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Caval Occlusion Improves Performance of Beating Heart Epicardial Radiofrequency Ablation
Yoshiyuke Watanabe, MD, PhD1, Matthew R. Schill, MD2, Toshinobu Kazui, MD, PhD3, Richard B. Schuessler, PhD2, Ralph J. Damiano, Jr, MD2.
1Nippon Medical School, Tokyo, Japan, 2Washington University in St. Louis, Saint Louis, MO, USA, 3University of Arizona, Tucson, AZ, USA.

Objective: Reliably creating transmural linear lesions on the beating heart using an epicardial approach is an important component of minimally invasive surgical ablation for atrial fibrillation (AF). However, previous studies have shown this to be extremely difficult, primarily due to the heat sink effect of the circulating intracavitary blood. The purpose of this study was to evaluate the effect of vena caval occlusion on the efficacy of linear surface bipolar radiofrequency ablation on the beating heart.
Methods: Six pigs were anesthetized. Median sternotomy was performed. Using a surface bipolar ablation device and an epicardial approach, two 40-second ablations were performed on the right atrium of each pig. Ablations were performed with the normal caval blood flow and the with vena caval occlusion (VCO). Ultrasonic flow probes were used to verify occlusion. The animals were then sacrificed. The hearts were removed and stained with 2,3,5-triphenyl-tetrazolium chloride. Each section was examined for lesion depth and transmurality using digital photography and custom software. Student’s t-test, Fisher’s exact test and the chi-square test were used for statistical analysis.
Results: With VCO, 42/52 (81%) sections were transmural; however without caval occlusion, only 12/50 (24%) sections were transmural (p < 0.01). In thick (>2 mm) tissue, 10/17 (59%) VCO sections were transmural compared with only 2/24 (8%) with normal caval blood flow. In thin (<2 mm) tissue, 32/35 (91%) VCO sections were transmural compared with 10/24 (42%) without VCO.
Conclusions: In an acute animal model, caval occlusion improved the efficacy of linear surface bipolar ablation on the beating heart. Maneuvers that lower intracavitary blood flow such as caval occlusion and cardiopulmonary bypass should improve the efficacy of beating heart epicardial RF ablation and thus improve outcomes in minimally invasive AF ablation.
Performance of the device, showing wall thickness plotted against lesion depth for all cross-sections analyzed: (A) with and (B) without caval occlusion.

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