Atrioventricular Block and Atrioventricular Dissociation
Atrioventricular (AV) block is not only linked to some important electropathophysiologic mechanisms such as conduction slowing and escape rhythm, but also to typical ECG patterns such as Wenckebach period or Mobitz block, and to other potential precursors
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Atrioventricular Block and Atrioventricular Dissociation
AtaGlance Atrioventricular (AV) block is not only linked to some important electropathophysiologic mechanisms such as conduction slowing and escape rhythm, but also to typical ECG pattems such as Wenckebach period or Mobitz block, and to other potential precursors of complete AV block such as fascicular blocks and their combinations. All in all, AV block in its various degrees is of great clinical importance. Principally a 'conduction block' represents a prolongation of conduction time and not necessarily an absolute and flXed conduction block. Therefore, any conduction block (bundlebranch, fascicular, sinoatrial, or AV block) may be a variable condition, which may be reversible under some circumstances. AV dissociation represents a complex term and its significance depends on several conditions.
ECG
,
Anatomie Localization of AV Block
This is illustrated in Figure localized:
12.1.
i. in AV block 1° every atrial impulse is conducted to the ventrieles, with a prolonged PQ interval ii. in AV block 2° (subdivided into three different types) there is a change of conduction and complete AV block of the atrial impulses iii. in AV block 3° (complete AV block) all atrial impulses are AV blocked. The actions of the atria and the ventrieles occur absolutely independently from each other. If no (AV nodal or ventricular) escape rhythm arises, ventricular asystole occurs.
2.1
Defined by PQ interval > 0.20 sec (ECG 12.1). Isolated AV block 1° does not represent a block but a prolonged AV conduction; it is mostly harmless, gene rally showing little or no progression over years or decades. It is also found in healthy individuals or may be due to digitalis and other drugs. The prolongation of the AV conduction generally occurs in the AV node ('supra-His').
Anatomically, AV block is
i. either within the AV node or in the upper part of the His bundle (a supra-His block) ii. or it is localized within the infra-hissian fascicles of the right and left ventriele (right bundle branch, left anterior and posterior (and 'medial') fasciele) or within the lower part of the His bundle where it spreads into the fascicles (an infra-His block).
2
AVblock 1°
AVnode----
-~~~......... - - - - Lek posterior la5 6 sec leads to syncope. In patients with preexisting impairment of cerebral circulation, an asystole of 3-4 sec may provoke a syncope. A syncope due to cardiac arrhythmia is called a MorgagniAdams-Stokes attack (MAS attack). If asystole lasts more than about 4-7 min, irreversible organic damage results (especially cerebrai). Longer ventricular asystole leads to death, sometimes provoked by secondary ventricular fibrillation.
2.4
Types of Complete AV Block
As mentioned before, there are two types of complete AV block, which differ in evolution, etiology, and clinical significance.
2.4.1
Infra-His Complete AV Block
This AV block is localized distal to the His bundle (infra-His), within the ventricular fascicles and bundles respectively (Figure 12.1). Thus, fascicular bl
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