Questions: Valvular Disease: Stenosis and Regurgitation

Question 1

A patient with severe chronic aortic regurgitation has remained asymptomatic for 15 years. The primary mechanism that allows this prolonged compensation is:

• A. Concentric hypertrophy normalizing wall stress by thickening the ventricular wall in response to pressure overload
• B. Eccentric hypertrophy accommodating the increased volume load while maintaining forward stroke volume via the Frank-Starling mechanism
• C. Decreased systemic vascular resistance reducing afterload on the left ventricle
• D. Diastolic dysfunction slowing ventricular filling and reducing the regurgitant fraction

Answer: (B)

Aortic regurgitation creates volume overload — the ventricle receives both normal pulmonary return and the regurgitant diastolic volume. Compensation is eccentric hypertrophy: the chamber dilates (sarcomeres added in series) to accommodate the extra volume, and increased preload drives Frank-Starling-mediated maintenance of stroke volume. This gradual remodeling can sustain normal cardiac output for years. Concentric hypertrophy (option A) is the response to pressure overload — the pattern seen in stenosis, not regurgitation.

Question 2

In aortic stenosis, exertional syncope occurs because:

• A. The hypertrophied ventricular wall becomes ischemic during effort, triggering a vagal response and bradycardia
• B. The stenotic valve fixes cardiac output — it cannot increase to match peripheral vasodilation that exercise demands
• C. The regurgitant fraction reduces net forward output during the increased metabolic demands of exercise
• D. Atrial fibrillation from elevated left ventricular end-diastolic pressure causes sudden hemodynamic compromise

Answer: (B)

In severe aortic stenosis, the stenotic valve limits the maximum rate of forward flow. At rest, this fixed output may be sufficient. Exercise demands increased cardiac output and induces peripheral vasodilation. When the stenotic valve cannot allow output to increase to match vasodilation, blood pressure falls and cerebral perfusion is transiently inadequate — syncope. This 'fixed output' physiology is distinct from the diastolic dysfunction driving exertional angina, or the elevated filling pressures causing dyspnea.

Question 3

Acute aortic regurgitation is better tolerated than chronic aortic regurgitation because the heart has had time to adapt gradually to the volume load.

• T. True
• F. False

Answer: False

The opposite is true. Chronic regurgitation allows gradual eccentric remodeling — the ventricle dilates over years to accommodate extra volume, keeping filling pressures from rising sharply. Acute regurgitation (from endocarditis or aortic dissection) gives no time for adaptation: the normal-sized ventricle is suddenly overwhelmed, filling pressures spike acutely, and pulmonary edema can develop within hours — a cardiac emergency. The compensation that makes chronic regurgitation tolerable for years is entirely absent in the acute setting.

Question 4

Mitral stenosis elevates left atrial pressure, which can predispose patients to atrial fibrillation and intracardiac thrombus formation.

• T. True
• F. False

Answer: True

Mitral stenosis impedes flow from the left atrium into the left ventricle, causing chronic left atrial pressure elevation and progressive atrial dilation. The enlarged, hypertensive atrium develops a substrate for atrial fibrillation — disorganized electrical activity replacing coordinated contraction. Atrial fibrillation is doubly harmful: it eliminates the atrial 'kick' (20–30% of ventricular filling) and causes blood stasis in the atrial appendage, predisposing to thrombus formation and embolic stroke. This chain — stenosis → pressure → dilation → AF → thrombus — follows directly from the hemodynamics of the lesion.

Question 5

Explain why stenosis and regurgitation produce different types of ventricular hypertrophy, relating each pattern to the specific mechanical stress imposed on the chamber.

Model answer: Stenosis creates pressure overload — the ventricle must generate higher pressure to force flow across a narrowed orifice. By Laplace's law (wall stress = pressure × radius / 2 × wall thickness), the ventricle normalizes wall stress by adding sarcomeres in parallel, thickening the wall without increasing chamber volume: concentric hypertrophy. Regurgitation creates volume overload — extra volume fills the chamber each cycle. The ventricle accommodates this by adding sarcomeres in series, dilating the chamber (increasing radius) while wall thickness increases proportionally: eccentric hypertrophy. The type of mechanical stress — pressure versus volume — determines the direction of sarcomere addition.

Laplace's law is the bridge between mechanics and morphology. Pressure overload increases the numerator (pressure), so the compensatory response must increase wall thickness to normalize stress — concentric pattern. Volume overload increases the radius term from dilation, and both thickness and radius increase together — eccentric pattern. These are geometrically distinct responses to distinct hemodynamic insults, and recognizing which is occurring tells you what type of valvular lesion is present.