Transmural atrial insulating lesions using epicardially applied radiofrequency energy coupled with saline irrigation

The Maze procedure has been demonstrated to eliminate atrial fibrillation (AF) refractory to medical management. The procedure, however, is technically difficult and requires prolonged cardiopulmonary bypass (CPB). We investigated the use of epicardially applied radiofrequency (RF) energy delivered using a saline-irrigated probe to functionally reproduce the linear lesions of the surgical Maze procedure. The goals of this study were to safely produce transmural atrial insulation lines without CPB and to investigate whether they could retain their electrical insulation properties and structural integrity over an acute time period. Baseline pacing thresholds were measured on the atria of six swine. Then, circular insulating lesions (n = 11) were created around each pacing site using a saline-irrigated RF probe and specifically designed radiofrequency generator. Pacing thresholds were repeated at the same atrial sites, and in adjacent areas, immediately following lesion creation and at 7 days. At sacrifice the areas of interest were removed for histopathology. Pacing thresholds increased from 0.9 +/- 0.09 V to 9.59 +/- 0.87 V immediately following lesion formation (p <.05) and remained supraphysiologic at 4.05 +/- 0.36 V after 7 days (p <.05). Thresholds from outside the lesions were unchanged from baseline. There was no evidence of perforation and histologic analysis demonstrated transmural necrosis with advancing granulation tissue. Our data suggest that epicardially applied RF energy coupled with saline irrigation can produce transmural electrical insulation lines for up to 7 days. However, the decreasing trend in thresholds toward baseline suggests further investigation is needed to verify insulation line continuity over a chronic time period. These lines were created safely and efficiently without CPB, and may be applicable to a minimally invasive Maze procedure.