Sequential change in action potential of rabbit epicardium during and following radiofrequency ablation

Introduction: Although radiofrequency (RF) catheter ablation is used to treat certain cardiac arrhythmias, little is known regarding transient changes in cellular electrophysiology during and following RF delivery. Optical recordings of action potential (OAP) with voltage-sensitive dyes allow immunity from electrical noise during RF delivery. The purpose of this study was to clarify the possible synergistic effects of both the thermal and electrotonic components of RF ablation. Methods and Results: In this study, OAPs were recorded on the epicardium of 16 isolated Langendorff-perfused rabbit hearts within or adjacent to lesions made by RF catheters. Hearts were perfused at room temperature with Tyrode's solution containing 2,3- butanedione monoxime and stained by the voltage-sensitive dye di-4-ANEPPS. OAPs were recorded before, during, and after RF pulses. Within the lesion, the action potential duration at 80% repolarization (APD₈₀) of OAP decreased rapidly during the RF pulse, without recovery following the pulse. In the border zone surrounding the lesion, the RF energy resulted in a rapid decrease in APD₈₀, which recovered promptly after the pulse (recovery time constant: 82 ± 37 sec). APD₈₀ was nonlinearly related to temperature during the RF ablation and responded faster to RF ablation than to purely thermal injury. Conclusion: The application of RF energy results in significant changes in myocardial cellular electrophysiologic properties. The RF energy has a combination of thermal and electrotonic effects on the myocardial tissue. The results of this in vitro study may illustrate the cellular basis for commonly observed phenomena in clinical practice.