System and method for representation and visualization of catheter applied force and power

In the present invention, a system and method for determining the orthogonality and applied force vector of an ablation catheter includes the steps of providing an electrophysiology system including an RF generator, a processor operably connected to the RF generator, a display operably connected to the processor and an ablation catheter operably connected to the RF generator and the processor, the catheter including an ablation electrode disposed opposite the RF generator and a number of microelectrodes disposed on and electrically isolated from the ablation electrode, the processor configured to compare data signals obtained from the microelectrodes with one another to derive a difference value for each pair of data signals, obtaining data signals from the microelectrodes, comparing the data signals from microelectrode pairs to determine difference values and generating a visual representation on the display of the orthogonality and applied force vector of the ablation electrode using the difference values.

BACKGROUND OF INVENTION

The invention relates to a system and method for providing a representation on a display of the direction of force and power being applied via a catheter utilized in an invasive procedure, e.g., an ablation procedure.

In performing invasive cardiac catheterization procedures, such as ablation procedures, it is necessary to provide the clinician with various information on the catheter used in the procedure, including the force exerted on the catheter as well as a visual indication of the location of the ablation catheter tip relative to the tissue being treated. In many procedures these parameters of the catheter tip are determined utilizing electrodes disposed on the catheter adjacent the tip of the catheter that are used to sense the various parameters of the catheter relative to the tissue as the catheter is moved. These electrodes provide signals to a processor operably connected to the catheter that interprets the signals and provides an indication of the forces exerted on and the location of the catheter tip, and thus the ablation electrode disposed on the catheter tip relative to the tissue being treated.

Many different methods, structures and systems have been developed for the interpretation of these signals in order to provide an accurate and useful representation of the catheter tip and surrounding tissue. One such system and method is disclosed in U.S. Pat. No. 8,876,817, entitled “ELECTROPHYSIOLOGY SYSTEM AND METHODS”, which is expressly incorporated herein by reference for all purposes. In this reference, an ablation catheter has a tissue ablation electrode and a plurality of microelectrodes distributed about the circumference of the tissue ablation electrode adjacent the tip of the catheter and electrically isolated therefrom. The plurality of microelectrodes defines a plurality of bipolar microelectrode pairs. A mapping processor connected to the microelectrodes is configured to acquire output signals from the bipolar microelectrode pairs, compare the output signals, and generate an output to a display to provide a clinician with a visual indication of an orientation of the tissue ablation electrode relative to the tissue, i.e., an indication of whether the tissue ablation electrode is in contact with the tissue.

In this system and method, the mapping processor can additionally utilize the signals from the microelectrodes to generate an electronic map of the tissue in which the catheter is positioned. This can enable the clinician utilizing the catheter to identify abnormal tissues within the tissue being mapped and/or examined.

However, while the representation on the display of the orientation of the electrode relative to the tissue is instructive in assisting the clinician in the performance of the procedure, it is desirable to be able to provide the clinician with a representation on the display that provides more information to the clinician than simply the structure of the tissue around the catheter, the orientation of the ablation electrode relative to the tissue or whether the ablation electrode is in contact with the tissue.

Accordingly, it is desirable to develop system and method for the determination of various parameters of the ablation catheter that enhances the information presented to the clinician based on the signals obtained from the microelectrodes on the catheter.

BRIEF DESCRIPTION OF THE INVENTION

There is a need or desire for an improved system and method for the determination of the orientation and contact of a catheter with the surrounding tissue. The above-mentioned drawbacks and needs are addressed by the invention embodiments in the following descriptions.

According to one exemplary aspect of the invention, a system and method is provided to present a uniform presentation relative to all known variants of force sensing, including specialist multipole ablation catheters, that illustrates both applied force and applied power in a manner such that a representation of the expected tissue transformation can be easily visualized. The ability to adapt multipole ablation catheters for applied force sensing is also within the scope of the invention.

According to another aspect of an exemplary embodiment of the invention, the system and method utilizes a catheter including a sequence of axial differential pairs a subset electrodes positioned thereon. The signals obtained by the pairs of electrodes are utilized in an equation that defines the orthogonality of the catheter relative to the tissue based on the signals. This determination of orthogonality in turn may be utilized by itself as a new noise-reduced signal to assist in the performance of the particular procedure, or as a detection process to define vector of greatest conduction in the tissue surrounding the catheter. This conduction vector may be a primary signal in its own right or can be utilized to selectively steer the clinician to position the catheter tip, i.e., the ablation electrode, at the region of greatest interest determined by the vector. This method is useful in identification of either new ablation targets or indicative of additional burn relative to a previously selected target close by.

