ROLE OF POWER AND THERMAL REGULATION IN R ADIOFREQUENCY ABLATION

Variations of temperature, impedance and power and the relationship be tween these three factors were studied in 20 patients during 351 appli cations of radiofrequency energy delivered by a generator with a regul ated output power. The applications were divided into 3 groups accordi ng to the maximal temperature attained: group I (< 50 degrees C;n = 11 2), group II (50-60 degrees C;n = 100), and group III (60-70 degrees C ;n = 139).Analysis of the total duration of time of applications (aver age +/- standard deviation) showed : the duration (seconds) was 23.9 /- 11.9 seconds for group I, 36.1 +/- 18.7 seconds for group II and 45 +/- 23.6 seconds for group III. The time to attain maximal temperatur e was 6.8 +/- 9.6 seconds in group I, 11.7 +/- 12.7 in group II and 10 +/- 10.4 seconds in group III. The impedance remained under 200 Omega in all applications, the target temperature being set at 70 degrees C . Analysis of the first three seconds of application : correlations co efficients between temperature and Impedance were -0.08 (p < 0.001) in group I and -0.23 (p < 0.0001) in groups II and III. These coefficien ts were recalculated with respect to the average power delivered durin g the applications : < 40 watts (n = 79), r = -0.33; < 30 watts (n = 5 5), r = -0.41; < 20 watts (n = 33), r = 0.49 and < 10 watts (n = 15), r = -0.7 (p < 0.0001). The authors conclude that radiofrequency genera tors with thermal regulation allow early interruption of ineffective a pplications of radiofrequency and avoid increases in impedance. The po or correlations observed between increase in temperature (measured at the tip of the catheter) and the fall in impedance (related to tissue heating) for the first 3 groups, show that temperature alone is not a good indicator of contact. The improvement of the correlations for dec reasing output power applications indicates better thermal transfer be tween the electrode and endocardium. Therefore a low power delivered i n the first seconds at > 50 degrees C is to be interpreted as a marker of the quality of contact and a predictive factor of efficacy.