Ablation electrodes with capacitive sensors for resolving magnitude and direction of forces imparted to a distal portion of a cardiac catheter

Abstract

A catheter assembly for assessing contact between the catheter assembly and tissue is disclosed. In an exemplary embodiment the assembly includes a catheter shaft and a trio of pressure sensitive capacitive members each of whose electrical resistance varies with a pressure vector applied to the catheter assembly. The assembly also includes at least one measurement terminal to permit the measurement of changes in the electrical characteristics of the pressure sensitive capacitive members. The assembly may optionally include a measurement device to measure resistance, impedance and/or other electrical characteristics. The assembly may utilize a reference electrode secured to the patient's tissue, which permits the measurement device to measure changes between the reference electrode and the at least one measurement terminal. Optionally, the assembly may include a conductive outer layer. Also disclosed are sensor assemblies, contact sensor, methods of contact sensing, and methods of manufacturing relating to the use of pressure sensitive capacitors.

1 . A system for estimating magnitude and direction of a force applied to an object, the system comprising:
 a sensor including:   a housing adapted for assembly to the object,   at least three capacitive sensing components retained by the housing and each including:   a first electrode plate,   a second electrode plate arranged parallel to and spaced from the first electrode plate to form a capacitor,   wherein the housing retains the first and second electrode plates such that the first electrode plate is movable relative to the second electrode plate in response to a force placed upon the housing in establishing a variable gap therebetween;   
       an energy source electrically connected to the sensing components; and
 a detector electrically connected to the sensing component; 
 wherein the energy source delivers energy to the sensing components and the detector receives an output signal affected by the sensing components, the output signal varying as a function of a size of the gap associated with each of the sensing components such that the output signal is indicative of a magnitude and direction of a force placed upon the housing. 
 
     
     
         2 . A system according to  claim 1 , further comprising:
 at least three inductors electrically connected to respective ones of the sensing components.   
     
     
         3 . A system according to  claim 2 , wherein the sensing components and the inductors combine to define an LC circuit generating the output signal. 
     
     
         4 . A system according to  claim 3 , wherein the detector is an impedance detector. 
     
     
         5 . A system according to  claim 4 , wherein the impedance detector determines voltage versus frequency information in the output signal, with the voltage versus frequency information being indicative of magnitude and direction of a force placed upon the housing. 
     
     
         6 . A system according to  claim 5 , wherein the impedance detector further determines phase versus frequency information in the output signal, with the phase versus frequency information being indicative of direction. 
     
     
         7 . A system according to  claim 5 , wherein the energy source is adapted to apply a sweeping voltage to the sensing components. 
     
     
         8 . A system according to  claim 2 , wherein the sensor further includes a first common electrode assembled to the housing and electrically connected to the first electrode plate of each of the sensing components, and respective ones of the inductors are electrically connected to the second electrode plate of the corresponding sensing component. 
     
     
         9 . A system according to  claim 8 , wherein the sensing components each further include:
 a contact pad electrically coupled to the corresponding second electrode plate;   wherein the contact pads are retained by the housing in an electrically isolated manner.   
     
     
         10 . A system according to  claim 1 , wherein the housing includes:
 an upper housing structure maintaining the first electrode plate of each of the sensing components; and   a lower housing structure maintaining the second electrode plate of each of the sensing components;   wherein the upper housing structure is assembled to the lower housing structure to complete the housing.   
     
     
         11 . A system according to  claim 10 , wherein the upper and lower housing structures are formed of a polymer material. 
     
     
         12 . A system according to  claim 1 , wherein the housing has a cylindrical ring shape. 
     
