What changes in the electrocardiogram (EKG) tracing would the nurse monitor for in the patient with a myocardial infarction?

ST-segment elevation is the most critical and classic EKG finding in an acute myocardial infarction (AMI), specifically indicating a ST-elevation myocardial infarction (STEMI). The ST segment represents the period between ventricular depolarization and repolarization. When myocardial tissue is acutely injured due to ischemia from coronary artery occlusion, the injured cells are unable to maintain their normal membrane potential, causing the ST segment to elevate above the isoelectric baseline in the leads overlying the infarcted area. This elevation reflects transmural injury of the myocardium and is the EKG change that prompts emergent reperfusion therapy. ST-segment depression is seen in subendocardial ischemia or non-ST-elevation MI (NSTEMI), not transmural infarction. Flattened or inverted T waves can occur with ischemia or electrolyte abnormalities but are not the primary hallmark of an acute MI. Flattened P waves may indicate atrial abnormalities or electrolyte disturbances such as hyperkalemia, but they have no specific association with myocardial infarction. Nurses must recognize ST-segment elevation as a time-critical finding requiring immediate physician notification and preparation for reperfusion intervention.