Identifying cardioversion while constructing a location map

Abstract

The invention is entitled "Identifying cardioversion while building a position map." The invention describes a method comprising: computing a position of an intrabody probe within a heart of a subject based on an inductive signal received from an electromagnetic sensor, the intrabody probe comprising one or more electrodes and the electromagnetic sensor; determining a set of attributes of a signal transmitted between the electrode and a plurality of reference electrodes located at respective reference positions based on a set of attributes; responsive to a distance between the computed position and an estimated position being greater than a predetermined threshold, deriving an estimated position of the probe from a position map that maps the sets of attributes to respective estimated positions; determining whether an electrocardiogram signal from the subject is saturated; and responsive to the electrocardiogram signal not being saturated, updating the position map so as to map the set of attributes to the computed position. Other embodiments are described.

Description

Technical Field

[0001] This invention relates to a tracking probe during intracardiac surgery. Background Technology

[0002] U.S. Patent 7,536,218 to Govari et al. describes a position sensing system including a probe suitable for insertion into a subject's body cavity, the disclosure of which is incorporated herein by reference. The probe includes a magnetic field transducer and at least one probe electrode. A control unit is configured to use the magnetic field transducer to measure the position coordinates of the probe. The control unit also measures impedance between at least one probe electrode and one or more points on the subject's body surface. The control unit uses the measured position coordinates to calibrate the measured impedance. Summary of the Invention

[0003] According to some embodiments of the present invention, a system is provided comprising a memory and a processor, the memory being configured to store a location mapping map that maps multiple sets of attributes to corresponding estimated locations. The processor is configured to calculate the location of an in vivo probe within the heart of a subject based on inductive signals received from an electromagnetic sensor, the in vivo probe including one or more electrodes and the electromagnetic sensor. The processor is further configured to determine a set of attributes of signals transmitted between the electrodes and multiple reference electrodes located at corresponding reference locations. The processor is further configured to derive the estimated location of the probe from the location mapping map based on the set of attributes. The processor is further configured to determine whether an electrocardiogram (ECG) signal from the subject is saturated in response to a distance greater than a predetermined threshold between the calculated location and the estimated location. The processor is further configured to update the location mapping map in the memory in response to an ECG signal that is not saturated, so as to map the set of attributes to the calculated location.

[0004] In some implementations, the predetermined threshold is between 8 mm and 15 mm.

[0005] In some implementations, the predetermined threshold is a first predetermined threshold, and the processor is configured to update the location mapping in response to the distance not exceeding a second predetermined threshold.

[0006] In some implementations, the processor is configured to determine whether the electrocardiogram signal from the subject is saturated in response to the distance not exceeding a second predetermined threshold.

[0007] In some implementations, the second predetermined threshold is greater than 15 mm.

[0008] In some implementations, the second predetermined threshold is between 15 mm and 30 mm.

[0009] In some implementations, the processor is further configured to:

[0010] Calculate another location of the probe and determine another set of properties, and

[0011] In response to the saturation of the ECG signal, the mapping at that location is not updated in order to map another set of attributes to another calculated location.

[0012] In some implementations, the processor is further configured to avoid updating the location mapping for a predetermined duration in response to ECG signal saturation.

[0013] In some implementations, the predetermined duration is between 4 and 5 seconds.

[0014] According to some embodiments of the present invention, a method is also provided, the method comprising calculating the position of an in vivo probe within the heart of a subject based on an inductive signal received from an electromagnetic sensor, the in vivo probe comprising one or more electrodes and the electromagnetic sensor. The method further comprises determining a set of properties of a signal transmitted between the electrodes and a plurality of reference electrodes located at corresponding reference locations. The method further comprises deriving an estimated position of the probe from a location mapping map that maps the plurality of properties to corresponding estimated locations based on the set of properties. The method further comprises determining whether an electrocardiogram (ECG) signal from the subject is saturated in response to a distance between the calculated position and the estimated position being greater than a predetermined threshold. The method further comprises updating the location mapping map in response to the ECG signal being unsaturated, so as to map the set of properties to the calculated position.

[0015] According to some embodiments of the present invention, a computer software product is also provided, comprising a tangible, non-transitory, computer-readable medium storing program instructions therein, which, when read by a processor, cause the processor to calculate the position of an in vivo probe within the heart of a subject based on inductive signals received from an electromagnetic sensor, the in vivo probe including one or more electrodes and an electromagnetic sensor. The instructions also cause the processor to determine a set of properties of signals transmitted between the electrodes and a plurality of reference electrodes located at corresponding reference locations. The instructions further cause the processor to derive an estimated position of the probe from a location mapping map that maps the plurality of properties to corresponding estimated positions based on the set of properties. The instructions further cause the processor to determine whether an electrocardiogram (ECG) signal from the subject is saturated in response to a distance greater than a predetermined threshold between the calculated position and the estimated position. The instructions further cause the processor to update the location mapping map in response to an ECG signal that is not saturated, so as to map the set of properties to the calculated position.

