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BACKGROUND: Epicardial, beating heart cryoablation for the treatment of atrial fibrillation (AF) may be limited by heat from intra-cardiac blood flow. We therefore evaluated the ability to perform cryolesions using an argon-based cryoclamp device (CC), which temporarily occludes blood flow and facilitates transmurality.
METHODS: Six mongrel dogs underwent sternotomy. A clamp employing a 10 cm argon-based linear cryoablation device was used epicardially to isolate the pulmonary veins (PV) and left atrial appendage (LAA). Following these clamp lesions, the probe was removed from the CC device and the remaining linear lesions, analogous to the Cox Maze III, were performed. PV stenosis was evaluated using magnetic resonance imaging (MRI). Left atrial (LA) function was assessed with trans-esophageal echocardiography (TEE). Transmurality was confirmed both electrically and histologically. All animals were sacrificed 30-days following cryoablation.
RESULTS: All acute and chronic CC lesions produced conduction block. There was no change in PV diameter as assessed by MRI at baseline and at sacrifice (RPV-1: 19.6+/-2.9mm and 16.9+/-2.8mm p=0.22, RPV-2: 13.2+/-2.0mm and 11.8+/-1.6mm p=0.22, and LPV: 12.2+/-2.4mm and 11.2+/-1.9mm p=0.30). LA function was unchanged (TEE transmitral velocity E/A at baseline vs sacrifice: 1.78+/-0.4 vs 1.62+/-0.3 p=0.49). Histology confirmed transmurality in 93% of CC lesions and 84% of linear cryolesions.
CONCLUSIONS: Epicardial application of this CC device on the beating heart produced transmural lesions, which persisted 30 days. There was no evidence of PV stenosis or LA dysfunction. This novel, versatile device may be useful in treating patients with AF on the beating heart without cardiopulmonary bypass.