Thermal Latency in Radiofrequency Ablation

BACKGROUND: Progression of unintentionally induced atrioventricular delay is occasionally observed directly after termination of radiofrequency delivery in the vicinity of the atrioventricular node. We postulated that the application of a radiofrequency pulse may result in a tissue temperature rise that continues after the pulse. METHODS AND RESULTS: Using the thigh muscle preparation, 5-, 10-, 20-, and 30-second pulses were applied as 30 to 40 W via a standard 4-mm tip electrode with 10-g contact pressure. Forty-one undisturbed pulses were delivered while recording intramural temperatures at 2-, 4-, and 7-mm depth. Maximal "thermal latency" was observed with the shortest pulse duration and at greatest depth. With 5-second applications, tissue temperature at 7-mm depth peaked 11.6 seconds after termination of radiofrequency delivery and stayed above end-of-pulse value as long as 34.5 seconds after the pulse. The additional rise in tissue temperature was 2.9 degrees C. If only recording within the lesion border zone were considered, the duration of latency was maximal with 10-second pulses: an additional gain in tissue temperature of 3.4 degrees C was observed 6.4 seconds after the pulse while tissue temperature stayed above end-of-pulse value during 18.3 seconds. CONCLUSIONS: With relatively short applications, tissue temperature continues to rise after termination of radiofrequency delivery. This "thermal latency" may result in lesion growth after the pulse and may so explain the incidentally observed progression of conduction block after short pulses in the vicinity of the atrioventricular node. It also may explain the apparent discrepancy between lesion growth rate and intramural temperature rise studies.