[0016] This disclosure will be more fully understood through the following detailed description of embodiments of the invention, taken in conjunction with the accompanying drawings, wherein: Attached Figure Description

[0017] Figure 1This is a schematic diagram of a system for calculating location mapping according to some embodiments of the present invention;

[0018] Figures 2A to 2B This is a schematic diagram of an in vivo probe according to some embodiments of the present invention;

[0019] Figure 3 This is a flowchart of an algorithm according to some embodiments of the present invention for identifying cardiac cardioversion while constructing a location mapping map; and

[0020] Figure 4 Experimental data obtained from procedures performed on human subjects according to some embodiments of the invention are shown. Detailed Implementation

[0021] Overview

[0022] U.S. Patent 7,536,218 to Govari et al., cited in the background section above, describes a hybrid tracking system for tracking the position of an in vivo probe. In this system, the probe is equipped with an electromagnetic sensor and one or more position tracking electrodes. As the probe moves within a subject's body cavity, a signal is sensed in the electromagnetic sensor by an external magnetic field, and a processor calculates the probe's position based on the sensed signal. Furthermore, a position tracking signal, whose properties vary with the probe's position, is transmitted between the position tracking electrodes and one or more reference electrodes on the subject's body surface. The processor constructs a position mapping map that maps the properties of the position tracking signal to the probe's position calculated based on the sensed signal. Subsequently, the position tracking electrodes and the position mapping map can be used to track another probe that does not include an electromagnetic sensor but does include the position tracking electrodes.

[0023] When constructing a position mapping as described above, a challenge lies in the fact that any cardiac cardioversion procedure performed on the subject can alter the properties of the position tracking signal, causing it to fail to accurately indicate the probe's position. Therefore, if position mapping continues to be constructed during a cardiac cardioversion procedure, the accuracy of the mapping is compromised. Furthermore, since the cardioverter used for cardiac cardioversion is typically not connected to a processor, the processor is unaware of when to perform cardiac cardioversion.

[0024] To address this challenge, embodiments of the present invention use a position mapping map to calculate the estimated position of the probe based on the position tracking signal. If the estimated position deviates from the “true” position (calculated based on the sensed signal) by more than a threshold distance, the processor checks whether the electrocardiogram (ECG) signal from the subject is saturated. If the signal is saturated (indicating that cardioversion may be in progress), the processor avoids updating the position mapping map, typically until a predetermined amount of time has elapsed.

[0025] Typically, a higher second threshold distance is also defined. If the estimated position deviates from the true position by more than the second threshold distance, the processor can avoid updating the position mapping map even without checking the ECG signal.

[0026] System Description

[0027] First refer to Figure 1 , Figure 1 This is a schematic diagram of a system 20 for calculating a location mapping map according to some embodiments of the present invention. Reference is also made to... Figures 2A to 2B This is a schematic diagram of an in vivo probe 40 according to some embodiments of the present invention. The probe 40 includes a shaft 22, which is coupled at its distal end to a plurality of deflectable arms 54. Figure 2A ), inflatable balloon 45 ( Figure 2B (or any other suitable structure.)

[0028] The probe 40 includes one or more position tracking electrodes 52. For example, such as Figures 2A to 2B As shown, the probe may include a proximal position tracking electrode 52a and a distal position tracking electrode 52b. The probe 40 also includes an electromagnetic sensor 50, which is positioned between the two tracking electrodes. Figure 2A Tracking electrode 52a at the proximal position ( Figure 2B The probe is attached to shaft 22 proximal to the heart tissue or at any other suitable location. Optionally, the probe may also include additional electrodes 55 for ablating cardiac tissue and / or sensing electrogram signals from the tissue. The aforementioned sensors and electrodes are connected to interface circuitry 44 in console 24 via wires extending through shaft 22. Interface circuitry 44 may include an analog-to-digital (A / D) converter and / or any other suitable components.

[0029] like Figure 1 As shown, the physician 30 inserts the probe 40 into the vascular system of the subject 28, and then typically uses the control handle 32 to navigate the probe to a target location in the heart 26 of the subject 28 to manipulate the axis 22. Typically, the probe is navigated via a sheath 23, which restrains the distal end of the probe. Upon reaching the target location, the sheath 23 retracts and the distal end of the probe expands.

