Page 124 - Clinical Pearls in Cardiology

112 Clinical Pearls in Cardiology

also occur at the subvalvular level (discrete subvalvular
obstruction, hypertrophic cardiomyopathy) or above the
valve (supravalvular stenosis).
19. What is the natural history of aortic stenosis?
The normal area of the aortic valve in adults is between
2.5 and 3.5 sq cm. The narrowing of the outflow orifice
in aortic stenosis causes a systolic overload on the
left ventricle and this evokes certain compensatory
mechanisms. The physiological compensation is an
increase in the pressure generated by the left ventricle.
The anatomic compensation is an increase in the
contractile muscle mass without dilatation (concentric
type of left ventricular hypertrophy). As long as these
compensatory mechanisms maintain normal left
ventricular emptying, the patient may be entirely
asymptomatic. The increased left ventricular muscle
mass raises the myocardial oxygen demand and impedes
systolic coronary perfusion. This leads to an imbalance
between myocardial oxygen supply and demand. This
may clinically manifest as anginal attacks, or paroxysmal
arrhythmias (may cause sudden death). Exertional
syncope occurs, because exercise-induced decrease in
peripheral vascular resistance is uncompensated due to
the restriction of the cardiac output by the stenotic valve.
Left ventricular hypertrophy in aortic atenosis is
associated with reduced ventricular compliance, leading
initially to diastolic heart failure. When the capacity for
concentric hypertrophy is exhausted, left ventricular
dilatation occurs (eccentric type of left ventricular
hypertrophy), and this ultimately results in left ventricular
failure (manifested as worsening dyspnea). Thus patients
with aortic stenosis typically remain asymptomatic for
many years, but they deteriorate rapidly when symptoms