Pulmonary veins are blood vessels that transport oxygen-rich blood from the lungs to the heart, a function opposite to that of other veins. As part of the pulmonary circuit, these vessels move blood between the lungs and heart. The system includes left and right pulmonary veins, which all channel blood into the heart’s left atrium.
Anatomy and Location of the Left Pulmonary Veins
The left pulmonary veins are typically a pair of vessels emerging from the left lung: a superior (upper) and an inferior (lower) vein. The superior vein drains the upper lobe and lingula of the left lung, while the inferior vein drains the lower lobe. This standard anatomy is present in about 60% to 70% of individuals.
These veins begin at the hilum (root) of the left lung, the central area where vessels and airways enter the organ. From the hilum, they travel medially to connect with the posterior wall of the left atrium. Each vein has a distinct opening, known as an ostium, into the atrium.
Near their connection to the left atrium, the pulmonary veins are partially covered by a thin layer of heart muscle tissue called a “sleeve.” The superior pulmonary veins have longer sleeves of this myocardial tissue than the inferior ones. In some individuals, an anatomical variation occurs where the two left pulmonary veins merge into a common trunk, draining through a single opening.
Primary Function in Circulation
The primary role of the left pulmonary veins is to transport oxygen-rich blood from the left lung to the heart’s left atrium. This is part of the pulmonary circuit, which starts when the right ventricle pumps oxygen-poor blood to the lungs. In the lungs, blood releases carbon dioxide and collects oxygen before returning to the heart.
Once this oxygenated blood enters the left pulmonary veins, it is delivered to the left atrium. From the left atrium, the blood is pumped into the left ventricle, the heart’s main pumping chamber.
The left ventricle then contracts to pump this blood into the aorta, the body’s largest artery. From the aorta, it is distributed throughout the body to supply tissues and organs with oxygen and nutrients.
Associated Medical Conditions
The junction where the pulmonary veins enter the left atrium is clinically significant, particularly for atrial fibrillation (A-Fib). This common heart rhythm disorder is often caused by irregular electrical signals that originate from the muscular sleeves of the pulmonary veins. The left superior pulmonary vein is the most frequent source of these disruptive signals. A common treatment, catheter ablation, targets these areas to isolate the erratic electrical triggers and restore a normal heart rhythm.
Pulmonary vein stenosis is another condition characterized by a narrowing of one or more pulmonary veins, which obstructs blood flow. In adults, it can develop as a complication of catheter ablation procedures for A-Fib. This narrowing increases pressure within the veins and lungs, causing symptoms like shortness of breath.
Partial anomalous pulmonary venous return (PAPVR) is a congenital condition where one or more pulmonary veins connect to the wrong chamber of the heart. Instead of draining into the left atrium, an anomalous vein might connect to the right atrium. This causes oxygenated blood to be incorrectly recirculated back to the lungs, forcing the right side of the heart to work harder.