Patent Publication Number: US-2015073245-A1

Title: System and method for measuring force and torque applied to a catheter electrode tip

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/347,607, filed 31 Dec. 2008, now pending, which is hereby incorporated by reference as though fully set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     a. Field of the Invention 
     This invention relates to a system and method for assessing the force and torque between an electrode and tissue in a body. In particular, the instant invention relates to a system and method for assessing the force and torque between an electrode tip on a diagnostic and/or therapeutic medical device such as a mapping or ablation catheter and tissue, such as cardiac tissue. The instant invention also relates to a method for sensing and calculating contact force exerted by another component on a tissue, and generally, a method for sensing and calculating contact force on an elongate member when in contact with another component or structure, for medical or non-medical purposes. 
     b. Background Art 
     Electrodes are used on a variety of diagnostic and/or therapeutic medical devices. For example, electrodes may be used on cardiac mapping catheters to generate an image of the internal geometry of a heart and electrical potentials within the tissue. Electrodes are also used on ablation catheters to create tissue necrosis in cardiac tissue to correct conditions such as atrial arrhythmia (including, but not limited to, ectopic atrial tachycardia, atrial fibrillation, and atrial flutter). Arrhythmia can create a variety of dangerous conditions including irregular heart rates, loss of synchronous atrioventricular contractions and stasis of blood flow which can lead to a variety of ailments and even death. It is believed that the primary cause of atrial arrhythmia is stray electrical signals within the left or right atrium of the heart. The ablation catheter imparts ablative energy (e.g., radiofrequency energy, cryoablation, lasers, chemicals, high-intensity focused ultrasound, etc.) to cardiac tissue to create a lesion in the cardiac tissue. This lesion disrupts undesirable electrical pathways and thereby limits or prevents stray electrical signals that lead to arrhythmias. 
     The safety and effectiveness of many of diagnostic and/or therapeutic devices is often determined in part by the proximity of the device and the electrodes to the target tissue. In mapping catheters, the distance between the electrodes and the target tissue affects the strength of the electrical signal and the identity of the mapping location. The safety and effectiveness of ablation lesions is determined in part by the proximity of the ablation electrode to target tissue and the effective application of energy to that tissue. If the electrode is too far from the tissue or has insufficient contact with the tissue, the lesions created may not be effective. On the other hand, if the catheter tip containing the electrode contacts the tissue with excessive force, the catheter tip may perforate or otherwise damage the tissue (e.g., by overheating). Therefore, to successfully ablate live tissue, the electrode should be applied to the tissue with proper force. When ablating and moving an electrode, in addition to the magnitude of the force, knowledge of direction of the force (i.e. multi-axial measurement) and further the torque acting on the electrode tip are important for estimating the distribution of pressure and stress over an electrode tip surface. 
     Contact force between a catheter electrode and tissue has typically been determined using one or more of the following methods: clinician sense, fluoroscopic imaging, intracardiac echo (ICE), atrial electrograms (typically bipolar D-2), pacing thresholds, evaluation of lesion size at necropsy and measurement of temperature change at the energy delivery site. Each of these methods has disadvantages, however. 
     For example, although a clinician can evaluate contact force based on tactile feedback from the catheter and prior experience, the determination depends largely on the experience of the clinician and is also subject to change based on variations in the mechanical properties of catheters used by the clinician. The determination is particularly difficult when using catheters that are relatively long (such as those used to enter the left atria of the heart). 
     Because fluoroscopic images are two-dimensional projections and blood and myocardium attenuate x-rays similarly, it can be difficult to quantify the degree of contact force and detect when the catheter tip is not in contact with the tissue. 
     Intracardiac echo can be time consuming and it can be difficult to align the echo beam with the ablation catheter. Further, intracardiac echo does not always permit the clinician to confidently assess the degree of contact and can generate unacceptable levels of false positives and false negatives in assessing whether the electrode is in contact with tissue. 
     Atrial electrograms do not always correlate well to tissue contact and are also prone to false negatives and positives. Pacing thresholds also do not always correlate well with tissue contact and pacing thresholds can be time-consuming and also prone to false positives and negatives because tissue excitability may vary in hearts with arrhythmia. Evaluating lesion size at necropsy is seldom available in human subjects, provides limited information (few data points) and, further, it is often difficult to evaluate the depth and volume of lesions in the left and right atria. Finally, temperature measurements provide limited information (few data points) and can be difficult to evaluate in the case of irrigated catheters. 
