[Biophysical aspects of high frequency catheter ablation. Studies of the significance of sudden changes in impedance].

Unlabelled: To determine the effects and the underlying mechanisms of sudden rise of impedance during radiofrequency (RF) catheter ablation, 60 RF applications were delivered to isolated preparations of ventricular myocardium at three different power levels (mean: 3.7, 11.3, 19.3 watts). Pulse duration was 30 s, current voltage and catheter tip temperature were continuously monitored. Impedance rise occurred during 34 of 60 applications; the incidence of impedance rise increased at higher power levels. Impedance rise was significantly more often observed when the preparations were superfused with heparinized blood compared to saline solution (p less than 0.05). Catheter-tip temperature during radiofrequency application without impedance rise was significantly lower compared to applications with impedance rise (mean = 108 degrees C vs. 121 degrees C, p less than 0.01). The increase of catheter-tip temperature and maximal-tip temperature following impedance rise was significantly higher in blood when compared to saline solution (mean = +48 degrees C vs. +13 degrees C (p less than 0.001), Tmax: 121 degrees C vs. 245 degrees C). Following impedance rise, insulation defects of the electrode catheter and vaporized crater formation of the myocardium was often observed.
Conclusions: During radiofrequency catheter ablation impedance rise occurs following overheating of the catheter electrode (greater than 110 degrees C). After impedance rise, catheter-tip temperature markedly increases. Insulation defects of the catheter and vaporized craters in the myocardium frequently occur after impedance rise. The results have important implications for the clinical use of RF-currents for catheter ablation; energy application should be immediately stopped after the occurrence of impedance rise.