ECG Conduction Blocks

ECG Library summary of the different types of conduction disturbance, with links to read more about each type of conduction block

Conduction Blocks

First-degree block

Second-degree block

Third-degree block
  • Third-degree block: absence of any relationship between P waves of sinus origin and QRS complexes (AV dissociation)

Fascicular Blocks

Left anterior fascicular block (LAFB)
  • Left axis deviation
  • qR complexes in leads I, aVL
  • rS complexes in leads II, III, aVF
  • Prolonged R wave peak time in aVL > 45ms

Left posterior fascicular block (LPFB)
  • Right axis deviation
  • rS complexes in leads I, aVL
  • qR complexes in leads II, III, aVF
  • Prolonged R wave peak time in aVF

Right bundle branch block
  • QRS > 120 ms
  • Dominant R wave in V1
  • RSR’ pattern (“M”) in V1 with wide, slurred S wave (“W”) in V6 (=MaRRoW)

Left bundle branch block
  • QRS > 120 ms
  • Dominant S wave in V1
  • Deep S wave (“W”) in V1 with broad R wave (“M”) in V6 (=WiLLiaM)

Bifascicular block

Trifascicular block

Interventricular conduction disturbance

Advanced Reading

Online

Textbooks


LITFL Further Reading

ECG LIBRARY

Electrocardiogram

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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