Coronary sinus (CS) catheter movement detection

A method includes receiving (i) a plurality of electrocardiogram (ECG) signals acquired by a mapping catheter at a plurality of locations on a surface of a heart of a patient, (ii) a reference ECG signal from a reference catheter positioned at a nominal location in a coronary sinus (CS) of the patient, and (iii) position signals indicative of a position of the reference catheter in the CS. An electrophysiological (EP) map of at least part of the heart is calculated by time-referencing the ECG signals relative to the reference ECG signal. Based on the position signals, a displacement of the reference catheter from the nominal location in the CS, which distorts the time-referencing, is estimated. The distortion in the EP map is mitigated using the estimated displacement.

FIELD OF THE INVENTION

The present invention relates generally to sensing a position of an object placed within a living body, and specifically to providing an accurate intracardiac reference signal for intracardiac electrophysiological mapping.

BACKGROUND OF THE INVENTION

Invasive cardiology techniques involving tracking a position of cardiac catheters has been previously proposed in the patent literature. For example, U.S. Patent Application Publication 2008/0161681 describes a method of tracking a three-dimensional (3D) position of a catheter within a patient including securing a navigational reference at a reference location within the patient. The method further includes defining the reference location as the origin of a coordinate system, determining a location of an electrode moving within the patient relative to that coordinate system, and monitoring for a dislodgement of the navigational reference from the initial reference location. For example, the dislodgement is monitored by measuring the navigational reference relative to a far field reference outside the patient's body, and generating a signal indicating that the navigational reference has dislodged from the reference location. Upon dislodgement, a user may be provided with guidance to help reposition and secure the navigational reference to the initial reference location. Alternatively, the navigational reference may be automatically repositioned and secured to the initial reference location. Alternatively, a reference adjustment may be calculated to compensate for the changed reference point/origin.

As another example, U.S. Patent Application Publication 2018/0132938 describes a method for aligning a cardiac model including receiving an initial position signal from three position sensors disposed along a distal end of a coronary sinus catheter positioned in a coronary sinus of a heart. The method can further include receiving a subsequent position signal from the three position sensors. The method can include determining a positional change vector based on a change in position between an initial position associated with the initial position signal and a subsequent position associated with the subsequent position signal. The method can also include shifting a point of interest associated with a cardiac model, using the positional change vector. The method can include dynamically aligning the cardiac model based on an updated position of the three position sensors.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a method including receiving (i) a plurality of electrocardiogram (ECG) signals acquired by a mapping catheter at a plurality of locations on a surface of a heart of a patient, (ii) a reference ECG signal from a reference catheter positioned at a nominal location in a coronary sinus (CS) of the patient, and (iii) position signals indicative of a position of the reference catheter in the CS. An electrophysiological (EP) map of at least part of the heart is calculated by time-referencing the ECG signals relative to the reference ECG signal. Based on the position signals, a displacement of the reference catheter from the nominal location in the CS, which distorts the time-referencing, is estimated. The distortion in the EP map is mitigated using the estimated displacement.

In some embodiments, the method further includes producing the position signals by performing electrical measurements between the reference catheter and multiple electrodes attached to the body of the patient.

In some embodiments, performing the electrical measurement includes performing one of current measurements, voltage measurements, and impedance measurements.

In an embodiment, estimating the displacement includes calculating the displacement using an empirical formula that translates the electrical measurements to the displacement.

In another embodiment, the method further includes presenting to a user a magnitude and a direction of the displacement.

In some embodiments, mitigating the distortion includes prompting a user to move the reference catheter to the nominal location.

In some embodiments, mitigating the distortion includes adapting the ECG signals, or the EP map, to compensate for the displacement of the reference catheter.

There is additionally provided, in accordance with an embodiment of the present invention, a system including an electrical interface and a processor. The electrical interface is configured to receive (i) a plurality of electrocardiogram (ECG) signals acquired by a mapping catheter at a plurality of locations on a surface of a heart of a patient, (ii) a reference ECG signal from a reference catheter positioned at a nominal location in a coronary sinus (CS) of the patient, and (iii) position signals indicative of a position of the reference catheter in the CS. The processor is configured to: (a) calculate an electrophysiological (EP) map of at least part of the heart, by time-referencing the ECG signals relative to the reference ECG signal, (b) based on the position signals, estimate a displacement of the reference catheter from the nominal location in the CS, which distorts the time-referencing, and (c) mitigate the distortion in the EP map using the estimated displacement.

