What defines a pathological Q wave on ECG?

• A. Q waves ≥0.04 seconds and at least 25% of the following R wave height
• B. Q waves ≥0.08 seconds with 50% R wave height
• C. Q waves <0.02 seconds and absent R waves
• D. Q waves only in lateral leads

Answer: (A)

Pathological Q waves reflect prior myocardial infarction with scar, and they are defined by a specific combination of width and depth in a single lead. The standard criterion is a Q wave that lasts at least 0.04 seconds (40 ms) and is at least one-quarter the height of the following R wave in that lead. This ensures the Q wave is truly representing scar tissue rather than a normal variant.

That matches the correct choice: a Q wave of ≥0.04 seconds with at least 25% of the following R wave height.

The other descriptions don’t fit the defining pattern. A Q wave that’s longer, such as 0.08 seconds, still isn’t paired with the correct depth criterion (25% of the R wave, not 50%), and the combination isn’t the accepted standard. Q waves shorter than 0.02 seconds and absent R waves don’t describe a pathologic Q; they point to different abnormalities. Lastly, limiting Q waves to lateral leads isn’t how a pathologic Q wave is defined—it can appear in various leads depending on infarct location.