What changes on an ECG suggest ischemia?

Ischemia in the heart occurs when there is an inadequate supply of blood and oxygen to the cardiac muscle, often due to narrowed or blocked arteries. On an electrocardiogram (ECG), one of the key indicators of myocardial ischemia is ST-segment depression.

When there is ischemia, the heart's electrical activity is altered during the repolarization phase, which reflects as a downward deviation (depression) of the ST segment from the baseline. This is often seen during periods of exertion or stress when the heart requires more oxygen than it is receiving. ST-segment depression can be indicative of stable angina, indicating transient ischemia, or it can suggest more concerning issues depending on the clinical context.

In contrast, other ECG changes such as ST-segment elevation typically indicate injury or acute myocardial infarction, which is different from ischemia, and normal sinus rhythm suggests no current electrical abnormalities in the heart. Complete heart block does not indicate ischemia directly; rather, it signifies a serious disruption in the heart’s electrical conduction system. Thus, ST-segment depression is the most relevant ECG change for suggesting ischemia.