System and process for optimising the placement of an intra-cardiac implant of a pulsed field ablation system

Abstract

A method for determining electrode-tissue contact for a multi-electrode catheter implant of a Pulsed Field Ablation system, the method including: selecting one of the multiple electrodes as a test electrode; applying an electrical pulse to said test electrode; receiving an electrical signal on at least one of the other electrodes of the multiple of electrodes; calculating an impedance value based on the received electrical signal; and outputting an indication of electrode-tissue contact for the test electrode based on the calculated impedance value.

Description

SYSTEM AND PROCESS FOR OPTIMISING THE PLACEMENT OF ANINTRA-CARDIAC IMPLANT OF A PULSED FIELD ABLATION SYSTEMTECHNICAL FIELD

[0001] The present invention relates to the field of Pulsed Field Ablation (PF A) in the treatment of atrial fibrillation; in particular, a system and methodology for optimising the placement of an intra-cardiac implant in a PFA system.BACKGROUND

[0002] Atrial fibrillation (AF) is a widespread heart rhythm disorder that can lead to blood clots and strokes. Catheter ablation has shown promise as a treatment for AF, but conventional methods using heat or cold can cause serious complications.

[0003] Pulsed Field Ablation (PFA) is an innovative technology that offers a safer and more effective alternative. Unlike traditional therapies, PFA uses nonthermal electric fields to precisely ablate heart tissue in a matter of seconds. This tissue-selective approach leads to faster and more durable clinical outcomes for patients. The therapy is performed using an implanted multi-electrode catheter.

[0004] In a paper entitled ‘Multielectrode Contact Measurement Can Improve Long-Term Outcome of Pulmonary Vein Isolation Using Circular Single-Pulse Electroporation Ablation’ Groen et al., Circ. Arrhythm. Electrophsiol., August 2022, it is noted that electrode-tissue contact, or at least electrode-tissue proximity, is an important factor that influences ablation efficacy. The paper proposed a method of applying an electrical pulse signal to each electrode in an implanted catheter and measuring the voltage and current between each electrode and an externally applied electrode. Based on the measured voltage and current, an impedance value could be calculated. A high impedance value could be taken to be a good indicator of ideal electrode-tissue contact, whereas a low impedance value would indicate poor electrode-tissue contact.

[0005] The present inventors noted that the proposed method is a cumbersome and clumsy method that disconnects the catheter movement while the clinician adjusts the catheter position from the results of that movement. In effect it becomes a process of adjust position, test position, readjust, re-test and so on. This is exacerbated if the external electrode requires repositioning for subsequent tests.

[0006] It is an objective of the present invention to provide an alternative system and method for determining electrode-tissue contact which addresses at least some of the shortcomings of the Groen method.SUMMARY

[0007] According to a first aspect of the present invention there is provided a method for determining electrode-tissue contact for a multi-electrode implant of a Pulsed Field Ablation system, the method including: selecting one of the multiple electrodes as a test electrode; applying an electrical pulse to said test electrode; receiving an electrical signal on at least one of the other electrodes of the multiple of electrodes; determining a voltage value and a current value based on the received electrical signal; calculating an impedance value based on the determined voltage value and current value; and outputting an indication of electrode-tissue contact for the test electrode based on the calculated impedance value.

[0008] According to another aspect of the invention there is provided a system for determining electrode-tissue contact for a multi-electrode implant of a Pulsed Field Ablation system, the system including: a module adapted to be in electrical connection with the multiple electrodes of the implant; and a controller programmed to: select one of the multiple electrodes as a test electrode; apply an electrical pulse to said test electrode; receive an electrical signal on at least one of the other electrodes of the multiple of electrodes; determine a voltage value and a current value based on the received electrical signal; calculate an impedancevalue based on the determined voltage value and current value; and output an indication of electrode-tissue contact for the test electrode based on the calculated impedance value.

[0009] In exemplary embodiments, the steps are consecutively repeated for each electrode of the multiple of electrodes being consecutively selected as the test electrode.

[0010] Ideally, a plurality of the other electrodes of the multiple of electrodes receives an electrical signal, for each received signal, a voltage value and a current value is determined and an impedance value is calculated, wherein the indication of electrode-tissue contact for the test electrode is based on an average of the impedance values calculated for each received signal.

[0011] Preferably, the method is continuously performed while the implant is physically moved so that updated indications are outputted in response to movement of the implant.

