Prolonged QRS Interval
Overview
The duration of the QRS interval is useful for determining the origin of an abnormal rhythm, particularly in the setting of tachycardia.
Normal Duration
- 80 - 120ms (2-3mm)
Interpretation
- Narrow QRS complexes (<120ms) - indicative of a supraventricular rhythm from the SA node, atria or AV node.
- Wide QRS complexes - indicative of a ventricular rhythm, or aberrant conduction of a supraventricular rhythm.
Causes of Wide QRS Complexes
Ventricular Origin
- Premature ventricular complexes
- Ventricular tachycardia
- Pacemaker rhythm
Aberrant Conduction
- Bundle branch block
- Accessory pathway, e.g. Wolff-Parkinson-White
- Hyperkalaemia
- Sodium channel blocker toxicity - tricyclic antidepressants, type I antiarrhythmics, local anaesthetics
Example
- Wide QRS complexes in the setting of left bundle branch block.
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