What ECG finding suggests significant myocardial ischemia?

The presence of ST-segment depression on an ECG is a significant indicator of myocardial ischemia. This finding suggests that there is a discrepancy between the blood supply to the heart muscle and the oxygen demand of that muscle, which can occur during conditions of stress such as angina or an impending myocardial infarction.

When there is ischemia, it generally disrupts the normal electrical activity of the heart, resulting in changes reflected on the ECG. ST-segment depression specifically indicates that part of the heart is not receiving sufficient oxygen during the repolarization phase of the cardiac cycle. This finding can manifest as a downsloping or horizontal drop in the ST segment from the baseline and is often observed during physical exertion or stress testing in patients with coronary artery disease.

In contrast, a normal ST segment reflects healthy myocardial perfusion, and tall T-waves can sometimes indicate hyperkalemia or other conditions, but are not definitive signs of ischemia. Widened QRS complexes can indicate a bundle branch block or other electrical conduction issues, but they do not specifically point to ischemia in the way that ST-segment depression does.