Patent Description:
<CIT> describes electrodes and electrode array apparatus and systems for in vivo delivery of electrical waveforms by utilizing an electrode array having at least three individually addressable electrodes disposed so as to form a triangle in a plane intersecting the electrodes and an electrical signal generating device operatively connected to the electrodes for delivering electrical waveforms to said electrodes and generating electroporation-inducing electrical fields between the electrodes.

<CIT> describes an electrophysiology system for mapping tissue, including a catheter having a plurality of electrodes. The system may be a catheter having a dense collection of small electrodes on its tip. The electrodes may be arranged in a pattern that is constant regardless of rotational orientation. The system may be an electrophysiology apparatus having a catheter, the catheter having a body with a proximal end and a distal end. At the distal end of the catheter body is a distal tip comprising a plurality of electrodes and/or coaxtrodes. A signal processor may be operably connected to the plurality of electrodes and/or coaxtrodes and can measure at least one electrophysiological parameter.

<CIT> describes an electrophysiology catheter with a distal electrode assembly having a covered spine carrying a plurality of microelectrodes. The position of the microelectrodes on each spine is staggered relative to microelectrodes on adjacent spines so as to minimize the risk of electrodes on adjacent spines touching each other during use of the catheter. The staggered electrode configuration provides the distal electrode assembly with a greater effective contact surface because the effective concentric electrode arrays is increased or at least doubled.

In <CIT>, there is described an array of electrodes on a flexible scaffolding, with the ability to collapse into an axial configuration suitable for deploying through a narrow cylindrical channel. The electrode arrays can be placed into the ventricular system of the brain, constituting a minimally invasive platform for precise spatial and temporal localization of electrical activity within the brain, and precise electrical stimulation of brain tissue, to diagnose and restore function in conditions caused by abnormal electrical activity in the brain.

Possible configurations of the array of electrodes include hexagonal lattices and square lattices, as well as nonperiodic and quasiperiodic arrangements.

In <CIT>, there are described high-density mapping catheters with an array of mapping electrodes. These catheters can be used for diagnosing and treating cardiac arrhythmias, for example. The catheters are adapted to contact tissue and comprise a flexible framework including the electrode array. The array of electrodes may be formed from a plurality of columns of longitudinally-aligned and rows of laterally-aligned electrodes.

In <CIT>, there are described devices, systems, and methods for therapeutically treating tissue. The devices and methods are suitable for minimally invasive surgery or open surgical procedures. More particularly, methods and devices described herein permit treating large areas of tissue with a therapeutic device. In some variations, the method and devices allow for large area treatment without having to reposition the device.

Then invention is defined by the appended claims. There is provided, in accordance with some embodiments of the present invention, an apparatus including a shaft, configured for insertion into a body of a subject, and an expandable element coupled to a distal end of the shaft. The expandable element includes multiple electrodes arranged in a hexagonal grid when the expandable element is expanded.

In some embodiments, a distance between each pair of adjacent ones of the electrodes is between <NUM> and <NUM>.

The expandable element includes an assembly of parallel splines, and the electrodes are grouped into rows coupled to the splines, respectively, the rows being staggered with respect to each other such that the electrodes are arranged in the hexagonal grid.

In some embodiments, each of the electrodes includes a ring fitted over a respective one of the splines.

The expandable element includes a plurality of looped elements, each of which includes a different respective pair of the splines.

In some embodiments, the expandable element includes at least one rollable substrate, and the electrodes are coupled to the substrate such that the electrodes are arranged in the hexagonal grid when the substrate is unrolled.

In some embodiments, the substrate includes a printed circuit board (PCB).

In some embodiments, the expandable element includes an inflatable balloon, and the electrodes are coupled to the balloon such that the electrodes are arranged in the hexagonal grid when the balloon is inflated.

There is further disclosed a method including inserting a shaft into a body of a subject. The method further includes, subsequently to inserting the shaft, expanding an expandable element coupled to a distal end of the shaft and including multiple electrodes arranged in a hexagonal grid when the expandable element is expanded. The method further includes, using the electrodes, acquiring electrical signals from tissue of the subject.

There is further disclosed a method including obtaining a plurality of bipolar signals between respective pairs of electrodes contacting tissue of a subject, the electrodes being arranged in a hexagonal grid. The method further includes, based on the bipolar signals, computing an estimated path of bioelectrical propagation along the tissue.

In some examples, obtaining the bipolar signals includes:.

