Which of the following factors affects myocardial oxygen delivery?

• A. Heart rate only
• B. Systemic blood pressure only
• C. Coronary perfusion pressure
• D. Ventricular size only

Answer: (C)

Oxygen delivery to the heart muscle hinges on coronary blood flow, which is governed by the driving pressure across the coronary circulation—coronary perfusion pressure. This pressure is essentially the gradient pushing blood through the coronary vessels, and during the heart’s relaxation phase (diastole) it matters most because coronary flow occurs mainly then. Coronary perfusion pressure is roughly the aortic diastolic pressure minus the right atrial pressure; when this gradient falls (lower diastolic pressure or higher right atrial pressure), myocardial oxygen delivery drops due to reduced coronary flow.

Among the options, coronary perfusion pressure best represents the direct determinant of coronary blood flow and thus myocardial oxygen delivery. Heart rate can influence delivery indirectly by shortening diastole and reducing filling time, systemic blood pressure contributes to the gradient but is not the direct measure of coronary flow, and ventricular size affects oxygen demand more than supply.