When measuring QRS width, the lead with the widest QRS complex is chosen.

  The width of the QRS increases as the left ventricular dimensions increase.

  The width of the QRS complexes in precordial leads are wider than those of the limb leads.

  The QRS width is accepted to be
increased if it is

-
90 ms or more in children < 4 years of age,

-
100 ms or more in children between 4-16 years of age,

-
> 110 ms in subjects > 16 years of age.



Q waves as normal variants

  Isolated Q wave in lead III

  QS pattern in lead C1 (V1)

  Q wave in lead aVL (in vertical hearts)

  Q waves in inferior and left lateral leads in children


Pathologic Q waves: Q/R ratio ≥ 0.25 or ≥ 40 ms in duration in two or more leads (excluding III and aVR).


Causes of wide QRS complex

  Left ventricular hypertrophy

  Bundle branch blocks

  Hyperkalemia

  Wolff-Parkinson-White (WPW) syndrome

  Cardiac pacemaker stimulation (except His bundle pacing)




References

  J Am Coll Cardiol 2017;69:1057-1075. (International Recommendations for Electrocardiographic Interpretation in Athletes.) (free full-text)

  Circulation 2009;119;e235-e240.





ECG 1. The ECG above belongs to an apparently healthy, 7 years-old boy.
His echocardiogram is normal.
The narrow q waves in leads II, III, aVF, V5 and V6 are benign.

Click here for a more detailed ECG





ECG 2. The compact ECG above belongs to an apparently healthy, 18 years-old lean male.
His echocardiogram is normal.
The narrow q waves in leads II, III, aVF, V5 and V6 are benign.