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

Definition

• 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.

Example

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

Further Reading

• ECG BASICS — Waves, Intervals, Segments and Clinical Interpretation
• ECG CLINICAL CASES — Your favourite ECG’s placed in clinical context with a challenging Q&A approach
• ECG and Cardiology Eponymous Syndromes — Cheats guide to eponymous emancipation
• ECG Exam Template — a framework for the FACEM part 2 exam.
• ECG Reference Sites on the WEB — the best of the rest

Author Credits

References

• Hampton, JR. The ECG in Practice (5th edition), Churchill Livingstone 2008.
• Wagner, GS. Marriott’s Practical Electrocardiography (11th edition), Lippincott Williams & Wilkins 2007.