ECG Conduction Blocks

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

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Conduction Blocks

First-degree block

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Second-degree block

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Third-degree block

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

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Fascicular Blocks

• Left axis deviation
• qR complexes in leads I, aVL
• rS complexes in leads II, III, aVF
• Prolonged R wave peak time in aVL > 45ms

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• Right axis deviation
• rS complexes in leads I, aVL
• qR complexes in leads II, III, aVF
• Prolonged R wave peak time in aVF

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

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

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Advanced Reading

Online

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

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LITFL Further Reading

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