ECG Conduction Blocks

ECG Library summary of the different types of conduction disturbance. Follow the links below 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
  • Q waves in leads I and aVL
  • Small R in lead III, in the absence of LVH.

Left posterior fascicular block (LPFB)

  • Right axis deviation
  • Small R in lead I
  • Small Q in lead III, in the absence of RVH

Right bundle branch block

  • QRS > 120 ms
  • Dominant R wave in V1
  • RSR’ pattern (“M”) in V1 with wide 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 slurred R wave (“M”) in V6 (=WiLLiaM)

Bifascicular block

Trifascicular block

Interventricular conduction disturbance

LITFL Further Reading

Advanced Reading




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

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