According to yet another exemplary embodiment of the invention, the signals obtained by the microelectrodes that are used to provide the enhanced visualization and correlations of the data related to the applied user pressure exerted on the catheter tip and the applied energy to achieve tissue necrosis and disruption to the physiological conduction path. The system and method has the ability to record and process this multivariate data in multiple planes of tissue to enable a three dimensional (3D) visualization of the associated changes to the tissue pathology allowing the user to better characterize the result of the procedure being performed.

According to another exemplary embodiment of the invention, an electrophysiology system includes an RF generator, a processor operably connected to the RF generator and an ablation catheter operably connected to the RF generator and the processor, the catheter including an ablation electrode disposed opposite the RF generator and forming a tip of the ablation catheter and a number of microelectrodes disposed on and electrically isolated from the ablation electrode, wherein the processor is configured to compare data signals obtained from the microelectrodes with one another to derive a difference value for each pair of data signals and create a visual representation of a degree of orthogonality of the ablation electrode relative to tissue within which the ablation electrode is positioned.

According to still another exemplary embodiment of the invention, a method for determining the orthogonality and applied force vector of an ablation catheter, includes the steps of providing an electrophysiology system including an RF generator, a processor operably connected to the RF generator, a display operably connected to the processor and an ablation catheter operably connected to the RF generator and the processor, the catheter including an ablation electrode disposed opposite the RF generator and forming a tip of the ablation catheter and a number of microelectrodes disposed on and electrically isolated from the ablation electrode, the processor configured to compare data signals obtained from the microelectrodes with one another to derive a difference value for each pair of data signals; positioning the ablation electrode within the tissue to be ablated; obtaining data signals from the microelectrodes; comparing the data signals from microelectrode pairs to determine difference values; and generating a visual representation on the display of the orthogonality and applied force vector of the ablation electrode relative to the tissue using the difference values.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1is a schematic illustration of an electrophysiology system, e.g., a radio frequency (RF) ablation system1according to one embodiment of the invention, such as that disclosed in U.S. Pat. No. 8,876,817, entitled “ELECTROPHYSIOLOGY SYSTEM AND METHODS”, which is expressly incorporated herein by reference for all purposes. As shown inFIG. 1, the system1includes an ablation catheter2, an RF generator3, and a processor4. The ablation catheter2is operatively coupled to both the RF generator2and the processor4, as will be described in greater detail herein. As further shown, the ablation catheter2includes a proximal handle5having a control knob6, a flexible body having a distal portion including a plurality of ring electrodes7, a tissue ablation electrode8, and a plurality of microelectrodes9(also referred to herein as “pin” electrodes) disposed within and electrically isolated from the tissue ablation electrode8. Each microelectrode9is also separately connected to the processor4by a connection10, e.g., a wire, extending between the microelectrode9and the processor4along the catheter2.

In various embodiments, the ablation catheter2is configured to be introduced through the vasculature of the patient, and into one of the chambers of the heart, where it can be used to map and ablate myocardial tissue using the microelectrodes9and the tissue ablation8. Thus, the tissue ablation electrode8is configured to apply ablation energy to the myocardial tissue. In the illustrated embodiment, the ablation catheter2is steerable, such that the distal portion can be deflected (as indicated by the dashed outlines inFIG. 1) by manipulation of the control knob6. In other embodiments, the distal portion of the ablation catheter2has a pre-formed shape adapted to facilitate positioning the tissue ablation electrode8and the microelectrodes9adjacent to specific target tissue. In one such embodiment, the pre-formed shape is generally circular or semi-circular and is oriented in a plane transverse to the general direction of the catheter body.

In various embodiments, such as shown inFIGS. 1 and 2, the microelectrodes9are circumferentially distributed about the tissue ablation electrode8and electrically isolated therefrom. The microelectrodes9can be configured to operate in unipolar or bipolar sensing modes. In various embodiments, the plurality of microelectrodes9define a plurality of bipolar microelectrode pairs, each bipolar microelectrode pair being configured to generate an output signal corresponding to a sensed electrical activity of the myocardial tissue proximate thereto. The generated output signals from the microelectrodes9can be sent to the mapping processor4for processing as described herein.

