ESTIMATION OF CONTACT FORCE OF CATHETER EXPANDABLE ASSEMBLY

A system includes a medical probe and a processor. The medical probe includes a shaft for insertion into a cavity of an organ of a patient; an expandable assembly fitted at a distal end of the shaft, wherein the expandable assembly has elastic properties; a position sensing element mounted on the distal end of the shaft; and at least one distal position sensing element on a distal end of the expandable assembly. The processor senses relative location of each of the at least one distal position sensing element and the proximal position sensing element; determines deflection of the expandable assembly based on the relative location; relates the deflection to the contact force applied on the expandable assembly; and provides an indication of the contact force on a display.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to invasive medical probes, and particularly to detection of contact force of cardiac catheters.

BACKGROUND OF THE DISCLOSURE

Cardiac catheters typically comprise an elongated shaft for insertion into the body of a patient and a distal end including one or more electrodes and/or sensors. The catheter may further comprise a magnetic position sensor fitted at the distal end of the shaft.

Using signals acquired by the magnetic location sensor, a processor can accurately estimate the position and orientation of the distal end of the shaft inside the body of the patient.

It is also known to sense contact force applied on the distal end. One way to estimate the contact force of the distal end assembly is described in U.S. Pat. No. 8,535,308. The patent describes a spring-loaded joint that couples the distal tip to the distal end of the shaft. A joint sensor, contained within the catheter senses a position of the distal tip relative to the distal end of the shaft. The joint sensor includes first and second subassemblies, which are disposed within the catheter on opposite, respective sides of the joint and each includes one or more magnetic transducers. The deflection is estimated from the relative locations of the subassemblies based on position signals they emit and receive. The tip contact force is estimated from the deflection based on the known spring constant of the joint.

The present disclosure will be more fully understood from the following detailed description of the examples thereof, taken together with the drawings, in which:

DETAILED DESCRIPTION OF EXAMPLES

Overview

A wall cavity of an organ of a patient, such as a cardiac cavity, can be mapped and/or ablated using a catheter having multiple electrodes fitted at an expandable distal end assembly of the catheter. The expandable distal-end assembly is coupled at a distal end of a catheter shaft for insertion into the cavity. The expandable distal end assembly may be shaped in the form of a balloon, basket and/or another type of cage and may include a plurality of electrodes configured for sensing and/or delivering therapeutic signals. The expandable distal end assembly may comprise a plurality of splines connected at their proximal and distal ends. When expanded, the splines bow radially outwardly. When collapsed, the splines are arranged generally along the axis of the shaft. The electrodes and/or sensors may be arranged on the spline and/or on a membrane of a balloon, for a balloon distal end. The expandable distal-end assembly may also be referred to herein as the expandable assembly.

In a mapping and/or ablation procedure of a cardiac chamber, the physician expands the assembly and manipulates the expanded distal-end assembly for the electrodes to contact chamber walls. The quality of electroanatomical mapping (e.g., based on acquired depolarization signals by the electrodes) and/or ablation depends on the contact force of the electrodes with wall tissue. The estimation of such a force on the shaft may be difficult, as the elasticity of the expandable distal end assembly can cause contraction, tilt, and deformation of the expandable distal end assembly relative to a distal end of the shaft.

Therefore, when displaying visual indicia of the distal end assembly on an EA map in real-time, there may be a significant discrepancy between electrode locations as estimated based on the location and orientation of the magnetic sensor and actual locations of the electrodes. It is, however, clinically important to know the actual deflection of the distal end assembly and the contact force on the distal end assembly (e.g., to evaluate readiness for ablating tissue).

Examples of the present disclosure that are described herein provide a technique in which a processor estimates a contact force of an expandable distal-end assembly based on locally estimating a change in the expandable assembly's deflection. The disclosed technique involves sensing relative location of one or more first position sensing elements at the distal end and the at least second position sensing element at a distal end of the shaft (or a proximal end of the expandable distal-end assembly).

In some example embodiments, the one or more first position sensing elements at the distal end of the distal-end assembly and the at least one second position sensing elements at the distal end of the shaft, are electromagnetic coils (EMCs). Position sensing based on transmission between EMCs mounted on a catheter and EMCs embedded in a location pad are described in more detail herein.

