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AV Conduction: Difference between revisions
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{{authors| | |||
|mainauthor= [[user:Drj|J.S.S.G. de Jong]] | |||
|moderator= [[user:Vdbilt|I.A.C. van der Bilt]] | |||
|supervisor= | |||
}} | |||
[[Image:AV_block_sequence.png|thumb|Sequence of AV block from incomplete to complete]] | |||
Conduction disturbances can occur at the level of the sinoatrial (SA) node, the atrioventricular (AV) node and the bundle branch system. | 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 | In atrioventricular block the conduction between atria and ventricles is disturbed, leading to an increased [[Conduction#PQ interval|PQ interval]] or to P waves that are not followed by QRS complexes: atrial activity that is not followed by ventricular activity. Three degrees of block can be distinguished. | ||
[[Image:Conduction_ap.svg|300px|thumb|right|The PR duration depends on the conduction velocity in the atria, AV node, His bundle, bundle branches and Purkinje fibers.]] | |||
==First degree AV block== | ==First degree AV block== | ||
[[Image:Rhythm_1stAVblock.png|thumb| 1st degree AV block. Although the PQ interval is prolonged all | [[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 complexes]] | ||
In first degree AV block there is a prolongation of PQ duration (PQ time > 0.20 sec). Still every | 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. | ||
First degree AV block is present in 16% of >90-year olds <cite>kelley</cite> and is mostly caused by a degeneration of the conduction system. First degree AV block is relatively harmless. | First degree AV block is present in 16% of >90-year olds <cite>kelley</cite> and is mostly caused by a degeneration of the conduction system. First degree AV block is relatively harmless. | ||
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===Second degree AV block type I (Wenckebach)=== | ===Second degree AV block type I (Wenckebach)=== | ||
[[Image:Wenckebach.png|thumb|Example of type I second degree AV block (Wenckebach)]] | [[Image:Wenckebach.png|thumb|Example of type I second degree AV block (Wenckebach)]] | ||
[[Image:Wenckebach2.png|thumb|Example of type I second degree AV block (Wenckebach)]] | |||
[[Image:Wenckebach3.jpg|thumb|Example of type I second degree AV block (Wenckebach)]] | |||
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: | 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) | * QRS complexes cluster (e.g. a 5:4 block or 4:3 block) | ||
* The PQ interval prolongs every consecutive beat | * The PQ interval prolongs every consecutive beat | ||
* The PQ interval that follows upon a dropped beat is the | * The PQ interval that follows upon a dropped beat is the shortest. | ||
* The RR interval shortens (!) every consecutive beat. | * The RR interval shortens (!) every consecutive beat. | ||
* The amount of block decreases during exercise (e.g. a 4:3 block improves into a 6:5 block) | * The amount of block decreases during exercise (e.g. a 4:3 block improves into a 6:5 block) | ||
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[[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_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]] | [[Image:Rhythm_totalAVblock.png|thumb| Short lasting total AV block (initiated by adenosine infusion). P-waves are present, but no QRS complexes follow]] | ||
Third degree AV block is synonymous to ''total block'': absence of atrioventricular conduction. P-waves and QRS complexes have no temporal relationship. | Third degree AV block is synonymous to ''total block'': absence of atrioventricular conduction. The P-waves and QRS complexes have no temporal relationship, which is called to [[AV dissociation]]. | ||
The ventricular rhythm can [[ | The ventricular rhythm can be [[Nodal Rhythm|nodal]], [[Idioventricular Rhythm|idioventricular]] or absent. Absent ventricular rhythm results in asystole and death. | ||
During third degree AV block the blood supply to the brain can insufficient, leading to loss of consciousness. [[w:Stokes-Adams_Attack|Adams Stokes (or Stokes-Adams) attacks]] (often misspelled as Adam Stokes) attacks | During third degree AV block the blood supply to the brain can insufficient, leading to loss of consciousness. [[w:Stokes-Adams_Attack|Adams Stokes (or Stokes-Adams) attacks]] (often misspelled as Adam Stokes) attacks are attacks of syncope or pre-syncope in the setting of third degree AV block. | ||
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==References== | |||
<biblio> | |||
#kelley pmid=17126661 | |||
</biblio> | |||