     
         13 . A system for use in surgical procedures performed on a human body, the system comprising:
 a surgical instrument including an elongate body terminating at a distal end;   a sensor assembled to the instrument proximate the distal end for sensing forces applied to the distal end, the sensor comprising:   a housing,   at least three capacitive sensing components retained by the housing and each including:   a first electrode plate,   a second electrode plate arranged parallel to and spaced from the first electrode plate to form a capacitor,   wherein the housing retains the first and second electrode plates such that the first electrode is movable relative to the second electrode plate in response to a force placed upon the housing in establishing a variable gap therebetween a size of which varies as a function of a force applied to the distal end;   an energy source electrically connected to the sensing components; and   a detector electrically connected to the sensing components;   wherein the energy source delivers energy to the sensing components, and the detector receives an output signal affected by the sensing components, and further wherein the output signal varies as a function of a size of the gap associated with each of the sensing components such that the output signal is indicative of a magnitude and direction of a force applied to the distal end.   
     
     
         14 . A system according to  claim 13 , wherein the elongate body comprises a tubular structure having a central lumen, and further wherein the sensor has a cylindrical ring shape forming a central bore, and even further wherein upon final assembly, the central lumen and the central bore are axially aligned. 
     
     
         15 . A system according to  claim 14 , wherein the elongate body is selected from the group consisting of a cannula and a catheter. 
     
     
         16 . A system according to  claim 13 , further including at least three inductors electrically connected to respective ones of the sensing components. 
     
     
         17 . A system according to  claim 16 , wherein the sensing components and the inductors combine to define an LC circuit generating the output signal. 
     
     
         18 . A system according to  claim 17 , wherein the impedance detector determines voltage versus frequency information in the output signal, with the voltage versus frequency information being indicative of magnitude and direction. 
     
     
         19 . A system according to  claim 16 , wherein the sensor further includes a first common electrode assembled to the housing and electrically connected to the first electrode plate of each of the sensing components, and further wherein respective ones of the inductors are electrically connected to the second electrode plate of the corresponding sensing component. 
     
     
         20 . A method of determining a magnitude and direction of a force applied to an object, the method comprising:
 applying energy to a sensor assembled to the object, the sensor comprising:   a housing,   at least three capacitive sensing components retained by the housing and each including:   a first electrode plate,   a second electrode plate arranged parallel to and spaced from the first electrode plate to form a capacitor,   wherein the housing retains the first and second electrode plates such that the first electrode plate is movable relative to the second electrode plate in response to a force placed upon the housing in establishing a variable gap therebetween;   subjecting the object to a force of unknown magnitude and direction, wherein the force is transferred to the housing via the object and is sufficient to cause a change in a size in the gap associated with at least one of the sensing components;   receiving an output signal from the sensor, the output signal being affected by the sensing components; and   analyzing the output signal to determine magnitude and direction of the force.   
     
     
         21 . A method according to  claim 20 , wherein the applied energy comprises a sweeping voltage and the output signal includes voltage versus frequency information indicative of a current across each of the sensing components, and further wherein analyzing the output signal includes designating a change in a frequency pitch of the voltage versus frequency information as being collectively indicative of magnitude and direction of the applied force. 
     
     
         22 . A method according to  claim 21 , wherein analyzing the output signal further includes:
 plotting the voltage versus frequency information as a curve;   correlating individual spikes in the curve with respective ones of the sensing components;   establishing a baseline frequency value for each of the sensing components; and   comparing a currently-reviewed spike with the corresponding baseline value.   
     
     
         23 . A method according to  claim 22 , wherein a difference in a currently-reviewed spike relative to a corresponding baseline value is indicative of magnitude, and differences between each of the currently-reviewed spikes is indicative of direction. 
     
     
         24 . A method according to  claim 23 , wherein the sensing components are arranged relative to one another to define a circular shape. 
     
     
         25 . A method according to  claim 21 , wherein an inductor electrically couples to respective ones of the sensing components, the inductors and the sensing components combining to define an LC circuit generating the output signal. 
     
     
         26 . A method according to  claim 20 , wherein the object comprises a surgical instrument and the method is performed as part of a surgical procedure. 
     
     
         27 . A method according to  claim 26 , wherein the surgical instrument is selected from the group consisting of a cannula and a catheter.