Temperature and Impedance Monitoring During Slow Pathway Ablation in Patients with AV Nodal Reentrant Tachycardia

INTRODUCTION: Successful radiofrequency ablation of an accessory pathway has been demonstrated to be associated with an electrode-tissue interface temperature of approximately 60 degrees C or an impedance change of -5 to -10 omega. However, the temperature and impedance changes associated with ablation of AV nodal reentrant tachycardia (AVNRT) using the slow pathway approach have not been reported. Therefore, the purpose of this study was to define the temperature and impedance changes achieved during ablation of AVNRT: METHODS AND RESULTS: The study included 35 consecutive patients with AVNRT undergoing radiofrequency ablation of the slow pathway with a fixed power output of 32 W, and using a catheter with a thermistor bead embedded in the distal 4-mm electrode. The procedure was successful in each patient. The steady-state electrode-tissue interface temperature during successful applications of energy was 48.5 +/- 3.3 degrees C (range 42 degrees to 56 degrees C), and the steady-state temperature during ineffective applications was 46.8 degrees +/- 5.5 degrees C (P = 0.03). The mean impedance change during all applications of energy was -1.4 +/- 2.8 omega, and did not differ significantly during effective and ineffective applications. Coagulum formation resulted during five applications (2.7%) in two patients (5.7%). There were no recurrences during 114 +/- 21 days of follow-up. CONCLUSIONS: Successful ablation of AVNRT using fixed power output is achieved at an electrode-tissue interface temperature of approximately 48 degrees C and is associated with a drop in impedance of 1 to 2 omega. These findings suggest that slow pathway ablation requires less heating at the electrode-tissue interface than does accessory pathway or AV junction ablation.