TEMPERATURE-MEASUREMENT AS A DETERMINANT OF TISSUE HEATING DURING RADIOFREQUENCY CATHETER ABLATION - AN EXAMINATION OF ELECTRODE THERMISTORPOSITIONING FOR MEASUREMENT ACCURACY

Thermometry and Radiofrequency Catheter Ablation. Introduction: Temper ature monitoring has been proposed as a control for lesion occurrence and dimension during radiofrequency transcatheter ablation. Effective temperature measurement depends on thermistor positioning relative to the heated cardiac tissue and the convective cooling effects of the ci rculation. But the accuracy of a single tip thermistor as a measure of peak electrode-tissue interface temperature is unknown. Methods and R esults: A standard 8-French, 4-mm electrode catheter with 5 thermistor s (1 tip thermistor, 4 radial thermistors) was used to deliver radiofr equency energy in vitro to 3 porcine right ventricles and in vivo to 7 mongrel dogs. In vitro, the catheter orientation was varied. In vivo the catheter was positioned under fluoroscopy at a variety of atrial, tricuspid annular, and ventricular sites, with no attempt to adjust ca theter orientation. In both cases varied discrete power levels were us ed so that a wide temperature range was attained. Lesions created in v ivo with a standard, single thermistor tipped electrode were compared to those of a catheter with a thermistor extending 1 mm from the tip. Power was varied and tip thermistor temperatures recorded. All lesions were examined pathologically. Comparisons of radial thermistor temper ature to tip thermistor temperature for 3 catheter orientations in vit ro resulted in tip thermistor underestimation of peak electrode-tissue interface temperature by a median of 0.5 degrees C in 35% of the perp endicular orientations, 1.9 degrees C in 82% of the 45 orientations, a nd 5 degrees C in 83% of the parallel orientations. During in vivo tri als, the tip thermistor underestimated the peak electrode-tissue inter face temperature during 2 of 51 lesions by 1.2 degrees C and 7.6 degre es C. There was a sudden rise in electrical impedance in 17 of 51 radi ofrequency energy deliveries. Only one case was observed where the pea k electrode-tissue interface temperature was below 95 degrees C. The n ormal to extended tip thermistor configurations analysis showed simila r relationships between lesion size and temperature. Conclusions: Accu racy of a single tip thermistor was found to be dependent upon cathete r-tissue orientation. With routine catheter positioning in vivo, the t ip thermistor was a good indicator of peak electrode-tissue interface temperature. Thus with power regulation to avoid temperatures greater than 90 degrees C, a single flush-mounted tip thermistor is probably a dequate for temperature monitoring of lesion formation and avoidance o f impedance rises.