     The inventors herein have thus recognized a need for a system and method for determining the contact force and torque upon an electrode tip, both during RF ablation and when driving the RF electrode to the ablation site, that will minimize and/or eliminate one or more of the above-identified deficiencies. 
     BRIEF SUMMARY OF THE INVENTION 
     It is desirable to provide a system and method for determining the degree of coupling between an electrode and a tissue in a body. In particular, it is desirable to be able to determine a degree of electrical coupling between electrodes on a diagnostic and/or therapeutic medical device such as a mapping or ablation catheter and tissue, such as cardiac tissue. 
     A system for assessing a degree of coupling between an electrode and a tissue in a body in accordance with one embodiment of the invention may include a contact sensing assembly including a catheter having a body having a proximal end and a distal end, and an electrode including a tip portion and a base portion mounted adjacent a head portion of the catheter body. One or more force and torque sensors may be disposed generally adjacent the base portion and may include one or more pressure sensors for measuring pressure applied to the electrode tip portion and providing a pressure signal related to the measured pressure, with the pressure sensor including a predetermined sensitivity. The base and head portions may include a predetermined rigidity so that force applied to the electrode tip portion may be determinable as a function of the predetermined sensitivity and the pressure signal. 
     For the assembly described above, in an embodiment, the assembly may include a plurality of pressure sensors, and the individual pressure sensor output signals allow a vector reconstruction of a net tip contact force using a vector addition algorithm or relationship. In an embodiment, the assembly may further include a plurality of pressure sensors, and the force applied to the electrode tip portion may be determinable as a sum of a voltage output signal of each pressure sensor respectively divided by the predetermined sensitivity of each pressure sensor. In an embodiment, the assembly may further include a plurality of pressure sensors, and torque applied to the electrode tip portion may be determinable as a function of a voltage output signal of each pressure sensor respectively divided by the predetermined sensitivity of each pressure sensor, and a distance of the pressure sensors from a central axis of the electrode. 
     For the assembly described above, in an embodiment, the assembly may include three symmetrically disposed pressure sensors, and for an electrode having a central axis disposed along a z-direction, torque applied to the electrode tip portion may be determinable as follows: T_y=¾*D*(V_c/α_c−V_a/α_a−V_b/α_b), where T_y may be the torque applied to the electrode tip portion in a y-direction, D may be a diameter of a circle passing through the centers of each pressure sensor, V may be a voltage output of each respective pressure sensor, and α may be the predetermined sensitivity of each respective pressure sensor. In an embodiment, the assembly may include three symmetrically disposed pressure sensors, and for an electrode having a central axis disposed along a z-direction, torque applied to the electrode tip portion may be determinable as follows: T_x=sqrt(3)/2*D*(V_a/α_a−V_b/α_b), where T_x may be the torque applied to the electrode tip portion in a x-direction, D may be a diameter of a circle passing through the centers of each pressure sensor, V may be a voltage output of each respective pressure sensor, and a may be the predetermined sensitivity of each respective pressure sensor. 
     For the assembly described above, in an embodiment, the generally distal end of the catheter may include a coupling member connecting the electrode to the catheter body. In an embodiment, the coupling member may include an elastic material. In an embodiment, the pressure sensors may be emplaced in an interface between two or more annular or circular rings. In an embodiment, the tip portion of the electrode may include an irrigation port. The electrode may include an RF ablation electrode, a HIFU ablation transducer, a laser ablation assembly, a cryogenic ablation assembly, an ultrasonic imaging apparatus, an electrical cardiac pacing electrode, or an electrical cardiac sensing electrode. The pressure sensors may be fabricated using flex circuit technology, lithographic technology, thin-film technology, and/or thick film technology. In an embodiment, the assembly may further include a proximal control handle including one or more catheter deflection or articulation controls, and one or more switches for controlling a diagnostic or therapeutic function of the electrode. The force applied to the electrode tip may be utilized for automatically limiting a maximum force, warning of a high or unacceptable force, giving visual or audible feedback to a practitioner regarding a tissue contact force, warning of a loss of contact force or contact, and/or warning of a contact force which may be too low. 
     In an embodiment, a system for assessing a degree of coupling between an electrode and a tissue in a body may include a contact sensing assembly including a catheter including a body having a proximal end and a distal end, and an electrode including a tip portion and a base portion mounted adjacent a head portion of the catheter body. One or more sensors may be disposed generally adjacent the base portion for measuring compression or tensile forces applied to the electrode tip portion and providing an output signal related to the measured forces, with the sensor including a predetermined sensitivity. The base and head portions may include a predetermined rigidity so that the compression or tensile forces applied to the electrode tip portion are determinable as a function of the predetermined sensitivity and the output signal. 
