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 700

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 Emergency Medicine Advanced Trainee based in Melbourne, Australia. Co-author of the LITFL ECG Library. Likes Ultrasound, Echo, ECGs, and anything and everything with caffeine. Part of the 2021 ANZCEN Clinician Educator Incubator Programme | @rob_buttner | ECG Library |

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