Endocardial laser ablation for the treatment of atrial fibrillation in an acute sheep model

Background. The purpose of this study was to test the feasibility, effectiveness, and safety of the use of a new laser energy catheter for linear endocardial ablation in an acute sheep model. Methods: Bipolar pacing electrodes were positioned on the left atrial appendage (LAA) and the pulmonary veins (PVs). Laser ablation within the left atrium was performed around the LAA and PVs in six sheep. The temperature in the esophagus was measured continuously during ablation. The animals were weaned from cardiopulmonary bypass (CPB) and were sacrificed two hours after ablation. The heart, lungs, and esophagus were retrieved for histological examination. Results: Aortic cross clamp time was 26.2 +/- 6.1 minutes and CPB time was 81 +/- 29 minutes. Electrical isolation of the LAA and PVs was confirmed in all sheep. On histological analysis, there was an extensive transmural alteration of the left atrial tissue including vascular lesions, myocardial degeneration, and necrosis, and epi- and endocardial necrosis. In six out of six cases, extensive lesions of the esophagus (muscular layer) were also found. Significant changes in esophageal temperature were observed, reaching up to 70 degrees C. The epithelial layer of the esophagus was not affected by the laser energy, but mild focal degeneration of the subepithelial connective tissue was observed in all sheep. There were no injuries to the circumflex coronary artery. Conclusions: Laser is an effective tool in endocardial ablation, resulting in electrical isolation and transmurality. Future studies should more completely assess the safety of laser ablation, especially with regards to the nearby esophagus, as well as examine the results of epicardial application.