What is the characteristic sign of an ischemic heart condition on an ECG?

An ischemic heart condition is primarily characterized by alterations in the ST segment on an electrocardiogram (ECG). These changes can manifest as either ST-segment elevation or depression. ST-segment depression often indicates subendocardial ischemia or insufficient blood flow during periods of stress, whereas ST-segment elevation is typically associated with more severe, transmural ischemia, often seen in conditions like acute myocardial infarction.

The presence of these ST-segment changes is crucial for diagnosing various cardiac conditions, as they reflect underlying ischemic processes and can guide treatment decisions in clinical scenarios. In contrast, the other options indicate different types of cardiac issues or are associated with other conditions: a prolonged QT interval is related to the risk of arrhythmias, widened QRS may indicate a conduction block or abnormal ventricular depolarization, and inverted T waves can suggest a range of conditions but are less definitive for ischemia alone. Therefore, observing ST-segment changes provides a direct indication of ischemic events affecting the heart's supply of oxygen and nutrients.