Patent Application
20230181243
The present application relates the field of medical diagnosis and treatment using medical probes and in particular, to assessment of lesion formation during ablation using multi-electrode cardiac ablation catheters.
Medical personnel, such as ear, nose and throat (ENT) physicians and cardiologists, use medical tools for performing medical procedures within patient anatomy. Medical tools, such as multi-electrode cardiac ablation catheters, are used to ablate portions of dysfunctional tissue, such as tissue of a heart, lung, ear, nose, throat or other organs. For example, a radio-frequency (RF) catheter ablation procedure typically includes inserting a catheter through an incision in the skin and guiding the catheter to an organ where the catheter is used to create ablation lesions on the organ tissue.
A method of lesion assessment for a medical ablation procedure is provided which comprises acquiring first impedance measurements between each of a plurality of ablation electrodes of a medical probe and a stem electrode of the medical probe, acquiring second impedance measurements between each of the ablation electrodes of the medical probe and an edge electrode of the medical probe, ablating tissue of patient anatomy, determining, during ablation of the tissue, changes to at least one of the first and second impedance measurements, and indicating lesion formation based on the changes to at least one of the first and second impedance measurements.
A processing device for use during a medical procedure is provided which comprises memory configured to store data and a processor. The processor is configured to acquire first impedance measurements between each of a plurality of ablation electrodes of a medical probe and an edge electrode of the medical probe, acquire second impedance measurements between each of the ablation electrodes and a stem electrode of the medical probe, determine, during ablation of tissue of patient anatomy, changes to at least one of the first and second impedance measurements, and indicating lesion formation based on the changes to at least one of the first and second impedance measurements.
A system for use with performing a medical procedure is provided which comprises a balloon catheter and a processing device. The balloon catheter comprises a plurality of ablation electrodes configured to ablate tissue of patient anatomy, a stem electrode and an edge electrode. The processing device comprises a processor configured to acquire first impedance measurements between each of the ablation electrodes of the balloon catheter and an edge electrode of the balloon catheter, acquire second impedance measurements between each of the ablation electrodes of the balloon catheter and a stem electrode of the balloon catheter, determine, during ablation of the tissue, changes to at least one of the first and second impedance measurements, and indicating lesion formation based on the changes to at least one of the first and second impedance measurements.
A more detailed understanding can be had from the following description, given by way of example in conjunction with the accompanying drawings wherein:
As used herein, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance which allows the part or collection of components to function for its intended purpose as described herein. More specifically, “about” or “approximately” can refer to the range of values±20% of the recited value. For example, “about 90%” can indicate a range of values from 71% to 99%.
Dynamic maps of the patient anatomy (e.g., organs) are created to facilitate accurate determination of regions for ablation. Target ablation sites (i.e., regions of interest (ROI)) of an organ are identified by viewing the maps. Based on the identified ablation sites, an ablation procedure, which includes one or more ablations, is performed on the organ.
A multi-electrode ablation catheter, such as a balloon ablation catheter or a basket catheter, can be used to perform the ablation procedure. A multi-electrode ablation catheter typically comprises an expandable frame (e.g., an inflatable balloon), which is coupled to the distal end of a shaft for insertion into a cavity of an organ of a patient, and a plurality of ablating electrodes disposed over the frame.
Successful ablation treatment is facilitated when each of the ablating electrodes are in physical contact with cavity wall tissue to be ablated. For example, when a balloon catheter with multiple ablation electrodes is used to ablate an ostium of a pulmonary ventricle (PV), typically each of the ablation electrodes of the catheter should be positioned so they are in full contact with the PV tissue. The ablation electrodes are often not in full contact with tissue, however, and portions of ablation electrodes are instead immersed in blood, resulting in these electrodes not ablating tissue and potentially causing problematic side effects such as clot formation.
Some conventional techniques determine if each of the electrodes of an ablation catheter are in full contact with tissue based on impedance measurements between ablation electrodes and a stem electrode as well as between the ablation electrodes and the edge electrode (i.e., tip electrode) on the catheter. While these conventional techniques provide a good indication of the ablation electrodes being in full contact with the tissue, these techniques do not provide an indication as to whether an ablation resulted in a lesion being formed.