In some examples, , the estimated path includes multiple linear segments, each of which passes between a respective one of the pairs of electrodes.

In some examples, the electrodes belong to an expandable element coupled to a distal end of a shaft disposed within a body of the subject.

Conventionally, a rectangular grid of electrodes is used to estimate a path of bioelectrical propagation along intrabody tissue, such as intracardiac tissue. However, a rectangular grid provides limited accuracy, due to the fact that each electrode in the grid has, at most, four nearest neighbors.

Hence, embodiments of the present invention provide a hexagonal grid of electrodes, in which each electrode has up to six nearest neighbors. To facilitate deploying and using the hexagonal grid, the hexagonal grid is coupled to an expandable element, comprising, for example, a rollable substrate, an inflatable balloon, or an assembly of splines. Following the expansion of the expandable element, the hexagonal grid is pressed against the tissue, and bipolar signals between pairs of the electrodes are obtained. Based on the bipolar signals, a processor computes an estimated path of bioelectrical propagation.

Reference is initially made to <FIG>, which is a schematic illustration of an electrophysiological mapping system <NUM>, in accordance with some embodiments of the present invention.

System <NUM> comprises an intrabody probe <NUM>, comprising a shaft <NUM> configured for insertion into a body of a subject <NUM>. Probe <NUM> further comprises an expandable element <NUM> coupled to the distal end of the shaft. Expandable element <NUM> comprises multiple electrodes <NUM> arranged in a hexagonal grid when the expandable element is expanded (i.e., when the expandable element is in its expanded configuration). Electrodes <NUM> may be made of gold, platinum, palladium, and/or any other suitable metal or metallic alloy.

To perform an electrophysiological mapping, a physician <NUM> first inserts probe <NUM> into the body of subject <NUM>. Subsequently, physician <NUM> navigates the probe to the target portion of the body that is to be mapped, such as a chamber of the heart <NUM> of the subject. Subsequently, electrodes <NUM> are used to measure electrogram voltages across tissue of the subject.

In some embodiments, expandable element <NUM> is made from a shape-memory material, such as Nitinol. In such embodiments, the expandable element is self-expanding, in that the expandable element expands by virtue of the shape-memory effect. To deploy the expandable element, the probe is first inserted into, and navigated through, a sheath <NUM>, the distal end of which is located at the target portion of the body. Subsequently to the distal end of the probe reaching the target portion of the body, sheath <NUM> is withdrawn from over the expandable element, such that, by virtue of the expandable element being made from the shape-memory material, the expandable element expands from a compressed configuration, which the expandable element assumes while inside of the sheath, to an expanded configuration.

In other embodiments (e.g., as described below with reference to <FIG>), the expandable element is actively expanded from its compressed configuration to its expanded configuration, by application of electrical and/or mechanical energy.

According to the invention, as shown in <FIG>, the expandable element comprises an assembly of parallel splines <NUM>, and the electrodes are coupled to splines <NUM>. For example, each of the electrodes may comprise a ring fitted over a respective one of the splines. According to the invention, the electrodes are grouped into rows <NUM> coupled to the splines, rows <NUM> being staggered with respect to each other such that the electrodes are arranged in a hexagonal grid.

Typically, in such embodiments, the splines are coupled to one another such that, in the absence of any unusually large forces applied to the splines, the relative positions of the splines are fixed. For example, pairs of the splines may belong to different respective looped elements <NUM> that are coupled to each other at a distal junction <NUM>. In particular, each looped element <NUM> may comprise a pair of splines, along with an arched portion <NUM> that runs between the respective distal ends of the splines and a pair of proximal portions <NUM> that couple the looped element to the inner wall of shaft <NUM> such that the looped element protrudes from the shaft. Typically, each looped element has a circular transverse cross-sectional shape.

For example, as shown in <FIG>, the probe may comprise three looped elements: a first looped element 36a, which comprises splines 32a1 and 32a2, a second looped element 36b, which comprises splines 32b1 and 32b2, and a third looped element 36c, which comprises splines 32c1 and 32c2.

In some embodiments, the looped elements overlap each other, such that each spline is adjacent to one or two other splines belonging to other looped elements. For example, as shown in <FIG>, looped elements 36a-c may overlap each other such that the splines are arranged in parallel to each other in the following sequence: 32a1, 32b1, 32c1, 32a2, 32b2, 32c2.

