Atrial septal defect (ASD): A hole in the septum, the wall, between the atria, the upper chambers of the heart. Commonly called an ASD. ASDs constitute a major class of heart formation abnormalities present at birth (congenital cardiac malformations). Normally, when clots in veins break off, they travel first to the right side of the heart and, then to the lungs where they lodge as an obstruction (embolus). The lungs act as a filter to prevent the clots from entering the arterial circulation. However, when there is an ASD, a clot can cross from the right to the left side of the heart, then pass into the arteries as a paradoxical embolism. Once in the arterial circulation, a clot can travel to the brain, block a vessel there, and cause a stroke (cerebrovascular accident). Because of the risk of stroke from paradoxical embolism, it is usually recommended that even small ASDs be closed (repaired).
- Atrioventricular (AV)
Atrioventricular (AV): Pertaining to the atria (the upper chambers of the heart) and the ventricles (the lower chambers of the heart). The AV node is an electrical relay station between the atria and the ventricles. Electrical signals from the atria must pass through the AV node to reach the ventricles. The AV node is a […]
- Atrioventricular node
Atrioventricular node: The electrical relay station between the upper and lower chambers of the heart. Abbreviated AV node. Electrical signals from the atria must pass through the AV node to reach the ventricles. The AV node, which controls the heart rate, is one of the major elements in the cardiac conduction system. The AV node […]
Atrium: An entry chamber. On both sides of the heart, the atrium is the chamber that leads to the ventricle.
- Atrophic vaginitis
Atrophic vaginitis: Thinning of the lining (endothelium) of the vagina due to decreased production of estrogen. Atrophic vaginitis may occur with menopause.
Atrophy: A wasting away or diminution. Muscle atrophy is a decrease in muscle mass, often due to extended immobility.