[0012] In preferred embodiments, the indication of electrode -tissue contact is output on a visual display. The display can use colour coding to show whether the indication of electrode-tissue contact is poor or acceptable. The display may be provided with an update rate between 5-47 updates per second in order that no discernible latency is observable with movement of the implant and displayed indications.

[0013] In exemplary embodiments, the electrical pulse applied to the test electrode is applied at a frequency selected to avoid or minimise noise interference to or from other components in the Pulsed Field Ablation system. Frequency domain analysis (such as Fast Fourier Transform or Digital Fourier Transform) may be performed on the received electrical signal(s) to allow for monitoring of interference on the selected frequency. If excessive interference isdetected at the selected frequency, then a different frequency may be selected to be used to apply subsequent electrical pulses.

[0014] Preferably, the method can be automatically discontinued if a signal is received indicating that the method is causing interference with the functioning of other components in the Pulsed Field Ablation system.

[0015] Embodiments of the present invention provides the advantage of employing only the electrodes of the implant to perform an assessment of electrode-catheter contact. Consequently, the need to employ an external electrode is removed.

[0016] Preferably, the implant is a catheter.

[0017] In preferred embodiments, the step of selecting one of the multiple electrodes as a test electrode includes selecting at least one other of the multiple electrodes as a second test electrode; and the step of applying an electrical pulse to said test electrode includes simultaneously applying a second electrical pulse to said second test electrode. The second electrical pulse may have different characteristics compared with the first electrical pulse. A plurality of other of the multiple electrodes may be selected as second test electrodes, the number of second test electrodes being selected based upon a predetermined performance optimisation of the implant configuration.

[0018] Exemplary embodiments allow for the advantageous continuous assessment of electrode-tissue contact while the implant is being moved and displays the same to an operator to help guide the operator in moving the catheter in real time.BRIEF DESCRIPTION OF THE FIGURES

[0019] The present invention will herein be described with embodiments illustrated in the accompanying drawings, in which:

[0020] Fig. 1 shows a multi-electrode catheter; and

[0021] Fig. 2 shows a preferred embodiment of a CIM system.DESCRIPTION OF THE INVENTION

[0022] An example of a multi-electrode catheter 10 employed as an implant in a PFA system is shown in Fig. 1.

[0023] During implant, it is desirable that the catheter 10 is positioned with each electrode 12 having optimum electrode- tissue contact or proximity to improve the efficacy of the PFA therapy. For this purpose, embodiments of the present invention provide a system for determining and indicating to an implant clinician, the local impedance at each electrode in the catheter. The impedance value is directly correlated with the electrode-tissue contact. For reference in this specification the system is a Catheter Impedance Monitoring System (CIM).

[0024] The CIM can be designed to be a module to complement and function alongside other subsystems in a PFA system. The CIM could be an integral component of a PFA system or an add-on module to be operably connected to or retro-fitted to a PFA system.

[0025] Given that during an implant procedure, other subsystems are employed, such as an electrophysiological (EP) recorder and 3D mapping system, it is important that the CIM functions without interfering with or being interfered by such other subsystems, including the PFA system itself. The CIM uses signals at frequencies that have no impact on cardiac function and can therefore take readings for contact assessment continuously. The frequencies used (around 500kHz) and the arrangement of the CIM function also make the CIM operation invisible to the EP Recorder and 3D mapping systems, so use of the CIM can coexist with these other systems without impairing the operation of the other systems.

[0026] The QMS employs a number of sequential steps in use. Firstly, one electrode is selected for testing and an electrical test pulse is applied to the test electrode. At least oneof the other electrodes receives a signal in response to the test pulse. Based on the test pulse and the received signal, values of voltage and current are determined. Local impedance is then calculated (impedance = voltage / current), and the calculated impedance is output as an indicator of electrode-tissue contact for the test electrode. The steps are repeated with each electrode being selected as a test electrode.

[0027] In practice, all the other electrodes receive a signal in response to the test pulse. The CIM considers all of the received signals and undertakes a process of calculating an average.

[0028] To ensure use of the CIM is as simple as possible, a visual display, such as a Graphic User Interface (GUI) is used that provides a visual representation of the catheter and the electrodes; wherein the electrode colour is used to indicate the contact or otherwise of each electrode independently. It has been found that with an update rate between 5 and 47 updates per second there is no discernible latency between movement of the catheter and the results shown on the GUI. The simple colour-coded display provides intuitive feedback to a clinician.