In other embodiments, the looped elements are arranged within each other. For example, looped elements 36a-c may be arranged within each other such that the splines are arranged in parallel to each other in the following sequence: 32a1, 32b1, 32c1, 32c2, 32b2, 32a2.

In some embodiments, the assembly of splines <NUM> is flat (i.e., the splines are coplanar with each other) when the assembly is expanded and in the absence of any force applied to the expandable element. Nonetheless, the assembly may be sufficiently compliant so as to curve when pressed against the tissue. Thus, advantageously, the assembly of splines may conform to the tissue such that all the electrodes contact the tissue simultaneously. In other embodiments, the assembly of splines has slight curvature even in the absence of any force applied to the expandable element.

System <NUM> further comprises circuitry (CIRC) <NUM>, which is typically contained within a console <NUM>. Circuitry <NUM> is connected to the proximal end of probe <NUM>, e.g., via an electrical interface <NUM> in console <NUM> such as a port or socket. Circuitry <NUM> comprises a processor <NUM>, configured to perform the functionality described below. Typically, the circuitry further comprises analog-to-digital (A/D) and digital-to-analog (D/A) conversion circuitry for interfacing between processor <NUM> and probe <NUM>.

Wires running through probe <NUM> transfer electrical signals between electrodes <NUM> and circuitry <NUM>. Based on measurements of electrogram voltages obtained from electrodes <NUM>, the processor may construct an electrophysiological map <NUM> and, optionally, display map <NUM> on a display <NUM>.

In some embodiments, probe <NUM> further comprises an electromagnetic sensor <NUM> coupled to the distal end of the shaft. In such embodiments, the location of the probe may be tracked by an electromagnetic tracking system. In particular, a magnetic field generated in the vicinity of the subject may induce, in sensor <NUM>, a signal that varies with the location and orientation of the sensor. Based on this signal, processor <NUM> may ascertain the location and orientation of the probe, as described, for example, in <CIT>, <CIT>, and <CIT>, in <CIT>, in <CIT>, and in <CIT>.

Alternatively or additionally to an electromagnetic tracking system, other types of tracking systems may be used to track the probe. For example, electric currents may be passed between electrodes <NUM> and one or more electrode patches on the body of subject <NUM>. Based on the distribution of the currents and/or physiological impedances computed therefrom, processor <NUM> may ascertain the location of the probe. Methods for impedance-based location sensing are disclosed, for example, in <CIT>,<CIT>, and<CIT>. In addition, methods for utilizing a calibrated current-position map to ascertain the location of the probe based on the distribution of the currents are disclosed, for example, in <CIT> and <CIT>.

In some embodiments, probe <NUM> further comprises an irrigation tube (not shown), configured to deliver an irrigating fluid, such as saline, from console <NUM> to the distal end of the shaft. The irrigating fluid may inhibit the blood of subject <NUM> from clotting near expandable element <NUM>, e.g., near the area in which proximal portions <NUM> are coupled to shaft <NUM>.

In general, the functionality of processor <NUM> may be implemented solely in hardware, e.g., using one or more fixed-function or general-purpose integrated circuits, Application-Specific Integrated Circuits (ASICs), and/or Field-Programmable Gate Arrays (FPGAs). Alternatively, this functionality may be implemented at least partly in software. For example, processor <NUM> may be embodied as a programmed processor comprising, for example, a central processing unit (CPU). Program code, including software programs, and/or data may be loaded for execution and processing by the CPU. The program code and/or data may be downloaded to the processor in electronic form, over a network, for example. Alternatively or additionally, the program code and/or data may be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory. Such program code and/or data, when provided to the processor, produce a machine or special-purpose computer, configured to perform the tasks described herein.

Although <FIG> relates mainly to heart electrograms, it is noted that embodiments of the present invention may also be applied to the acquisition of brain electrograms, e.g., during a neurosurgical procedure.

Reference is now made to <FIG>, which is a schematic illustration of an arrangement of electrodes <NUM>, in accordance with some embodiments of the present invention.

As described above with reference to <FIG>, electrodes <NUM> are arranged in a hexagonal grid, which may also be referred to as a "close-packed pattern. " In this arrangement, each electrode is located at the center of a respective hypothetical hexagon in a hexagonal grid (or "tessellation"). A distance D0, which is typically between <NUM> and <NUM>, separates each pair of adjacent (or "nearest-neighbor") electrodes from one another. In the context of the present application, including the claims, the distance between two elements refers to the distance between the respective centers of the elements. To achieve this arrangement for the embodiment of <FIG>, successive electrodes on the same spline <NUM> are spaced apart from one another by distance D0, while adjacent splines are spaced apart from one another by a distance <MAT>.

