Atrioventricular Blocks

Atrioventricular BlocksAV blocks are delays or failure of one, some, or all sinus impulses to travel through the AV pathway to the ventricles.

The primary consideration in managing any of the AV blocks is the ventricular rate.

The AV path can be blocked at several points: lower atrial tissue, AV node, His bundle.

The result is a prolonged PR interval or non-conducted P waves.

Classifying BlocksAV blocks are classified as incomplete (partial) or complete blocks.Incomplete blocks are divided into first or second degree.

First Degree BlockIn first degree block, none of the impulses are blocked, only delayed.

First-Degree AV BlockCopyright 2007, 2004, 2000, Mosby, Inc., an affiliate of Elsevier Inc. All Rights Reserved.Fig. 36-16A

Second Degree BlocksIn second degree blocks, one or more of the impulses (p waves) are blocked.

Second degree blocks are further divided into two types.

Second DegreeType I ( Mobitz Type I, Wenckebach)Type II (Mobitz Type II)

Second Degree AV BlockMobitz Type IRate depends on AV conduction ratio, may be less than 60RhythmirregularP wave normal, some P waves are not followed by a QRS (conduction ratios are 3:2, 4:3, 5:4 etc. )PRIprogressively lengthens until one p wave is not conducted (missing QRS)

QRS normal

Second-Degree AV Block, Type 1 (Mobitz I, Wenckebach) Copyright 2007, 2004, 2000, Mosby, Inc., an affiliate of Elsevier Inc. All Rights Reserved.Fig. 36-16B

Second Degree AV BlockMobitz Type IIRate depends on AV conduction ratio, usually the rate is less than 60RhythmirregularP wave normal, some P waves are not followed by a QRS (conduction ratios are 2:1, 3:1, 4:1 etc. )PRImay be normal or prolonged: constant before the conducted beats.

QRS may be normal or greater than .12 seconds

Second-Degree AV Block, Type 2 (Mobitz II)Copyright 2007, 2004, 2000, Mosby, Inc., an affiliate of Elsevier Inc. All Rights Reserved.Fig. 36-16C

Complete Heart BlockComplete block is referred to as third degree AV Bock or as AV dissociation. No impulses are conducted from atrium to ventricle. The atria and ventricles work independently of each other. An escape rhythm (junctional or ventricular) paces the ventricle.

Third Degree AV Block(AV Disociation)Rate Ventricular rate will depend on the escape pacemakerRhythmregularP wave normal but no relationship between the P waves and QRS PRINone (none of the waves are conducted)

QRS may be normal or greater than .12 seconds

Third-Degree AV Heart Block (Complete Heart Block)

Fig. 36-16 DCopyright 2007, 2004, 2000, Mosby, Inc., an affiliate of Elsevier Inc. All Rights Reserved.

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