Radio-frequency catheter ablation of cardiac arrhythmias: Appraisal of an evolving therapeutic modality

Abstract

Since its introduction in 1985, there have been numerous reports of the use of radio-frequency (RF) current as an alternative energy source for catheter ablation. RF current (frequency range 150 kHz to 1 MHz), when delivered in bipolar mode, causes desiccation of tissue by creating a localized area of heat that results in discrete coagulation necrosis. An equivalent energy source such as direct current (DC) shock can be delivered at lower power (5 to 30 W) and lower voltage (30 to 80 V) for a longer pulse duration (10 to 60 seconds), thus eliminating barotraumatic effects. Because of its high frequency, RF current does not stimulate neuromuscular fibers, and general anesthesia during ablation is not needed. Studies in animals have shown that catheter-delivered RF energy can safely produce permanent complete or partial AV block, necrosis of atrial and ventricular myocardium adjacent to the mitral and tricuspid anuli potentially suitable for ablation of accessory pathways, and discrete lesions in the left and right ventricular myocardium. Recently, investigators from several centers have reported successful ablation of the AV junction (either complete or partial AV block) in patients with refractory supraventricular tachyarrhythmias, ablation of accessory pathways, and ablation of focal ventricular myocardium or a segment of a bundle branch in patients with drug-resistant ventricular tachycardia. Specific modification of AV conduction to cure AV nodal reentrant tachycardia has been successfully attempted. In all studies the application of RF current has not caused any serious complications. However, the size of lesions is generally smaller as compared with DC ablation when the conventional electrode catheter is used. Delivery of higher power (> 30 W) and longer pulse duration (> 40 seconds) is often limited due to a sudden impedance rise as a result of coagulum formation around the electrode. Increase in lesion size and decrease in impedance rise may be achieved by using a larger electrode or a cooled porous electrode with saline infusion or by the use of a thermistortipped temperature-guided electrode. In conclusion, RF catheter ablation is a safe and useful technique in selected patients with cardiac arrhythmias. It may prove to be a better energy source for modification of AV conduction and for ablation in patients with poor ventricular function.