The hexagonal-grid arrangement illustrated in <FIG> has several advantages over a rectangular-grid arrangement.

First, by virtue of the rows of electrodes being staggered, there is less of a chance of electrodes <NUM> colliding with each other, e.g., when expandable element <NUM> (<FIG>) is collapsed. Thus, there may be less noise added to the signals received from the electrodes.

Second, in the embodiment in which expandable element <NUM> comprises an assembly of splines as described above with reference to <FIG>, the distance between each pair of adjacent electrodes lying on different respective splines is less sensitive to a change in distance between the splines, relative to a rectangular-grid arrangement. For example, supposing the distance between spline 32a1 and spline 32b1 (<FIG>) increases by x*D1<NUM>, where D1<NUM> is the original distance between the two splines, the distance between any given electrode on spline 32a1 and each of its nearest neighbors on spline 32b1 would increase by only <MAT>, where D0<NUM> is the original distance between each pair of nearest neighbors. In contrast, with a rectangular-grid arrangement (in which D1 = D0), the inter-electrode distance would increase by x*D0<NUM>.

Third, each of the electrodes, with the exception of those electrodes at the edges of the arrangement, has six nearest neighbors spaced equidistantly (at distance D0) from the electrode. In contrast, in a rectangular grid, each electrode has, at most, four such nearest neighbors. Thus, the hexagonal-grid arrangement facilitates obtaining a greater number of bipolar signals, where each bipolar signal represents, as a function of time, the voltage between a respective pair of nearest-neighbor electrodes.

Aside from the intrinsic diagnostic benefit of obtaining a greater number of bipolar signals, the greater number of bipolar signals may provide greater accuracy in computing an estimated path <NUM> of bioelectrical propagation along the tissue of the subject. In this regard, reference is now additionally made to <FIG>, which is a flow diagram for an algorithm <NUM> for computing path <NUM>, in accordance with some embodiments of the present invention.

Per algorithm <NUM>, processor <NUM> (<FIG>) performs a signal-obtaining step <NUM> for each position of the probe. At signal-obtaining step <NUM>, the processor obtains a plurality of bipolar signals from the probe, while the electrodes contact the tissue. In particular, the processor may obtain the bipolar signal between each electrode and each of its nearest neighbors. Thus, for example, for an electrode 34a shown in <FIG>, the processor may obtain six bipolar signals.

In some embodiments, the processor measures each bipolar signal directly. In other embodiments, the processor measures a respective unipolar signal from each electrode, the unipolar signal representing, as a function of time, the voltage between the electrode and a common reference electrode. The processor then obtains each bipolar signal by subtracting the corresponding pair of unipolar signals from one another.

Subsequently, based on the bipolar signals, the processor computes at least a portion of path <NUM>. In particular, the processor first selects the electrode that is currently at the end of the path, at an electrode-selecting step <NUM>. Subsequently, at an adjacent-electrode-identifying step <NUM>, the processor identifies the electrode that is adjacent to the selected electrode and that lies in the direction of the bioelectrical wavefront propagation (to the degree of precision provided by the hexagonal-grid arrangement). The identification of this adjacent electrode is performed by comparing the amplitudes, derivatives with respect to time, and/or any other properties of the bipolar signals for the selected electrode. For example, the processor may identify the adjacent electrode for which the amplitude or time-derivative of the bipolar signal is greatest. Subsequently, at a path-extending step <NUM>, the processor extends the path to the identified adjacent electrode.

Thus, for example, the processor may identify that the wavefront is moving from an electrode 34b to electrode 34a. In response thereto, the processor may add, to path <NUM>, a linear segment <NUM> between electrode 34b and electrode 34a.

Following path-extending step <NUM>, the processor checks, at a first checking step <NUM>, whether the path has reached the edge of the grid. If not, the processor returns to electrode-selecting step <NUM>. Otherwise, the processor checks, at a second checking step <NUM>, whether the probe is at a new location. Upon the probe reaching a new location, the processor returns to signal-obtaining step <NUM>.