[0029] In practical use, typical electrosurgery will produce relatively minor signal levels inside the heart. In order to combat those signals and maintain simultaneous use compatibility the CIMS can perform continuous frequency domain analysis of the signals received and if excessive interference is detected at the frequency in use the CIM can dynamically adapt by using a different frequency it has identified by frequency domain analysis. The frequency domain analysis is the computation of a Fast Fourier Transform or Digital Fourier Transform, FFT or DFT, directly from the signal samples. The signal used by the CIM is derived using Direct Digital Synthesis which provides for very fine tuning of signal frequency and over an extreme range of frequencies.

[0030] This adaptive frequency hopping to avoid noisy spectral areas is useful for any noise interference that does not exceed the dynamic range of the CIM signal path. Any suitable frequency over 300kHz has no negative affect on tissue. The CIM receive signalpath has a headroom of over 15dB and filters to provide frequency dependent improvements on the headroom to suit the CIM hardware.

[0031] If one or more electrodes are being used to provide PFA pacing pulses the CIM has dedicated hardware with adjustable sensitivity that can detect these pulses so the CIM can be disconnected from the electrode using a high speed solid state switch to ensure little if any distortion of even the shortest of pacing pulses. The CIM function must be suspended during a pacing pulse and if the pacing rate is fast the CIM must be suspended continuously while pacing is happening. Infrequent pacing pulses that allow for a CIM reading cycle will not cause complete suspension of the CIM function although it will necessarily be operating at a slower update rate.

[0032] By employing only the electrodes built into the catheter for the CIM function, no additional external electrodes are required.

[0033] To produce a reliable value for electrode impedance the system of electrodes can be modelled as a matrix of measurements being the readings from each electrode to each of all the other electrodes individually and the matrix of measurements solved as a set of simultaneous equations to reveal the impedance of each electrode individually. The matrix required is relatively sparse, requiring only the values above or below the diagonal to be populated. The results are effectively an average impedance value derived mathematically from the measurements.

[0034] This approach can be simplified by using the system directly to do the averaging by including all of the untested electrodes in the initial measurement simultaneously.

[0035] A further simplification of the method is to provide a source impedance for the test signal to remove the explicit current measurement and use the difference between the transmitted signal measured before the source impedance and the electrode signal measured after the source impedance to provide a relativistic albeit uncalibrated electrode impedance value against the source impedance. The remaining electrodes, ie those not being actively measured can be used as the return path for the purposes of the test.

[0036] An improvement to this approach could be to apply the given impedance, the same for each electrode, to each electrode such that the electrode is only connected to through that impedance. This method allows the impedance to also be used for protection of the system against signals such as cardiac defibrillation pulses.

[0037] The improvement this approach provides is to allow a version of the Central or Wilson Terminal to be established by taking the average of the signals provided by the electrodes not being tested. This provides a virtual reference point, the ‘Central Terminal’, in the immediate vicinity of the test electrode which can be used in a differential measurement technique to effectively eliminate extraneous factors from affecting the measurements, to provide a degree of noise cancellation of common mode signals and to eliminate the need for an external electrode.

[0038] As the system is expected to operate and provide contact measurement results in a continuous manner and a further implicit requirement then is also that the system should be able to operate simultaneously with, and invisibly to, an EP recorder and a mapping system both of which are connected to the same electrodes. It is also an obvious imperative that there be no discernible effect on cardiac function caused by the system. To achieve this the test signal is chosen to be a relatively small, low power signal in the same frequency range as that used for Radio Frequency Ablation (RFA). The amplitude is set to a level insufficient to cause electrolysis of the blood or any of the dissolved substances in it. The frequency is significant because the RFA frequencies are applied at significant power levels for periods that are several heart beats in duration and have no discernible effect on cardiac function. These frequencies are also an expected interference for EP Recorders and mapping systems, so they already have significant capabilities to reject signals in that range of frequencies.

[0039] Because the test signals are applied momentarily, the windowing function describing the transient nature of the applied signal will produce artefacts in the frequency spectrum outside the RFA range. Even with the window being aligned to the zero-crossing point of the test signal, the sudden appearance of the test signal, having an amplitude significantly greater than the signals the EP Recorder is monitoring, canmomentarily over excite or saturate the input filter stages of the EP Recorder and an artefact will appear on the EP Recorder waveforms.

[0040] To eliminate these artefacts from the EP Recorder and the mapping system that the test signal application and removal can cause, the application and removal of the test signal involves the fading of the test signal in and out and over several cycles thereby reducing the harmonic content and amplitude and the convolved frequency products generated by the windowing of the test signal.