[0030] like Figure 1 As further shown, the subject 28 is positioned within the magnetic field generated by the magnetic field generator coil 42. Specifically, a first signal generator (SIG GEN) 43 drives a signal through the coil 42, causing the coil to generate a magnetic field. The magnetic field induces a signal in the electromagnetic sensor 50, and the induced signal changes with the position of the sensor. The induced signal from the sensor 50 is received by the interface circuit 44.

[0031] Furthermore, as the probe moves within the heart 26, the second signal generator 47 transmits a position tracking signal between the position tracking electrode 52 and the reference electrode 49. The reference electrode 49 is located at a corresponding reference position that does not move with the probe. For example, the reference electrode may be coupled to the subject's body surface, such as to the subject's chest and / or back. Specifically, three reference electrodes may be coupled to the subject's chest (e.g., Figure 1 (As shown), and three additional reference electrodes can be coupled to the back of the subject. (The reference electrodes are typically connected to the interface circuitry 44 via cable 39.) As the probe moves, the impedance between the position tracking electrode 52 and the reference electrode 49 changes, causing the properties of the position tracking signal to change with the position of the probe.

[0032] System 20 also includes a processor 41 (PROC) typically housed in console 24. Processor 41 is configured to control various other components of system 20, such as a first signal generator 43 and a second signal generator 47. Processor 41 is further configured to receive sensed signals from electromagnetic sensor 50 via interface circuitry 44. Based on the sensed signals, the processor calculates the position of probe 40. (The position of the probe can be defined as the position of the sensor, or the position of another portion of probe 40 at a fixed displacement from the sensor.) In performing this calculation, the processor may use any suitable technique, such as those described in U.S. Patents 5,391,199, 5,443,489, and 6,788,967 to Ben-Haim, U.S. Patent 6,690,963 to Ben-Haim et al., U.S. Patent 5,558,091 to Acker et al., and U.S. Patent 6,177,792 to Govari, the corresponding disclosures of which are incorporated herein by reference.

[0033] The processor 41 is further configured to receive the position tracking signal via interface circuitry and determine corresponding sets of attributes for the position tracking signal. Each set of attributes may include, for example, the voltage and / or current between each pair of electrodes, such as the voltage and / or current between the proximal position tracking electrode 52a and each of the reference electrodes, and between the distal position tracking electrode 52b and each of the reference electrodes. (Specifically, for an embodiment where the second signal generator 47 is used as a voltage source, each set of attributes may include current, and for an embodiment where the second signal generator is used as a current source, each set of attributes may include voltage.) Alternatively or additionally, each set of attributes may include calculated impedance between each pair of electrodes.

[0034] (It should be noted that each of the aforementioned voltage, current, and impedance can be expressed as an absolute or relative number. As an example of the latter, the current between the proximal position tracking electrode 52a and one of the reference electrodes can be expressed as a proportion of the total current between the proximal position tracking electrode 52a and the reference electrode.)

[0035] The processor 41 is further configured to receive electrocardiogram (ECG) potentials from electrocardiogram (ECG) electrodes (not shown) coupled to the subject's body via an interface circuit. (The ECG electrodes may be connected to the interface circuit via cable 39 or another cable.) Using techniques known in the art, the processor combines the potentials into a single ECG signal.

[0036] See below for reference Figure 3 Furthermore, the processor is configured to construct a position mapping map 36 that maps each set of attributes (PROP) to the corresponding position (POS) of the probe. During the construction of the mapping map 36, it can be stored in memory 34, such as random access memory (RAM). The process of constructing the position mapping map 36 can be referred to as the “calibration” of the electrode-based tracking system including the position tracking electrode 52 and the reference electrode 49, because the processor learns how the attributes of the position tracking signal indicate the position of the probe. After calibrating the electrode-based tracking system, it can be used to track another probe, including the position tracking electrode 52 but not the sensor 50, during subsequent procedures.

[0037] When performing calibration, probe 40 can be used to ablate intracardiac tissue, construct electrophysiological mapping of the target location, and / or perform any other suitable procedure. Alternatively, calibration can be performed without performing any other procedures simultaneously; in such embodiments, the probe does not necessarily include any electrodes located distal to axis 22.

[0038] Typically, system 20 also includes a display 27. Based on the calculated position of the probe, processor 41 can display on display 27 an icon representing the probe superimposed on an image at the target position.

[0039] In some embodiments, electrode 55 is used for position tracking, i.e., position tracking signals are transmitted between electrode 55 and reference electrode 49, and the processor determines the properties of these signals and constructs a position mapping map 36 in response to these properties. In such embodiments, probe 40 does not necessarily include position tracking electrode 52.