DETAILED DESCRIPTION OF EMBODIMENTS

Overview

Intracardiac electrophysiological (EP) mapping (also named herein “electroanatomical mapping”) is a catheter-based method that may be applied to characterize cardiac EP abnormalities of a patient, such as an arrhythmia. In intra-cardiac EP mapping, the analyzed EP signals are assumed to be intra-cardiac electrocardiogram (ECG) potential-time relationships. In order to fully characterize such relationships, the signals at various intra-cardiac locations need to be referenced in time to each other. The time referencing is accomplished by annotating measured signals relative to a reference-time (e.g., an instance), such as the beginning of each QRS complex of an ECG reference signal (i.e., the beginning of every heartbeat).

Based on time referencing (e.g., annotating) the ECG signals with the timings of the acquired reference signal, a processor analyzes the propagation paths and velocities of EP potentials in the heart and produce an EP map that a physician can analyze to diagnose the patient. A method for generating an EP map is described in U.S. Pat. No. 9,050,011, whose disclosure is fully incorporated herein by reference.

In some embodiments, during an electro-anatomical mapping session, a mapping-catheter moves in a cardiac chamber and measures EP signals, such as ECG signals, at respectively measured intracardiac locations. At the same time, a reference catheter comprising a sensing-electrode, such as a coronary sinus (CS) catheter, is statically placed in the CS, in order to measures a stable reference EP signal.

In order to maintain an accurate reference EP signal, it is important that the CS catheter remains fixed in-place. Any unintended CS catheter movement along the CS impacts the quality of the reference annotation and can cause inconsistencies in the electro-anatomical maps. Embodiments of the present invention that are described hereinafter provide methods and systems to verify and/or correct a placement position of the reference catheter, e.g., a CS catheter, along the CS (e.g., to compensate for possible displacement of the CS catheter), for example, during an EP mapping session. For that purpose, the disclosed embodiments produce position signals indicative of a position of the reference catheter by performing electrical measurements between the reference catheter and electrodes on the body. The electrical measurements may comprise measurements of currents, voltages and/or impedances.

In the description hereinafter, an Active Current Location (ACL) impedance-based system and technique, made by Biosense-Webster (Irvine, Calif.), serves as an example of an impedance-based position tracking system that is further configured to perform EP mapping, and this mapping-catheter using multiple electrodes is named hereinafter “ACL catheter.” The body surface electrodes are named hereinafter “ACL patches.” Examples of mapping-catheters are the Lasso® and Pentaray® catheters, made by Biosense-Webster. Examples of CS catheters typically used for referencing the signals that a mapping-catheter acquires are the CS Uni-Directional® and the CS Bi-Directional® Catheters, also made by Biosense-Webster.

In some embodiments, the disclosed technique includes receiving in a processor (i) a plurality of electrocardiogram (ECG) signals acquired by a mapping catheter at a plurality of locations on a surface of a heart of a patient, (ii) a reference ECG signal from a reference catheter positioned at a nominal location in a coronary sinus (CS) of the patient, and (iii) position signals indicative of a position of the reference catheter in the CS. Next, the processor calculates an EP map of at least part of the heart, by time-referencing the ECG signals relative to the reference ECG signal. Based on the position signals, the processor estimates a displacement of the reference catheter from the nominal location in the CS, which distorts the time-referencing, mitigates the distortion in the EP map using the estimated displacement.

In some embodiments, two or more electrodes of the CS catheter inject electrical current to the CS tissue, and the ACL system measures the currents acquired by six ACL patch electrodes. If the CS catheter does not move, these six currents maintain a relatively constant pattern, or ratio, between themselves. If there is movement, the pattern is disturbed (i.e., changes). If the movement stops, a new constant pattern is formed. Embodiments of the present invention use the change of electrical current pattern to indicate the presence of movement. In addition, based on a calibration, embodiments of the present invention determine, from the changed currents, a magnitude of the CS catheter shift, e.g., in millimeters, as well as a direction along the CS for the shift.

In some embodiments, a processor uses an empirical formula that translates current measurements to location in order to calculate the CS catheter shift. The formula is based on known mechanical values of the CS catheter, and has several parameters that are optimized to give the same computed interelectrode distances as the real ones. In some embodiments, the calculation is optimized (e.g., calibrated) at some early stage of the mapping procedure, when the CS catheter is already in place in the CS. The calibration uses the known distance between at least one pair of electrodes of the CS catheter.

In some embodiments the processor visually presents the calculated shifted values of the CS catheter movement, and such a visual presentation assists the physician in compensating (e.g., correcting) any CS catheter movement, for example, by moving the CS catheter back to the nominal location. In another embodiment, the processor compensates for a displacement of the CS catheter by adapting the EP measurements to the displaced location of the CS catheter. In an embodiment, mitigating the distortion in the EP map includes adapting the ECG signals, or the EP map, to compensate for the displacement of the reference catheter.

