MYOCARDIAL TEMPERATURE RESPONSE DURING RADIOFREQUENCY CATHETER ABLATION

During radiofrequency catheter ablation, steady-state electrode-tissue interface temperatures are reached within 5 seconds. Within the myoca rdium, however, a much slower temperature rise has been observed in vi tro with stabilization after approximately 2 minutes. This discrepancy suggests that tissue temperature rise time depends on distance from t he ablation electrode and, thus, that temperature rise measured at the electrode-tissue interface does not correspond with temperature rise within the myocardium. In five beagles, closed-chest radiofrequency ca theter ablation was performed in the vicinity of intramural thermocoup les. Sequences of 60 seconds, 10- and 25-watt pulses were delivered in the unipolar mode via the 4-mm distal electrode of a 7 French steerab le catheter. At all distances > 3 mm from the ablation electrode, the rate of myocardial temperature rise was low: relative rise after 5, 10 , 20, and 30 seconds was 22%, 32%, 48%, and 63% of that achieved at 60 seconds, and even then steady-state temperatures had not yet been rea ched. Temperature rise was faster at sites closer to the ablation elec trode. There was no difference in rate of rise between first and secon d pulses at the same site. A 6% higher myocardial temperature was reac hed with a second identical pulse at the same site. Tissue temperature s achieved with 25 watts were 2.4 times higher than with a preceding 1 0-watt pulse at the same ablation site.