     For the assembly described above, in an embodiment, the assembly may include a plurality of sensors, and the individual sensors each generate an output signal that together provide a vector reconstruction of a net tip contact force using a vector addition algorithm or relationship. In an embodiment, the assembly may include a plurality of sensors, and the compression or tensile forces applied to the electrode tip portion may be determinable as a sum of the output signals of each sensor respectively divided by the predetermined sensitivity of each sensor. In an embodiment, the assembly may include a plurality of sensors, and torque applied to the electrode tip portion may be determinable as a function of the output signal of each sensor respectively divided by the predetermined sensitivity of each sensor, and a distance of the sensors from a central axis of the electrode. 
     For the assembly described above, in an embodiment, the assembly may include three symmetrically disposed sensors, and for an electrode having a central axis disposed along a z-direction, torque applied to the electrode tip portion may be determinable as follows: T_y=¾*D*(V_c/α_c−V_a/α_a−V_b/α_b), where T_y may be the torque applied to the electrode tip portion in a y-direction, D may be a diameter of a circle passing through the centers of each sensor, V may be a voltage output of each respective sensor, and α may be the predetermined sensitivity of each respective sensor. In an embodiment, the assembly may include three symmetrically disposed sensors, and for an electrode having a central axis disposed along a z-direction, torque applied to the electrode tip portion may be determinable as follows: T_x=sqrt(3)/2*D*(V_a/α_a−V_b/α_b), where T_x may be the torque applied to the electrode tip portion in a x-direction, D may be a diameter of a circle passing through the centers of each sensor, V may be a voltage output of each respective sensor, and a may be the predetermined sensitivity of each respective sensor. 
     For the assembly described above, in an embodiment, the generally distal end of the catheter may include a coupling member connecting the electrode to the catheter body. In an embodiment, the coupling member includes an elastic material. In an embodiment, the sensors may be emplaced in an interface between two or more annular or circular rings. In an embodiment, the tip portion of the electrode may include an irrigation port. The electrode may include an RF ablation electrode, a HIFU ablation transducer, a laser ablation apparatus, a cryogenic ablation assembly, an ultrasonic imaging transducer, a cardiac pacing electrode, or a cardiac sensing electrode. The sensors may be fabricated using flex circuit technology, lithographic technology, thin-film technology, and/or thick film technology. In an embodiment, the assembly may include a proximal control handle including one or more catheter deflection or articulation controls, and one or more switches for controlling a diagnostic or therapeutic function of the electrode. The compression or tensile force applied to the electrode tip may be utilized for automatically limiting a maximum force, warning of a high or unacceptable force, giving visual or audible feedback to a practitioner regarding a tissue contact force, warning of a loss of contact force or contact, and/or warning of a contact force which may be too low. The sensor may be a resistive force sensor, a capacitive force sensor, or an optical force sensor. 
     In an embodiment, a system for assessing a degree of coupling between an electrode and a tissue in a body may include a contact sensing assembly including a catheter having a body having a proximal end and a distal end, an electrode pipe disposed in the catheter body, and an electrode wire disposed in the electrode pipe and including isolation thereon. A change in capacitance resulting from movement of the electrode wire toward the electrode pipe or contact of the electrode wire with the electrode pipe during bending of the catheter may directly correlate to a force applied to the catheter. 
     For the assembly described above, in an embodiment, the electrode wire and electrode pipe may be mechanically coupled toward a distal end thereof An electrode operatively connected to the catheter may include an RF ablation electrode, a HIFU ablation transducer, a laser ablation apparatus, a cryogenic ablation assembly, an ultrasonic imaging transducer, a cardiac pacing electrode, or a cardiac sensing electrode. In an embodiment, the assembly may further include a proximal control handle including one or more catheter deflection or articulation controls, and one or more switches for controlling a diagnostic or therapeutic function of an electrode operatively connected to the catheter. The compression or tensile force applied to the electrode tip may be utilized for automatically limiting a maximum force, warning of a high or unacceptable force, giving visual or audible feedback to a practitioner regarding a tissue contact force, warning of a loss of contact force or contact, and/or warning of a contact force which may be too low. 
