In which condition does the valve area become less than 1 cm², indicating severe obstruction?

Aortic stenosis is characterized by a narrowing of the aortic valve, which impedes blood flow from the heart into the aorta. This obstruction typically results in a decrease in the effective valve area. An aortic valve area of less than 1 cm² is indicative of severe obstruction, leading to significant hemodynamic changes and symptoms such as exertional dyspnea, angina, and syncope. In severe cases, the left ventricle must work harder to compensate, which can result in left ventricular hypertrophy and eventually heart failure if left untreated.

In contrast, pulmonary hypertension, mechanical heart valve issues, and Eisenmenger syndrome involve different pathophysiological mechanisms that do not specifically relate to aortic valve area measurements. Pulmonary hypertension refers to high blood pressure in pulmonary arteries, mechanical heart valve issues pertain to problems with artificial valves, and Eisenmenger syndrome involves a long-standing left-to-right shunt leading to pulmonary vascular disease and eventual right-to-left shunt, but none of these conditions specifically define severe obstruction through valve area as aortic stenosis does.