A myocardial infarction, or heart attack, is most often caused by
Correct answer: D. blockage of a coronary artery by a thrombus on an atherosclerotic plaque
- A. failure of the sinoatrial node to fire
- B. leakage of the bicuspid valve
- C. an increase in the number of red blood cells
- D. blockage of a coronary artery by a thrombus on an atherosclerotic plaque
Explanation
Fatty plaques narrow a coronary artery over years, and when one ruptures a clot forms and cuts off the blood supply, so the muscle beyond it dies within minutes for lack of oxygen. Damaged cardiac muscle is not replaced, which is why the loss is permanent. Failure of the sinoatrial node disturbs rhythm rather than starving the muscle, and a leaking valve reduces efficiency without killing tissue.
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The human heart is a four chambered muscular pump that maintains double circulation through the pulmonary and systemic circuits. Questions cover atria, ventricles, valves, major blood vessels, the cardiac cycle, pressure changes, the conduction system and ECG, while distinguishing arteries and veins from the chambers that receive or eject blood.
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