Small - septal - Q waves in the left ventricular leads result from depolarisation
of the septum from left to right. A Q wave in lead III may represent a normal
Pathological Q waves occur if they are 25% or more of the height
of the partner R wave and/or they are greater than 0.04 seconds in width - one
small square - and greater than 2mm (two small squares) in depth (1).
waves are a marker of electrical silence, which, when pathological, implies full
thickness death of myocardium, which happened a long time ago. They are negative
because they are effectively windows through which can be seen the opposite side
of the heart, in which depolarisation will be moving away from the electrode.
If a Q wave occurs in lead I then check for Q waves in AVL and the chest leads.If
a Q wave occurs in lead II or AVF then check for Q waves in the other inferior
As stated previously, a Q wave in lead III alone may be positional
and a normal finding
- Q waves which are 25 % of the depth of the succeeding R wave, and which
last for more than 20 ms may still not be pathological in lead III as long
as there are no accompanying Q waves in aVF and II - these Q waves often disappear
on deep inspiration
- 1) Sahay P. E.C.G. Mystery solved.Publishing Initiatives, 1996.
- 2) Wright RA et al (1993). Prognosis in ischaemic heart disease. Medicine
International, 21(10), 384-88.