Also called first-degree AV block is a disease of the electrical conduction system of the heart in which the PR interval is lengthened beyond 0.20 seconds.
This lengthening of the PR interval is caused by a delay in the electrical impulse from the atria to the ventricles through the AV node
Normally and in the case of ACLS, first-degree heart block is of no consequence unless it involves myocardial infarction or an electrolyte imbalance.
Although first-degree heart block is not clinically significant for ACLS, recognition of the major AV blocks is important because treatment decisions are based on the type of block present.
There are a number of disorders that can cause first-degree AV block, but it may be a normal variant in the conduction system of the heart. Some of the most common causes are listed below:
- Causes of First degree AV block:
- Increased vagal tone (well trained athlete)
- Electrolyte disturbances
- Myocarditis caused by infections
- hypoxemia (see more in infants and children)
- Cardiac surgery
- Congenital abnormalities (see more in infants and children)
- Myocardial infarction
- Medications that inhibit AV node conduction (amiodarone, beta-blockers, calcium channel blockers, digoxin)
- Acute rheumatic fever (see more in infants and children)
Below is a short video which will help you quickly identify first-degree AV block on a monitor. Please allow several seconds for the video to load. (3.40 mb)
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