Which event occurs when myocardial oxygen demand exceeds oxygen supply?

• A. Myocardial ischemia
• B. Enhanced oxygen diffusion
• C. Decreased heart rate
• D. Increased cardiac output

Answer: (A)

Verified step by step guidance

1. Understand the concept of myocardial oxygen demand and supply: Myocardial oxygen demand refers to the amount of oxygen the heart muscle requires to function effectively, while oxygen supply refers to the amount of oxygen delivered to the heart muscle via coronary blood flow.
2. Recognize the physiological consequence of an imbalance: When the oxygen demand exceeds the oxygen supply, the heart muscle does not receive enough oxygen to meet its metabolic needs, leading to a condition known as myocardial ischemia.
3. Eliminate incorrect options: Enhanced oxygen diffusion is not a direct result of oxygen demand exceeding supply; it would require physiological adaptations. Decreased heart rate typically reduces oxygen demand rather than being a consequence of ischemia. Increased cardiac output would increase oxygen demand, not supply.
4. Focus on the correct answer: Myocardial ischemia is the event that occurs when the oxygen demand of the heart muscle surpasses the oxygen supply, leading to insufficient oxygenation and potential damage to the heart tissue.
5. Relate this to clinical significance: Myocardial ischemia can lead to symptoms such as chest pain (angina) and, if prolonged, may result in more severe conditions like myocardial infarction (heart attack).