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MBBS QUESTION #10242
Question 1
Left ventricular myocardium receives the majority of its coronary blood flow during which phase of the cardiac cycle, and why does tachycardia worsen myocardial ischemia in coronary artery disease?
  • Predominantly during diastole, because systolic compression of intramural vessels by contracting myocardium impedes flow; tachycardia disproportionately shortens diastole, reducing perfusion time✔️
  • Predominantly during systole, when ventricular pressure is highest
  • Equally throughout the cardiac cycle regardless of heart rate
  • Only during isovolumetric relaxation, independent of heart rate
Correct Answer Explanation
Unlike other organs, the left ventricle perfuses mainly during diastole because systolic myocardial contraction compresses intramural coronary vessels. As heart rate rises, diastole shortens proportionally more than systole, reducing the time available for coronary perfusion — explaining why tachycardia can precipitate ischemia in patients with coronary stenosis.