Apparatus and method for creating, maintaining, and controlling a virtual electrode used for the ablation of tissue

A method for ablating tissue of a patient, comprising:

• providing an electrode, a generator for supplying RF energy to the electrode and a return electrode returning RF energy back from the electrode to the generator;
• applying the electrode to a selected tissue to be ablated;
• ablating the selected tissue by supplying RF energy to the electrode at a power level;
• measuring at least one change in impedance to the passage of the RF energy over a predetermined period of time;
• and
• increasing the power level of the RF energy supplied to the electrode by a predetermined amount in response to a measured change in impedance being below a predetermined value.

A method of ablating a target tissue of a body of a patient, the method comprising:

• providing an electrode;
• placing the electrode adjacent the tissue;
• delivering an RF current power to the tissue through the electrode;
• measuring a first impedance of the tissue;
• measuring a second impedance of the tissue following a first predetermined time interval;
• determining a first impedance rate of change of the tissue during the first predetermined time interval, the first impedance rate of change being the difference between the first impedance measurement and the second impedance measurement divided by the first predetermined time interval;
• measuring a third impedance of the tissue following a second predetermined time interval;
• determining a second impedance rate of change of the tissue during the second predetermined time interval, the second impedance rate of change being the difference between the second impedance measurement and the third impedance measurement divided by the second predetermined time interval;
• determining an average impedance rate of change of the tissue, the average rate of change being the average of the first impedance rate of change and the second impedance rate of change;
• and
• adjusting the delivery of RF current power to the tissue in response to the determined average impedance rate of change.

A method of ablating a target tissue of a body of a patient, the method comprising:

• providing an electrode;
• placing the electrode adjacent the tissue;
• delivering an RF current power to the tissue through the electrode;
• measuring a first impedance of the tissue;
• measuring a second impedance of the tissue following a first predetermined time interval;
• determining a first impedance rate of change of the tissue during the first predetermined time interval, the first impedance rate of change being the difference between the first impedance measurement and the second impedance measurement divided by the first predetermined time interval;
• measuring a third impedance of the tissue;
• measuring a fourth impedance of the tissue following a second predetermined time interval;
• determining a second impedance rate of change of the tissue during the second predetermined time interval, the second impedance rate of change being the difference between the third impedance measurement and the fourth impedance measurement divided by the second predetermined time interval;
• determining an average impedance rate of change of the tissue, the average rate of change being the average of the first impedance rate of change and the second impedance rate of change;
• and
• adjusting the delivery of RF current power to the tissue in response to the determined average impedance rate of change.