Correlation of Temperature and Pathophysiological Effect During Radiofrequency Catheter Ablation of the AV Junction

BACKGROUND: Accelerated junctional rhythms have been observed before the development of AV nodal block during radiofrequency (RF) catheter ablation of the AV junction. However, the time course and temperatures required to induce an accelerated junctional rhythm and AV nodal block during this procedure have not yet been characterized. METHODS AND RESULTS: Nineteen patients underwent RF ablation of the AV junction with a thermistor ablation catheter. RF energy was initially delivered at 10 W for 9 seconds and then increased by 5-W increments for 9 seconds at each power level up to a maximum power of 50 W. If a junctional rhythm was observed during the power titration, a 30- to 60-second RF application was then delivered at the same power level. The power was then further increased to a maximum of 50 W if AV nodal block was not observed after 20 seconds of RF delivery. The procedure was successful in all 19 patients. A median of one RF application (range, one to eight applications) was required to produce permanent AV nodal block. An accelerated junctional rhythm was observed during 89% of successful attempts versus 70% of unsuccessful deliveries (P = NS). The median time to onset of the junctional rhythm was significantly shorter during successful compared with unsuccessful applications (1.8 versus 7.7 seconds, respectively; P < .001). Similarly, the mean time to appearance of AV nodal block was significantly shorter during successful compared with unsuccessful attempts (19.6 +/- 9.4 versus 36.8 +/- 19.0 seconds, respectively; P < .01). The catheter tip temperatures associated with the development of an accelerated junctional rhythm were significantly lower than those associated with the appearance of AV nodal block (51 +/- 4 degrees C versus 58 +/- 6 degrees C, respectively; P < .001). Mean temperatures in the range of 60 +/- 7 degrees C were required to produce permanent AV nodal block. CONCLUSIONS: The development of an accelerated junctional rhythm within 5 seconds and the appearance of AV nodal block within 30 seconds of RF onset were both highly characteristic of successful target sites during RF ablation of the AV junction. The accelerated junctional rhythm and AV nodal block were both highly temperature dependent. The temperatures associated with the onset of AV nodal block were significantly higher than the temperatures resulting in an accelerated junctional rhythm.