Features of the present disclosure provide additional techniques for performing a lesion assessment by monitoring changes to impedance characteristics during ablation. The lesion assessment includes measurements (e.g., impedance changes), in addition to the impedance measurements for determining full contact with tissue, and providing (e.g., displaying) the results of the additional measurements physician for predicting whether or not a lesion was formed. The lesion assessment is performed by acquiring impedance measurements between ablation electrodes and both stem and edge electrodes before ablation, acquiring second impedance measurements between the ablation electrodes and both the stem and edge electrodes during ablation and determining changes between the first and second impedance measurements during ablation. A change in the impedance measurements is indicative of the formation of a lesion.
The example computing device 24 shown in
In some embodiments, processor 41 controls a relay 60 to switch electrical connections between two or more of: (i) a first configuration having a connection (62) between the ablation electrodes and surface electrodes 49 for measuring impedances between the ablation electrodes and one or more body-surface electrodes, (ii) a second configuration having a connection (64) between the ablation electrodes and the stem and edge electrodes of the balloon catheter for measuring impedances between the ablation electrodes and the stem and edge electrodes, where connections 62 and 64 are used in order to interchangeably measure electrode position and degree of electrode contact with tissue at the location, and (iii) a connection (66) between the ablation electrodes and a back patch electrode (not shown) in order to perform ablation by driving electrical signal between the ablation electrodes and the back patch electrode.
Physician 30 navigates balloon catheter 40 to a target location in a heart 26 of a patient 28 by manipulating shaft 22 using a manipulator 32 near the proximal end of the catheter and/or deflection from a sheath 23. Balloon catheter 40 is inserted, in a folded configuration, through sheath 23, and only after the balloon is retracted from the sheath 23 does balloon catheter 40 regain its intended functional shape. By containing balloon catheter 40 in a folded configuration, sheath 23 also serves to minimize vascular trauma on its way to the target location.
Balloon catheter 40 comprises elongated and large area ablation electrodes 50, which are disposed on an outer surface of the balloon membrane. A stem electrode 51 is disposed on a distal end of shaft 22 proximally to the balloon. An edge electrode 52 is disposed on the distal end of shaft 22 just distally to the balloon. Electrodes 51 and 52 are used to determine whether each of ablation electrodes 50 is in full contact with tissue or at least partially immersed in blood.
Ablation electrodes 50, stem electrode 51, and edge electrode 52 are electrically connected to each other, for example, via wires running through shaft 22 to interface circuits 44 in computing device 24. Additionally, ablation electrodes 50 can be used to determine a position of balloon catheter 40 inside heart 26, by sensing impedances relative to surface electrodes 49 via wires running through a cable 39 to the chest of patient 28. The position of the balloon catheter 40 is determined, for example, using advanced catheter location (ACL), which uses a position tracking sub-system that measures impedances between the ablation electrodes and surface electrodes to track positions of electrodes on the balloon catheter inside the organ. ACL is implemented in various medical applications, for example in the CARTO system, produced by Biosense-Webster Inc. (Irvine, Calif.) and described in U.S. Pat. Nos. 7,756,576, 7,869,865, 7,848,787, and 8,456,182, whose disclosures are all incorporated herein by reference.
As shown in
As shown in
The catheter 202 also includes electrodes 208. The electrodes 208 include, for example, the ablation electrodes 50, the stem electrode 51 and the edge electrode 52 shown in
Memory 212 includes non-volatile memory, such as random access memory (RAM), dynamic RAM, or a cache. Memory 212 also includes, for example, storage, such as, fixed storage (e.g., a hard disk drive and a solid state drive) and removable storage (e.g., an optical disk and a flash drive).
Display device 206 is configured to display one or more maps of the heart in the 3D space including data corresponding to the acquired electrical signals (i.e., electrical signal data) of the portion of patient anatomy (e.g., the heart). For example, display device 206 is configured to display maps representing a spatio-temporal manifestation of the heart as well as the electrical signal data at regions of the heart on the maps. Display device 206 may be in wired or wireless communication with processing device 204. In some embodiments, display device may be separate from computing device 24. Display device 206 may include one or more displays each configured to display one or more maps.
Processor 41 is configured to perform measurements during an ablation procedure, which include measuring one or more first impedances between one or more of the ablation electrodes and the stem electrode, measuring one or more second impedances between one or more of the ablation electrodes and the edge electrode and, based on the first and second impedances, determine, for at least an ablation electrode from among the one or more ablation electrodes, whether the ablation electrode is in physical contact with the wall tissue.
