What defines acute myocardial infarction (MI)?

• A. Reversible ischemia due to partial occlusion of a coronary vessel.
• B. Ischemia with preserved cell membranes.
• C. Necrosis of cardiac myocytes caused by prolonged ischemia due to complete blockage of a coronary vessel.
• D. Sudden death due to ventricular fibrillation.

Answer: (C)

Acute myocardial infarction is defined by death of heart muscle cells (necrosis) caused by prolonged lack of blood flow due to a complete blockage of a coronary artery. When flow is fully obstructed, the oxygen-deprived cells cannot maintain their membranes and ion pumps, leading to irreversible injury and cell death. This distinguishes it from reversible ischemia, which happens with partial occlusion or brief interruptions where cells survive if perfusion is restored. Sudden death from a dangerous rhythm can accompany an MI but does not define the infarction itself.