Third degree AV block classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sara Zand, M.D.[2] Soroush Seifirad, M.D.[3] Cafer Zorkun, M.D., Ph.D. [4] Qasim Khurshid, M.B.B.S [4]

Overview

Third-degree or complete atrioventricular block suggests no conduction at all from atria to ventricles and may be paroxysmal or persistent and is usually associated with either a junctional or ventricular escape rhythm. Complete atrioventricular block may be identified in the setting of atrial fibrillation when the ventricular response is slow (<50 bpm) and regular. However, junctional rhythm in the setting of atrioventricular block may be present.

Classification

Term	Classification	Definition
Atrioventricular block	First-degree atrioventricular block	P waves associated with 1:1 atrioventricular conduction PR interval >200 ms atrioventricular delay because no P waves are blocked
	Second-degree AV block	P waves with a constant rate (<100 bpm) Atrioventricular conduction is present but not 1:1 Mobitz type I P waves with a constant rate (<100 bpm) Presence of periodic single non conducted P wave associated with P waves before and after the non conducted P wave with inconstant PR intervals Mobitz type II Presence of P waves with a constant rate (< 100 bpm) with a periodic single non conducted P wave associated with other P waves before and after the non conducted P wave with constant PR intervals (excluding 2:1 atrioventricular block) 2:1 atrioventricular block P waves with a constant rate (or near-constant rate because of ventriculophasic sinus arrhythmia) rate (<100 bpm), every other P wave conducts to the ventricles Advanced, high-grade or high-degree atrioventricular block ≥2 consecutive P waves at a constant physiologic rate that do not conduct to the ventricles with evidence for some atrioventricular conduction
	Third-degree AV block (complete heart block)	No evidence of atrioventricular conduction Vagally mediated atrioventricular block Any type of atrioventricular block due to increased parasympathetic tone Infranodal block Atrioventricular conduction block with evidence of conduction block distal to the atrioventricular node