Clinical features

Aortic stenosis (AS), the most common cardiac valve lesion among people living in the United States, is found in one fourth of all patients with chronic valve disease. Left ventricular outflow tract obstruction can occur in the subvalvular, valvular, and supravalvular regions. Stenosis of the aortic valve itself is most common, occurring in 75% of patients with outflow tract obstruction. The three major types of AS are (1) a congenital malformation (bicuspid instead of the normal tricuspid valve) that becomes stenotic over decades, (2) calcification or degeneration in a previously normal tricuspid aortic valve, and (3) rheumatic aortic valve disease, which usually occurs in conjunction with mitral valve abnormalities. In developed countries, the number of people with rheumatic AS has declined significantly, so that congenital stenosis (a bicuspid valve that later calcifies) and calcific stenosis of a tricuspid valve have emerged as the more common causes of AS. Between 1% and 2% of the population has a bicuspid aortic valve, which is thought to be inherited as an autosomal-dominant trait with variable penetrance. Flow through a bicuspid valve is turbulent, creating abnormal pressures on the leaflets that lead to thickening of the leaflets and, eventually, stenosis.

The risk factors for calcific degenerative AS are similar to those for atherosclerosis (e.g., older age, male sex, hypertension, hyperlipidemia with evidence of inflammation at the site of disease). However, systemic hypertension occurs in only about half of all patients with AS; a systolic pressure above 200 mm Hg is thought to generally exclude severe narrowing of the valve.

Eighty percent of patients with symptomatic AS are men, approximately 50% will have coronary artery disease, and most of these patients will be at least 70 years old (AS due to a bicuspid valve tends to occur in patients younger than 70 years of age [Figure 149-1]). Overall, however, AS is a disease of the elderly, with a prevalence of more than 4% in North American adults older than 75 years. In a study of 5201 men and women over the age of 65 years, 26% had aortic sclerosis (a thickening of the valve without hemodynamic sequelae), and 2% had AS. The prevalence of aortic sclerosis increased with age in this study: 20% in patients aged 65 to 75 years, 35% in those aged 75 to 85 years, and 48% in patients older than 85 years (AS rates were 1.3%, 2.4%, and 4%, respectively, in these groups).

Natural history

Patients with AS are at increased risk of dying suddenly (likely from cardiac arrhythmia due to ischemia from mismatching of O₂ supply and demand), yet the typical natural history of AS is a gradual onset of symptoms manifesting in the fifth to seventh decades of life. Aortic sclerosis is not an uncommon finding in patients older than 65 years, but about 16% of patients with sclerosis develop AS within 7 years. Patients with aortic sclerosis are asymptomatic, but once the pressure gradient across the valve exceeds the upper limits of normal, exertional dyspnea, angina, and syncope–the cardinal symptoms of AS–can appear within 5 years. The mortality rate is approximately 25% per year among symptomatic patients (Figure 149-2), with three quarters of those whose AS is untreated dying within 3 years of the onset of symptoms (Figure 149-3). Asymptomatic patients, on the other hand, even those with severe disease, have a more favorable outlook (risk of death <1% per year).

The typical timeframes from the onset of symptoms until death are 4.5 years for patients with angina, 2.6 years for patients with syncope, 2 years for patients with dyspnea, and 1 year for patients with congestive heart failure, with the latter being the cause of death in one half to two thirds of patients with untreated AS.

Anatomic considerations

The internal cross-sectional area of a normal aortic valve during systole is 3.0 to 4.0 cm²; significant hemodynamic obstruction does not occur until the valve area is less than 1.5 cm²