In some example embodiments, the one or more first position sensing elements at the distal end of the distal-end assembly and the at least one second position sensing elements at the distal end of the shaft, are electrodes that sense position based on impedance tracking as described in more detail herein. Other position sensing elements (also referred to as position sensors) may be contemplated.

Using an elastic model of the expandable assembly and/or calibration, the processor estimates from the change of shape and/or deflection, the amount of force exerted on tissue by the expandable distal end assembly.

In some example embodiments, the relative location of is defined based on determining location of each position sensor (or electrode) within a defined a global coordinate system and determining a relative location. In other example embodiments, the relative location of each position sensor is based on measuring one or more location signals acquired in a local transmitter-receiver mode that does not require first determining location of each position sensor (or electrode) within a defined a global coordinate system. Using the local signals, the processor calculates the relative position of a transmitting element to a receiving element where one of them is on the shaft and the other is on the expandable assembly.

In some example embodiments, the processor uses the local transmitter-receiver mode by using proximal and distal EMCs, where the distal EMCs are disposed on a distal portion of the expandable assembly and the proximal EMC is disposed on a distal end of the shaft. Typically, three distal EMCs may be used.

In the local transmitter-receiver mode, one EMC group (e.g., the distal EMC(s)) emits magnetic fields, and the other EMC (the proximal EMC(s)) outputs electrical signals in response to picking up the magnetic fields. This local transmitter-receiver mode may yield a more accurate estimation of deflection and of changes in the shape of the expandable distal end assembly as compared to methods that require first determining each position of each position sensor within a global coordinate system.

Depending on the number of distal EMCs and/or their distribution over the expandable distal end assembly, the disclosed technique can provide an accurate estimation of the contact force of the expandable distal end assembly. For example, the processor can estimate where the contact occurs over a lateral circumference of the expandable distal end assembly by detecting a tilt direction of the expandable distal end assembly. By detecting a deformation, the processor can estimate the location of an epicenter of the contact on the lateral circumference (e.g., whether the location is on a portion closer to the shaft or at a more distal portion of the expandable distal end assembly).

In one example, based on the magnetic fields generated by the distal EMC and sensed by the proximal EMC, a processor determines the distance and angle between the two EMCs and converts changes in distance and angle values from free space values to contact force exerted on the assembly.

The expandable distal end assembly is typically made of Nitinol or some other material that has elastic properties. Each of the splines of the expandable distal end assembly is an elastic beam and as the splines are all connected at their proximal and distal ends, the expandable distal end assembly can be elastically modeled as a structure made of elastic beams. The processor can therefore deduce a force applied on the expandable distal end assembly as an elastic element. When a simple spring model for expandable distal end assembly contraction and tilt is too limited (e.g., for some types of expandable distal end assemblies), the processor may use a more complex elastic model (e.g., based on a set of springs or beams) for the expandable distal end assembly deformation. One example of a system and method for tracking coordinates of elements (e.g., spline portion, sensors, electrodes) of an expandable distal end assembly in contact with tissue is described in U.S. patent application Publication Ser. No. 17/874,224 filed on Jul. 26, 2022. Another example of such a system and method for tracking coordinates of elements is described in U.S. patent application Publication Ser. No. 18/089,428 filed on Dec. 27, 2022. A processor using these techniques can find the location of electrodes under the deformed shape of the expandable distal end assembly.

Additionally, or alternatively, the processor can estimate the contact force using empirical data comprising calibration of the forces against expandable distal end assembly deformations. The processor may use weights to interpolate between calibration values. In such a case, a memory of the system is configured to store a relationship between EMC output and contact force based on the empirical data (e.g., a look-up table). The processor is configured to use the stored empirical data to relate EMC output to contact force.

In another example, the force on each spline (or each electrode) can be estimated based on modeling the shape of the expandable distal end assembly for different calculated forces. The modeled forces on the splines can be compared to pre-measured values, and the comparison can then be used to calibrate the model with weights. (Such weights can also be of a neural network model.)