[0041] The combination of these techniques and frequencies means that for a system of ten electrodes a full set of signal captures for all ten electrodes that can be post processed to provide impedance values for all ten electrodes can be completed in a few milliseconds which means it is possible to have real time results with no humanly discernible latency and a system that is invisible to the EP Recorder and mapping system and that adds to and improves the tactile method and nature of manual electrode location and placement.

[0042] A significant factor in correlating impedance measurements with tissue contact is the relative conductivities of the mediums involved. The conductivities of blood and tissue are not greatly different but critically, there is a measurable and reliable difference. As blood is more conductive than the tissues and taking the simplification that the volume away from the vicinity of the myocardia is, for all intents and purposes, devoid of any material that can vary the impedance measurement from that of the impedance measurement with the electrode in blood alone, the impedance measurement with the electrodes not in the vicinity of the myocardia will be greater than the impedance measurement with the electrode in contact or partial contact with the myocardia.

[0043] The underlining principle is that the relative contributions of the blood and tissues will effect the impedance measurement as a function of the conductivities of the two mediums and the proportion of the electrode surface area in exclusive contact with the one or the other. In absolute terms this difference is useless in the context of assessing myocardia contact. Only a measurement considered relative to a measurement taken with only blood contact can be used to assess myocardia contact. As blood is the moreconductive medium of the two (which is a universal fact), the blood only measurements for the reference level against which the impedance measurements can be used to assess myocardia contact.

[0044] To improve the utility of the system, the introduction of the electrodes into the heart is monitored and a capture initiated as the electrodes exit the introducer and enter the heart. The appearance event is detectable as an abrupt variation in the measured impedance of the electrode.

[0045] While the electrodes are in the introducer there is very little conductive medium around and between the electrodes. So a detection algorithm based on the signal amplitude measured on the same electrode with the test signal routed to it is sufficient to detect this event reliably. As the electrodes must appear in a given order the monitoring can also be targeted to the next electrode to appear.

[0046] As the electrodes appear a capture can be initiated and an initial measurement of the blood based impedance can be made. The accuracy of the measurement made this way will be a function of the number of electrodes that have already appeared, so a further algorithm is required to improve the accuracy of the impedance in blood measurement especially for the first electrodes to appear.

[0047] To improve the noise rejection capabilities of the system and to make the system more robust the signal captures are made digitally and the capture system and the test signal generator are frequency locked which makes the use of high resolution (Digital) Fast Fourier Transforms (DFT) possible which allows for the noise inherent in biological measurements of this kind to be all but eliminated from the measurement of the test signal.

[0048] To further improve the test signal measurements, the test signal frequency can be changed on the fly if the DFT bin is found to be coincident with an interfering signal or if the bin contains excessive noise from any source. The system test signal is generated by Direct Digital Synthesis (DDS) and the minor harmonic content of the test signal isremoved with low order analogue filters. This method allows for the signal generation and signal capture to be phase synchronous so the DFT bin corresponding to the test signal frequency is deterministic and predictable. The method of signal generation also allows for the test signal frequency to be modifiable with very fine resolution and have near perfect frequency accuracy relative to the capture system.

[0049] To ensure these measures to give the system a robust quality the signal chain has a significant amount of headroom beyond the expected range of signal amplitude. A high order ADC is used with the input range matched to the dynamic range of the analogue signal chain of the capture system. A separate indication is provided with the digitised signal to indicate if the dynamic range has been exceeded as this may make contact assessment unreliable.

[0050] A common event during cardiac ablation procedures is the application of pacing pulses through the same electrodes as the ablation and the electrodes being assessed for tissue contact. These pulses can be of similar amplitude or greater amplitude than the test signal and it is impossible for pacing and contact assessment to be concurrent. However, as the pacing pulses are of short duration and will appear at regular intervals, they can be avoided with the interruption of contact assessment for the duration of the pulse being indiscernible to the Operator.

[0051] To provide for the detection of pacing pulses, a high pass filter is used to isolate the pulse as it appears at the system input before being compared with a configurable detection threshold.

[0052] A separate means of isolating the electrode from the system is provided and has the characteristics of being fast enough that no appreciable distortion of the pacing pulse is caused thereby maintaining the integrity of the pacing pulse.

[0053] Together these features enable the system to also remain invisible to pacing pulses.

