Pathological Q wave
A Q wave that is abnormally deep and broad, rather than the small initial downward deflection that normally comes from the septum depolarizing.
Key ECG features
- ✓Initial negative deflection deeper and wider than a septal q
- •Present on every beat in the same lead
- ±In leads where a q wave is normally small or absent
- ±Reproducible when the recording is repeated
✓ required · • typical · ± may be present
ECG characteristics
An initial negative deflection ahead of the R wave that is deeper and wider than the small septal q normally seen, appearing in the same lead on every beat rather than on an isolated complex. Repeat the recording with attention to lead placement and body position before calling it real, because both can create or erase an apparent Q wave.
This illustration is schematic. Dashed line is a normal complex. The grid is not drawn to scale.
Common causes
Loss of viable myocardium beneath the recording lead is the classical explanation, whether from infarction, fibrosis or an infiltrative process. In dogs and cats true myocardial infarction is far less common than in people, so a deep Q more often reflects cardiomyopathy, myocarditis, or chamber enlargement that has changed the direction of septal activation. Positional and technical causes are common enough that they are worth excluding first.
Why it matters
On its own this is a prompt to look at the myocardium, not a diagnosis. It carries weight when it is reproducible, confined to particular leads, and accompanied by other evidence of myocardial disease. Echocardiography answers the question the ECG only raises.
Differentiate from
- Bundle branch blockA wide QRS can begin with a broad negative deflection that mimics a pathological Q. The QRS width and the shape of the whole complex separate them, not the initial deflection alone.
- Ventricular premature complexesAn ectopic complex may open with a deep negative deflection, but it arrives early and does not recur in the same position on every beat.