Typically, the processor is programmed in software containing a particular algorithm that enables the processor to conduct each of the processor related steps and functions outlined above.

The disclosed CS catheter movement detection technique provides means to control, in real-time, the EP referencing of an EP mapping. Therefore, the disclosed technique may improve the diagnostic quality of catheter-based EP mapping procedures. By virtue of the improved mapping quality, the disclosed technique can also be used for better identifying and mitigating distortions in the EP map, such as aberrant EP activation patterns (e.g., indicative of an arrhythmia), which may otherwise be incorrectly identified, potentially leading to an ablation at a wrong location.

System Description

FIG. 1is a schematic, pictorial illustration of an electrophysiological (EP) mapping system20, in accordance with an embodiment of the present invention. System20is used for generating an EP map of at least part of a patient heart using a mapping catheter32and a coronary sinus (CS) catheter50(seen in an inset25). CS catheter50is fitted at a distal end of a shaft22. As seen, CS catheter50incorporates sensing-electrodes55.

CS catheter50is inserted through a sheath23into the CS of a heart26. Physician30navigates CS catheter50to a target location along the inside of the CS by manipulating shaft22using a manipulator near the proximal end of the catheter and/or deflection from the sheath23.

CS catheter50is used for time referencing or propagating electrical potentials in the heart in order to produce an accurate EP map. In parallel, a mapping-catheter (not shown) moves inside heart26and acquires the EP potentials referenced using the EP signal acquired by CS catheter50. As noted above, in order for CS catheter50to acquire meaningful reference signals, the catheter has to be kept in one place along the CS during the mapping session.

Two or more sensing-electrodes55are connected by wires running through shaft22to driver circuitry in a console24. Console24comprises a processor41, typically a general-purpose computer, with suitable front end and electrical interface circuits37for receiving signals from ACL patches49. Processor41is connected to ACL patches49, which are attached to the chest skin of patient26, by wires running through a cable39.

In some embodiments, processor41accurately determines a change in the position of sensing-electrodes55along the inside of the CS, as described below. Processor41determines the change in position based on, among other inputs, measured currents between sensing-electrodes55(on the CS catheter) and ACL patches49(i.e., based on injecting electrical current as described above). Console24drives a display27, which shows the distal end of catheter position change relative to a nominal position along the CS, that physician30selected for use for referencing an EP mapping.

The method of electrode position sensing using system is implemented in various medical applications, for example in the CARTO™ system, produced by Biosense Webster and is described in detail in U.S. Pat. Nos. 8,456,182, 7,756,576, 7,869,865, and 7,848,787, whose disclosures are all incorporated herein by reference.

The elements of system20and the methods described herein may be performed by applying a voltage gradient using ACL patch electrodes49or other skin-attached electrodes, and measuring the potential voltage with sensing electrodes55on CS catheter50. (e.g., using the Carto®4 technology produced by Biosense Webster). Thus, embodiments of the present invention apply to any position-sensing method used for EP mapping in which a sensing-electrode generates signals indicative of its position in the heart.

Coronary Sinus (CS) Catheter Movement Detection

FIG. 2is a schematic detail view showing mapping catheter32and coronary sinus (CS) catheter50inside heart26, in accordance with an embodiment of the present invention.

FIG. 2shows PENTARY® mapping catheter32having mapping-electrodes33inside left atrium34in order to EP map the atrium. CS catheter50is seen in three different positions along the inside of coronary sinus60. Any lateral shift between positions of CS catheter50(i.e., over a cross-section of the CS) is negligible, and is illustrated larger inFIG. 2only for clarity of presentation.

Of the three locations along the CS, location64is a “nominal” (i.e., a selected) location where physician30initially positions catheter50. During the EP mapping, CS catheter50may be displaced from its nominal position64distally by an amount Δ1, to a position62, or proximally by an amount Δ2, to a position66.

As noted above, such displacements may result in degraded quality of the reference annotation based on the EP signal acquired by two or more electrodes of CS catheter50, such as electrodes55, and can cause inconsistencies in the electro-anatomical maps generated based on signals acquired by mapping-electrodes33and referenced by respective signals acquired by sensing-electrodes55of CS catheter50.

The catheter configuration described inFIG. 2is chosen purely for the sake of conceptual clarity. Other devices on CS catheter50, such as additional electrodes, and other sensors, such as contact force sensors, are not described.