Exemplary catheters that can be used as the ablation catheter2can include those described in U.S. Patent App. Pub. Nos. US2008/0243214 entitled “High Resolution Electrophysiology Catheter,” and US2010/0331658, entitled “Map and Ablate Open Irrigated Hybrid Catheter,” which are hereby incorporated by reference in their entireties for all purposes. In various exemplary embodiments, the tissue ablation electrode8can have a length of between six (6) and fourteen (14) mm, and a plurality of microelectrodes9equally spaced about the circumference of the tissue ablation electrode8. In one embodiment, the tissue ablation electrode8can have an axial length of about eight (8) mm. In one exemplary embodiment, the ablation catheter2includes at least two (2) but optionally three (3) microelectrodes9equally spaced about the circumference of the tissue ablation electrode8and at the same longitudinal position along the longitudinal axis of the tissue ablation electrode8, the microelectrodes9forming at least first, second and third bipolar microelectrode pairs. In one exemplary embodiment, the catheter2includes a forward-facing microelectrode9generally centrally-located within the tissue ablation electrode8, e.g. the tip of the ablation electrode8. An exemplary such RF ablation catheter is illustrated in FIGS. 3 and 4 of the aforementioned U.S. Patent Application Pub. No. US2008/0243214.

In some exemplary embodiments, microelectrodes9can be located at other positions along the ablation catheter2in addition to or in lieu of the microelectrodes9in the tissue ablation electrode8. In still other embodiments, the ablation catheter2can include up to “n” microelectrodes9spaced around the circumference of the ablation electrode8, with “n” defined as the maximum number of axial microelectrodes9that can be equidistantly spaced around the longitudinal central axis of the ablation catheter2in relation to the size of the microelectrodes9being utilized.

In various exemplary embodiments, the tissue ablation electrode8has an exterior wall that defines an open interior region (not shown). The exterior wall includes mapping electrode openings for accommodating the microelectrodes9, and, in some embodiments, irrigation ports (not shown). The irrigation ports, when present, are in fluid communication an external irrigation fluid reservoir and pump (not shown) for supplying irrigation fluid to the myocardial tissue being mapped and/or ablated. Exemplary irrigated catheters for use as the catheter2can be any of the catheters described in the aforementioned U.S. Patent App. Pub. No. 2010/0331658. In various exemplary embodiments, the catheter system may also include noise artifact isolators (not shown), wherein the microelectrodes9are electrically insulated from the exterior wall by the noise artifact isolators.

The RF generator3is configured to deliver ablation energy to the ablation catheter2in a controlled manner in order to ablate the target tissue sites identified by the mapping processor4. Ablation of tissue within the heart is well known in the art, and thus for purposes of brevity, the RF generator3will not be described in further detail. Further details regarding RF generators are provided in U.S. Pat. No. 5,383,874, which is expressly incorporated herein by reference. Although the mapping processor4and RF generator3are shown as discrete components, they can alternatively be incorporated into a single integrated device.

The RF ablation catheter2as described may be used to perform various diagnostic functions to assist the physician in an ablation treatment. For example, in some embodiments, the catheter is used to ablate cardiac arrhythmias, and at the same time provide real-time assessment of a lesion formed during RF ablation. Real-time assessment of the lesion may involve any of monitoring surface and/or tissue temperature at or around the lesion, reduction in the electrocardiogram signal, a drop in impedance, direct and/or surface visualization of the lesion site, and imaging of the tissue site (e.g., using computed tomography, magnetic resonance imaging, ultrasound, etc.). In addition, the presence of the microelectrodes within the RF tip electrode can operate to assist the clinician in locating and positioning the tip electrode at the desired treatment site, and to determine the position and orientation of the tip electrode relative to the tissue to be ablated.

In various exemplary embodiments, the mapping processor4is configured to detect, process, and record electrical signals within the heart via the ablation catheter2. Based on these electrical signals, a physician can identify the specific target tissue sites within the heart, and ensure that the arrhythmia causing substrates have been electrically isolated by the ablative treatment. The processor4is configured to process the output signals from the microelectrodes9and/or the ring electrodes7, and to generate an output to a display (not shown) for use by the physician. In some exemplary embodiments, the display can include electrocardiograms (ECG) information, which can be analyzed by the user to determine the existence and/or location of arrhythmia substrates within the heart and/or determine the location of the ablation catheter2within the heart. In various exemplary embodiments, the output from the processor4can be used to provide, via the display, an indication to the clinician about a characteristic of the ablation catheter2and/or the myocardial tissue being mapped.

