System and method for intracardiac scar tissue identification using impedance sensing and contact measurement

Abstract

The present disclosure relates to a system comprising an electrical interface and a processor. The electrical interface is configured to communicate with a probe inserted into a patient's heart. The processor is configured to receive via the electrical interface (i) a first indication of an electrical impedance measured by the probe at a given location on an inner surface of the heart, and (ii) a second indication of the quality of mechanical contact between the probe and the inner surface of the heart during the measurement of the electrical impedance. The processor is further configured to classify tissue at the given location as scar tissue based on the first indication and the second indication.

Description

Technical Field

[0001] The present invention relates generally to cardiac mapping, and in particular to mapping of scar tissue within the heart. Background Art

[0002] Invasive cardiac procedures often employ techniques for mapping the electroanatomical properties of cardiac tissue. For example, U.S. Patent Application Publication 2013 / 0072774 describes a method and system for determining the mechanism of a patient's arrhythmia. The method essentially entails measuring the impedance of cardiac tissue in a portion of the patient's heart using a catheter to produce an iso-impedance map of the cardiac tissue on a video display, and analyzing the pattern of the iso-impedance map to distinguish localized arrhythmias caused by circumscribed areas of localized firing. The method can also be used to identify areas of coherent rapidly conducting tissue to determine localized "mother rotors" throughout the left atrium that can participate in the generation and maintenance of atrial fibrillation.

[0003] As another example, U.S. Pat. No. 5,673,704 describes a method for locating infarcted myocardial tissue in a beating heart. The method includes inserting the impedance measuring end of a catheter into a ventricle of a beating heart (specifically the left ventricle or the right ventricle), and measuring the impedance of the endocardium at various locations within the ventricle of the beating heart. The measured value is compared with an impedance value having a predetermined range of values ​​to identify an infarcted area of ​​the myocardium and to distinguish such an area from normal myocardium. The measured value is also compared with a range of values ​​of an infarct border zone. According to the present invention, the infarct border zone can be located. The infarct border zone is an important source of arrhythmias (especially tachycardia). In addition, according to the method of the present invention, by using the same catheter tip to ablate the endocardium within the infarct border zone, the risk of arrhythmias occurring in a beating heart can be greatly reduced or eliminated. Impedance measurements can also be used to assess the adequacy of electrode-tissue contact, particularly the adequacy of electrode-tissue contact in fluid-filled body organs or cavities. Summary of the invention

[0004] Embodiments of the present invention provide a system including an electrical interface and a processor. The electrical interface is configured to communicate with a probe inserted into a patient's heart. The processor is configured to receive via the electrical interface (i) a first indication of an electrical impedance measured by the probe at a given position on the inner surface of the heart, and (ii) a second indication of the quality of mechanical contact between the probe and the inner surface of the heart during the measurement of the electrical impedance. The processor is further configured to classify the tissue at the given position as scar tissue based on the first indication and the second indication.

[0005] In some embodiments, the processor is configured to distinguish scar tissue from blood based on the second indication. In some embodiments, the processor is configured to classify the tissue as scar tissue by detecting that the tissue has an impedance lower than a given baseline impedance. In one embodiment, the baseline impedance comprises a measured blood impedance in the heart. In another embodiment, the baseline impedance comprises a measured tissue impedance averaged over a portion of the inner surface of the heart.

[0006] In some embodiments, the processor is configured to receive a second indication from one or more sensors mounted at the distal end of the probe. In some embodiments, the processor is configured to calculate the corresponding estimated position of the probe in the heart from the first indication. In one embodiment, the processor is configured to update the diagram by incorporating the estimated position of the probe into a diagram of at least a portion of the heart.

[0007] In another embodiment, the processor is configured to update the map with the measured electrical impedance at the estimated location.In some embodiments, the processor is configured to use at least one of a digital code and a visual code to distinguish scar tissue from healthy tissue on the map.

[0008] According to an embodiment of the present invention, a method for detecting scar tissue in the heart is further provided. The method includes receiving from a probe inserted into the heart of a patient (i) a first indication of electrical impedance measured by the probe at a given location on the inner surface of the heart, and (ii) a second indication of the quality of mechanical contact between the probe and the inner surface of the heart during the measurement of the electrical impedance. Based on the first indication and the second indication, the tissue at the given location is classified as scar tissue.

