What is the net effect of epinephrine on myocardial oxygen demand and supply?

What is the net effect of epinephrine on myocardial oxygen demand and supply?

• A. Increases MVO2 and increases supply
• B. Increases MVO2 but decreases supply
• C. Decreases MVO2 and increases supply
• D. Decreases MVO2 and decreases supply

Answer: (B)

The key idea is myocardial oxygen balance: demand versus supply. Epinephrine drives up the heart’s work by increasing heart rate and contractility, so the myocardium uses more oxygen (higher MVO2). At the same time, it can narrow coronary vessels and shorten the time the heart spends in diastole due to tachycardia. Since coronary blood flow is greatest during diastole, a shorter diastolic period reduces oxygen supply to the heart. Put together, oxygen demand rises while supply falls, creating a mismatch. That’s why the net effect is increased MVO2 with decreased myocardial oxygen supply.

The key idea is myocardial oxygen balance: demand versus supply. Epinephrine drives up the heart’s work by increasing heart rate and contractility, so the myocardium uses more oxygen (higher MVO2). At the same time, it can narrow coronary vessels and shorten the time the heart spends in diastole due to tachycardia. Since coronary blood flow is greatest during diastole, a shorter diastolic period reduces oxygen supply to the heart. Put together, oxygen demand rises while supply falls, creating a mismatch. That’s why the net effect is increased MVO2 with decreased myocardial oxygen supply.