In a patient with severe aortic stenosis, myocardial oxygen consumption (MVO2) is markedly elevated. Using the law of Laplace, which component contributes most to this increased oxygen demand?

• A Stroke volume (volume work)
• B Ejection velocity
• C Heart rate alone
• D Systolic wall tension (pressure work) ✓

Explanation

The major determinants of MVO2 are systolic wall tension, contractility, and heart rate. By Laplace's law, wall stress = (Pressure × Radius) / (2 × Wall thickness). In aortic stenosis, the pressure overload dramatically increases wall tension during systole. Pressure work (generating high pressure) consumes substantially more oxygen than volume work (ejecting volume). This is why aortic stenosis, not aortic regurgitation, causes angina despite normal coronaries.

Reference: Braunwald's Heart Disease, 12th ed.

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