Non-infarction Q waves

Most of us think of myocardial infarction when pathological Q waves are seen on the ECG. But Q waves of different types can occur without myocardial infarction. Here is a brief review of some of them. The so called septal q waves in lateral leads indicate initial left to right activation of the interventricular septum. That is because impulse from the AV node travels faster down the left bundle branch and activates septum from left to right. Septal Q waves can become prominent in left ventricular volume overload situations like chronic severe aortic regurgitation. Unlike the pathological Q waves of myocardial infarction, these septal Q waves are narrower than 40 ms.

Q waves can occur in takotsubo cardiomyopathy, hypertrophic cardiomyopathy, myocarditis, tumours, sarcoidosis and amyloidosis. Among conduction abnormalities which can cause Q waves are left bundle branch block and Wolff-Parkinson-White syndrome. In WPW syndrome, the initial negative delta wave manifests as a Q wave.

Absence of initial left to right septal activation in left bundle branch block makes the first wave a Q wave or a QS complex in right oriented leads in left bundle branch block. QS complex means that there is only a single negative wave and no positive waves.