Interventricular Conduction Delay (QRS widening)


  • QRS duration > 100 ms in the presence of a supraventricular rhythm.
  • Most commonly due to bundle branch block or left ventricular hypertrophy.
  • The most important life-threatening causes of QRS widening are hyperkalaemia and tricyclic antidepressant poisoning.


Follow the links to read more about each condition.

Fascicular and bundle-branch blocks

Ventricular hypertrophy and dilatation

Electrolyte abnormalities



Arrhythmogenic cardiac conditions

  • Brugada syndrome – localised QRS widening in V1-2 with RBBB morphology.
  • Arrhythmogenic right ventricular dysplasia (AVRD) – localised QRS widening in V1-2 plus epsilon waves and variable signs of right ventricular hypertrophy.

“Non-specific” IVCD

  • Not due to any of the causes above — Before making this diagnosis, be sure to check the serum potassium level and scrutinise the ECG for any signs of TCA toxicity.

Differential Diagnosis

Ventricular Rhythms

Further Reading


  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.
  • Edhouse J, Thakur RK, Khalil JM. ABC of clinical electrocardiography. Conditions affecting the left side of the heart. BMJ. 2002 May 25;324(7348):1264-7. Review. PubMed PMID: 12028984; PubMed Central PMCID: PMC1123219 [Full Text].
  • Surawicz B, Knilans TK. Chou’s Electrocardiography in Clinical Practice. 6th Edition. Saunders Elsevier 2008.
  • Wagner, GS. Marriott’s Practical Electrocardiography (11th edition), Lippincott Williams & Wilkins 2007.
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