     In an embodiment, a system for assessing a degree of coupling between an electrode and a tissue in a body may include a contact sensing assembly including a catheter having a body having a proximal end and a distal end, an electrode pipe operatively connected to the catheter body for movement and/or bending with the catheter body, and an electrode wire disposed in the electrode pipe and including isolation thereon. A change in capacitance resulting from movement of the electrode wire toward the electrode pipe or contact of the electrode wire with the electrode pipe during bending of the catheter may directly correlate to a force applied to the catheter. 
     The foregoing and other aspects, features, details, utilities and advantages of the invention will be apparent from reading the following description and claims, and from reviewing the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial perspective view of a catheter assembly in accordance with an embodiment of the invention; 
         FIG. 2  is an isometric diagrammatic view of an electrode area according to the invention, illustrating exemplary force and torque sensors; 
         FIG. 3  is a top view of the electrode area of  FIG. 2 , with the electrode removed for clarity; 
         FIG. 4  is a partial diagrammatic view of a catheter assembly in accordance with another embodiment of the invention; 
         FIGS. 5   a - 5   d  are partial isometric diagrammatic views of a catheter structure in accordance with another embodiment of the invention; and 
         FIGS. 6   a - 6   f  are schematic overviews of a system for measuring force and torque in accordance with alternate embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Referring now to the drawings wherein like reference numerals are used to identify like components in the various views,  FIG. 1  illustrates an exemplary embodiment of a contact sensing assembly  10  as provided by the invention. In a general form, referring to  FIGS. 1 and 2 , contact sensing assembly  10  may include a catheter  12 , an electrode  14  connected to the catheter, and a force and torque sensor  16  for interacting with base  18  of electrode  14  or alternatively with head  20  of catheter body  22  if sensor  16  is mounted on base  18 . In another embodiment, contact sensing assembly  10  may include a first interactive component and a second interactive component. The contact sensing assembly may be used in the diagnosis, visualization, and/or treatment of tissue (such as endocardial tissue) in a body. Contact sensing assembly  10  may be used in a number of diagnostic and therapeutic applications, such as for example, the recording of electrograms in the heart, the performance of cardiac ablation procedures, and/or various other applications. The catheter assembly can be used in connection with a number of applications that involve humans, or other mammals, for tissue observation, treatment, repair or other procedures. Moreover, the invention is not limited to one particular application, but rather may be employed by those of ordinary skill in the art in any number of diagnostic and therapeutic applications, and for medical or non-medical purposes. For example, the contact sensing assemblies disclosed herein may be usable in combination with a robotic catheter system (e.g. disclosed in commonly owned and copending applications titled “Robotic Catheter System,” “Robotic Catheter Manipulator Assembly,” “Robotic Catheter Device Cartridge,” “Robotic Catheter Rotatable Device Cartridge,” “Robotic Catheter Input Device,” “Robotic Catheter System Including Haptic Feedback,” and “Robotic Catheter System with Dynamic Response,” the respective disclosures of which are incorporated herein by reference in their entirety), for example, for coupling to a computer controlled catheter or surgical instrument for real-time feedback and precise control during a procedure. 
     Referring to  FIGS. 1-4 , catheter  12  of the invention may include body  22  having a distal end  24  and a proximal end  26 . Body  22  of catheter  12  is generally tubular in shape, although other configurations of the catheter may be used as known in the industry. If desired, the outer portion of catheter  12  may have a braided outer covering therein providing increased flexibility and strength. The catheters of the invention vary in length and are attached to a handle or other type of control member that allows a surgeon or operator of the catheter to manipulate the relative position of the catheter within the body from a remote location, as recognized by one of ordinary skill in the art. 
     An embodiment of a system and method for measuring force and torque applied to the tip of electrode  14 , namely contact sensing assembly  10 , will now be described in detail. 
     As shown in  FIG. 3 , body  22  of catheter  12  may generally include sensors  28 ,  30 ,  32  of force and torque sensor  16  mounted on head  20  in a tri-axial arrangement. Alternatively, sensors  28 ,  30 ,  32  may be generally located between a “neck” area of electrode  14  and a support portion on the body. The body of electrode  14 , particularly near base  18  and the area of body  22  adjacent head  20 , may be sufficiently rigid to permit any forces (axial or transverse) applied to distal end  24  to be measured by force and torque sensor  16 . The sensor arrangement of  FIGS. 2  and  3  may specifically measure force along the electrode axis F z , and two components of torque in a plane perpendicular to the electrode axis, namely T x  and T y . If needed, the force in the x and y directions may be determined from the torque components. 