[0054] Protection against defibrillation energy uses an unusual technique that exploits the high frequency nature of the system to use a reactive series element that is low impedance for the test signal but is also an effective block to the bulk of the defibrillation energy pulse. This element is rated for the full defibrillation potential and in the unlikely case of a breakdown of this element it has a self-healing property. This technique provides the advantage that the inputs to the system are not required to carry the large currents that might otherwise flow and the inputs do not have to dissipate that energy either. Because the currents are not large the safety of the operator is also enhanced because the energy does not need to be shunted off to an earth terminal which has the possibility of presenting a portion of the 5kV defibrillation pulse on conductive parts exposed to the operator.

[0055] Because the environment tends to be electrically noisy and the impedance measurements of contact and non-contact may not be different by more than a small percentage, the assessment of contact and the presentation of that information must be carefully handled to avoid erratic or misleading results.

[0056] To achieve this the hardware and software implementations have features to reduce the influence of noise in the measurements.

[0057] The hardware implementation is a differential system similar to an ECG front end ie high input impedances, high CMRR and the ability to adapt to the baseline offset determined at the electrodes.

[0058] For maximum flexibility in adapting to the environment the hardware incorporates the following functions and features:

[0059] The test signal can be applied to any two electrodes independently of all other settings.

[0060] The measurement can be made from any electrode independently of all other settings.

[0061] The reference for the measurement can be the local ground (baseline potential), any one of the electrodes individually or the Central Terminal which automatically excludes the electrode or electrodes with the test signal connected to them.

[0062] High pass filters to limit the bandwidth of the measured signal (the bandwidth limit is a function of the length of the digitised waveform captures)

[0063] Selectable capture length to tune the capture to suit the test signal frequency and to improve noise rejection if required.

[0064] The ability to adjust the frequency of the test signal to avoid frequencies where there is interference or excessive noise.

[0065] Fast pacing pulse detection with adjustable threshold and a high speed disconnect solid state switch to isolate the test signal driver from the electrode.

[0066] Fade controls to eliminate switching artefacts from the EP Recorder, mapping system and any other equipment connected to the same electrodes.

[0067] The software functions are the most critical for the performance of the overall system. They include:

[0068] A DFT algorithm with variable width to control the bin size and hence the noise included in the measurements.

[0069] Software filters to maintain responsiveness of the indicated contact assessment while controlling the assessment to avoid erratic behaviour of the indicated assessment.

[0070] Managed thresholds for the contact assessment determination that can adapt to the dynamics of the assessments to eliminate erratic indications.

[0071] Adaptive algorithms to monitor and track changes to the contact assessment Reference Level to maintain the accuracy and reliability of the contact assessments.

[0072] The contact assessment results are displayed on a large screen as a graphic representation of the physical catheter in use. This graphical representation virtually eliminates the need for language to convey the intended meaning.

[0073] The graphical representation is self-explanatory, easily understood and conveys all necessary information with just a glance.

[0074] All controls, except for the power switches, are handled on the large touch screens.

[0075] There are no extraneous or ambiguous controls. All aspects of the function of the system are handled by the system and any information required by the operator is made available when necessary, to avoid complex or confusing screens of information.

[0076] Detailed screens do exist but access is restricted to avoid issues with errors in the settings.

[0077] In the graphic representation, the electrodes are used to indicate the contact assessment. This avoids any confusion regarding correlation of electrode and electrode number and electrode position on the catheter.

[0078] Contact assessment may be a go / no go indication using two colours to differentiate between the two assessments or a graduated assessment where the electrode has a dividing line separating the two colours and the dividing line moves between the ends of the electrode representation according to the degree of contact assessed.

[0079] The electrode representation also uses different colours to indicate the status of the electrode. The status is not a function of degree so only one colour is involved and isa different colour for the status of the electrode being; ‘still in the introducer’, ‘not connected’, ‘short circuit to another electrode’ or ‘invalid or no reference level set’.

[0080] The software uses the electrode status and the changes of electrode status to trigger processes such as the initial reference level measurements as the electrodes appear in the heart as they exit the introducer. Short circuit status can be used to isolate electrodes which will limit the efficacy of the ablation but avoids the entire application being cancelled. An open circuit electrode is a warning situation where ideally the catheter connections would be checked and the catheter would be replaced if required.

[0081] It is not always be possible to automate the reference level measurements to an indiscernible event as the electrodes appear out of the introducer. The software incorporates an adaptive algorithm that continually monitors and updates the reference level measurements to improve the utility of the system under those conditions.

[0082] The CIMS system is illustrated in Fig. 2.

