Q waves are pathological if they exceed what length?

Pathological Q waves are indicative of myocardial infarction and are characterized by their duration and depth. For Q waves to be considered pathological, they typically need to be greater than 40 milliseconds in duration. This means they last long enough to suggest that there has been necrosis of the myocardium, primarily seen in conditions such as a previous heart attack.

In general, Q waves that are narrower than this, such as those measuring 10 ms, 20 ms, or 30 ms, may be present in normal physiologic conditions or may not indicate significant myocardial damage. The 40 ms measurement serves as a critical threshold to differentiate between normal and pathological Q waves, making it a key point in the interpretation of an electrocardiogram (EKG) when assessing for potential heart conditions.