Duration and Morphology of the QRS Complex

QRS complexes will all have a similar shape and size with a duration of 0.12 seconds or longer. As a general rule the broader the QRS complex the more likely the rhythm is to be ventricular in origin, particularly if the complexes are over 0.16 seconds.

The pattern of the QRS complexes will usually be similar to those of the right bundle branch block (RBBB) or left bundle branch block (LBBB).

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Fig 1: Ventricular tachycardia right bundle branch block pattern	Fig 2: Ventricular tachycardia left bundle branch block pattern

More commonly, it is RBBB pattern suggesting that the origin of the arrhythmia is within the left ventricle.