the audio sensor is greater than the amplitude of the threshold audio signal amplitude. The method may further include retrievably storing information about the presence of phrenic nerve injury as a result of ablation, the information including at least one of a location of the treatment element when phrenic nerve injury was determined to be present and an ablation energy level delivered when the phrenic nerve injury was determined to be present, and this information may be used to determine a location for re-ablation.
In another embodiment, the method may generally include activating a treatment element in contact with target tissue, stimulating a phrenic nerve with a pacing electrode, obtaining a heart audio signal with an audio sensor, transmitting the heart audio signal from the audio sensor to a processor, executing an algorithm within the processor to determine whether phrenic nerve stimulation is present based on the obtained heart audio signal, and maintaining activation of the treatment element to ablate the target tissue when the processor determines phrenic nerve stimulation is present. The heart audio signal may have an amplitude. The method may further include determining a patient-specific threshold audio signal amplitude, executing an algorithm within the processor to compare the amplitude of the obtained heart audio signal to the threshold amplitude, and executing an algorithm within the processor to determine that phrenic nerve stimulation is present when the amplitude of the obtained heart audio signal is greater than the threshold amplitude. The treatment element may ablate the target tissue by radiofrequency ablation, phased radiofrequency ablation, cryoablation, microwave ablation, ultrasound ablation, and/or laser ablation. Further, the processor may determine that phrenic nerve injury is present when phrenic nerve stimulation is absent.
The system may generally include a treatment device defining a distal portion and including a treatment element and a pacing electrode coupled to the treatment device distal portion; an audio sensor coupled to one of the treatment device or an auxiliary device, the auxiliary device being at least one of located within the patient's body and attached to an outer surface of the patient's body, the audio sensor obtaining an audio signal from the patient's heart; and a processor in communication with the audio sensor, the processor including an algorithm for determining phrenic nerve stimulation when the pacing electrode is activated. The processor may determine whether phrenic nerve stimulation is present based at least in part on an amplitude of a heart sound signal obtained by the audio sensor, and the treatment element may be activated when the processor determines that phrenic nerve stimulation is present, the presence of phrenic nerve stimulation indicating an absence of phrenic nerve injury.
A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:
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The treatment device 12 may be a catheter with ablation, mapping, and audio sensing capabilities. The treatment device 12 may additionally include pacing capabilities. As a non-limiting example, the treatment device 12 may generally include a handle 16, an elongate body 18 having a distal portion 20 and a proximal portion 22, one or more recording electrodes 24 for detecting electrophysiological signals, one or more treatment elements 26 for ablating or thermally treating tissue, and one or more audio sensors 27 for recording sounds generated from the thoracic region of the patient's body (for example, audio signals from the heart and/or diaphragm). Alternatively, the treatment device 12 may include one or more treatment elements 26 and optionally one or more audio sensors 27, whereas one or more recoding electrodes 24 and pacing electrodes 28 may be included on an electrophysiology catheter 30, which may be used as a component of the treatment device 12 (as shown in
The one or more recording elements 24 may be sensors or electrodes capable of sensing and recording electrical activity within the myocardial cells as the cells polarize and depolarize. The one or more recording elements 24 may be coupled to or disposed on the distal portion 20 of the elongate body 18 of a medical device 12 with ablation capabilities (as shown in
The elongate body 18 of the treatment device 12 may include one or more lumens 33. If the treatment device 12 is a cryoablation catheter, for example, the elongate body 18 may include a main lumen, a fluid injection lumen in fluid communication with a coolant reservoir 34, and a fluid return lumen in fluid communication with a coolant return reservoir 36. In some embodiments, one or more other lumens may be disposed within the main lumen, may be disposed within the elongate body 18 along the longitudinal axis 29 parallel to the main lumen, and/or the main lumen may function as the fluid injection lumen or the fluid return lumen. If the treatment device 12 includes thermoelectric cooling elements or electrodes capable of transmitting RF (for example, the device shown in
The console 14 may be in electrical and/or fluid communication with the treatment device 12 and may include one or more fluid (such as coolant or saline) reservoirs 34, fluid return reservoirs 36, energy generators 38 (for example, an RF or electroporation energy generator), and one or more computers 40 with displays 42, and may further include various other displays, screens, user input controls, keyboards, buttons, valves, conduits, connectors, power sources, and computers for adjusting and monitoring system 10 parameters. The computer 40 may be in electrical communication with the one or more treatment elements 26, the one or more recording electrodes 24, and/or the one or more audio sensors 27. Further, the computer 40 may include a processor 44 that includes one or more algorithms 46 executable to evaluate signals received from the one or more recording electrodes 24 and audio sensors 27 and to control, monitor, and/or suggest repositioning of the one or more treatment elements 26.
