Evaluation of epicardial microwave lesions in the pig model using an electroanatomic mapping system.

BACKGROUND: Surgical ablation techniques using microwave energy are an alternative to catheter-based ablation therapy in the treatment of atrial fibrillation. We investigate electrical conduction properties of linear lesions after epicardial ablation in a pig model by using an electroanatomic mapping system.
METHODS: After medial sternotomy in eight pigs epicardial pacing wires were placed on the anterior and posterolateral wall of the right atrium. Endocardial electroanatomical mapping was performed during pacing from anterior and posterolateral. Epicardial ablation was implemented in between the superior and inferior caval vein using microwave energy. Mapping was repeated to demonstrate conduction block or gap across the ablation line. When conduction gap was present the ablation procedure was repeated. Hearts were removed for histologic evaluation.
RESULTS: Conduction block was observed in two pigs after the first ablation and in two additional pigs after the second ablation. Conduction gap was present in three pigs after the second ablation. One animal died during the second ablation. Histologic evaluation showed more severe transmural cellular damage in lesions with conduction gap. Complete lesions with conduction block more often showed moderate alterations.
CONCLUSIONS: Epicardial microwave ablation can induce bidirectional conduction block, which is believed to be essential for therapeutic efficacy. However, the intraoperative macroscopic visible lesion and histological findings are not reliable markers of bidirectional conduction block. The Carto-Qwik-Map-System is an effective system to evaluate epicardial microwave lesions and to locate conduction gap areas intraoperatively. This increased the success rate regarding acute bidirectional conduction block after ablation in our experimental setting.