Early Morphologic Changes Following Microwave Endocardial Ablation for Treatment of Chronic Atrial Fibrillation During Mitral Valve Surgery

Abstract

The aim of this study was to investigate the early qualitative and quantitative structural changes in the left atrial wall after endocardial microwave ablation in patients with chronic atrial fibrillation (AF) undergoing mitral surgery. Seven patients with chronic AF of for at least 6 months underwent surgical microwave energy ablation. Linear isolation of pulmonary veins was performed in all patients by microwave energy applications to the endocardial surface delivered by catheter at 65-W constant power for 45 seconds. Biopsies were obtained from a selected site (below the right lower pulmonary vein) of the left atrial posterior wall before and after the ablation procedure in all patients. Control tissues from the same sites were obtained at autopsy from patients with noncardiac causes of death. Light and electron microscopy was used to examine qualitative and quantitative changes in tissue morphology. Tissues after endocardial ablation procedure showed significantly increased loss of contractile material. Electron microscopy of atrial tissue demonstrated loss of profile of perinuclear and plasma membranes of myocytes, disruption of the endothelial cells of capillary vessels, and presence of macrophages. Lesions created by endocardial microwave energy ablation revealed a transmural effect on the left atrial wall without a significant reduction in thickness but a significant increase in the myolytic areas involving the entire cytosol and occlusion of the small intramyocardial vessels within the ablative lesion.