Acute and Chronic Electrophysiologic Changes Surrounding Radiofrequency Lesions

INTRODUCTION: Arrhythmia recurrences may occur after acutely successful radiofrequency (RF) ablation, suggesting reversible electrophysiologic effects on myocardial tissue. The aim of this study was to examine the electrophysiologic changes occurring in myocardium surrounding acute and chronic RF lesions. METHODS AND RESULTS: RF lesions (60 degrees C for 30 sec) were produced on the epicardial left ventricular surface of 35 isolated perfused rabbit hearts. Microelectrode transmembrane action potential recordings were made at 0.25-mm intervals along the epicardial (n = 20) or intramural (n = 6) aspects of the lesions for up to 3.5 mm from the lesion edge at baseline and after acute RF lesion formation. In nine hearts, chronic lesions were studied with epicardial recordings made 22 +/- 13 days after RF lesion formation. In the acute hearts at 600-msec paced cycle length, action potential duration at 50% repolarization (APD50) and 90% repolarization (APD90) were reduced by up to 41% and 19%, respectively, within 2.5 mm from the lesion edge (all P < 0.05). Maximal action potential amplitude (APDmax) was reduced by 16% at 0.25 mm from the lesion edge (P = 0.009) but dV/dt was not changed. Conduction time (CT) from the outermost recording site to the lesion edge (3.5-mm distance) was reduced from 16 +/- 3 msec at baseline to 13 +/- 4 msec post ablation (P = 0.006). Qualitatively similar findings occurred at 200-msec cycle lengths. There were no changes in APD, CT, APDmax, or dV/dt surrounding the chronic lesions at 22 +/- 13 days after lesion formation. CONCLUSION: Acutely following RF energy delivery, APD, APDmax, and CT are reduced in the tissue surrounding the lesion. These electrophysiologic changes resolve within 22 +/- 13 days of lesion formation.