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
- First-degree block PR interval >200 msec (1 large square)
Second-degree block
- Mobitz Type I (Wenckebach Block): progressive prolongation of the PR interval before the missed QRS complex
- Mobitz Type II (Hay Block): absence of progressive prolongation of the PR interval before the missed QRS complex
- Fixed ratio blocks (e.g. 2:1, 3:1): constant relationship between P waves and QRS complexes (e.g. 2:1 = 2 P waves for each QRS complex).
- High grade AV block: 2nd degree AV block with a high P:QRS ratio, producing a very slow ventricular rate
Third-degree block
- Third-degree block: absence of any relationship between P waves of sinus origin and QRS complexes (AV dissociation)
Fascicular Blocks
Left anteriorfascicular 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
- Bifascicular block plus 3rd degree AV block
Interventricular conduction disturbance
- QRS > 100 ms, not due to LBBB or RBBB. Most important causes are hyperkalaemia or tricyclic antidepressant poisoning
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.
- Wiesbauer F. Little Black Book of ECG Secrets. Medmastery PDF
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
ECG LIBRARY
Ed Burns
Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |
Robert Buttner
MBBS DDU (Emergency) CCPU. Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Co-creator of the LITFL ECG Library. Twitter: @rob_buttner
