RELATION BETWEEN IMPEDANCE AND TEMPERATURE DURING RADIOFREQUENCY ABLATION OF ACCESSORY PATHWAYS

Temperature monitoring is a useful tool for radiofrequency ablation of accessory pathways. Impedance monitoring is also helpful, and an impe dance fall of 20 ohm may predict coagulum formation. Therefore the pur pose of this study was to prospectively quantitate the correlation bet ween impedance and temperature during radiofrequency ablation. Thirty- three consecutive patients underwent radiofrequency ablation with a th ermistor ablation catheter with continuous temperature and impedance m onitoring during each energy application. The initial and final impeda nce and temperature measurements for 319 applications of radiofrequenc y energy were 109 +/- 17 ohm and 102 +/- 17 ohm (p < 0.0001), respecti vely, and 37 +/- 1 degrees C and 57 degrees +/- 11 degrees C (p < 0.00 01), respectively. Among the 319 applications of radiofrequency energy , 158 were associated with greater than or equal to 20 degrees C incre ase in tissue temperature, and 10 were associated with coagulum format ion. A greater than or equal to 20 degrees C increase in tissue temper ature was observed in 84 of 104 applications associated with a 5 to 10 ohm decrease in impedance (81% positive predictive value and 93% nega tive predictive value). The mean change in impedance for applications associated with and without coagulum formation was -19 +/- 7 ohm and - 6 +/- 6 ohm (p < 0.0001), respectively, and coagulum formation never o ccurred with less than a 12 ohm decrease. In conclusions successful ti ssue heating without coagulum formation can he achieved by titrating t he power to achieve a 5 to 10 ohm decrement in impedance. Impedance de crements beyond 10 ohm increase the likelihood of coagulum formation.