In one example, the distal EMC is a magnetic single-axial sensor (SAS) configured to generate at least one respective oscillating magnetic field signal. The distal end of the shaft comprises a magnetic tri-axial sensor (TAS) made of three mutually orthogonal EMCs, the TAS configured to output electrical signals in response to magnetic field signal reception. In another example, the distal end of the shaft comprises three EMCs that are parallel and displaced for one another on the shaft.

The distal EMC is configured to pick up magnetic fields generated by a location pad, and the processor is configured to sample the resulting output and use it to determine a position of the distal coil in a 3D coordinate system. The TAS comprises three mutually orthogonal EMCs configured to pick up magnetic fields generated by a location pad, whereas the processor is configured to sample the resulting output and to use it to determine position and orientation of the shaft in a 3D coordinate system.

Any given frequency used for contact force detection is different from frequencies generated by an external location pad of a position-tracking system for position sensing.

In yet another example, the distal EMC (e.g., SAS) is embedded in a respective electrode disposed on a spline of the expandable distal end assembly.

System Description

FIG.1is a schematic, pictorial illustration of a catheter-based electroanatomical (EA) mapping and ablation system10, in accordance with an example of the present disclosure.

System10includes one or more catheters, which are percutaneously inserted by physician24through the patient's vascular system into a chamber or vascular structure of a heart12. Typically, a delivery sheath catheter is inserted into the left or right atrium near a desired location in heart12. Thereafter, one or more catheters in turn can be inserted into the delivery sheath catheter to arrive at the desired location. The one or more catheters may include catheters dedicated for sensing intracardiac electrogram (IEGM) signals, catheters dedicated for ablating and/or catheters dedicated for both sensing and ablating. An example basket catheter14that is configured for sensing IEGM is illustrated herein. As seen in inset45, physician24brings a basket type of expandable distal end assembly28(also called hereinafter “expandable distal-end assembly28”) fitted on a shaft44of catheter14into contact with the heart wall for sensing a target site in heart12. For ablation, physician24similarly brings a distal end of an ablation catheter to a target site for ablating.

As seen in inset65, catheter14is an exemplary catheter that includes one, and preferably multiple, electrodes26optionally distributed over a plurality of splines22at expandable distal-end assembly28and configured to sense IEGM signals. Catheter14additionally includes (i) a proximal position sensor29(e.g., TAS29comprising three EMCs) embedded in a distal end46of shaft44near expandable distal end assembly28, and (ii) two distal position sensors39(e.g., SAS39comprising a single EMC) to track the position of the distal end of expandable assembly28. Optionally, and distal end preferably, position sensors29and39are magnetic-based position sensors that include magnetic coils for sensing three-dimensional (3D) position.

FIGS.2B and2Cbelow show two scenarios where the EMCs of distal sensors39and proximal sensor29are used together for estimating the contact force of an elastic expandable distal end assembly with tissue. InFIG.2Bthe force is estimated from expandable distal end assembly contraction relative to the distal end of the shaft, while inFIG.2Cthe force is estimated from expandable distal end assembly tilt relative to the distal end of the shaft.

In the disclosed contact force estimation technique, the EMCs of distal and proximal sensors39and29are operated in a transmitter-receiver mode, with one EMC (e.g., of sensor39) emitting magnetic fields, and the other EMC (e.g., of sensor29) outputting electrical signals in response to receiving the magnetic fields. This transmitter-receiver mode, used by a processor to estimate contact force, yields more accurate location and orientation data than data yielded by using EMCs with a magnetic field source that is external to the patient's body.

Moreover, magnetic position sensors (29,39) may also be operated together with an external location pad25that includes a plurality of magnetic coils32configured to generate magnetic fields in a predefined working volume. The frequencies of these fields are different from any given frequency used in the local transmitter-receiver mode for contact force detection, thus eliminating confusion between signals. Using the operation with external location pad25(at a different frequency for each EMC), the processor can determine the position of EMC39on a coordinate system of the position tracking system.

Real-time orientation of expandable distal end assembly28of catheter14can, in this way, be calculated from tracked locations of sensors29and39(locations being tracked using magnetic fields generated with location pad25and sensed by magnetic-based position sensors29and39). This relative orientation is manifested by an angle formed between distal end46and a longitudinal axis42of expandable assembly28(to a distal edge16of the assembly). Distal end46of shaft44may comprise an amplifying circuit configured to amplify the output from the three EMCs of sensor29.