[0083] The CIM includes a controller 20 for controlling the CIM functions. The controller 20 connects with a signal matrix block 22. The signal matrix is a block responsible for isolating the CIM and an EP Recorder Interface 24 from the electrodes 26 during PFA delivery; for connecting the CIM 20 and EP Interface 26 to the electrodes otherwise and, when the Generator is powered on, for providing the transmit and receive connections to each electrode for the CIM and for the defibrillation pulse protection of the CIM.

[0084] The Signal Matrix allows for individual connection control to each electrode independently of the other connections. Which electrodes are connected is indicated by onboard LEDs. Local power rails are monitored and a fault is indicated if either rail is outside specified limits.

[0085] The Signal Matrix is ideally shared for PFA delivery, CIM and self-testing functions. An arbiter is used to maintain separation of control and each function, delivery,CIM and self-test, are responsible for leaving the Matrix in a safe state before relinquishing control back to the arbiter.

[0086] Each of the functions is also responsible for configuring the Signal Matrix for its own purposes and making no assumptions in the process. The default state for the Signal Matrix is to disconnect the catheter electrodes 26 from the EP Recorder interface 24 and the CIM 20. The normal state for the Signal Matrix under normal operating conditions is to have the electrodes 26 connected to the CIM 20 and EP interface 24. Disconnection happens only during self-test, as part of the self-test of the disconnection mechanism, when the device is powered off and when PFA delivery is in progress. The electrodes and CIM 20 and EP interface 26 are all connected at all other times.

[0087] The EP Recorder Interface 26 provides a 10 and a 20 way connector for connection to the EP Recorder and the 3D mapping system. These are connected to the electrodes 26 of the catheter whenever the CIM 20 is connected to the electrodes 26 which is while the Generator is powered up and not delivering PFA.

[0088] A (channel) hybrid block is where the transmitted signal is injected, the returned signal is tapped for measurement and where the pacing pulse detection is done. The block also includes a high speed solid state signal relay that enables the transmitter to be disconnected quickly if a pacing pulse is detected. Each electrode has a dedicated channel.

[0089] The sensitivity of the pacing pulse detection is set by a voltage externally and the same voltage is used for all channels. It is a function outside the scope of this block that responds to pace detection by disabling the high speed solid state signal relay.

[0090] A Direct Digital Synthesizer (DDS) is responsible for generating the test signal. This technique allows for a wide range of frequencies to be generated and selected easily and on the fly.

[0091] To limit the disturbances on the EP Recorder waveform display and the 3D Mapping system and to avoid saturating the input filters in those devices, the CIM test signal is ideally faded in and out rather than just switched on and off.

[0092] The fade time and the number of steps used in fading are variable quantities to cater for EP Recorder or Mapping system being more sensitive.

[0093] The Ts Mux 28 block allows the test signal to be connected to 2 channels at the same time. This allows for one channel to be faded in while another is faded out which keeps the scan time for all channels to a minimum.

[0094] The Ms Mux 30 block selects the measured quantity which can be any channel or the raw test signal as part of a self-test routine.

[0095] The Ct Mux 32 block connects all channels except the channel being transmitted to be connected via a resistor to a Central Terminal which is used as the reference for measurement of the driven channel.

[0096] The Rn Mux block selects the reference for the measurement. It can be any one of the channels, the Central Terminal or the ground reference.

[0097] The analogue to digital converter (ADC) 34 is ideally a high speed high resolution ADC that provides good signal resolution while still providing a generous head room. Most of the signal path has a 10 to 1 ratio of headroom to signal level to avoid clipping the signal and rendering analysis and measurements impossible to do accurately.

[0098] White noise is the worst case scenario for noise rejection by FFT 36. In practice the noise the CIM has to deal with will have a more defined spectral content such that by using a long enough sample set which we can change on the fly by zero padding the extra samples, we can increase the resolution to yield a quiet bin we can use for our test signal and effectively ignore the noise when making measurements.

[0099] As previously mentioned, Fast Fourier Transform (FFT) or in a digital (sampled) system, a Digital Fourier Transform (DFT) is an effective way of separating the signal from the noise.

[0100] For this to be a practical option, it should be done in hardware and not in a processor and software. A 1024 point FFT can be employed which will require several thousand multiplications involving complex numbers. To keep the update rate on the GUI at an acceptable speed, a hardware solution that can perform many of the multiplications in parallel will be the best solution and yield a high update rate.

