Definition
Aortic stenosis (AS) is a narrowing of the aortic valve orifice that obstructs the outflow of blood from the left ventricle (LV) into the aorta, creating a systolic pressure gradient between the LV and the aorta.
- The aortic valve normally has three cusps (right coronary, left coronary and non-coronary) and an area of 3–4 cm². The obstruction becomes severe at about 1 cm² or less.
- AS is the most common valve disease needing intervention in Europe and North America, and its frequency rises steeply with age.
- Obstruction of the LV outflow tract (LVOT) can also be subvalvular (membrane, hypertrophic obstructive cardiomyopathy) or supravalvular (Williams syndrome); this note deals with valvular AS.
Image: “Blausen 0040 AorticStenosis” by BruceBlaus, CC BY 3.0, via Wikimedia Commons.
Etiology
- Calcific (degenerative) AS of a tricuspid valve: the most common cause in Europe, usually after 65–70 years. It is an active process resembling atherosclerosis (lipid infiltration, inflammation, then bone-like calcification) with the same risk factors: age, male sex, hypertension, smoking, diabetes, dyslipidaemia, high lipoprotein(a), chronic kidney disease. It starts as aortic sclerosis (thickened cusps without obstruction).
- Bicuspid aortic valve: the most common congenital heart defect (1–2% of people, more often men). It stenoses earlier, typically at 50–65 years. It is associated with dilatation of the ascending aorta (risk of dissection), coarctation of the aorta and Turner syndrome, and may also cause aortic regurgitation and endocarditis.
Bicuspid aortic valve in the short-axis echo view: two cusps open like a clam shell (small drawings, closed to open) instead of the three-cusp "Mercedes star" of a normal valve.
Image: “Heart bicuspid aortic valve” by Patrick J. Lynch, medical illustrator, CC BY 2.5, via Wikimedia Commons.
- Rheumatic AS: fusion of the commissures; almost always together with mitral valve disease; the main cause where rheumatic fever is common.
- Rare: unicuspid valve (symptoms in youth), mediastinal radiotherapy, chronic kidney failure, Paget disease of bone, alkaptonuria, familial hypercholesterolaemia (supravalvular).