title: 2:1 Atrioventricular block: order from chaos.
abstract: 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.
authors.affiliation: Electrophysiology Institute, Broward General Hospital, Ft. Lauderdale, FL, USA. ssbarold@aol.com
authors.forename: S S
authors.initials: SS
authors.lastname: Barold
mesh_terms: D000889:Anti-Arrhythmia Agents / Q000627:therapeutic use; D001283:Atrioventricular Node / Q000503:physiopathology; D001285:Atropine / Q000627:therapeutic use; D000075202:Contraindications; D004562:Electrocardiography; D004632:Emergency Medical Services; D006327:Heart Block / Q000145:classification / Q000175:diagnosis / Q000188:drug therapy / Q000503:physiopathology; D006439:Hemodynamics; D006801:Humans; D011690:Purkinje Fibers / Q000503:physiopathology
chemical_list: D000889:Anti-Arrhythmia Agents; D001285:Atropine