Which ECG finding is most consistent with acute myocardial infarction?

• A. ST elevation
• B. Q waves only
• C. T wave inversion only
• D. ST depression without elevation

Answer: (A)

ST-segment elevation on an ECG signals acute transmural injury of the heart muscle, which is the hallmark of an acute myocardial infarction. When ischemia is ongoing in a full-thickness block of the myocardium, the injury current alters the ventricular repolarization pattern, causing the ST segment to rise in the leads facing the affected area. This elevation reflects active, ongoing infarction and typically prompts urgent reperfusion therapy.

Other patterns can occur in different contexts but are less specific for an acute, full-thickness infarct. Q waves alone usually indicate established necrosis from a prior infarct and are not the immediate sign of an acute event. T wave inversion can occur with ischemia or evolving infarction but alone it is not diagnostic of an acute STEMI. ST depression without elevation points to subendocardial ischemia or NSTEMI, where the infarction may not be transmural.

So the presence of ST-segment elevation best fits acute myocardial infarction, signaling ongoing transmural injury and the need for rapid treatment.