impedance monitoring during radiofrequency catheter ablation in humans radiofrequency catheter ablation of accessory pathways and the atrioventricular junction often requires multiple applications of energy the inability to determine the effects of any given application on the underlying tissue may contribute to this problem in the present study impedance was monitored in 20 patients undergoing radiofrequency catheter ablation and the relationship between an initial decrease in impedance and subsequent effects were examined an initial fall in impedance of more than 10 omega was 78 sensitive and 88 specific for predicting subsequent evidence of tissue heating interruption of conduction or an abrupt rise in impedance due to coagulum formation in contrast initial values of voltage current or impedance did not distinguish between effective and ineffective applications of radiofrequency energy continuous monitoring of impedance may facilitate radiofrequency catheter ablation