First 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] Ahmed Elsaiey, MBBCH [3]

Overview

An atrioventricular block (or AV block) is a type of heart block involving impairment of the conduction between the atria and the ventricles of the heart. It usually involves the atrioventricular node, but it can involve other structures. AV block is categorized according to the degree and the site of conduction block. In first-degree AV block, all atrial impulses are conducted to the ventricles; however, there is a delay in conduction within the AV node resulting in a prolonged PR interval on ECG (>200 msec or >5 small blocks). In other words, a first-degree AV block is a slowed conduction without loss of atrioventricular synchrony.

Classification

• There is no established system for the classification of First degree AV block.
• Table below shown the classification of atrioventricular block.

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