     The method of calculating force and torque from sensors  28 ,  30 ,  32  will now be described in detail. 
     Without loss of generality, all three sensors  28 ,  30 ,  32  may be presumed to have the same sensitivity “α” (α is the proportionality constant between force applied to a sensor and the sensor&#39;s electrical output, and represents a predetermined value for each sensor). Given forces in the z-direction applied to each sensor F_a, F_b, F_c (e.g. forces applied to sensors  28 ,  30 ,  32 ), the sensor outputs will be V_a=α F_a, V_b=α F_b, V_c=α F_c, respectively. It should be noted that the term “forces in the z-direction” does not imply force and torque sensor  16  only measures forces in the z-direction. Namely, if a force is applied in the y-direction in  FIG. 2 , while sensors  28 ,  32  may measure a negative (e.g. tensile) force, sensor  30  would measure a positive (e.g. compression) force, with force and torque sensor  16  determining the force in the z-direction based on the respective measurements at each sensor  28 ,  30 ,  32 . 
     The force/torque components may be given by the following equations: 
         F   —   z =( V _a+V —   b+V   —   c )/α,
 
         T   —   y =sqrt(3)/(2*α)* D *( V   —   c−V   —   a/ 2 −V   —   b/ 2), and
 
         T   —   x =sqrt(3)/(2*α)* D *( V   —   a−V   —   b ),
 
     where “D” is the diameter of circle  34  in the x-y plane passing through the centers of sensors  28 ,  30 ,  32 . 
     If each sensor  28 ,  30 ,  32  has a different sensitivity α (e.g. α_a, α_b, α_c), then the sensor outputs would be: 
       V —a=α _aF_a, V_b=α_bF_b,V_c=α —   cF _c.
 
     The force and torque components may be given by the following equations: 
     
       
      
       F 
       — 
       z=V 
       — 
       a/a 
       — 
       a+C 
       — 
       b/a 
       — 
       b+V 
       — 
       c/a 
       — 
       c,  
      
     
         T   —   y= ¾ *D* ( V   —   c/a   —   c−V   —   a/a−C   —   b/a   —   b ), and
 
         T   —   x =sqrt(3)/2 *D* ( V   —   a/a   —   a−V   —   b/a   —   b ) 
     Thus the sensor arrangement of  FIGS. 2 and 3  may specifically measure force along the electrode axis F z , and two components of torque in the plane perpendicular to the electrode axis, namely T x  and T y , with the force and torque being determined as discussed above. 
     Referring to  FIG. 4 , electrode  14  and body  22  may optionally be connected by an elastic hermetic neck, with elastic hermetic neck  38  further allowing only predetermined relative movement of electrode  14  and body  22 , and thus force and torque determination by sensors  28 ,  30 ,  32 . It should be noted that while neck  38  is illustrated as including ridges, neck  38  may optionally be a smooth structure, or another elastic coupling element such as those disclosed in commonly owned and copending application titled “Optic-Based Contact Sensing Assembly and System.” 
     Thus by measuring the z-directional forces applied to each sensor  28 ,  30 ,  32 , force and torque sensor  16  provides feedback on the amount of force of electrode  14  onto a tissue (e.g. F z ), as well as the torque applied to electrode  14  (e.g. T x  and T y ). 
     Referring next to  FIGS. 5   a - 5   d,  another embodiment of a system and method for measuring force applied to the tip of an electrode, namely contact sensing assembly  100 , will be described in detail. 
     Generally, contact sensing assembly  100  of  FIGS. 5   a - 5   d  may estimate the lateral (x-y) force of an electrode tip (e.g. electrode  14 ) onto tissue (e.g. heart or other tissue) from the bending curvature of a catheter  102  near the tip of an electrode. Such a sensor of curvature may be either resistive or capacitive. If capacitive, an inner electrode wire  104  (made for example of stainless steel) may be disposed inside a coaxial outer electrode pipe  106 , with wire  104  and electrode pipe  106  being mechanically connected at bottom area  108 . Outer electrode pipe  106  may be made of a flexible plastic, with the interior surface thereof covered with a thin metal film (e.g. gold). Electrode wire  104  may be covered with a thin layer of isolation  110  made of, for example, Teflon®, to prevent shorts, and may also include isolation at the mechanical coupling at bottom area  108 . Outer electrode pipe  106  may be mechanically coupled to catheter body  112  so that they both bend similarly. 