FIGS. 3A and 3Bare graphs of measured ACL currents vs. time and of respective estimated movements of the catheter ofFIG. 2, in accordance with an embodiment of the present invention. AsFIG. 3Ashows, while CS catheter50is stably located in its nominal position64between the times of 0 s and 30 s, the six currents received by ACL patches49maintain a relatively constant pattern, or ratio, between themselves. When CS catheter50moves, e.g., first distally to location62, as illustrated in the 30 s-40 s region of theFIG. 3A, the pattern is disturbed. If the movement stops, e.g., at location66proximal to location64, a new constant pattern forms, as illustrated in the times 45 s and onward.

FIG. 3Bshows CS catheter displacements Δ1and Δ2along CS60that processor41calculates based on the signals ofFIG. 3A. Processor41calculates the magnitude of the displacement in millimeters, as well as providing a direction along the CS for the shift. For the calculation, processor41uses an empirical formula (e.g., based on calibration) that translates ACL current measurements to shifts in locations.

The disclosed empirical model states that the normalized current measured by an ACL patch49kis equal to normalized reciprocals of adjusted distances of electrode55to ACL patches49:

Ik∑j⁢Ij=1/(x→-p→k+ak)∑j⁢1/(x→-p→j+aj)Eq.⁢1
where{right arrow over (x)}—Electrode55position (unknown){right arrow over (p)}k—Position of ACL patch49number k (ACL patches have magnetic location sensors)ak—Distance adjustment parameter (will be optimized)Ik—Current measured at an ACL patch49number k

Given the parameters ak, patch positions {right arrow over (p)}k, and current measurements Ik, we calculate electrode55position by optimization:

x→=arg⁢⁢minx→⁢⁢∑k⁢(Ik∑j⁢Ij-1/(x→-p→k+ak)∑j⁢1/(x→-p→j+aj))2Eq.⁢2
For simplicity the above formula is written as:
{right arrow over (x)}=F(Ik,{right arrow over (p)}k;ak)  Eq. 3

To use the above formula, processor41need as inputs the parameters ak, which are found using the known distances between pairs of electrodes on the catheter: Dm,n—known distance between electrodes m and n. The parameters akare the result of the following optimization:

arg⁢⁢minak⁢∑(m,n)∈{ep}⁢(F⁡(Ikm,p→k;ak)-F⁡(Ikn,p→k;ak)-Dm,n)2Eq.⁢4
subject to constraints on ak. {ep} is the group of electrode pairs.

Where Ikmand Iknare the currents measured at patch number k from electrodes m and n respectively.

In an embodiment, the constraint used is that all akare equal (a1=a2=a3=a4=a5=a6).

Alternatively, other constraints over akmay be used.

The above formula is based on known mechanical values of CS catheter50, and has several parameters that are optimized to give the same computed interelectrode distances as the real ones. The optimization happens at some early stage of an EP mapping procedure, when the CS catheter is already in location64.

FIG. 4is a flow chart that schematically illustrates a method and algorithm for correcting the position of CS catheter50along coronary sinus60, in accordance with an embodiment of the present invention. The algorithm, according to embodiments of the present invention, drives a process that begins with physician30positioning CS catheter50at nominal location64inside CS60, at a CS catheter positioning step70. Next, after the catheter is in nominal position, the disclosed model (i.e., Eq. 2) is calibrated at a calibration step71, using the known distances between pairs of electrodes55, to find the parameters akis done one time—once parameters akare found, they are fixed.

Next, based on reading ACL currents that electrodes injects and are read by ACL patches49, which are indicative CS catheter position (i.e., position signals), processor41, using the dedicated algorithm, monitors the location of CS catheter50, at a CS catheter location monitoring step72.

At a checking step74, processor41checks if the location of CS catheter50inside CS60has shifted. Processor41uses the parameters akto estimate the position of electrodes55and detect shifts of the catheter shaft position along the CS.

If the location remains the same (i.e., nominal location64), then the process returns to location monitoring step72. If processor41identifies that the location of CS catheter50has shifted from nominal location64, then processor41calculates, using the disclosed dedicated algorithm, the direction and the amount of the shift, at a catheter shift calculation step76. Processor41then presents to physician30the direction and amount of shift, at a presenting step78. Next, physician30corrects the catheter location (e.g., brings it back to nominal location64), at a CS catheter location correction step80. The process then loops back to location monitoring step72.

The example algorithm shown inFIG. 4is chosen purely for the sake of conceptual clarity. Embodiments of the present invention also comprises additional steps of the algorithm, which have been omitted from the disclosure herein purposely in order to provide a more simplified flow chart. For example, in alternative embodiments, additional steps may be used, such as magnetic sensing of the CS catheter position.

Although the embodiments described herein mainly address cardiac EP mapping, the methods and systems described herein can also be used in other applications, such as in neurology.