Question

A 50 yr old female presented with dyspnoea and chest pain. Which of the following proves that she has aortic stenosis rather than aortic regurgitation?

• A. Increase in myocardial oxygen consumption is seen with increased pressure work than volume
• B. Aortic stenosis causes reduced pressure at aortic valve
• C. Workload has nothing to do with myocardial oxygen consumption
• D. Increase in preload more than afterload than after load

Hint:

AS = pressure (afterload) overload; AR = volume (preload) overload. Recall which type of work costs the myocardium more oxygen (Laplace's law).

Answer 1

The Correct Option is A

Step 1: Contrast the haemodynamic load in the two lesions.
Aortic stenosis (AS) is a fixed obstruction to LV outflow, so the left ventricle must generate very high systolic pressure to eject blood - this is a pressure overload (high afterload). Aortic regurgitation (AR) is backflow of blood into the LV during diastole, so the ventricle handles a large extra blood volume - this is a volume overload (high preload).

Step 2: Relate the load to myocardial oxygen consumption (MVO\(_2\)).
Myocardial oxygen demand is driven mainly by wall tension, heart rate and contractility. By the law of Laplace, wall tension \(=\dfrac{P\times r}{2h}\), so MVO\(_2\) is far more sensitive to the pressure developed than to the volume handled. Therefore pressure work (afterload) raises MVO\(_2\) more than volume work (preload). This pressure-work pattern is characteristic of aortic stenosis, so this statement supports/identifies AS over AR.

Step 3: Eliminate the distractors.
(B) is false - AS actually causes a high LV pressure and a large pressure gradient ACROSS the valve, not reduced pressure. (C) is false - increased cardiac workload definitely increases myocardial oxygen consumption. (D) describes increased preload over afterload, which is the pattern of aortic REGURGITATION (volume overload), not stenosis.

Final answer: A - myocardial oxygen consumption rises more with pressure work, which is the hallmark of aortic stenosis.