Tuned rf energy for selective treatment of atheroma and other target tissues and/or structures

Abstract

A catheter and catheter system can use energy tailored for remodeling and/or removal of target material along a body lumen, often of atherosclerotic material of a blood vessel of a patient. An elongate flexible catheter body with a radially expandable structure may have a plurality of electrodes or other electrosurgical energy delivery surfaces to radially engage atherosclerotic material when the structure expands. An atherosclerotic material detector system may measure and/or characterize the atherosclerotic material and its location, optionally using impedance monitoring.

1 . A catheter system for remodeling a tissue adjacent a blood vessel, the system comprising:
 a catheter including an elongate flexible catheter body having a proximal end and a distal end with an axis therebetween, a radially expandable support structure disposed near the distal end of the catheter body, and a plurality of electrodes disposed on the radially expandable support structure for engaging a luminal wall of the blood vessel;   a power source coupled to the electrodes such that, when the one or more electrodes engage the luminal wall and energized by the power source, the power source, the electrode, and engaged luminal wall defines an electrical circuit;   a processor coupled with the power source, the processor configured to control delivery of remodeling energy from the power source to the target tissue adjacent the blood vessel while inhibiting collateral tissue damage by monitoring and controlling a temperature of the electrical circuit.   
     
     
         2 . The system of  claim 1 , wherein the plurality of electrodes are distributed circumferentially about the support structure to define an electrode array. 
     
     
         3 . The system of  claim 2 , wherein the processor is configured to remodel the tissue with the electrode array by energizing a subset of the electrodes with the remodeling energy. 
     
     
         4 . The system of  claim 2 , wherein the electrodes are axially offset on the radially expandable support structure. 
     
     
         5 . The system of  claim 2 , wherein the electrode array comprises a plurality of bipolar electrode pairs. 
     
     
         6 . The system of  claim 2 , wherein the power source comprises a variable frequency power source, and wherein the processor is configured to regulate the remodeling energy in response to a measurement of impedance phase angle. 
     
     
         7 . The system of  claim 6 , wherein the processor, in response to feedback signals generated by monitoring the phase angle, alters the delivery of the remodeling energy to the target tissue. 
     
     
         8 . The system of  claim 7 , wherein the processor is configured to respond to feedback on the target tissue by monitoring a characteristic of the electrical circuit after applying at least a portion of the therapeutic energy. 
     
     
         9 . The system of  claim 8 , wherein the processor is configured to halt the remodeling energy in response to a change in at least one of temperature, frequency range, impedance magnitude, impedance phase angle of the circuit, the change associated with heating of tissue to 62° C. or more. 
     
     
         10 . The system of  claim 9 , wherein the variable frequency power source generates bipolar RF energy, and wherein a frequency range of the variable frequency power source extends from below about 50 KHz to over 1 MHz. 
     
     
         11 . The system of  claim 6 , wherein the processor is further configured to determine a specific frequency or range of frequencies at which the target tissue is more conductive by monitoring the temperature and/or frequency-dependent characteristic of the electrical circuit. 
     
     
         12 . The system of  claim 11 , wherein the processor is configured to selectively heat the target tissue adjacent the body lumen while inhibiting injury to collateral tissue by applying energy in a range of frequencies for which the target tissue is more conductive. 
     
     
         13 . The system of  claim 1 , wherein the processor is configured to control energy delivery as a closed loop control system, wherein inputs to the closed loop control system include tissue impedance and/or temperature change. 
     
     
         14 . The system of  claim 1 , wherein the processor is configured so that dosage of energy delivery is controlled using dynamic measurement of change in temperature of tissue contacting the catheter. 
     
     
         15 . The system of  claim 1 , wherein the processor is configured to asymmetrically deliver energy of differing power levels to differing bipolar pairs of the electrodes. 
     
     
         16 . The system of  claim 1 , wherein the processor is configured to deliver pulsed energy. 
     
     
         17 . The system of  claim 1 , wherein the processor is configured to control delivery of energy so as to provide tissue temperatures in a range between 55° C. and about 80° C. 
     
     
         18 . The system of  claim 1 , wherein the processor is configured so that energy delivery includes multiple bursts of the same frequency. 
     
     
         19 . The system of  claim 1 , wherein the processor is configured to control delivery of energy by energizing differing electrodes according to a duty cycle. 
     
     
         20 . A system for remodeling a tissue material adjacent a body lumen, the system comprising:
 an elongate flexible catheter body having a proximal end and a distal end with an axis therebetween;   a radially expandable member disposed near the distal end and supporting a plurality of electrodes distributed circumferentially about the axis to define an electrode array for engaging the lumen wall; and   a power source electrically coupled to the plurality of electrodes and configured to energize the electrodes with a remodeling energy that heats the tissue material and inhibits damage of collateral tissues.   
     
     
         21 . A method for remodeling of a tissue adjacent a body lumen, the method comprising:
 engaging a vessel wall of a blood vessel with a radially expandable array of electrodes supported by an expandable member near a distal end of a catheter, the electrodes being circumferentially distributed and axially offset;   energizing the engaged electrodes with a power source so as to define an electrical circuit with the power source, the electrodes and the engaged vessel wall; and   remodeling the tissue by delivering a controlled remodeling energy to the tissue with the electrodes so as to heat the tissue with the remodeling energy while inhibiting damage to collateral tissues.   
     
     
         22 . The method of  claim 21  wherein delivering remodeling energy with the electrodes comprises energizing selected electrodes of the array with bipolar RF energy. 
     
     
         23 . The method of  claim 21  wherein the remodeling energy is controlled by monitoring and controlling a characteristic of the electrical circuit. 
     
     
         24 . The method of  claim 23  wherein the characteristic comprises a temperature of the electrical circuit. 
     
     
         25 . The method of  claim 23  wherein the characteristic comprises a load impedance. 
     
     
         26 . The method of  claim 21  wherein delivery of remodeling energy is controlled so as to provide tissue temperatures in a range between 55° C. and about 80° C.