Electrophysiological and histological assessment of transmurality after epicardial ablation using unipolar radiofrequency energy.

Abstract

BACKGROUND: The transmurality of the ablation lesions created on a beating heart has not been examined histologically or electrophysiologically. This study aimed to assess the feasibility of an atrial epicardial or endocardial ablation in an off-pump setting using unipolar radiofrequency (RF) energy. METHODS: A linear ablation lesion of 5 cm was made in the lateral left atrium using unipolar RF energy with a temperature-controlled algorithm in 16 canines either epicardially (n=8) or endocardially (n=8) on the beating heart without any cardiopulmonary bypass. The ablation depth and transmurality were examined histologically two hours after the ablation. A conduction block across the linear ablation lesion was tested by epicardial mapping in two animals four weeks after each epicardial and endocardial ablation. RESULTS: There was no significant difference in the ablation depth between the epicardial and endocardial ablations (2.5+/-0.7 mm vs. 3.0+/-1.4 mm, p=0.055) in the histological examination. However, the ablation lesion was transmural in only 14 of 30 (46.7%) evaluated points after the epicardial ablation, while in 28 of 30 (93.3%) after the endocardial ablation (p<0.0001). The thin atrial tissue adjacent to the endocardium survived after the epicardial ablation. The activation maps demonstrated a complete linear conduction block in all animals after the endocardial ablation, but in none after the epicardial ablation. CONCLUSIONS: Epicardial unipolar radiofrequency ablation on the beating heart does not necessarily create a complete linear conduction block. An alternative ablation device that creates a transmural lesion is needed, and intraoperative electrophysiologic assessment of the lesion should be crucial in off-pump AF surgery.