There are three causes of aortic valve stenosis:
1 Congenital aortic valve stenosis develops progressively because of turbulent blood flow through a congenitally abnormal (usually bicuspid) aortic valve. Most congenitally abnormal aortic valves occur in men.
2 Rheumatic fever results in progressive fusion, thickening and calcification of a previously normal threecusped aortic valve. In rheumatic heart disease the aortic valve is affected in about 45% of cases and there is usually associated mitral valve disease.
3 The wear and tear of age may lead to arteriosclerotic degeneration and calcification of the aortic valve. It is not usually severely stenotic and symptoms are not usually present.
Valvular aortic stenosis should be distinguished from other causes of obstruction to left ventricular emptying (Fig. 11.70), which include:
SUPRAVALVULAROBSTRUCTION -a congenital fibrous diaphragm above the aortic valve HYPERTROPHIC CARDIOMYOPATHY-Septal muscle hypertrophy obstructs left ventricular outflow SUBVALVULAR AORTIC STENOSIs-a congenital condition in which a fibrous ridge or diaphragm is situated immediately below the aortic valve.
Obstructed left ventricular emptying leads to increased left ventricular pressure and compensatory left ventricular hypertrophy. In turn, this results in relative ischaemia of the left ventricular myocardium, and consequent angina, arrhythmias and left ventricular failure. The obstruction to left ventricular emptying is relatively more severe on exercise. Normally, exercise causes a many-fold increase in cardiac output, but when there is severe narrowing of the aortic valve orifice the cardiac output can hardly increase. Thus, the blood pressure falls, coronary ischaemia worsens, the myocardium fails and cardiac arrhythmias
develop particularly on exercise.
There are usually no symptoms until aortic stenosis IS moderately severe (when the aortic orifice is reduced to one-third of its normal size). At this stage, exerciseinduced syncope, angina and dyspnoea may develop. When symptoms occur, the prognosis is poor-on average, death occurs within 2-3 years if there has been no surgical intervention.
Aortic stenosis is characterized by abnormalities of the pulse, precordial pulsation and auscultation.
The carotid pulse is of small volume and is slow rising or plateau in nature.
The apex beat is not usually displaced because hypertrophy (as opposed to dilatation) does not produce noticeable cardiomegaly. However, the pulsation is sustained and obvious-a heaving apex beat. A double impulse is sometimes felt because the fourth heart sound or atrial contraction (‘kick’) may be palpable. A systolic thrill may be felt in the aortic area.
The most obvious auscultatory finding in aortic stenosis is a mid-systolic ejection murmur that is usually ‘diamond’ shaped (crescendo-decrescendo). The murmur is usually longer when the disease is more severe, as a longer left ventricular ejection time is needed. The intensity of the murmur is not a good guide to the severity of the condition because it is lessened by a reduced cardiac output. The murmur is usually rough in quality and best heard in the aortic area. It radiates widely and is usually easily heard over the clavicles and the carotid arteries.
A SYSTOLIC EJECTION CLICK, unless the valve has become immobile and calcified
SOFT OR INAUDIBLE AORTIC SECOND HEART SOUND when the aortic valve becomes immobile
REVERSED SPLITTING OF THE SECOND HEART SOUND (splitting on expiration) A PROMINENT FOURTH HEART SOUND,
unless coexisting mitral stenosis prevents this Degenerative disease of the aortic valve (aortic sclerosis) results in a loud mid-systolic murmur but, because there is little stenosis, there are no signs of left ventricular hypertrophy or of a slow rising pulse. This murmur can be ignored.