Atrioventricular block

Atrioventricular block
Classification and external resources
Specialty	cardiology
ICD-10	I44.0-I44.3
ICD-9-CM	426.0-426.1
eMedicine	med/189
MeSH	D054537
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Atrioventricular block (AV block) is a type of heart block in which the conduction between the atria and ventricles of the heart is impaired. Under normal conditions, the sinoatrial node (SA node) in the atria sets the pace for the heart, and these impulses travel down to the ventricles. In an AV block, this message does not reach the ventricles or is impaired along the way. The ventricles of the heart have their own pacing mechanisms, which can maintain a lowered heart rate in the absence of SA stimulation.

The causes of pathological AV block are varied and include ischaemia, infarction, fibrosis or drugs, and the blocks may be complete or may only impair the signaling between the SA and AV nodes. Certain AV blocks can also be found as normal variants, such as in athletes or children, and are benign. Strong vagal stimulation may also produce AV block. The cholinergic receptor types affected are the muscarinic receptors.

There are three types:

In order to differentiate between the different degrees of the atrioventricular block (AV block), the First-Degree AV block occurs when an electrocardiogram (ECG) reads a PR interval that is more than 200 msec. This degree is typically asymptomatic and is only found through an ECG reading. Second-Degree AV block, although typically asymptomatic, has early signs that can be detected or are noticeable such as irregular heartbeat or a syncope. A Third-Degree AV block, has noticeable symptoms that present itself as more urgent such as: dizziness, fatigue, chest pain, pre syncope, or syncope.

Sinus rhythm with acute inferior infarction complicated by Type I A-V block manifest in the form of 5:4 Wenckebach periods; R-P/P-R reciprocity.

Sinus rhythm (rate = 100/min) with 3:2 and 2:1 Type II A-V block; RBBB

Sinus tachycardia with complete A-V block and resulting junctional escape

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