[0040] During calibration, the subject may need to use a cardioversion device 51 to perform an electrical cardioversion procedure. See below for reference. Figure 3 In detail, the processor 41 is configured to recognize any situation of cardiac cardioversion and suspend calibration in response to it.

[0041] Generally, processor 41 may be embodied as a single processor or a group of cooperative networked or clustered processors. The functionality of processor 41 may be implemented solely in hardware, for example, using one or more fixed-function or general-purpose integrated circuits, application-specific integrated circuits (ASICs), and / or field-programmable gate arrays (FPGAs). Alternatively, the functionality may be implemented at least partially in software. For example, processor 41 may be embodied as a programmable processor including, for example, a central processing unit (CPU) and / or a graphics processing unit (GPU). Program code (including software programs and / or data) may be loaded for execution and processing by the CPU and / or GPU. For example, program code and / or data may be downloaded to the processor electronically via a network. Alternatively or otherwise, program code and / or data may be provided and / or stored on a non-transitory tangible medium, such as magnetic, optical, or electronic memory. Such program code and / or data, when provided to the processor, create a machine or special-purpose computer configured to perform the tasks described herein.

[0042] Identifying cardiac cardioversion

[0043] Now for reference Figure 3 This is a flowchart of an algorithm 56 according to some embodiments of the present invention for identifying cardiac cardioversion while constructing a location mapping map 36. The algorithm 56 is typically executed in real time by a processor 41 while the probe is inside the subject's heart.

[0044] According to Algorithm 56, at position calculation step 58, the processor iteratively calculates the probe's position within the subject's heart based on the induced signal received from the electromagnetic (EM) sensor. For each probe position calculation, at attribute setting determination step 60, the processor also determines a set of attributes of the position tracking signal. At position estimation derivation step 62, based on this set of attributes, the processor derives the position from position mapping map 36 (…). Figure 1 Derive the estimated position of the probe.

[0045] (It should be noted that during each iteration of Algorithm 56, the attribute setting determination step 60 and the optional estimated position derivation step 62 may be performed before the position calculation step 58.)

[0046] After calculating the probe's position and deriving the estimated position, at distance calculation step 64, the processor calculates the distance between that position and the estimated position. Next, at the first comparison step 66, the processor compares this distance with a first predetermined threshold, which is typically between 8 mm and 15 mm.

[0047] If the distance is not greater than a first threshold, then at mapping update step 74, the processor updates the location mapping map to map the determined set of attributes to that location. Otherwise, at saturation check step 70, the processor determines whether the electrocardiogram (ECG) signal from the subject is saturated, i.e., whether the amplitude of the ECG signal exceeds a predetermined threshold. If the ECG signal is not saturated, the processor updates the location mapping map; otherwise, given that ECG signal saturation indicates cardiac cardioversion and therefore indicates reduced reliability of the location tracking signal, the processor avoids updating the location mapping map.

[0048] After updating the location mapping map, the processor returns to the location calculation step 58.

[0049] Typically, if the distance is greater than a first threshold, the update of the location mapping needs to meet two conditions: first, the electrocardiogram signal is not saturated (as described above), and second, the distance does not exceed a second predetermined threshold, which is typically greater than 15 mm, for example, between 15 mm and 30 mm.

[0050] For example, before performing the saturation check step 70, the processor may compare the distance with a second predetermined threshold at the second comparison step 68. If the distance does not exceed the second predetermined threshold, the processor performs the saturation check step 70. Otherwise, the processor avoids updating the location mapping map.

[0051] In some implementations, the processor avoids updating the location mapping for a predetermined duration in response to ECG signal saturation (or in response to the distance exceeding a second threshold). In other words, at wait step 72, after determining that the ECG signal is saturated (or the distance exceeds the second threshold), the processor waits for a predetermined duration. Typically, this predetermined duration is between 4 and 5 seconds, which is generally sufficient time for an electrode-based tracking system to recover from a cardiac cardioversion event. After waiting, the processor returns to the location calculation step 58.

[0052] In other embodiments, the processor may update the location mapping at any subsequent time, provided that the conditions for updating the location mapping are met. In such embodiments, after determining that the ECG signal is saturated (or that the distance exceeds a second threshold), the processor returns to the location calculation step 58 without first waiting for a predetermined duration.

[0053] In some implementations, the algorithm is executed offline based on the recording of sensed signals, ECG signals, and location tracking signals. In such implementations, the processor can avoid using any recorded data acquired within a predetermined duration after ECG saturation occurs (or the distance begins to exceed a second threshold) to update the location mapping.