Thus, by virtue of the processor executing algorithm <NUM> (or any other suitable algorithm), path <NUM> may include multiple linear segments <NUM>, each of which passes between a respective pair of electrodes. If the electrodes were arranged in a rectangular grid, there would be only four possible directions for each segment <NUM>. Although it might be possible to compute an interpolated direction, such an interpolation might have limited accuracy, and/or might be computationally expensive. In contrast, given a hexagonal-grid arrangement, there are six possible directions for each segment <NUM>. Thus, path <NUM> may be computed inexpensively and with greater accuracy. It is noted that, notwithstanding the above, the processor may compute interpolated directions even for a hexagonal-grid arrangement.

Subsequently to computing path <NUM>, the processor may overlay the path on map <NUM> (<FIG>) and/or on an image showing the position of the probe relative to the anatomy of the subject.

Reference is now made to <FIG>, which is a schematic illustration of an alternate embodiment of expandable element <NUM>, in accordance with some embodiments of the disclosure.

In some embodiments, instead of an assembly of splines <NUM> (<FIG>), expandable element <NUM> comprises at least one rollable substrate <NUM>, and electrodes <NUM> are coupled to substrate <NUM> such that the electrodes are arranged in a hexagonal grid when the substrate is unrolled. Typically, substrate <NUM> comprises a printed circuit board (PCB), and the electrodes are printed onto the PCB. The substrate may be unrolled by withdrawing sheath <NUM> from over the expandable element, as described above with reference to <FIG>.

For example, as described in <CIT>, expandable element <NUM> may comprise a backing sheet <NUM>, which may be made of a shape-memory material such as Nitinol. A single substrate may be coupled to one side of backing sheet <NUM>; alternatively, two substrates may be coupled to different respective sides of backing sheet <NUM>. An advantage of two substrates is that while the electrodes on one substrate acquire signals from the tissue, the electrodes on the other substrate may be used for cancelling any far-field signals. Optionally, the backing sheet may be shaped to define an irrigation channel <NUM>, through which an irrigating fluid may flow.

In some embodiments, substrate <NUM>, when unrolled and in the absence of any force applied to the expandable element, is flat, as shown in <FIG>. Nonetheless, the expandable element may be sufficiently compliant so as to curve when pressed against the tissue. In other embodiments, the expandable element has slight curvature even in the absence of any force applied to the expandable element.

<FIG> shows yet another alternate embodiment, in which expandable element <NUM> comprises an inflatable balloon <NUM>, and the electrodes are coupled to balloon <NUM> (e.g., to a distal surface <NUM> of the balloon) such that the electrodes are arranged in a hexagonal grid when the balloon is inflated. <FIG> shows both a side view and a frontal view of the balloon. Wires <NUM>, which connect the electrodes to console <NUM> (<FIG>), run through shaft <NUM> and balloon <NUM>.

In general, the features of balloon <NUM> may be similar to those described in <CIT>. For example, the balloon may be inflated by pumping a fluid into the balloon via an inflation tube <NUM>. Optionally, the probe may be used with sheath <NUM> as described above with reference to <FIG>, and the balloon may be inflated following the withdrawal of the sheath from over the balloon. A support rod <NUM>, which is proximally coupled to shaft <NUM> and distally coupled to distal surface <NUM>, may help stabilize the distal surface as the distal surface is pressed against the tissue. The electrodes may comprise respective PCBs; alternatively, the electrodes may be swaged onto the balloon, or coupled to the balloon using any other suitable technique.

In some embodiments, distal surface <NUM> is flat when the balloon is inflated and in the absence of any force applied to the balloon. Nonetheless, the distal surface may be sufficiently compliant so as to curve when pressed against the tissue. In other embodiments, the distal surface has slight curvature even in the absence of any force applied to the balloon, as shown in <FIG>.

For each of the embodiments of <FIG>, the properties of the hexagonal grid of electrodes, as well as the manner in which the grid may be used, may be generally as described above with reference to <FIG>.

Claim 1:
An apparatus for electrophysiological sensing, the apparatus comprising:
a shaft (<NUM>), configured for insertion into a body of a subject; and
an expandable element (<NUM>) coupled to a distal end of the shaft and comprising multiple electrodes (<NUM>) arranged in a hexagonal grid when the expandable element is expanded, wherein the expandable element comprises an assembly of parallel splines (<NUM>), and
wherein the expandable element comprises a plurality of looped elements (<NUM>), each of which comprises a different respective pair of the splines, and
wherein the electrodes are grouped into rows (<NUM>) coupled to the splines, respectively, the rows being staggered with respect to each other such that the electrodes are arranged in the hexagonal grid.