Arteriovenous Malformation - Pathophysiology

Pathophysiology

Arteriovenous malformations, also known as AVMs, are deficiencies of the cardiovascular system. In a normal functioning human body, arteries carry oxygen-rich blood away from the heart to the rest of the body, and veins return oxygen-depleted blood to the lungs and heart. An AVM interferes with this cyclical process. Instead of the gradual transition through the capillaries from arteries to veins that is typical of normal functioning vasculature, AVMs cause direct associations of the arteries and veins. AVMs can cause intense pain and lead to serious medical problems. Although AVMs are often associated with the brain and spinal cord, they can develop in any part of the body.

Arteries and veins are part of the human cardiovascular system. Normally, the arteries in the vascular system carry oxygen-rich blood, except in the case of the pulmonary artery. Structurally, arteries divide and sub-divide repeatedly, eventually forming a sponge-like capillary bed. Blood moves through the capillaries, giving up oxygen and taking up waste products, including CO₂, from the surrounding cells. Capillaries in turn successively join together to form veins that carry blood away. The heart acts to pump blood through arteries and uptake the venous blood.

An AVM lacks the dampening effect of capillaries on the blood flow; it also causes the surrounding area to be deprived of the functions of the capillaries — removal of CO₂ and delivery of nutrients to the cells. The resulting tangle of blood vessels, often called a nidus (Latin for "nest") has no capillaries and abnormally direct connections between high-pressure arteries and low-pressure veins. It can be extremely fragile and prone to bleeding. The resultant sign, audible via stethoscope, is a rhythmic, whooshing sound caused by excessively rapid blood flow through the arteries and veins. It has been given the term "bruit", French for noise. On some occasions a patient with a brain AVM may become aware of the noise, which can compromise hearing and interfere with sleep in addition to causing psychological distress.