Wide QRS

Key Features

  • Sinus Rhythm
  • Wide QRS
  • Peaked T waves
  • Flattened p waves

Interpretation = Hyperkalaemia

… 20 minutes post calcium gluconate:

  • QRS narrows
  • T waves decrease in amplitude

40 year old lady found unconscious in bed. Seen completely well 2 hours earlier by husband.

Key Features

  • Irregular tachycardia ?AF
  • Wide complex
  • Prominent terminal R wave in aVR (Right axis deviation of the terminal QRS)


  • Given history of sudden deterioration in consciousness from well state and these ECG findings – Sodium Channel Blockade from overdose

Sodium Channel Blocking Drugs include:

  • TCA’s (tricyclic antidepressants): Amitriptyline, Desimipramine, Dothiepin, Imipramine, Nortripytline
  • Class 1A anti-arrhythmics: Disopyramide, Procainamide, Quinidine
  • Class 1C anti-arrhythmics: Flecanide
  • Local Anaesthetics:¬†Bupivacaine, Cocaine, Ropivacaine
    Antimalarials: Hydroxychloroquine/Chloroquine, Quinine
  • Other: Phenothiazines (Thioridazine), Amantadine, Carbamazepine, Chloroquine, Diltiazem, Diphenhydramine, Propoxyphene/Dextropropoxyphene, Propanolol

Source: Toxicology Handbook, 3rd edition, Murray et al

Key Features

  • Regular bradycardia
  • Wide complex
  • Baseline artefact (shivering)
  • Osborne J waves (prominent notching at end of QRS)

Further history

  • 80y.o lady fell over on way back to toilet in middle of night. Unable to get up and found on floor after 24hrs.



…. After rewarming 2 degrees

Key Features

  • Very slow rate
  • Wide
  • and…
  • ECG 4(a)
    • Near total absence of atrial activity
  • ECG (b)
    • Regular atrial activity without relationship to ventricular activity

Interpretation = Ventricular Escape Rhythms

  • 4(a) Due to sinus arrest
  • 4(b) Due to complete heart block

Key Features

  • Wide regular rhythms
    • Unusually “normal” rate
      • Faster than usual ventricular escape rhythms
      • Slower than VT
  • Nil other features to suggest a Tox/Metabolic cause

Interpretation – Accelerated IdioVentricular Rhythm (AIVR) due to

  • 5(a) MI post reperfusion
  • 5(b) Athlete’s heart (sinus beats with intermittent AIVR)

Key features

  • Wide QRS
  • Short PR
  • Delta waves

Interpretation: Accessory Pathway – Wolf Parkinson White (WPW)

Key causes of a Wide QRS

  • Bundle Branch Block
  • Accessory Pathway
  • Ventricular rhythm
    • Ventricular escape rhythm
    • AIVR – Accelerated Idioventricular Rhythm
    • Ventricular tachycardia
  • Toxicology/Metabolic (Cellular poisoning
    • Hyperkalaemia
    • Sodium Channel Blockade
    • Hypothermia

Key Diagnostic Clues

  • History:
    • Toxicological cause? Hypothermia? Reasons for hyperkalaemia?
  • ECG findings
    • Heart rate:
      • Slow – think ventricular escape rhythms; think hypothermia if history/temp supports
      • Very fast – think VT
    • QRS Morphology
      • Features/appearance of RBBB or LBBB?
    • Other ECG abnormalities
      • Peaked T waves, Short PR/delta waves, Osborne J waves, Terminal R wave in aVR