Openings of pulmonary veins

The openings of the pulmonary veins (Pulmonary vein ostia) are the anatomical sites where the pulmonary veins enter the posterior wall of the left atrium. These ostia represent the junction between the pulmonary venous system, which drains oxygenated blood from the lungs, and the left atrial chamber.

In the classic anatomical pattern (present in approximately 60-71% of individuals), there are four distinct pulmonary vein ostia: the left superior, left inferior, right superior, and right inferior pulmonary veins. However, significant anatomical variation exists—approximately 40% of patients have variant anatomy, most commonly a left common pulmonary vein (where the left superior and inferior veins share a common ostium) or an additional right middle pulmonary vein.

The ostia are characterized by myocardial sleeves—extensions of cardiac muscle tissue from the left atrium that extend 1-3 cm into the pulmonary veins, with thickness greatest at the proximal ends (1-1.5 mm) and gradually decreasing distally. These sleeves are clinically significant as they represent the anatomical substrate for ectopic electrical activity that can trigger atrial fibrillation.

The ostia have variable shapes and orientations: left-sided ostia tend to be smaller and more elliptical than right-sided ostia, with the average ratio between maximal and minimal diameter being 1.5±0.4 for left veins and 1.2±0.1 for right veins. The superior vein ostia are positioned more superiorly and project forward and upward, while the inferior vein ostia project backward and downward.