[0054] Experimental data

[0055] Now for reference Figure 4 The diagram illustrates experimental data obtained from procedures performed on human subjects according to some embodiments of the invention. The data includes a first graph 76 showing the distance between the probe position calculated based on inductive signals received from an EM sensor and the estimated probe position derived from a position mapping map. The data also includes a second graph 78 showing ECG signals obtained from the subject during the procedure. Both graphs are aligned with respect to the time axis, i.e., they are synchronized.

[0056] During the procedure, the cardiac cardioversion event occurred between approximately 4.525 s and 4.528 s. As a result of the cardiac cardioversion event, this distance increased significantly from its previous range centered at approximately 2 mm. Furthermore, the ECG signal became saturated; instead of showing a PQRST wave 80, the ECG signal was flat at zero, indicating that the ECG potential seen at each electrode in the ECG electrodes exceeded the maximum value (100 mV) that could be measured by the system 20, resulting in a potential difference of zero.

[0057] Therefore, the experimental data show that ECG signal saturation indicates cardiac cardioversion events. The data also show that the recovery time of electrode-based tracking systems from cardiac cardioversion events (and thus the distance to return to their pre-cardioversion range) can be significantly longer than the time required for ECG signal recovery (e.g., 4-5 seconds longer).

[0058] Those skilled in the art will understand that this invention is not limited to what has been specifically shown and described above. Rather, the scope of embodiments of this invention includes both combinations and sub-combinations of the various features described above, as well as variations and modifications outside the scope of the prior art that may occur to those skilled in the art upon reading the foregoing specification. Documents incorporated herein by reference are considered an integral part of this application, except that if any terminology defined in such incorporated documents conflicts with the definitions expressly or implicitly given in this specification, only the definitions in this specification shall be considered.

Claims

1. A system comprising: A memory configured to store location mapping maps that map multiple sets of attributes to their corresponding estimated locations; and Processor, the processor being configured to: The location of an in vivo probe within the subject's heart is calculated based on inductive signals received from an electromagnetic sensor. The in vivo probe includes one or more electrodes and an electromagnetic sensor. Determine a set of properties of the signal transmitted between the electrode and a plurality of reference electrodes located at respective reference positions. Based on the aforementioned set of attributes, the estimated location of the probe is derived from the location mapping map. In response to a distance greater than a predetermined threshold between the calculated and estimated locations, it is determined whether the electrocardiogram signal from the subject is saturated. In response to the ECG signal being unsaturated, the location mapping map in the memory is updated so that the set of attributes is mapped to the calculated location.

2. The system according to claim 1, wherein, The predetermined threshold is between 8mm and 15mm.

3. The system according to claim 1, wherein, The predetermined threshold is a first predetermined threshold, and the processor is configured to update the location mapping in response to the distance not exceeding a second predetermined threshold.

4. The system according to claim 3, wherein, The processor is configured to determine whether the electrocardiogram signal from the subject is saturated in response to the distance not exceeding the second predetermined threshold.

5. The system according to claim 3, wherein, The second predetermined threshold is greater than 15mm.

6. The system according to claim 5, wherein, The second predetermined threshold is between 15mm and 30mm.

7. The system according to claim 1, wherein, The processor is further configured to: Calculate another location of the probe and determine another set of properties, and In response to the saturation of the electrocardiogram signal, the location mapping is not updated in order to map the other set of attributes to another calculated location.

8. The system according to claim 7, wherein, The processor is further configured to avoid updating the location mapping for a predetermined duration in response to the saturation of the electrocardiogram signal.

9. The system according to claim 8, wherein, The predetermined duration is between 4s and 5s.

10. A computer software product comprising a tangible, non-transitory computer-readable medium therein storing program instructions, said instructions, when read by a processor, causing the processor to: The location of an in vivo probe within the subject's heart is calculated based on induced signals received from an electromagnetic sensor. The in vivo probe includes one or more electrodes and the electromagnetic sensor. Determine a set of properties of the signal transmitted between the electrode and a plurality of reference electrodes located at respective reference positions. Based on the aforementioned set of attributes, the estimated position of the probe is derived from a location mapping map that maps multiple sets of attributes to their corresponding estimated positions. In response to a distance greater than a predetermined threshold between the calculated and estimated locations, it is determined whether the electrocardiogram signal from the subject is saturated. In response to the ECG signal being unsaturated, the location mapping map is updated to map the set of attributes to the calculated location.

11. The computer software product of claim 10, wherein the instructions further cause the processor to: Calculate another location of the probe and determine another set of properties, and In response to the saturation of the electrocardiogram signal, the location mapping is not updated in order to map the other set of attributes to another calculated location.

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