AV Conduction: Difference between revisions

Conduction disturbances can occur at the level of the sinoatrial (SA) node, the atrioventricular (AV) node and the bundle branch system.  

In atrioventricular block the conduction between atria and ventricles is disturbed leading to an incread [[Conduction#PQ interval|PQ interval]] or to drop out of QRS complexes: atrial activity that is not followed by ventricular activity. Three degrees of block can be distinguished.

   

[[Image:Rhythm_1stAVblock.png|thumb| 1st degree AV block. Although the PQ interval is prolonged all p-waves are followed by QRS complexes: there is no dropout of beats]]

In first degree AV block there is a prolongation of PQ duration (PQ time > 0.20 sec). Still every p-wave is being followed by a QRS complex.

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In second degree AV block not all p-waves are being followed by QRS complexes: beat dropout occurs. Second degree AV block can be categorized in 3 types:

In second degree AV block type I, the PQ interval prolongs from beat to beat up until the drop-out of one QRS complex. The characteristics of a Wenkebach block:

* QRS complexes cluster (e.g. a 5:4 block or 4:3 block)

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[[Image:Rhythm_Mobitz.png|thumb| Second degree AV block type II (Mobitz)]]

In second degree AV block type II, beats are dropped irregularly without PQ interval prolongation. As the drop out of beats is irregular, no clustering of QRS complexes can be seen as in second degree block type I. Second degree AV block type II marks the starting of trouble and is a class I pacemaker indication. <cite>CITATION</cite>

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High grade AV block is defined as two or more p-waves not followed by QRS complexes.

[[Image:Rhythm_3rdAVblock.png|thumb| 3rd degree AV block. AV dissociation is present: there is no relation between p-waves and the (nodal) QRS complexes.]]

[[Image:Rhythm_totalAVblock.png|thumb| Short lasting total AV block (initiated by adenosine infusion). P-waves are present, but no QRS complexes follow]]