Histological findings induced by different energy sources in experimental atrial ablation in sheep

The aim of this study was a detailed comparative investigation of acute cardiac alterations induced by different energy sources and approaches in a sheep model. Experiments were performed on 39 sheep. Circular lesions were created endo- or epicardially in the left atrium and at the pulmonary veins using different energy sources: cryo, microwave, laser and unipolar or bipolar radiofrequency (RF). Electrophysiological examinations were performed immediately post treatment and 2 h after ablation to prove conduction block. Altered areas of the atria and pulmonary veins were investigated histopathologically. Endocardial ablation resulted in transmural lesions, confirmed by electrophysiological examinations. However, endocardial microwave and laser induced intensive thrombus formation, whereas radiofrequency and cryoablation induced more circumscribed necrosis and led to little endocardial thrombi. Epicardial cryoablation and microwave energy were not successful in acute phase in 8 of 9 animals. In contrast, epicardial bipolar RF was efficient and resulted in well demarcated slim lesion lines but induced marked thrombus formation. It can be summarized that surgical ablation techniques using different energy sources and approaches in this acute animal model resulted in different electrophysiological effectiveness and histomorphological lesions. Further mid and long term studies are necessary to confirm these results.