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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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