QRS Duration Normal <120 ms — FRCA Primary MCQ

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EasyPhysiology - CardiovascularQRS Duration Normal <120 msFRCA Primary

The QRS complex duration on the ECG should normally be less than:

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Correct answer: E — 120 ms

Normal QRS duration is <120 ms (3 small squares at standard paper speed 25 mm/s). Prolonged QRS (>120 ms) indicates abnormal intraventricular conduction: bundle branch block (RBBB or LBBB) / pre-excitation (WPW) / hyperkalaemia / Na+ channel blocker toxicity (local anaesthetics / tricyclics). Very wide QRS (>160 ms) is concerning for imminent arrest.

Reference: Power Kam 2018 Principles of Physiology for the Anaesthetist