Intraventricular Conduction Delay (QRS widening)

Definition of 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
• Tricyclic antidepressant poisoning.

Causes of Intraventricular Conduction Delay

Fascicular and bundle-branch blocks

• Left anterior fascicular block
• Left posterior fascicular block
• Left bundle branch block
• Right bundle branch block
• Bifascicular block
• Trifascicular block

Ventricular hypertrophy and dilatation

• Left ventricular hypertrophy
• Right ventricular hypertrophy
• Biventricular enlargement
• Dilated cardiomyopathy

Electrolyte abnormalities

• Hyperkalaemia

Toxins

• Sodium-channel blocker toxicity (e.g. TCA overdose) – wide QRS plus positive R’ wave in aVR.

Pre-excitation

• Wolff-Parkinson-White syndrome – wide QRS plus delta waves.

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

• Ventricular tachycardia
• Accelerated idioventricular rhythm
• Ventricular escape rhythm
• Ventricular-paced rhythm

References

• 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
  

Advanced Reading

Online

• Wiesbauer F, Kühn P. ECG Mastery: Yellow Belt online course. Understand ECG basics. Medmastery
• Wiesbauer F, Kühn P. ECG Mastery: Blue Belt online course: Become an ECG expert. Medmastery
• Kühn P, Houghton A. ECG Mastery: Black Belt Workshop. Advanced ECG interpretation. Medmastery
• Rawshani A. Clinical ECG Interpretation ECG Waves
• Smith SW. Dr Smith’s ECG blog.

Textbooks

• Zimmerman FH. ECG Core Curriculum. 2023
• Mattu A, Berberian J, Brady WJ. Emergency ECGs: Case-Based Review and Interpretations, 2022
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
• Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
• Hampton J, Adlam D. The ECG Made Practical 7e, 2019
• Kühn P, Lang C, Wiesbauer F. ECG Mastery: The Simplest Way to Learn the ECG. 2015
• Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
• Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004

LITFL Further Reading

• ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
• ECG A to Z by diagnosis – ECG interpretation in clinical context
• ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
• 100 ECG Quiz – Self-assessment tool for examination practice
• ECG Reference SITES and BOOKS – the best of the rest