Types of AV Blocks
AV blocks are partial or complete interruption of electrical transmission from the atria to the ventricles.
The most common causes are:
- Idiopathic fibrosis
- Ischemic heart disease
- Drugs (BBs, CCBs, Digoxin, Amiodarone)
- Valvulopathy
- Congenital heart, genetic or other disorders
The different types of heart blocks are as follows:
[1] FIRST DEGREE HEART BLOCK
PR interval is longer >0.20 secs, seen on the ECG. The conduction is slowed without any skipped beats. Rarely symptomatic and usually no treatment is required.
[2] SECOND DEGREE HEART BLOCK
This is further categorized into 2 more types; Mobitz type 1 and Mobitz type II
In Mobitz Type I the PR interval progressively lengthens until one beat is dropped. Treatment is rarely needed unless person becomes bradycardic or symptomatic.
In Mobitz Type II the PR interval remains constant, but the beats are intermittently dropped, either every 3rd (3:1 block) or 4th beat (4:1 block). Patients are at risk of developing symptomatic AV block or complete heart block. A pacemaker is indicated.
[3] THIRD DEGREE / COMPLETE HEART BLOCK
In this type of heart block, there is no communication between the atria and the ventricles. Patients require pacemaker, and the risk of a cardiac event is significantly higher.
References:
1. Merck Manual: Atrioventricular Block (Accessed Jan 25 2019)