Processor 41 is also configured to perform additional impedance calculations and measurements, as part of a lesion assessment, the results of which enable a physician to predict whether or not a lesion was formed by the ablation.
Processor 41 also configured to processes the acquired impedance calculations and measurements signals (e.g., from electrodes 208) as electrical signal data and store, in memory 212, the electrical signal data acquired via electrodes 208. Processing device 204 is also configured to filter the acquired electrical signal data according to one or more filter parameter settings, generate mapping information and drive display device 206 to display the maps using the mapping information.
The diagram in
|Z_insufficient|=RB∥RS Equation 1
For the case in which a balloon is mostly immersed in blood such that the shunt resistivity is dominated by blood resistivity, a minimum value of Z_insufficient is about RB/2. For the case in which the shunt resistivity is infinite, a maximum value of Z_insufficient is RB. For typical blood resistivity value of approximately 100 Ohms, Z_insufficient falls in the range of approximately 50 to approximately 100 Ohms.
The diagram in
|Z_sufficient|=(RB+RT)∥RS Equation 2
Because tissue impedance is considerably larger than blood impedance, a “sufficient” impedance is typically larger than an “insufficient” impedance by a value large enough to be measured (e.g., at least several ohms) and, therefore, a case in which an ablation electrode 50 is in partial contact with tissue (i.e., immersed in blood) can be distinguished from a case in which the ablation electrode 50 is full contact with the tissue 48, using, for example, a calibrated threshold impedance value.
For the case in which a balloon is mostly immersed in blood such that the shunt resistivity is dominated by blood resistivity, a minimum value of Z_sufficient is about RB. In this case, the balloon is repositioned due to low shunt resistivity. A practical threshold value for Z_sufficient is RT to account for the case in which a shunt resistivity is mainly via tissue. For a typical blood resistivity value of approximately 100 Ohms and a tissue resistivity value of approximately 300 Ohms, Z_sufficient is above approximately 150 Ohms. A lower number above approximately 100 ohms, can be used, however, as a threshold for Z_sufficient depending, for example, on measurement repeatability.
Although
Processor 41 determines, for example, that the ablation electrode is in physical contact with the tissue by determining that a measured first or second impedance is equal to or greater than a predetermined impedance value (e.g., a threshold impedance value) stored in a look-up table. An example of a look-up table which includes levels of contact and corresponding threshold impedance values is shown below in Table 1.
By measuring the impedance between ablation electrodes 50 and both stem electrode 51 and edge electrode 52, full physical contact with tissue from both ends of the elongated ablation electrodes can be confirmed. The levels and the number of levels shown in Table 1 are merely an example. Features of the disclosure can be implemented using different levels and different numbers of levels than those shown in Table 1.
As shown at block 502, a partially expanded balloon catheter (e.g., catheter 40) is positioned (e.g., by physician 30) at a target location inside a cavity of patient anatomy (e.g., an ostium of a pulmonary vein of a heart). As shown at block 504, the balloon is expanded to bring an ablation electrode (e.g., an ablation electrode 50) into full contact with tissue.
As shown at block 506, the method 500 includes acquiring impedance measurements between each of the ablation electrodes 50 (i.e., balloon electrodes) and the stem electrode 51 and impedance measurements between each of the ablation electrodes 50 and the edge electrode 52. For example, for each one of the ablation electrodes 50, the impedance Z1 between the edge electrode 52 and an ablation electrode 50 can be represented as shown in Equation 3 below:
Z1=ZEdge−ZBalloon Equation 3
For each one of the ablation electrodes 50, the impedance Z2 between the stem electrode 51 and an ablation electrode 50 can be represented as shown in Equation 4 below:
Z2=ZEdge−ZBalloon Equation 4
As shown at block 508, based on the acquired impedance measurements a level of contact sufficiency (e.g., full or partial contact) between each of the ablation electrodes and the tissue is determined (e.g., via processor 41). For example, processor 41 determines a level of contact for each ablation electrode 50 by comparing a measured unipolar impedance value to one or more stored unipolar threshold impedance values, such as those shown in Table 1 above. The levels of contact can be indicated (e.g., displayed) to a physician for identifying whether the electrode is in full contact with tissue. For example, a physician can determine that the electrode is in full contact from any of the displayed levels of contact (e.g., minimally sufficient, sufficient, good and excellent shown in Table 1.
