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Test Findings

Prolonged QRS Interval



  • 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.
    • Prolonged QRS Interval
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