[0101] Safety switches or separation barriers are ideally employed to maintain protection of separate subsystems. For example, defibrillation protection is mostly accomplished with a InF, 6kV polypropylene film capacitor to couple the test signal to the electrode. This has the side benefit of removing any residual DC from the test signal before it goes to the patient.

[0102] To avoid the loss of sensitivity in the measurement, an independent connection to the electrode via another InF 6kV capacitor is used for sensing the electrode voltage.

[0103] On the CIM end of capacitors bridge rectifiers connected to transient suppressors which are biased to keep the bridge rectifiers reverse biased and the junction capacitance of the bridge rectifier diodes to a minimum. The series InF capacitors reduce the absolute maximum current into the transient suppressors to less than 500mA during a defibrillation pulse.

[0104] The CIM measurement method allows for the electrodes to be stimulated in any configuration, with phase and frequency (100kHz~600Khz) being controlled via the synthesizer, under the control of the microcontroller and the Graphic user interface. The selection of which electrodes are stimulated, is controlled by the microcontroller and plays a key role in the system performance. When switching or changing the setup of theelectrode signals the signal is faded out and in as required to reduce noise on the EP system.

[0105] Stimulating the electrodes in an unchanging configuration for stimulating and sensing, with the signals at different phases, results in the reduction of noise and interference to the EP system, resulting in the addition of the CIM being undetectable. The setup for each electrode is optimised to provide the best performance based on the geometry of the electrodes in catheter or other device.

[0106] The geometry of the electrodes can be various catheters, including electrode v-loop, linear , big eye etc, with the configuration stored in the CIM and applied when the type is selected. This selection is done using the GUI.

[0107] The CIM allows for the contact detection to be used for external electrode contact when used in non-catheter implants (such as clamps, patches) and other externally applied means of contact.

[0108] The unused contact sensing electrodes can be enabled or disabled to allow the system to do the detection with desired electrodes only.

[0109] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms, in keeping with the broad principles and the spirit of the invention described herein.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method for determining electrode-tissue contact for a multi-electrode implant of a Pulsed Field Ablation system, the method including: selecting one of the multiple electrodes as a test electrode; applying an electrical pulse to said test electrode; receiving an electrical signal on at least one of the other electrodes of the multiple of electrodes; calculating an impedance value based on the received electrical signal; and outputting an indication of electrode-tissue contact for the test electrode based on the calculated impedance value.

2. The method of claim 1, further including the step of determining a voltage value and a current value based on the received electrical signal, wherein said impedance value is calculated based on the determined voltage value and current value.

3. The method of claim 1, wherein said step of applying an electrical pulse to said test electrode includes: applying a first electrical pulse to said test electrode with a known source impedance; and applying a second electrical pulse to said test electrode without said source impedance; wherein said step of receiving an electrical signal on at least one of the other electrodes of the multiple of electrodes includes:receiving a first electrical signal relating to said first electrical pulse; and receiving a second electrical signal relating to said second electrical pulse; wherein said step of calculating an impedance value includes comparing a difference between the first and second received electrical signals.

4. The method of any one of the preceding claims, wherein the steps are consecutively repeated for each electrode of the multiple of electrodes being consecutively selected as the test electrode.

5. The method of any one of the preceding claims, wherein a plurality of the other electrodes of the multiple of electrodes receives an electrical signal, for each received signal, an impedance value is calculated, wherein the indication of electrode-tissue contact for the test electrode is based on an average of the impedance values calculated for each received signal.

6. The method of any one of the preceding claims, wherein the method is continuously performed while the implant is physically moved so that updated indications are outputted in response to movement of the implant.

7. The method of any one of the preceding claims, wherein the indication of electrode -tissue contact is output on a visual display.

8. The method of claim 7, wherein the display uses colour coding to show whether the indication of electrode-tissue contact is poor or acceptable.

9. The method of claim 7 or 8, wherein the display is provided with an update rate between 5-47 updates per second in order that no discernible latency is observable with movement of the implant and displayed indications.

10. The method of any one of the preceding claims, wherein the electrical pulse applied to the test electrode is applied at a frequency selected to avoid or minimise noise interference to or from other components in the Pulsed Field Ablation system.

11. The method of claim 10, wherein frequency domain analysis is performed on the received electrical signal(s) to allow for monitoring of interference on the selected frequency.

12. The method of claim 11 , wherein the frequency domain analysis in conducted using Fast Fourier Transform or Digital Fourier Transform.

13. The method of claim 11 or 12, wherein if excessive interference is detected at the selected frequency, then a different frequency is selected to be used to apply subsequent electrical pulses.

