Atrioventricular block electrocardiogram

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Atrioventricular Block Electrocardiogram

First degree AV block EKG Examples

Shown below is an EKG image of first degree AV block. With PR interval exceeding 200 msec and prolonged PR conduction, a more appropriate classification for this conduction disturbance may be the result of conduction delay within the atrium, AV node, bundle of His or bundle branches. Prolongation of the PR interval most often indicates AV nodal conduction delay.

Shown below is an EKG image showing sinus rhythm with a prolonged pr interval (>120ms.) which is first degree A/V block. There is also a left axis deviation (axis between -30 and -90 degrees) with r waves in the inferior leads. This axis deviation is consitent with a left anterior fasicular block.

Second degree AV block EKG Examples

Mobitz I Second degree AV block EKG Examples

Shown below is an EKG image of ventriculophasic reflex during second degree AV block Mobitz I. The PP interval that follow upon the blocked sinus beat is prolonged.

Shown below is two rhythm strips show Mobitz I A/V block with a gradual increase in the PR interval before the dropped p wave. Note the 2:1 block in the lower strip, and that one can not use this to determine if the block is Mobitz I or II as more than one conducted P wave is required to do this.

Mobitz II Second degree AV block EKG Examples

Shown below is an EKG image of two-to-one AV block, which can represent benign block within the AV node or disease of the His-Purkinje system. Certain electrocardiographic features and maneuvers can help in distinguishing where the location of block exists. A long PR interval with a narrow QRS suggests an intranodal block. A short PR interval with intraventricular conduction delay or bundle branch block suggests disease below the node. Responses to atropine, exercise and carotid sinus massage can be helpful in diagnosis. Atropine will improve AV nodal conduction but will worsen block within diseased His-Purkinje fibers. Exercise has a similar effect, improving conduction in cases where block exists only in the node, but worsening when block is subnodal. Alternatively, Carotid Sinus Massage will slow conduction when block occurs in the AV node, but will improve conduction in diseased His-Purkinje tissue by allowing for refractoriness to recover.