Animal studies of epicardial atrial ablation

Abstract

The Cox-Maze procedure is an effective treatment for atrial fibrillation with a long-term freedom from recurrence of >90%. The original procedure was highly invasive and required cardiopulmonary bypass (CPB). Modifications of the procedure have been proposed so that the procedure can be done without CPB. These approaches proposed to use alternative energy sources, to replace cut and sew lesions with lines of ablation, made from the epicardium on the beating heart. This has been challenging because the atrial wall muscle thickness is extremely variable and can be covered with an epicardial layer of fat. Moreover, the circulating intracavitary blood acts as a potential heat sink, making transmural lesions difficult to obtain. In this report, we summarize the use of nine different unidirectional devices to create continuous transmural lines of ablation from the atrial epicardium in a porcine model. We define a unidirectional device as one in which all the energy is applied by a single transducer on a single heart surface. These include four radiofrequency, two microwave, two lasers, and one cryothermic device. The maximum penetration of any device was 8.3 mm. All devices except one, the Atricure IsolatorT pen, failed to penetrate 2.0 mm in some non-transmural sections. Future development of unidirectional energy sources should be directed at increasing the maximum depth and the consistency of penetration.

2012 HRS/EHRA/ECAS Expert Consensus Statement on Catheter and Surgical Ablation of Atrial Fibrillation: Recommendations for Patient Selection, Procedural Techniques, Patient Management and Follow-up, Definitions, Endpoints, and Research Trial Design

“…1162,1291,1292 Moreover, both unipolar and directional bipolar energy sources have had difficulty creating transmural lesions when used from the epicardial surface on the beating heart. 1293,1294,1295,1296,1297,1298 This difficulty occurs because the circulating intracavitary blood pool produces convective cooling, which makes transmural lesions difficult to achieve. 1299 In an attempt to obviate this problem, one device provides suction to pull two walls of atrial tissue into apposition in a shallow trough, thus excluding the circulating heat sink of intracavitary blood while the energy is applied.…”

2012 HRS/EHRA/ECAS expert consensus statement on catheter and surgical ablation of atrial fibrillation: recommendations for patient selection, procedural techniques, patient management and follow-up, definitions, endpoints, and research trial design

“…Since most of these ablation systems were released clinically without dose-response studies, their use has led to occasional collateral cardiac and extracardiac damage [575,668,669]. Moreover, unipolar energy sources have had difficulty creating transmural lesions when used from the epicardial surface on the beating heart [670][671][672][673][674][675]. This is because the circulating intracavitary blood pool makes transmural lesions difficult to achieve [676].…”

Minimally invasive surgery for atrial fibrillation

“…Finally, monopolar RF devices have been used as adjunctive energy sources, although caution should be used due to inconsistent lesion transmurality (18) and the risk of complications resulting from thermal spread, including coronary artery and esophageal injury (19,20). …”