Apparatus and method for predicting ablation depth

Abstract

During an ablation procedure in a chamber of the heart RF energy is used to form a myocardial lesion for treatment of some arrhythmias such as sustained supraventricular tachycardia and accessory pathways. A galvanic cell formed by a metallic electrode having a first work function at the ablation site, a second metallic electrode having a second work function located remote from the ablation site and the intervening tissue serving as an electrolyte, produces an output current signal reflective of the formation of a lesion at the ablation site and is used to control the RF energy applied. A curve depicting the output current signal has a maximum value at the point a burn or lesion formation and thereafter decreases in value. A short duration inflection or bump of the curve occurs prior to charring and carbonization of the lesion. A further curve representative of the impedance of the tissue between the electrodes is displayed; it shows a rapid impedance rise upon occurrence of carbonization and charring of the tissue. The impedance rise occurs after the bump of the output current signal occurs. By terminating application of RF power after occurrence of the bump, and before impedance rise charring of the tissue and other negative results will not occur. A physician can use the bump and the impedance rise as limit indicators for determining lesion formation of a predictable depth without incurring unwanted damage.