Diagnostics2:1 Atrioventricular block: Order from chaos*,**,*,★★
Section snippets
Incorrect use of type I and type II designations in 2:1 AV block
It is inappropriate to describe 2:1 or n:1 nodal AV block (n > 2) as type I block and 2:1 or n:1 infranodal block (n > 2) as type II block. This practice violates the well-accepted traditional definitions of type I and type II blocks based on electrocardiographic patterns rather than the anatomical site of block.9 Perhaps those who cling to the above designations still believe that all type I blocks are confined to the AV node (incorrect)10, 11, 12, 13 and all type II blocks are infranodal
Site of block
The significance of 2:1 AV block can be evaluated during changes in conduction to 3:2, 4:3, and so on. AV block that permit the emergence of the electrocardiographic patterns of type I or type II block. Type I block can occur either in the AV node or the His-Purkinje system. Type I block with a wide QRS complex (≥ 0.12 sec) is localized in the His-Purkinje system in 60% to 70% of cases outside of acute myocardial infarction.14, 16 Type I block with a narrow QRS complex occurs almost always in
Source of confusion
Mobitz30 in his original description of type II block included 2:1, 3:1, and so on AV block as a form of type II block but the renowned Chicago School of Electrocardiography in the mid 1950s seems responsible for the continuing misconceptions about 2:1 AV block.31, 32 These highly respected experts advocated calling 2:1 AV block type I block if the ECG showed evidence of decremental conduction with changing circumstances (when the AV conduction ratio does not change to at least 3:2 AV block so
Illogical arguments
Marriott, a renowned electrocardiographer,32, 33, 34, 35, 36 has repeatedly stated that (1) 2:1 AV block may be either type I (AV nodal with a narrow QRS) or type II (infranodal with a wide QRS). (2) Type I 2:1 AV block is more common than type II 2:1 AV block. (3) Type I and type II 2:1 AV block can often be differentiated by evaluating the “presence or absence of bundle branch block, the associated patterns of conduction and the clinical context.” Marriott's contentions really apply to the
Implications for emergency care
The reflex use of atropine in 2:1 AV block is strongly discouraged. Atropine can be administered to hemodynamically unstable patients with narrow QRS 2:1 AV block because the block is often AV nodal. Most of these patients respond to atropine by increasing the sinus rate and improving AV nodal conduction with a resultant increase in the ventricular rate. A paradoxical reaction to atropine is unusual in the setting of a narrow QRS complex. In His-Purkinje disease atropine increases the sinus
Bedside diagnostic approach
All the arguments about 2:1 AV block are also applicable to n:1 AV block where n > 2.
When faced with 2:1 AV block, bear in mind the following relatively simple points. (1) Avoid the “reflex” labels of type I or type II block. (2) Remember that the anatomical site of block should not be characterized in terms of either type I or type II because these designations refer only to electrocardiographic patterns. (3) The company 2:1 AV block keeps can provide information about the site of block. Wait
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Cited by (19)
Definitions and Pitfalls in the Diagnosis of Atrioventricular Block
2023, Heart Lung and CirculationElectrophysiology, pacing, and devices
2010, Paediatric CardiologyElectrophysiology, Pacing, and Devices
2009, Paediatric CardiologyElectrocardiographic manifestations: Diagnosis of atrioventricular block in the Emergency Department
2004, Journal of Emergency MedicineMobitz type II second-degree atrioventricular block during sleep: true or false?
2023, Herzschrittmachertherapie und Elektrophysiologie
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Returned July 27, 2000.
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Address reprint requests to S. Serge Barold, MD, 6237 NW 21st Court, Boca Raton, FL 33496. E-mail: ssbarold\@aol.com
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Am J Emerg Med 2001;19:214-217.
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