Which ECG changes most indicate myocardial ischemia?

• A. ST depression and/or T-wave inversion
• B. ST elevations in all leads
• C. Prolonged PR interval
• D. Prominent U waves

Answer: (A)

Ischemia changes how the heart’s cells repolarize, so the ECG shows tells-tale signs in the ST segment and T waves. When blood flow is reduced to the inner layer of the heart muscle (subendocardial ischemia), the ST segment tends to dip below baseline and the T waves often invert. These patterns are classically seen during chest pain or during stress testing and are the most consistent indicators of myocardial ischemia.

ST elevations, by contrast, point more toward transmural injury or acute infarction—full-thickness wall involvement—or can be seen with other conditions like pericarditis, so they are not the typical marker of reversible ischemia. Prolonged PR interval signals a conduction delay (AV block), not ischemia, and prominent U waves are linked to electrolyte issues or certain medications, not ischemia.

So the presence of ST depression and/or T-wave inversion best reflects myocardial ischemia on the ECG, highlighting subendocardial regions affected by reduced blood flow.