[0009] The present disclosure will be more fully understood through the following detailed description of embodiments of the present invention in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a schematic diagram of a system for electroanatomical mapping according to an embodiment of the present invention;

[0011] Figure 2 is a schematic diagram of an electroanatomical map of a portion of a patient's heart according to an embodiment of the present invention; and

[0012] Figure 3 The flowchart schematically shows a method for identifying a scar in the heart according to an embodiment of the present invention. DETAILED DESCRIPTION

[0013] Overview

[0014] Embodiments of the invention described herein provide systems and methods for identifying scar tissue within the heart. In some embodiments, a map is created indicating scar tissue and healthy tissue of the inner wall of the heart. The map can be used for any diagnostic / therapeutic procedure that can benefit from identifying scar tissue, such as selecting appropriate ablation sites, and excluding locations that have already been ablated.

[0015] In some embodiments, an electroanatomical mapping system is provided that uses an electroanatomical mapping catheter having a potential sensing electrode mounted at its distal end. The electroanatomical mapping catheter is used to obtain tissue impedance measurements of selected points on the inner wall tissue of the heart.

[0016] The measured electrical impedance of healthy heart tissue is generally higher than the measured impedance of blood, which is seen as an increased measured electrode impedance at or near healthy tissue. On the other hand, the measured impedance of scar is generally similar to or lower than blood, which is seen as a reduced measured electrode impedance. Therefore, scar tissue can be identified as an area of ​​particularly low electrical impedance.

[0017] When trying to distinguish scar tissue from healthy tissue and / or blood within the heart, a challenge is that it is difficult to distinguish scar tissue from blood using impedance measurements alone. For example, a low impedance reading may result from measuring scar tissue, or from measuring any tissue without good mechanical contact between the tissue and the electrical sensing electrodes. Thus, for example, under configuration, it may be unclear whether or how the location of a given electrode and / or any information carried by the impedance signal received from that electrode should be incorporated into a map, such as an electroanatomical map.

[0018] To address this challenge, in some embodiments, the disclosed system determines sufficient mechanical contact of the electrode with the tissue while measuring tissue impedance so that it is possible to distinguish blood from scar tissue. In some embodiments, mechanical contact with the tissue is confirmed by tracking the shape of the flexible distal end of the catheter, because the shape changes when the catheter contacts the tissue. In other embodiments, sufficient contact with the tissue is determined by one or more sensors that are mounted at the distal end of the electroanatomical mapping catheter and provide a measurement of the contact. Such sensors may include, for example, contact force sensors, pressure sensors, mechanical deformation detection sensors, or ultrasound-based contact sensors. Any type of sensor used to determine electrode contact with tissue is referred to herein as a "contact sensor."

[0019] In some embodiments, assuming that mechanical contact is sufficient, the system identifies scar tissue by comparing the measured tissue impedance to a baseline impedance. Examples of possible baseline impedances are average tissue impedance and peripheral blood impedance. For example, techniques for determining baseline impedance are described in U.S. Patent Application No. 15 / 788,286, entitled “Baseline Impedance Maps for Tissue Proximity Indications,” filed on October 19, 2017, which is assigned to the assignee of the present patent application, and the disclosure of which is incorporated herein by reference.

[0020] A given baseline impedance may be independent of the measurement of contact, as long as the contact is sufficient, for example by the measured contact force being greater than a given minimum value. Thus, the measurement of contact does not have to be uniform across the cardiac tissue.

[0021] The disclosed technique, which combines electrical impedance measurements with physical contact measurements for determining the quality of physical contact, and further applies an analysis method using a baseline impedance standard, can provide reliable identification of scars within the heart. Reliable identification of scars within the heart can assist physicians in diagnosing and planning treatment, as well as analyzing past treatment results.

[0022] System Description

[0023] Figure 1 is a schematic diagram of a system for electroanatomical mapping according to an embodiment of the present invention.

[0024] Figure 1 A physician 27 is shown performing electroanatomical mapping of a heart 23 of a patient 25 using an electroanatomical catheter 29. The catheter 29 includes at its distal end one or more arms 20 that may be mechanically flexible, with one or more electrodes 22 coupled to each of the one or more arms 20. During the mapping procedure, the electrodes 22 acquire and / or inject signals from tissue of the heart 23. The processor 28 receives these signals via an electrical interface 35 and uses the information contained in these signals to construct an electroanatomical map 31. During and / or after the procedure, the processor 28 may display the electroanatomical map 31 on the display 26.

