What is a pulmonary AVM, and what is the clinical presentation?
A pulmonary AVM is an abnormal communication between a pulmonary artery and a draining pulmonary vein, causing blood to bypass the pulmonary capillary bed before returning to the left heart. Pulmonary AVMs may be asymptomatic but can manifest with a wide range of clinical symptoms. Paradoxic emboli to the systemic arterial circulation may occur, leading to stroke, brain abscess, myocardial infarction, or acute limb ischemia, due to loss of the filter effect of the lung such that systemic venous clots are able to access the systemic arterial circulation. Pulmonary AVMs may cause vague symptoms and signs, such as chest pain and dyspnea on exertion, because of right-to-left shunting of deoxygenated blood. With severe shunting, high-output cardiac failure can result. One sign that may suggest pulmonary AVM is orthodeoxia, indicating oxygen desaturation in the upright position. Most pulmonary AVMs occur in the lower lobes of the lungs, and therefore shunting of blood and oxygen desaturation are maximal when blood flow to the lung bases is greatest (i.e., in the upright position).