System10includes one or more electrode patches38positioned for skin contact on patient23to establish a location reference for location pad as well as impedance-based tracking of electrodes26. For impedance-based tracking, electrical current is directed toward electrodes26and sensed at electrode skin patches38, such that the location of each electrode can be triangulated via electrode patches38. Details of the impedance-based location tracking technology are described in U.S. Pat. Nos. 7,536,218; 7,756,576; 7,848,787; 7,869,865; and 8,456,182.

A recorder11displays electrograms21captured with body surface ECG electrodes18and intracardiac electrograms (IEGM) captured with electrodes26of catheter14. Recorder11may include pacing capability for pacing the heart rhythm and/or may be electrically connected to a standalone pacer.

System10may include an ablation energy generator50that is adapted to conduct ablative energy to one or more electrodes at a distal tip of a catheter configured for ablating. Energy produced by ablation energy generator50may include, but is not limited to, radiofrequency (RF) energy or pulsed-field ablation (PFA) energy, including monopolar or bipolar high-voltage DC pulses that may be used to effect irreversible electroporation (IRE), or combinations thereof.

Patient interface unit (PIU)30is a controller with processing capability that is configured to establish electrical communication between catheters, electrophysiological equipment, power supply and a workstation55for controlling the operation of system10. Electrophysiological equipment of system10may include, for example, multiple catheters, location pad25, body surface ECG electrodes18, electrode patches38, ablation energy generator50, and recorder11. Optionally, and preferably, PIU30additionally includes processing capability for implementing real-time computations of catheter locations and for performing ECG calculations.

Workstation55includes memory57, processor unit56with memory or storage with appropriate operating software loaded therein, and user interface capability. Workstation55may provide multiple functions, optionally including (i) modeling endocardial anatomy in three-dimensions (3D) and rendering the model or anatomical map20for display on a display device27, (ii) displaying on display device27activation sequences (or other data) compiled from recorded electrograms21in representative visual indicia or imagery superimposed on the rendered anatomical map20, (iii) displaying real-time location and orientation of multiple catheters within the heart chamber, and (iv) displaying on display device27sites of interest such as places where ablation energy has been applied. One commercial product embodying elements of the system10is available as the CARTO™ 3 System, available from Biosense Webster, Inc., 31A Technology Drive, Irvine, CA 92618.

Estimation of Contact Force of Catheter Expandable Assembly

FIGS.2A-2Care schematic, pictorial illustrations of a catheter expandable distal end assembly281(i) in free space, (ii) compressed against tissue47, and (iii) tilted by contacting tissue47, respectively, in accordance with examples of the present disclosure.

Expandable distal end assembly281is formed by spines222and comprises two distal EMCs239, and a TAS229comprising three EMCs that are mutually orthogonal. In FIG.2A expandable distal end assembly281is in free space and has a given first length241. The transmitter-receiver layout229/239ofFIG.2is only one of many more possible realizations of the disclosed transmitter-receiver configuration for contact force sensing. As another example, there can be three EMCs at the distal end of the catheter expandable distal end assembly while the shaft has only a dual-axis magnetic sensor (DAS).

InFIG.2B, once pressed against tissue47(e.g., with some of electrodes226brought into firm contact with wall tissue), the elastic expandable distal end assembly281contracts into a second, shorter, length242. Such a scenario may be typical in cases of pulmonary vein isolation (PVI) procedures, where some distal electrodes226are used in this way to electrically ablate an ostium of a PV in a left atrium to eliminate an arrhythmia.

The transmitter-receiver mode of the EMCs239and one of TAS229enables accurate determination of the amount of expandable distal end assembly contraction DL (e.g., length241minus length242). Based on a known (e.g., measured) spring coefficient KL of expandable distal end assembly281, a contact force Fc can be estimated from FC=KL·DL.

InFIG.2C, expandable distal end assembly281is brought to side contact with tissue47. As a result, expandable distal end assembly281is tilted or bent from its zero-angle orientation (as seen inFIG.2A) into an angle β250(an angle between a longitudinal axis204of the distal end of shaft244and an axis206of the expandable distal end assembly). Such a scenario may be typical in cases where some electrodes226are used for ablating wall tissue of a ventricle to eliminate a ventricular arrhythmia.