     In operation, as shown in  FIG. 5   c , when electrode pipe  106  bends together with catheter body  112 , the capacitance between electrode wire  104  and electrode pipe  106  increases as electrode wire  104  (which has isolation thereon) begins to move toward electrode pipe  106 . As shown in  FIG. 5   d , as electrode pipe  106  bends more together with catheter body  112 , the contact area between electrode wire  104  and electrode pipe  106  increases, to thus further increase the capacitance between electrode wire  104  and electrode pipe  106 . The increase in capacitance is measured and correlated to the amount of force on the tip of the electrode (e.g. electrode  14 ) based on the degree of bending of catheter body  112 . For example, for a catheter body having a predetermined flexibility based on the application of a predetermined force, the capacitance may be directly correlated to the amount of force being applied to catheter body  112 . Likewise, for any given catheter body having a predetermined flexibility based on the application of a predetermined force, a capacitance factor may be provided to determine the amount of force being applied to the catheter body based on measured capacitance. 
     As discussed above, contact sensing assembly  100  may be either resistive or capacitive. For an assembly  100  based on changes in resistivity, a resistive solution may be injected inside electrode pipe  106  and anti-short standoffs (not shown) may be used instead of isolation  110 . The resistive solution, such as saline, may be used to fill assembly  100  right before or during surgery. 
     Thus by measuring the change in capacitance or resistivity between inner electrode wire  104  and outer electrode pipe  106 , contact sensing assembly  100  provides feedback on the amount of force of an electrode (e.g. electrode  14 ) onto tissue. 
     Those skilled in the art would appreciate in view of this disclosure that various modifications may be made to the aforementioned force and torque sensors without departing from the scope of the invention. 
     For example, for force and torque sensor  16 , more components of force and torque may be measured by using more sensors  28 ,  30 ,  32 . Sensors  28 ,  30 ,  32  may be positioned differently than the arrangement of  FIGS. 2 and 3  (e.g. asymmetrically relative to the central axis of the electrode), or the sensors may be positioned so that their axes of sensitivity are not parallel to the electrode central axis. 
     Further, electrode  14  may also be configured to include a means for irrigating. For example, without limitation, as shown in  FIG. 1 , the incorporation of at least one irrigation port  36  within electrode  14  may provide an irrigated electrode tip. An irrigated electrode tip allows for the cooling of electrode  14 , for instance, through the transporting of fluid through electrode  14  and around the surface of the tissue. A number of different types of electrodes, irrigated and non-irrigated, may be connected and incorporated for use of an electrode  14  according to embodiments of the invention depending on the type of procedures being done. Such irrigated electrodes include, but are not limited to, those disclosed in U.S. patent application Ser. Nos. 11/434,220 (filed May 16, 2006), 10/595,608 (filed Apr. 28, 2006), 11/646,270 (filed Dec. 28, 2006) 11/647,346 (filed Dec. 29, 2006) and 60/828,955 (filed Oct. 10, 2006), each of which is hereby incorporated by reference as though fully set forth herein. 
     The invention further discloses a force-based catheter system  200 , as shown in  FIGS. 6A-6F , that includes assemblies  10  or  100  (note: only assembly  10  illustrated) of the invention connected to a signal converter  210  (such as an analog to digital converter) and an operator interface  220 , which may further include a computer and display, for processing the force signals received from assemblies  10  or  100  in connection with positioning and contact with tissue, such as myocardial tissue  205 . This force-based information is processed to determine the contact force exerted on electrode  14  or the electrode for assembly  100 . A calibration system  230  (i.e., calibration software) may be further provided to readily correlate the pressure or capacitance measurements to the external force or torque on the electrode. A mapping system  240 , such as the Ensite system, also known as NavX®, may be integrated with system  200  to provide a visualization and mapping system for use in connection with assemblies  10  or  100  of the invention. In an alternate embodiment, as shown in  FIGS. 6D-6F , signal converter  210  may be integrated with assemblies  10 ,  100 , such that the force or torque signal is directly processed and provided on operator interface  220 . Overall, each of these components may be modified and/or integrated with one another depending on the design of the force/torque system as recognized by one of ordinary skill in the art. 
     Although several embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of this invention. All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise and counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the invention, and do not create limitations, particularly as to the position, orientation, or use of the invention. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not as limiting. Changes in detail or structure may be made without departing from the invention as defined in the appended claims.