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Background: Clinical experience with Cryoablation for the surgical treatment of atrial fibrillation has demonstrated consistent safety and efficacy. Current technologies require application of endocardial cryoenergy on the arrested heart. Direct access to the left atrium via a thoracoscopic or pericardial approach with a cryoballoon might facilitate endocardial cryoablation on the beating heart. We investigated the ability of a novel cryoballoon to produce endocardial pulmonary vein ostial cryolesions on the beating heart.
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James S. Gammie1, G. Kwame Yankey1, Timothy Nolan1, Z. J. Wu1, T. Dickfeld2, Bartley P. Griffith1.
1Division of Cardiac Surgery, University of Maryland Medical Center, Baltimore, MD, USA, 2Division of Cardiology, University of Maryland Medical Center, Baltimore, MD, USA.
Methods: Six 60 - 70-kg sheep underwent small left thoracotomy. A 10.5 F catheter with a 23 mm cryoballoon (Cryocath Inc., Montreal, Canada) was inserted directly into the left atrium under fluoroscopic and intracardiac echo (ICE) guidance. Cryoablation of the pulmonary vein ostia was performed. Freeze durations were four minutes. Animals were sacrificed at 14 days. Pulmonary venous electrical isolation was assessed immediately prior to sacrifice. Gross lesions were photographed, and Masson trichrome and Movats staining was performed in a radial fashion to assess transmurality.
Results: All animals survived balloon cryoablation with no periprocedural complications. Balloon occlusion was well-tolerated hemodynamically, with minimal change in blood pressure (-4 +/- 6 mmHg systolic BP) and no change in heart rate. ICE demonstrated an absence of intracardiac air or ice embolization during ablation. Mean balloon temperature was - 67 +/- 8 °C. All animals were neurologically intact post-procedure. Five of six (83 %) veins exhibited circumferential exit block. Phrenic nerve function was intact in all animals. Grossly all lesions were circumferential and continuous without evidence of endocardial thrombus (Figure). Pathology confirmed circumferential transmurality in all treated veins.
Conclusions: Direct left atrial access cryoballoon ablation was effective for isolating pulmonary veins. This technology is promising and may be an important component of a thoracoscopic beating heart CryoMaze procedure for the treatment of atrial fibrillation. 
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