AV block: 2nd degree, “high-grade” AV block

High Grade AV block

Second degree heart block with a P:QRS ratio of 3:1 or higher, producing an extremely slow ventricular rate.

• Unlike 3rd degree heart block there is still some relationship between the P waves and the QRS complexes.
• High-grade AV block may result from either Mobitz I or Mobitz II AV block.

ECG Example of High-grade AV block

• High-grade AV block (4:1 conduction ratio).
• Atrial rate is approximately 140 bpm.
• Ventricular rate is approximately 35 bpm.
• Broad QRS complexes suggest that this may be due to Mobitz II block (see “fixed ratio blocks” for a discussion of this concept).

Related Topics

• AV block: 1st degree
• AV block: 2nd degree, Mobitz II
• AV block: 2nd degree, “fixed ratio blocks” (2:1, 3:1)
• AV block: 3rd degree (complete heart block)

History

• Eponymythology: History of Second-degree AV block
• Eponym. Karel Frederik Wenckebach (1864 -1940)
• Eponym. Woldemar Mobitz (1889 – 1951)
• Eponym. John Hay (1873 – 1959).

Advanced Reading

Online

• Wiesbauer F, Kühn P. ECG Mastery: Yellow Belt online course – Become an ECG expert. Medmastery
• Wiesbauer F, Kühn P. ECG Blue Belt online course: Learn to diagnose any rhythm problem. Medmastery
• Rawshani A. Clinical ECG Interpretation ECG Waves
• Smith SW. Dr Smith’s ECG blog.

Textbooks

• Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
• Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• Hampton J. The ECG Made Practical 7e, 2019
• Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
• Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography 1e, 2009
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
• Mattu A, Brady W. ECG’s for the Emergency Physician Part I 1e, 2003 and Part II
• Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004
• Smith SW. The ECG in Acute MI. 2002 [PDF]

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