2:1 Atrioventricular block: order from chaos

Am J Emerg Med. 2001 May;19(3):214-7. doi: 10.1053/ajem.2001.21715.


2:1 AV block can occur in either the AV node or the His-Purkinje system and cannot be classified into type I or type II second-degree AV block because there is only one PR interval to examine before the blocked P wave. It is inappropriate to use terms such as 2:1 or 3:1 type I or type II AV block because this characterization violates the accepted traditional definitions of type I and type II block based on electrocardiographic patterns and not on the anatomical site of block. Type I and type II second-degree AV block can progress to 2:1 AV block, and 2:1 AV block can regress to type I or type II block. Consequently, the site of the lesion in 2:1 block can often be determined by seeking the company 2:1 AV block keeps. An association with type I block and a narrow QRS complex almost always reflects AV nodal block but type I block with a wide QRS complex occurs more commonly in the His-Purkinje system than the AV node. Type II block, if correctly defined, is always infranodal. Outside of acute myocardial infarction, sustained 2:1 and 3:1 AV block with a wide QRS complex occurs in the His-Purkinje system in 80% of cases and 20% in the AV node. Administration of atropine in patients with His-Purkinje disease may increase the degree of AV block.

Publication types

  • Comparative Study

MeSH terms

  • Anti-Arrhythmia Agents / therapeutic use
  • Atrioventricular Node / physiopathology
  • Atropine / therapeutic use
  • Contraindications
  • Electrocardiography*
  • Emergency Medical Services
  • Heart Block* / classification
  • Heart Block* / diagnosis
  • Heart Block* / drug therapy
  • Heart Block* / physiopathology
  • Hemodynamics
  • Humans
  • Purkinje Fibers / physiopathology


  • Anti-Arrhythmia Agents
  • Atropine