On an ECG, which segment is primarily analyzed for signs of ischemia?

The ST segment is primarily analyzed for signs of ischemia because it reflects the period of early repolarization of the ventricles after depolarization. In a normal ECG tracing, the ST segment should be at the same level as the baseline (isoelectric line). When there is ischemia, which occurs when blood flow to the heart muscle is compromised, the ST segment may become elevated or depressed.

For instance, ST segment elevation can indicate acute myocardial infarction or significant coronary artery blockage, while ST segment depression can suggest subendocardial ischemia. Therefore, any deviations from the isoelectric line in the ST segment are critical indicators of myocardial ischemia.

The other segments and waves provide useful information about different aspects of heart function but do not specifically indicate ischemia to the same extent as the ST segment. The P wave is associated with atrial depolarization, the QRS complex indicates ventricular depolarization, and the T wave represents ventricular repolarization. While abnormalities in these other components can reflect various cardiac pathologies, they are less directly tied to the detection of ischemia compared to the ST segment.