Additionally or alternatively, a level of contact by each ablation electrode with the tissue can be determined based on a relative bipolar impedance RI, which can be represented as shown in Equation 5 below:
When there is no contact between an ablation electrode 50 and the tissue, both impedance measurements (Z1 and Z2) will be approximately equal to each other and, therefore, the relative bipolar impedance RI is equal to or approximately equal to zero and can be represented as shown in Equation 6 below:
When there is contact between an ablation electrode 50 and the tissue, the impedance measurements (Z1 and Z2) will be different from each other and, therefore, the relative bipolar impedance RI is not equal to zero and can be represented as shown in Equation 7 below:
Accordingly, when there is contact between an ablation electrode 50 and tissue, the relative bipolar impedance has a value which is not equal to zero. When there is contact between an ablation electrode 50 and tissue, the relative bipolar impedance is equal to zero.
When it is determined, at decision block 510, that each of the ablation electrodes 50 are not in full contact with tissue (NO decision) due, for example, to insufficient impedance (Table 1) as measured by the electrodes, the catheter 40 is repositioned to improve contact, and the method proceeds back to block 506 to reassess a level of contact sufficiency between each of the ablation electrodes 50 and the tissue. When it is determined, at decision block 510, that each of the ablation electrodes 50 are in full contact with tissue (YES decision), ablation of the tissue begins at block 514.
Ablation of the tissue is performed by applying, for example, RF energy by one or more of the ablation electrodes to a region of the tissue 48. During the ablation procedure, changes to the impedance characteristics (e.g., changes to unipolar impedance values and changes to relative bipolar impedance values) are monitored, at block 516, and indications of the impedance changes are provided (e.g., displayed), at block 518, to a physician. The indicated changes can be used by the physician to predict whether a lesion is successfully formed on the tissue 48. The impedance measurements described herein correspond to an alternating current (AC) applied in an RF range of about 10 kHz to about 500 kHz.
The impedance of tissue is typically higher than the impedance of blood. When a lesion is formed by ablation of the tissue, however, the electrical characteristics of the tissue change and the impedance, at the region of the tissue 48 where the lesion is formed, is reduced (e.g., about 15-20 ohms). Accordingly, an impedance change of about 15 to about 20 ohms is an indication that a lesion is successfully formed at the target site of the tissue 48.
For example, processor 41 monitors changes between previously acquired unipolar impedance values (e.g., values between each of the ablation electrodes 50 and the edge electrode 52) and unipolar impedance values acquired during ablation and the changes between the unipolar impedance values are provided (e.g., displayed) to a physician. In some cases, the previously acquired unipolar impedance values are acquired prior to ablation. Alternatively, the previously acquired unipolar impedance values are also acquired during ablation.
Additionally or alternatively, processor 41 monitors changes to the relative bipolar impedance values described above. For example, as shown in by the dashed lines at block 704, the acquired impedance values are bipolar impedance values. For example, because the impedance at a region of tissue drops by about 15-20 ohms when a lesion is formed, the relative bipolar impedance values (shown above in Equation 5) also changes. When the ablation is started, the processor 41 can store the relative bipolar impedance values and then compare relative bipolar impedance values acquired during ablation to the stored relative bipolar impedance values. Similar to the unipolar impedance values described above, the processor 41 determines, for each electrode, a change in impedance at block 706, by comparing the stored bipolar impedance values to subsequently acquired relative bipolar impedance values (e.g., second unipolar impedance values) acquired prior to ablation or during ablation (e.g., by the monitoring at block 516 in
The displayed changes to impedance values can include different types of visually displayed information so that a physician can predict that a lesion is successfully formed.
A baseline relative impedance is acquired between time t0 and time t1 prior to the start of the ablation procedure at time t1. The baseline relative impedance shown in
The horizontal dashed line shown in
The methods provided can be implemented in a general purpose computer, a processor, or a processor core. Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine. Such processors can be manufactured by configuring a manufacturing process using the results of processed hardware description language (HDL) instructions and other intermediary data including netlists (such instructions capable of being stored on a computer readable media). The results of such processing can be maskworks that are then used in a semiconductor manufacturing process to manufacture a processor which implements features of the disclosure.
The methods or flow charts provided herein can be implemented in a computer program, software, or firmware incorporated in a non-transitory computer-readable storage medium for execution by a general purpose computer or a processor. Examples of non-transitory computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs).
It should be understood that many variations are possible based on the disclosure herein. Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements.