14. The method of any one of the preceding claims, wherein the method is automatically discontinued if a signal is received indicating that the method is causing interference with the functioning of other components in the Pulsed Field Ablation system.

15. The method according to any one of the preceding claims, wherein the implant is a catheter.

16. The method according to any one of the preceding claims, wherein the step of selecting one of the multiple electrodes as a test electrode includes selecting at least one other of the multiple electrodes as a second test electrode; and the step of applying an electrical pulse to said test electrode includes simultaneously applying a second electrical pulse to said second test electrode.

17. The method according to claim 16, wherein said second electrical pulse has different characteristics compared with the first electrical pulse.

18. The method according to claim 16 or 17, wherein a plurality of other of the multiple electrodes are selected as second test electrodes, the number of second test electrodes being selected based upon a predetermined performance optimisation of the implant configuration.

19. A system for determining electrode-tissue contact for a multi-electrode implant of a Pulsed Field Ablation system, the system including:a module adapted to be in electrical connection with the multiple electrodes of the implant; and a controller programmed to: select one of the multiple electrodes as a test electrode; apply an electrical pulse to said test electrode; receive an electrical signal on at least one of the other electrodes of the multiple of electrodes; calculate an impedance value based on the received electrical signal; and output an indication of electrode-tissue contact for the test electrode based on the calculated impedance value.

20. The system of claim 19, the controller further programmed to determine a voltage value and a current value based on the received electrical signal, wherein said impedance value is calculated based on the determined voltage value and current value.

21. The system of claim 19, wherein applying an electrical pulse to said test electrode includes: applying a first electrical pulse to said test electrode with a known source impedence; and applying a second electrical pulse to said test electrode without said source impedence;wherein receiving an electrical signal on at least one of the other electrodes of the multiple of electrodes includes: receiving a first electrical signal relating to said first electrical pulse; and receiving a second electrical signal relating to said second electrical pulse; wherein calculating an impedance value includes comparing a difference between the first and second received electrical signals.

22. The system of any one of claims 19 to 21, wherein the controller performs the steps consecutively repeatedly for each electrode of the multiple of electrodes being consecutively selected as the test electrode.

23. The system of any one of claims 19 to 22, wherein a plurality of the other electrodes of the multiple of electrodes receives an electrical signal, for each received signal, a voltage value and a current value is determined and an impedance value is calculated, wherein the indication of electrode-tissue contact for the test electrode is based on an average of the impedance values calculated for each received signal.

24. The system of any one of claims 19 to 23, wherein the controller continuously performs while the implant is physically moved so that updated indications are outputted in response to movement of the implant.

25. The system of any one of the claims 19 to 24, further including a visual display for receiving and displaying the output indication of electrode -tissue contact.

26. The system of claim 25, wherein the display uses colour coding to show whether the indication of electrode-tissue contact is poor or acceptable.

27. The system of claim 25 or 26, wherein the display is provided with an update rate between 5-47 updates per second in order that no discernible latency is observable with movement of the implant and displayed indications.

28. The system of any one of claims 19 to 27, wherein the electrical pulse applied to the test electrode is applied at a frequency selected to avoid or minimise noise interference to or from other components in the Pulsed Field Ablation system.

29. The system of claim 28, wherein frequency domain analysis is performed on the received electrical signal(s) to allow for monitoring of interference on the selected frequency.

30. The system of claim 29, wherein the frequency domain analysis in conducted using Fast Fourier Transform or Digital Fourier Transform.

31. The system of claim 29 or 30, wherein if excessive interference is detected at the selected frequency, then a different frequency is selected to be used to apply subsequent electrical pulses.

32. The system of any one of claims 19 to 31, wherein the method is automatically discontinued if a signal is received indicating that the method is causing interference with the functioning of other components in the Pulsed Field Ablation system.

33. The method according to any one of claims 19 to 32, wherein the implant is a catheter.

34. The method according to any one of claims 19 to 33, wherein the step of selecting one of the multiple electrodes as a test electrode includes selecting at least one other of the multiple electrodes as a second test electrode; and the step of applying an electrical pulse to said test electrode includes simultaneously applying a second electrical pulse to said second test electrode.

35. The method according to claim 34, wherein said second electrical pulse has different characteristics compared with the first electrical pulse.

36. The method according to claim 34 or 35, wherein a plurality of other of the multiple electrodes are selected as second test electrodes, the number of second test electrodes being selected based upon a predetermined performance optimisation of the implant configuration.

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