Which ECG finding indicates that a patient may have experienced a myocardial infarction?

The presence of significant Q waves on an ECG is a key indicator that a patient may have experienced a myocardial infarction. In the setting of a myocardial infarction, particularly a STEMI (ST elevation myocardial infarction), the myocardial tissue undergoes necrosis and damage. This damage results in changes in the electrical activity of the heart, which can be reflected on the ECG.

Significant Q waves appear as a sign of previous myocardial injury; they are characterized by their depth and width. When Q waves are wider than 1 small box in duration (greater than 0.04 seconds), and the amplitude is at least one-third of the height of the R wave, this is typically considered significant. These changes often arise hours to days after the event and remain even after the acute phase has resolved, indicating that myocardial necrosis has occurred.

In contrast to this, normal sinus rhythm reflects a healthy electrical pattern in the heart without any indications of ischemia or infarction. Inverted P waves can suggest issues related to atrial depolarization, possibly indicating atrial enlargement or ectopic rhythm, but they do not specifically point to myocardial infarction. Flat ST segments generally indicate a lack of acute changes, particularly T-wave inversion or ST segment elevation,