In addition to a mapping function of the processor4, the processor4utilizes the signals obtained from the axial microelectrodes9to define the orthogonality of the ablation electrode8relative to the tissue. In looking at the exemplary embodiment illustrated inFIGS. 3 and 4, the output signals100,102,104,106, such as ECG signals, obtained from the microelectrodes9, such as the three (3) microelectrodes9spaced around the circumference of the ablation electrode8and the one (1) microelectrode9disposed in the tip of the ablation electrode8in the exemplary embodiment inFIG. 3, are routed to analog or digital morphology comparators1000,1002,1004,1006in order to provide difference signals A, B, C, D representative of the comparisons of the various signals100,102,104,106from adjacent microelectrodes. In the exemplary embodiment, the comparators1000,1002,1004,1006compare the signals100,102,104,106obtained at the same particular instance of time to determine whether the compared signals100,102,104,106are an exact match (having a representative value of 1) or are not an exact match (having a representative value of 0). The values for the difference signals A, B, C, D are then analyzed to provide an indication of the orthogonality of the ablation electrode8relative to the tissue in which the ablation electrode8is disposed.

In an exemplary embodiment, the method250of analysis of the difference signals by the processor4as illustrated inFIG. 5is utilized to generate a wire frame space plot1010illustrated inFIG. 4that can be visually represented on a display associated/operably connected to the processor4. In the exemplary embodiment ofFIG. 4, after positioning the ablation electrode8within the tissue, in block255, six (6) electrodes9are present in the ablation electrode8, providing six (6) signals100,102,104,106,108,110to the processor4in block260. Pairs of these signals100,102,104,106,108,110are supplied to associated comparators (not shown) in order to derive difference signals A, B, C, D, E, F in block265. The difference signals A, B, C, D, E, F are analyzed in block270, e.g., averaged, and represented at each of the vertices/poles of the plot1010with the analysis results for the difference signals A, B, C, D, E, F represented by the shaded area1011of the plot101in order to indicate the angle of the ablation electrode8/catheter2relative to the tissue as well as the force applied to the ablation electrode8/catheter2by the tissue. In the exemplary plot1010ofFIG. 4, the shaded area1011indicated that the portion(s) of the ablation electrode8represented by difference signals A, B and F are in significant contact with the surrounding tissue, while the portions represented by difference signals C-E are in much less contact with the tissue.

This visualization employing the wire frame plot1010can work with any of the three alternate methods of force sensing utilized in catheters2—mechanical stiffness, impedance and optical methods. The wire frame space model/plot1010utilizes “n” nodes where in each node relates to a sensing electrode9, regardless of physical technology. As a result, the shape and resolution of the wire frame space plot1010tends to a circular shape as the number of electrodes9increases, with the plot1010taking various geometric shapes depending on the number of electrodes9actually present in the ablation electrode8. For example, in the exemplary embodiment of the catheter2ofFIGS. 1-3, the plot1010will realize as a triangle, while the plot1010in the exemplary embodiment ofFIG. 4, where six (6) microelectrodes are present, realizes as a hexagon.

Additionally, the processor4can apply a vector analysis to the signals100,102,104,106, etc. and/or on the difference signals A, B, C, D, etc. from the “n” electrodes9present on the catheter2to determine a region of interest (ROI) by peak signal analysis for each derived lead/electrode9at a given instance of time. Applying an averaging function to this vector analysis determines a vector of consistently greatest value in order to provide a localized axis from which the focus of the study can be determined. The focus may be determined by vector calculation of path to peak level or earliest activation, for example. In addition, this process can be automated such that the analysis will be performed by the processor4without any required user intervention as the signals100,102,104,106, etc. and/or on the difference signals A, B, C, D, etc. are received and/or calculated by the processor4. Additionally, this process can then be utilized to sequence/represent the best view of the plot1010on the display (not shown) relative to other channels that are set to be displayed for each vector view providing a sequenced or triggered view relative to the signal processed vector. Other functions that can also be associated and triggered with this process include gain increase of select channels and change of trace color on the signals nearest to the reference vector, among others. Additionally, the area inside the curve can be color-coded and/or shaded to represent other information provided by the signals, such as the percent of the colored/shaded area in the plot that is proportional to orthogonality.

