Questions: Aortic Stenosis: Progressive Left Ventricular Hypertrophy and Heart Failure

Question 1

A patient with severe aortic stenosis develops angina on exertion. Coronary angiography shows no significant coronary artery disease. What is the best explanation?

• A. Calcium emboli from the stenotic valve lodge in small coronary branches, blocking flow
• B. Hypertrophied ventricular walls compress subendocardial coronary vessels during systole, reducing perfusion to tissue with the highest oxygen demand
• C. Reduced stroke volume means insufficient blood reaches the coronary ostia during diastole
• D. Aortic stenosis causes atrial fibrillation, which eliminates the diastolic filling phase needed for coronary perfusion

Answer: (B)

Coronary blood flow occurs predominantly during diastole, when the ventricular wall is relaxed and not compressing the intramyocardial vessels. In concentric hypertrophy, the wall is dramatically thickened and maintains high systolic pressures. During systole, this thick, high-pressure wall compresses its own subendocardial coronary vessels, impairing perfusion precisely to the tissue working hardest. This explains angina in the absence of coronary artery disease — a classic and commonly tested feature of severe aortic stenosis. Reduced stroke volume (option C) would reduce overall cardiac output but does not specifically impair coronary perfusion the way intramyocardial compression does.

Question 2

Why might a patient with severe aortic stenosis remain asymptomatic for years despite markedly elevated left ventricular pressures?

• A. The body compensates through sustained tachycardia, maintaining cardiac output above the threshold for symptoms
• B. Concentric hypertrophy normalizes wall stress by thickening the ventricular wall, allowing the ventricle to maintain near-normal stroke volume despite the pressure load
• C. The kidneys compensate by retaining sodium, raising preload and preserving forward flow
• D. Collateral vessels develop around the stenotic valve, bypassing the obstruction

Answer: (B)

The law of Laplace states that wall stress is proportional to pressure and radius, and inversely proportional to wall thickness. When aortic stenosis forces the ventricle to generate far higher systolic pressure, the myocardium responds with concentric hypertrophy — adding sarcomeres in parallel to thicken the wall. This increased thickness normalizes wall stress, and the hypertrophied ventricle can maintain normal cardiac output. The period of asymptomatic compensation can last decades. The misconception is treating hypertrophy as purely harmful; initially, it is the mechanism that keeps the patient alive and symptom-free.

Question 3

Concentric hypertrophy in response to aortic stenosis is a harmful, pathological process that should be treated as soon as it is detected on echocardiography.

• T. True
• F. False

Answer: False

Concentric hypertrophy is initially a compensatory, adaptive response that normalizes wall stress and allows the patient to remain asymptomatic for years. It is the heart's correct response to a pressure overload state. It becomes pathological only secondarily — as the hypertrophied walls become stiffer (causing diastolic dysfunction), compress coronary vessels (causing ischemia), and eventually decompensate to systolic failure. The appropriate target of treatment is the underlying cause (valve stenosis), not the hypertrophy itself, which is the heart's way of coping with an obstruction it cannot remove.

Question 4

In aortic stenosis, diastolic dysfunction can cause pulmonary congestion and dyspnea even when ejection fraction (systolic function) is still preserved.

• T. True
• F. False

Answer: True

Diastolic dysfunction — the impaired ability of the stiff, hypertrophied ventricle to relax and fill during diastole — is the first mode of heart failure in aortic stenosis, often preceding systolic failure by years. Because the stiff ventricle requires higher filling pressures to accept the same volume, pressure backs up into the left atrium and pulmonary veins, causing pulmonary congestion and the symptom of dyspnea. This is 'heart failure with preserved ejection fraction' (HFpEF). The common misconception is that heart failure requires a reduced ejection fraction; diastolic failure disproves this.

Question 5

Explain why the same mechanism that helps the left ventricle cope with aortic stenosis eventually contributes to its failure.

Model answer: Concentric hypertrophy initially compensates for the pressure overload by normalizing wall stress — thicker walls bear the increased pressure without excessive strain, preserving stroke volume. But the same wall thickening that saves the ventricle in the short term creates two downstream problems: (1) thick walls are stiff walls — they resist relaxation during diastole, causing impaired filling and rising filling pressures (diastolic dysfunction); and (2) the hypertrophied mass has increased oxygen demand while simultaneously compressing its own blood supply (subendocardial ischemia). Over time, these insults accumulate. When the ventricle can no longer maintain wall thickness proportional to pressure, it dilates and ejection fraction falls — the compensation has been exhausted.

This is the essential paradox of pressure-overload heart failure: the adaptive response (hypertrophy) contains the seeds of decompensation. Understanding this arc — compensation, downstream consequences of compensation, decompensation — explains why valve replacement is the only effective treatment. Medical therapy manages the symptoms of diastolic dysfunction and ischemia but cannot remove the pressure load driving continued remodeling.