[0025] During the procedure, the respective positions of the electrodes 22 are tracked. Such tracking may be performed, for example, using the aforementioned ACL technique. According to the ACL technique, a plurality of external electrodes 24 are coupled to the body of the patient 25; for example, three external electrodes 24 may be coupled to the patient's chest and another three external electrodes may be coupled to the patient's back. (For ease of illustration, Figure 1) While electrode 22 is located within the patient's heart 23, current is passed between electrode 22 and external electrode 24. Processor 28 calculates the location of each of electrodes 22 within the patient's heart based on the ratio between the resulting current amplitudes (or between the impedances represented by these amplitudes) measured at external electrodes 24. Thus, the processor can associate any given impedance signal received from electrode 22 with the location where the signal was acquired.

[0026] In an embodiment, processor 28 is further configured to indicate the quality of mechanical contact between each of electrodes 22 and the inner surface of the heart during the measurement. The indication is based on the modeled deflection of arm 20 to indicate for each electrode whether the electrode is pressed against tissue (and possibly to estimate the degree of contact force).

[0027] Figure 1 The exemplary illustrations shown are chosen purely for conceptual clarity. Other types of sensing geometries may also be employed, such as Catheter (manufactured by Biosense Webster, Inc.) Sensing geometry. Alternative or additional contact sensors may be mounted on the distal end of the electroanatomical catheter 29. In an embodiment, measurements from some electrodes 22 may be discarded because their contact quality is poor, and measurements from other electrodes may be considered valid because their contact quality is high.

[0028] Generally speaking, processor 28 can be implemented as a single processor or a group of collaborative networking or cluster processors. Processor 28 is generally a programmed digital computing device, which includes a central processing unit (CPU), a random access memory (RAM), a non-volatile auxiliary storage (such as a hard disk drive or a CD ROM drive), a network interface and / or a peripheral device. As is well known in the art, the program code and / or data including the software program are loaded into the RAM for execution and processing by the CPU, and the results are generated for display, output, transmission or storage. For example, the program code and / or data can be downloaded to the computer via a network in electronic form, or alternatively or additionally, it can be provided and / or stored on a non-temporary tangible medium (such as a magnetic memory, an optical memory, or an electronic memory). Such program code and / or data, after being provided to the processor, produce a machine or a special-purpose computer configured to perform the tasks described herein.

[0029] Identification of scar tissue within the heart

[0030] Figure 2 Schematic diagram of an electro-anatomical map 31 of a portion of a heart 23 of a patient 25 in accordance with an embodiment of the present invention.

[0031] As shown, the electroanatomical map 31 indicates two regions using grayscale to visualize the measured tissue impedance: region 50 is indicated as including healthy tissue, while region 52 is classified as scar tissue. Such visualization may be accompanied by a bar 32 to provide further explanation. In the bar 32, a line 34 separates scar from healthy tissue, as shown by a legend 36.

[0032] In an embodiment, bar 32 represents an impedance scale, wherein line 34 represents a given baseline impedance. Accordingly, a tissue impedance above the given baseline impedance is indicated by legend 36 as healthy tissue, while a tissue impedance equal to or below the given baseline impedance is indicated by legend 36 as scar tissue. For example, the given baseline impedance represented by line 34 may be the impedance of surrounding blood or the average tissue impedance. Typical blood impedance values ​​are approximately 90-100 ohms, and during contact with normal tissue, the measured impedance may increase by up to 10%. However, this value is given purely by way of example.

[0033] Figure 2 The exemplary illustrations shown have been chosen purely for the sake of conceptual clarity. Other visualization schemes are possible, such as continuous scaling of the measured impedance and / or color coding.

[0034] Figure 3 is a flow chart schematically illustrating a method of identifying scar tissue within a heart, according to an embodiment of the present invention.At an inserting step 70, the procedure may begin with the physician 27 inserting the electrodissection catheter 29 into the heart.

[0035] Next, at a sensing step 72, physician 27 deploys and engages the tissue of heart 23 at a given location. System 21 senses impedance through electrodes 22 while simultaneously obtaining a measurement of their physical contact with the tissue.

[0036] The processor 28 of the system 21 can estimate the quality of the mechanical contact of a given electrode 22 with the tissue in any suitable manner. In some embodiments, sensors such as contact force sensors, pressure sensors, and ultrasound-based contact sensors mounted at the arm 20 are used. In an exemplary embodiment, each arm in the arm 20 is equipped with one or more strain sensors, which indicate the force of the flexible arm with the strain sensor pressed against the tissue. The measured force indicates the quality of the mechanical contact. In another embodiment, forcing the arm to press against the tissue will be measured by the bending arm relative to its original shape. Such technology is described in, for example, U.S. patent application 15 / 610,865 entitled "Using a Piecewise-Linear Model of a Catheter Arm to Identify Contact with Tissue" filed on June 1, 2017, which is assigned to the assignee of the present patent application and its disclosure is incorporated herein by reference. For example, if the flexible arm 20 deflects more than 20 degrees from its undisturbed state, the distal electrodes mounted on the arm 20 may be considered to be in contact. For example, if the deflection exceeds 35 degrees, the proximal electrodes on the arm 20 may also be considered to be in contact. However, in general, any suitable type of contact sensor or contact sensing method may be used.

