System and method for measuring subsurface temperature of tissue during ablation

A system for ablating tissue and estimating the surface and maximum subsurface temperature of said tissue comprising:

• a split tip electrode catheter comprising:
• an elongated catheter body having a proximal and distal end and at least one lumen extending therethrough;
• a catheter tip section at the distal end of the catheter body comprising a section of flexible tubing having proximal and distal ends and at least one lumen therethrough, the proximal end of the flexible tubing being fixedly attached to the distal end of the catheter body, said catheter tip section further comprising a split tip electrode which comprises at least two electrically isolated electrode members fixedly attached to the distal end of the flexible tubing each electrode member comprising at least one irrigation passage;
• at least one indifferent electrode attachable to the exterior of a patient;
• means for generating a low level RF impedance current and for transmitting said impedance current to each electrode member of the split tip electrode;
• means for generating an RF ablation current and for transmitting said ablation current to each electrode member of the split tip electrode;
• means for electrically connecting each electrode member of the split tip electrode to the low level RF impedance current generating means and the RF ablation current generating means;
• means, including a pump, for infusing a cooling fluid through the catheter and each of the electrode members to cool the electrode members during ablation;
• temperature sensing means, attached to each electrode member of the split tip electrode, for generating a signal indicative of the temperature of the electrode member to which it is attached;
• means for receiving electrical signals indicative of the impedance between each electrode member and the at least one indifferent electrode during the transmission of RF ablation current and for separating such impedance indicating signals from other signals received;
• and
• signal processing means, electrically connected to the RF impedance current generating means, the RF ablation current generating means, the pump of the infusing means, each of the electrode members of the split tip electrode, the at least one indifferent electrode, the temperature sensing means and the signal receiving means, for activating the RF impedance generating means to transmit an impedance current to each of the electrode members of the split tip electrode, for receiving electrical signals indicative of the impedance between each of the electrode members of the split tip electrode and the at least one indifferent electrode and for identifying the electrode member(s) associated with the highest impedance signal(s) received as the electrode member(s) in contact with tissue, and thereafter for intermittently activating the pump of the infusing means and the RF ablation current generating means so that there are ON periods wherein cooling fluid is delivered to the electrode members and RF ablation current is transmitted to the identified tissue-contacting electrode members and OFF periods wherein no cooling fluid is delivered to the electrode members and no RF ablation energy is transmitted to the identified tissue-contacting electrode members for estimating the surface temperature of tissue in contact with the electrode members from the signals received from the temperature sensing means during the OFF periods, for activating the RF impedance current generating means to transmit impedance current to the electrode members of the split tip electrode during at least the ON periods and for estimating the maximum subsurface temperature of tissue heated by the RF ablation current from the received impedance-indicating signals.

A method for ablating tissue and for estimating the increase in subsurface temperature of tissue at an ablation site during an ablation procedure comprising:

• providing a split tip electrode catheter comprising:
• an elongated catheter body having a proximal and distal end and at least one lumen extending therethrough;
• a catheter tip section at the distal end of the catheter body comprising a section of flexible tubing having proximal and distal ends and at least one lumen therethrough, the proximal end of the flexible tubing being fixedly attached to the distal end of the catheter body, said catheter tip section further comprising a split tip electrode which comprises at least two electrically isolated electrode members fixedly attached to the distal end of the flexible tubing;
• introducing the catheter into a lumen in the body of a patient and positioning the catheter so that at least one electrode member of the split tip electrode is in contact with the tissue to be ablated and at least one other electrode member of the split tip electrode is only in contact with the blood pool;
• positioning at least one indifferent electrode on the patient;
• transmitting an RF ablation current to at least one tissue-contacting electrode member of the split tip electrode;
• transmitting a low level RF impedance current through the at least one tissue contacting electrode member of the split tip electrode during transmission of RF ablation current to the at least one tissue-contacting electrode member;
• monitoring the impedance between the at least one tissue-contacting electrode member and the at least one indifferent electrode and the impedance between the at least one non-tissue-contacting electrode member and the indifferent electrode;
• and
• estimating the increase in subsurface tissue temperature from the change in the difference between the impedance associated with the at least one tissue-contacting electrode member and the impedance associated with the at least one non-tissue-contacting electrode member.