The transmitter-receiver mode of the EMCs239and these of TAS229enable accurate determination of the amount of expandable distal end assembly tilt6. Based on a known (e.g., measured) spring coefficient KA of expandable distal end assembly281, measured or pre-known distance L between the EMCs239and EMCs of sensor229, and L (e.g., length241), a contact force FA can be estimated from FA=KA·L·β.

As noted above, when a simple spring model for expandable distal end assembly contraction and tilt is limited (e.g., for some types of expandable distal end assemblies), the processor may use a more complex elastic model (e.g., based on a set of springs) for expandable distal end assembly deformation, as seen inFIG.3.

Additionally, or alternatively, the processor can estimate the contact force using empirical data comprising calibration of the forces against expandable distal end assembly tilt and/or deformation. The processor may use weights to interpolate between calibration values. In such a case, a memory of the system is configured to store a relationship between EMC output and contact force based on the empirical data. The processor is configured to use the stored empirical data to relate EMC output to contact force.

FIG.3is a schematic, pictorial illustration of the catheter expandable distal end assembly28in a deformed shape while being pressed against tissue47, in accordance with examples of the present disclosure.

As seen, expandable distal end assembly28develops an angle θ308with respect to the distal end46of shaft44. Angle308is defined between a longitudinal axis307of the expandable distal end assembly and a longitudinal axis304of distal end46. Using EMCs39, EMCs of TAS29, and known relations between a distal edge306of the assembly and distal end46, the processor can readily calculate angle θ308. The processor can calculate the amount of deflection of distal edge306based on the tilt angle and the length of the expandable distal end assembly (e.g., length241).

Unknown, however, is the shape followed by splines22, though it is evident that splines22on the pressed side (L1) are compressed inward, whereas splines22on the free side (e.g., in a cardiac chamber blood pool) are bowed outward. To estimate tilt, it is sufficient to know that sensors39move together with small relative change between their movement due to deformation, and this change can be largely considered. As a result, expandable distal end assembly deformation doesn't cause any significant error in the estimated contact force.

If smaller effects of deformation are of interest, the analysis of the deformed shape can be done using the aforementioned U.S. patent application Publication Ser. No. 18/089,428 by looking at a frontal cross-sectional plane L1-L2312(e.g., the azimuthal plane). Since splines22are elastic and continuous, the processor can reconstruct the entire expandable distal end assembly shape by finding spline locations314in one such plane.

Using a look-up table of measured contact forces against spline location values in plane L1-L2312(e.g., a look-up table stored in memory57), processor56can estimate (e.g., interpolate) exceedingly accurately the actual contact force inside the patient's body.

A Method for Estimating Contact Force of Catheter Expandable Assembly

FIG.4is a flow chart that schematically illustrates a method to estimate a contact force of an expandable distal-end assembly, such as ofFIG.2or3(e.g., basket expandable distal end assembly28or281) in contact with tissue, in accordance with an example of the present disclosure. The algorithm, according to the presented example, carries out a process that begins with physician24inserting the expandable distal-end assembly into a cavity (e.g., a cardiac chamber), at expandable distal end assembly insertion step402.

Next, at assembly contacting step404, the physician brings the expandable distal end assembly into contact with the cavity wall tissue (e.g., tissue47), which leads to the expandable distal end assembly changing shape or orientation relative to distal end of shaft, as seen inFIGS.2B,2C and3.

At signal acquisition step406, processor56receives location and/or orientation indicative signals acquired by EMCs (e.g., EMCs39/239or those of TAS29/329) implemented in a local transmitter-receiver mode as described above.

Using the location and/or orientation indicative signals, the processor estimates an amount of change in shape and/or orientation of the expandable distal end assembly relative to the distal end of the shaft, in an assembly change estimation step408.

Using an elastic model and/or empirical data (e.g., a look-up table stored in memory57), processor56relates the amount of change to contact force applied on the expandable distal end assembly (e.g., to a basket type of cage), at contact force estimation step410.

Finally, the processor provides an indication of the contact force (e.g., size and location over the expandable distal end assembly) to a user on a display, at contact force displaying step412.