[0037] At a position estimation step 74 , processor 28 calculates a corresponding estimated position of one or more of sensing electrodes 22 from the one or more current amplitudes measured at external electrodes 24 .

[0038] The method now proceeds to a contact verification step 76 where processor 28 determines whether one or more of sensing electrodes 22 are sufficiently in contact at the estimated location based on the calculated contact measurements.

[0039] If the determination at decision step 76 is negative, the method returns to step 72 and the physician 27 may retry engaging the tissue. If the determination at step 76 is positive, the method proceeds to a tissue classification step 78 where the physician 27 (or the processor automatically) determines whether the tissue impedance is below a given baseline impedance. If the determination at step 76 is negative, then the processor classifies the tissue at the location in question as healthy at a healthy tissue indication step 80. If the determination at step 78 is positive, then the processor classifies the tissue as scar tissue at a scar indication step 82.

[0040] The method proceeds to a map updating step 84 in which processor 28 marks a portion of electro-anatomical map 31 as including healthy tissue or scar tissue. In some embodiments, processor 28 updates the portion of electro-anatomical map 31 with the measured electrical impedance at a given location as estimated at step 74. In an embodiment, processor 28 updates the portion of electro-anatomical map 31 by incorporating into the map an estimated location of at least one of the electrodes determined to be in contact with tissue at the estimated location.

[0041] At the catheter movement step 86, the process can be repeated for multiple locations by moving the catheter to engage another location on the tissue. The method can then return to step 72.

[0042] Figure 3 The exemplary flow chart shown is chosen purely for conceptual clarity.In alternative embodiments, various steps may be performed to assess contact quality and analyze and visualize tissue impedance.

[0043] Although the embodiments described herein primarily discuss pulmonary vein isolation, the methods and systems described herein may also be used in other applications.

[0044] It should therefore be understood that the embodiments described above are cited by way of example, and that the present invention is not limited to the contents specifically shown and described above. On the contrary, the scope of the present invention includes combinations and sub-combinations of the various features described above, as well as variations and modifications thereof, which will occur to those skilled in the art when reading the above description, and which are not disclosed in the prior art. The documents incorporated by reference into this patent application are considered to be an integral part of this application, except that if any term defined in these incorporated documents conflicts with a definition explicitly or implicitly given in this specification, only the definition in this specification should be considered.

Claims

1. A system for identifying scar tissue in a heart, comprising: an electro-anatomical catheter configured for insertion into a heart of a patient, the catheter comprising a distal end including a plurality of electrodes; an electrical interface for communicating with the catheter; as well as A processor, the processor being configured to: receiving, via the electrical interface, for each electrode (i) a first indication of an electrical impedance measured by the electrode at a given location on an inner surface of the heart, and (ii) a second indication of a quality of mechanical contact between the electrode and the inner surface of the heart during measurement of the electrical impedance; as well as classifying the tissue at the given location as scar tissue by detecting that the tissue has an impedance below a given baseline impedance and that the quality of mechanical contact is sufficient based on the first indication and the second indication; Wherein, when the quality of the mechanical contact is insufficient, the corresponding electrode is configured to retry engaging the tissue.

2. The system of claim 1, wherein the baseline impedance comprises measured blood impedance in the heart.

3. The system of claim 1, wherein the baseline impedance comprises measured tissue impedance averaged over a portion of the inner surface of the heart. 4 . The system of claim 1 , wherein the processor is configured to receive the second indication from one or more sensors mounted at a distal end of the catheter.

5. The system of claim 1, wherein the processor is configured to calculate a respective estimated position of one or more of the plurality of electrodes in the heart from one or more current amplitudes measured at the external electrodes.

6. The system of claim 5, wherein the processor is configured to update the map of at least a portion of the heart by incorporating the estimated position into the map.

7. The system of claim 6, wherein the processor is configured to update the map with the measured electrical impedance at the estimated location.

8. The system of claim 6, wherein the processor is configured to use at least one of a numerical code and a visual code to distinguish the scar tissue from healthy tissue on the map.

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