What ECG finding is most indicative of a myocardial infarction?

Significant Q waves are a key marker on an ECG for diagnosing a myocardial infarction, especially when they are at least 1/4 the height of the R wave in the same lead, and they indicate that there has been damage to the myocardial tissue. These abnormal Q waves appear hours to days after an infarction and represent necrosis of the heart muscle, as the electrical activity in that region is altered. The presence of these significant Q waves suggests a past or current myocardial infarction, particularly when found in specific leads associated with the affected area of the heart.

In contrast, elevated or spiked T waves, while they can indicate myocardial ischemia or other conditions, are not definitive for myocardial infarction. Inverted T waves can also be a sign of ischemia but are less specific and may be associated with other cardiac issues. Flat P waves are not typically associated with myocardial infarction and indicate other types of atrial issues or may represent a normal variant in some individuals. Thus, the presence of significant Q waves distinctly points to myocardial damage, making it the most indicative finding of a myocardial infarction.