The flow chart shown inFIG.4is chosen purely for the sake of conceptual clarity. The present example may also comprise additional steps of the algorithm, such as estimating electrical conductivity between given electrodes and tissue. This and other possible steps are omitted from the disclosure herein purposely to provide a more simplified flow chart.

It is noted that although most of the examples have been described in reference to determining relative location using on a local transmitter-receiver mode, the system and method described herein may alternatively and/or additionally use position sensing of each position sensor (electrode) in reference to a global coordinate system to determine the relative locations.

EXAMPLES

A system (10) includes a medical probe (14) and a processor (56). The medical probe (14) includes (i) a shaft (44) for insertion into a cavity of an organ of a patient (23), (ii) an expandable assembly (28) fitted at a distal end (46) of the shaft (44), wherein the expandable assembly (28) has elastic properties, (iii) a proximal position sensing element (29) mounted on the distal end (46) of the shaft, and (iv) at least one distal position sensing element (39) on a distal end of the expandable assembly (28). The processor (56) is configured to (I) sense relative location of each of the at least one distal position sensing element (39) and the proximal position sensing element (29), (II) determine deflection of the expandable assembly (28) based on the relative location, (III) relate the deflection to contact force applied on expandable assembly (28), and (IV) provide an indication of the contact force on a display (27).

The system (10) according to example 1, wherein each of the proximal position sensing element (29) and the at least one distal position sensing element (39) is an electromagnetic coil (EMC).

The system (10) according to example 2, wherein a controller (30) is configured to apply a driving signal in a given frequency to one of the proximal EMC and the at least one distal EMC; andreceive and process output at the given frequency by the other of the proximal EMC and the at least one distal EMC to determine relative location of each of the at least one distal position sensing element (39) and the proximal position sensing element (29).

The system (10) according to example 3, wherein each of the EMCs (29,39) is configured to sense magnetic fields generated by a magnetic source (32) external to the patient and output respective signals indicative of a position in a 3D coordinate system of a position traction system, and wherein the driving signal has a frequency different from the frequencies used by the magnetic source external to the patient (23).

The system (10) according to any one of examples 3-4, and comprising an amplifying circuit fitted on the catheter, the circuit configured to amplify the output at the given frequency by the other of the proximal EMC and the at least one distal EMC.

The system (10) according to any one of examples 2-5, wherein the distal end (46) of the shaft (44) includes three EMCs (29) that are non-parallel oriented one with respect to the others, and wherein the processor is configured to detect, by processing the output from the three EMCs, at least one of an axial compression of the expandable assembly (28) and an angular deflection of the expandable assembly (28) relative to the distal end (46) of the shaft (44).

The system (10) according to any one of examples 2 through 6, wherein the at least one distal EMC (39) is embedded in a respective electrode disposed (26) on a spline (22).

The system (10) according to any of examples 2 through 7, wherein the distal end (46) of the shaft (44) comprises at least two EMCs (29) that are parallel and displaced for one another on the shaft (44).

The system (10) according to any one of examples 1 through 8, and comprising a memory (57) configured to store relationship between position sensing elements (29,39) output and contact force based on empirical data and wherein the processor (56) is configured to use the empirical data to relate position sensing elements output to contact force.

The system (10) according to any of examples 1 through 9, wherein the expandable assembly (28) is a basket assembly formed with a plurality of splines (22).

A method includes inserting a shaft (44) of a medical probe (14) into a cavity of an organ of a patient (23), the probe comprising (i) an expandable assembly (28) fitted at a distal end (46) of the shaft, wherein the expandable assembly (28) has elastic properties, (ii) a proximal position sensing element (29) mounted on the distal end of the shaft, and (iii) at least one distal position sensing element (39) on a distal end of the expandable assembly (28). Relative location of each of the at least one distal position sensing element (39) and the proximal position sensing element (29) is sensed. Deflection of the expandable assembly (28) is determined based on the relative location. Deflection is related to the contact force applied on the expandable assembly (28). An indication of the contact force is provided on a display (27).

Although the examples described herein mainly address cardiac diagnostic applications, the methods and systems described herein can also be used in other medical applications.