What is the earliest sign of myocardial infarction on an EKG tracing?

The earliest sign of myocardial infarction on an EKG tracing is ST segment elevation. When myocardial tissue is deprived of adequate blood flow, as seen in a heart attack, it leads to cellular injury and alters the electrical activity of the heart. This change manifests as an elevation in the ST segment on the EKG.

In the context of ischemia, the initial changes that occur in the myocardial tissue can present as ST segment elevation, particularly in cases of transmural infarction, where the injury extends through the full thickness of the heart muscle. The ST segment can elevate within minutes of ischemic event onset, making it a critical marker for early identification of myocardial infarction.

Other options, such as Q wave development and T wave inversion, are significant indicators of more advanced stages of myocardial infarction. Q waves typically develop later, indicating necrosis and irreversible damage to myocardial tissue, while T wave inversion can occur after the initial injury but is not as immediate as ST segment changes. Normal sinus rhythm suggests that there is no significant electrical disturbance in the heart, thus not pointing toward an infarction.