Aortic Stenosis - Acquired Valvular Disorders

AORTIC STENOSIS

Aortic valve stenosis is narrowing of the orifice between the left ventricle and the aorta. In adults, the stenosis may involve con-genital leaflet malformations or an abnormal number of leaflets (ie, one or two rather than three), or it may result from rheumaticendocarditis or cusp calcification of unknown cause. The leaflets of the aortic valve may fuse.

Pathophysiology

There is progressive narrowing of the valve orifice, usually over a period of several years to several decades. The left ventricle over-comes the obstruction to circulation by contracting more slowly but with greater energy than normal, forcibly squeezing the blood through the very small orifice. The obstruction to left ventricular outflow increases pressure on the left ventricle, which results in thickening of the muscle wall. The heart muscle hypertrophies. When these compensatory mechanisms of the heart begin to fail, clinical signs and symptoms develop.

Clinical Manifestations

Many patients with aortic stenosis are asymptomatic. After symp-toms develop, patients usually first have exertional dyspnea, caused by left ventricular failure. Other signs are dizziness and syncope because of reduced blood flow to the brain. Angina pec-toris is a frequent symptom that results from the increased oxy-gen demands of the hypertrophied left ventricle, the decreased time in diastole for myocardial perfusion, and the decreased blood flow into the coronary arteries. Blood pressure can be low but is usually normal; there may be a low pulse pressure (30 mm Hg or less) because of diminished blood flow.

Assessment and Diagnostic Findings

On physical examination, a loud, rough systolic murmur may be heard over the aortic area. The sound to listen for is a systolic crescendo-decrescendo murmur, which may radiate into the carotid arteries and to the apex of the left ventricle. The murmur is low-pitched, rough, rasping, and vibrating. If the examiner rests a hand over the base of the heart, a vibration may be felt. The vibration is caused by turbulent blood flow across the narrowed valve orifice. Evidence of left ventricular hypertrophy may be seen on a 12-lead ECG and echocardiogram.

Echocardiography is used to diagnose and monitor the pro-gression of aortic stenosis. After the stenosis progresses to the point that surgical intervention is considered, left-sided heart catheterization is necessary to measure the severity of the valvular abnormality and evaluate the coronary arteries. Pressure tracings are taken from the left ventricle and the base of the aorta. The sys-tolic pressure in the left ventricle is considerably higher than that in the aorta during systole.

Medical Management

Antibiotic prophylaxis to prevent endocarditis is essential for any-one with aortic stenosis. After left ventricular failure or dysrhyth-mias occur, medications are prescribed. Definitive treatment for aortic stenosis is surgical replacement of the aortic valve. Patients who are symptomatic and are not surgical candidates may benefit from one- or two-balloon percutaneous valvuloplasty procedures.