Histological Study of the Left Atrial Wall: A Consideration of the Compound Myocardial Architecture and Potential Durability with Respect to Catheter Ablation in Pulmonary Vein Isolation Procedures

Pulmonary vein isolation using radiofrequency energy is performed extensively to treat symptomatic, drug-refractory atrial fibrillation. However, anatomical knowledge of the left atrial wall surrounding the pulmonary vein (PV) openings is insufficient to create an ablation line. Using autopsy hearts from 23 individuals (median age of 63 years), we studied the histological nature of anatomical obstacles or related isthmuses near the PV openings. None of the individuals had a history of tachyarrhythmia or other major cardiac abnormalities. After macroscopic measurement of the minimum width of each isthmus, the following areas were excised and histologically prepared: atrial roof-mitral valve annulus (MVA), left superior pulmonary vein (LSPV) -left atrial appendage (LAA), LAA-MVA, left inferior pulmonary vein (LIPV) -MVA, right superior pulmonary vein (RSPV) -fossa ovalis (FO), right inferior pulmonary vein (RIPV) -FO, and FO-MVA. Within the obstacles near the PV openings, the LSPV-LAA isthmus was found to be the narrowest, whereas the LIPV-MVA was the widest and thickest isthmus. Histological complexity of each isthmus was determined, and the compound architecture of the myocardium was revealed. The further presence of a variety of nerve endings as well as myocardial blood supply enhanced the tissue diversity. Such an insight into the diversity of myocardial architecture or histological complexity in each isthmus might be helpful in creating a reliable ablation line in pulmonary vein isolation procedures