How does myocardial ischemia typically manifest on an ECG?

Myocardial ischemia is primarily characterized by changes in the ST segment of the ECG. When ischemia occurs, especially in the context of conditions such as angina or non-ST elevation myocardial infarction (NSTEMI), it often leads to ST segment depression. This is because the lack of adequate blood supply to the heart muscle alters its electrical activity during periods of stress or exertion.

ST depression typically appears as a downward shift of the ST segment below the baseline. This alteration indicates that the heart's muscle is not receiving enough oxygen, reflecting compromised perfusion and is one of the hallmark signs of myocardial ischemia on the ECG.

In contrast, other options such as ST elevation are typically indicative of acute myocardial infarction (AMI) where there is more extensive cardiac injury, and reversed P waves do not specifically relate to ischemic events. An elevated T wave might signify different cardiac conditions but is not a direct indicator of ischemia.