EFFECTS OF HEATING WITH RADIOFREQUENCY POWER ON MYOCARDIAL IMPULSE CONDUCTION - IS RADIOFREQUENCY ABLATION EXCLUSIVELY THERMALLY MEDIATED

Introduction: Although it is generally accepted that radiofrequency (R F) ablation causes exclusively thermally mediated effects, it has neve r been proved, Methods and Results: In a previous report, temperatures required to induce conduction block in superfused canine epicardial v entricular myocardium were identified by exposure to heated superfusat e: 50.3 degrees +/- 1,1 degrees C and, 53.6 degrees +/- 0,6 degrees C for transient and permanent block, respectively, In the present study, heating was performed using RF power in an otherwise identical model, Nine preparations from four dogs were used, A l-cm diameter electrode was placed beneath the center of each preparation for RF delivery, In cisions were made to create a conductive isthmus over the ablation ele ctrode, Preparations were paced to one side of the isthmus and electro grams recorded from the center of the isthmus and to either side, Temp erature was measured using a miniature thermocouple located just below the epicardial surface, adjacent to the recording electrode in the he ated zone, RF was delivered for 30 seconds at 5-minute intervals with increments in power per episode causing increments in temperature of a pproximately 2 degrees C, Temperature during pulses at which transient block occurred was 50.7 degrees +/- 3,0 degrees C; temperature at 30 seconds of heating in pulses leading to permanent block was 58.0 degre es +/- 3,4 degrees C, Conclusion: These findings provide evidence sugg esting that the electrophysiologic effects of RF ablation are exclusiv ely thermally mediated and are otherwise unrelated to the dissipation of high-frequency current.