BACKGROUND Radiofrequency ablation of tissues in pulmonary veins can eliminate paroxysmal atrial fibrillation.

OBJECTIVE To explore the characteristics of normal pulmonary veins so as to provide more information relevant to radiofrequency ablation.

RESULTS The longest myocardial sleeves were found in the superior veins. The sleeves were thickest at the venoatrial junction in the left superior pulmonary veins. For the superior veins, the sleeves were thickest along the inferior walls and thinnest superiorly. The sleeves were composed mainly of circularly or spirally oriented bundles of myocytes with additional bundles that were longitudinally or obliquely oriented, sometimes forming mesh-like arrangements. Fibrotic changes estimated at between 5% and 70% across three transverse sections were seen in 17 veins that were from individuals aged 30 to 72 years.

CONCLUSIONS The myocardial architecture in normal pulmonary veins is highly variable. The complex arrangement, stretch, and increase in fibrosis may produce greater non-uniform anisotropic properties.