The treatment device 12 may be used in association with an electrophysiology catheter 30, with the treatment device 12 being used to ablate tissue and the electrophysiology catheter 30 being used to stimulate the phrenic nerve and, optionally, to record one or more electrophysiologic signals from the heart. The electrophysiology catheter 30 may, for example, be slidably disposed within a lumen 33 of the device 12 such that the electrophysiology catheter 30 may be positioned within the patient's anatomy independently before advancing the treatment device 12 over the electrophysiology catheter 30 to a treatment location (as shown in
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In the third step 103 of the method, the one or more audio sensors 27 may be used to detect thoracic audio signals and transmit the signals to the processor 44. The one or more audio sensors 27 may be positioned at a location from which thoracic sounds may be detected. If, for example, the one or more audio sensors 27 are located on a device separate from the EP catheter 30, the amplitude of the sound signal in response to the stimulation may be used to optimize the location of the audio sensors 27. That is, the one or more audio sensors 27 may be repositioned if reception of thoracic audio signals is poor. In the fourth step 104 of the method, the obtained thoracic audio signals may be processed using the processor 44 and/or one or more filters. For example, the signals may be band-pass filtered or ensemble-averaged, and digital envelopes may be obtained and a threshold for the digital envelopes determined.
In the fifth step 105 of the method, the one or more processors 44 may determine whether phrenic nerve stimulation (PNS) is present. In general, the absence of PNS may be indicative of phrenic nerve injury (PNI). Under normal conditions, the frequency of slow diaphragmatic contractions is approximately 10-15 contractions per minute. If PNS is present, then the audio sensor signal will have a harmonic at the same frequency as the frequency of the pacing pulses. The one or more processors 44 may include a PNS detection algorithm that monitors the Fourier amplitude of the audio sensor signal at a frequency equal to the frequency of the pacing pulses, when the pulses are delivered. If the amplitude exceeds a predetermined threshold, which threshold may be patient specific, then the algorithm will determine that PNS is present. In this case, the pacing pulses may be temporarily stopped for a number of heart beats and the amplitude may be examined again. If, as a result, amplitude is detected that is below the predetermined threshold, the one or more processors 44 may determine that PNS is absent. PNS tests may be performed once within a certain period of time. In general, the detection of PNS may take place during delivery of energy to target tissue, but the automatic detection algorithm may be “trained” during periods when ablation energy is not being transmitted. That is, the phrenic nerve may be stimulated and the thoracic sounds recorded, then stimulation may be stopped and thoracic sounds recorded. This method may be used to obtain a threshold amplitude that is personal to the patient. A previously detected presence of PNS may affect the frequency of subsequent PNS tests. Information obtained from PNS testing (for example, presence or absence of PNS, energy delivery levels, activated electrodes, etc.) may be transmitted to a mapping system for visualization and/or recording. This information may be stored (for example, in a computer) for later access by the user, such as with the use of a mapping system. For example, the mapping system may be integrated within the system 10 or may be part of another system, and may include one or more processors including mapping software and algorithms, displays, user input devices, and the like. Further, the mapping system may be in communication with the one or more recording electrodes 24. The mapping system may use the information to identify “hot spots” or areas at which phrenic nerve injury occurred and to supply the user with information about, for example, the energy levels at which injury occurred. Thus, a user may avoid these locations and/or energy levels to prevent future phrenic nerve injury in the same patient.
In the sixth step 106 of the method, if one or more consecutive PNS tests yield negative results (that is, if PNS is absent), the ablation energy delivery may be reduced (in a cryoablation system, the temperature of the treatment element may be allowed to increase) until a PNS test yields positive results (that is, until PNS is present). Additionally or alternatively, since PNS may be absent due to inadequate capture of the pacing pulses, the pacing output may be increased (as shown in
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It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.