Each pole or vertex of the wire frame plot1010can be further convolved with additional parametric information, such as impedance measurements or electrical current conduction, to represent the angulation of the ablation electrode8through distortion of the wire frame. This information can be deduced from the screen presentation of the wire frame plot1010, and/or through a computer derived line representing the overall applied force vector/axis1012illustrated on the plot1010where force is proportional to the colored/shaded area of the wire plot1010. Energy applied to the ablation catheter and through applied force can also be translated to a visual shading scheme on or within the wire frame plot1010, which can be further sub-shaded relative to the pole or vertex of the plot1010representing the greatest force vector (e.g., the pole corresponding to difference signal B inFIG. 4). Additionally, the average applied pressure may also be calculated for the entire surface of the ablation catheter8using the force vector values determined for each pole of the plot1010, e.g., the values for each of the difference signals (e.g., values A-F inFIG. 4).

In another exemplary embodiment, additional orthogonal microelectrodes9can be positioned within the ablation electrode8spaced from the microelectrodes9opposite the tip of the ablation catheter8, in order to provide the catheter2with the ability to represent a depth x of the ablation electrode8relative to the tissue. The depth x has a number of layers y identified by each array or set of microelectrodes9such that the ablation catheter force, and “depth” of insertion within the muscle/heart or other tissue can be determined as before. However, the measurements made can now be repeated for each layer y relative to available depth x, and represented on the screen via multiple wire frame plots1010/vectors1012. Applying the principles developed previously the user can display an aggregated view, or switch between layers y such that the overall performance of the system1can be evaluated and the depth of insertion into the tissue can be similarly deduced.

Further, this method for generating the display/plot1010can be applied to a different type of catheter2including an ablation electrode8configured to create linear burns versus the described spot burns, such as the nMarq linear catheter developed by Biosense Webster or Phased RF Catheter PVAC, MAAC and MASC specialist catheters made by Medtronic. In an as-is model using this type of catheter2, the system1can generate the wire frame plots1010in the aforementioned manner which can then be stacked to represent the applied energy from the catheter2. In another exemplary embodiment, a modification of the catheter2uses impedance sensing electrodes (not shown) inserted axially along the median of the ablation electrode8/catheter2at periodic intervals. In this configuration, contact impedance can be triangulated between the electrodes relative to the ablation electrode8to allow applied force to be determined.

Further, in still another exemplary embodiment a multi-dimensional stack of wire frame space plots1010(FIG. 4) can be developed to allow the user to better monitor the overall performance of the catheter2relative to the desired tissue pathology and/or tissue changes that are desired. The wire frame space plots or models1010obtained from the microelectrodes9can be layered in a known manner to overlap and join the shaded areas1011using the known spacing of the sets/arrays of microelectrodes9forming each shaded area1011to provide a three-dimensional (3D) representation or image of the tissue contacted by the catheter2, both before the catheter2is operated and after a burn has been performed using the catheter2, such as in the performance of a percutaneous coronary intervention (PCI). In this manner, the three-dimensional (3D) image constructed via the layered plots1010obtained using signals from the microelectrodes9can show the isolation achieved in the tissue as a result of the 3D images of the tissue taken before and after the burn, such as by an overlapped, collated, correlated and/or comparative 3D image of the before and after tissue structure(s). This process using the catheter2including the spaced arrays of microelectrodes9can also be employed when performing a pulmonary vein isolation (PVI), or a pulmonary vein antral isolation (PVAI). Some exemplary embodiments of this pathology correlation are known in the art, such as Lesion Size Index (LSI) which provides a numerical estimation of cautery effect.

In summary, some of the technical advantages of the system1and method250of the invention include:1. The system1and method250use wire frame plots1010/visualization technology allowing scalable solution from two (2) or three (3) to n electrodes9.2. The system1and method250can be utilized independent of the type of technology employed in the catheter2to sense force.3. The system1and method250are capable of multi-variant information representation.4. The system1and method250are scalable beyond one layer y.5. The system1and method250are 3D representation capable.6. The system1and method250can support a single contact burn catheter, and multipole devices for specialist or linear burns.

In summary, some of the commercial advantages of the system1and method250of the invention include:1. The system1and method250can be employed independent of ablation catheter technology.2. The system1and method250enable advanced procedures using complex ablation catheters.3. The system1and method250provides axis of force analysis, convolved with applied power to provide visual metaphor for resultant tissue transformation.4. The system1and method250provides for multi-polar ablation catheters.5. The system1and method250provides for depth of burn monitoring.6. Catheters2used in the system1and method250may be substantially less expensive than state of the art mechanical force sensing catheters.