World Library  
Flag as Inappropriate
Email this Article

First-degree atrioventricular block

Article Id: WHEBN0000665829
Reproduction Date:

Title: First-degree atrioventricular block  
Author: World Heritage Encyclopedia
Language: English
Subject: Second-degree atrioventricular block, Heart block, List of ICD-9 codes 390–459: diseases of the circulatory system, First degree, Cardiac dysrhythmia
Collection: Cardiac Dysrhythmia
Publisher: World Heritage Encyclopedia
Publication
Date:
 

First-degree atrioventricular block

First-degree AV block
Classification and external resources
ICD-10 I44.0
ICD-9-CM 426.11
DiseasesDB 10477
eMedicine emerg/233

First-degree atrioventricular block (AV block), or PR prolongation, is a disease of the electrical conduction system of the heart in which the PR interval is lengthened beyond 0.20 seconds.[1]

In first-degree AV block, the impulse conducting from atria to ventricles through the atrioventricular node (AV node) is delayed and travels slower than normal. It has a prevalence in the normal (young adult) population of 0.65-1.1% and the incidence is 0.13 per 1000 persons.

Contents

  • Causes 1
  • Diagnosis 2
  • Treatment 3
  • Prognosis 4
  • See also 5
  • References 6

Causes

The most common causes of first-degree heart block are an AV nodal disease, enhanced vagal tone (for example in athletes), myocarditis, acute myocardial infarction (especially acute inferior MI), electrolyte disturbances and medication. The drugs that most commonly cause first-degree heart block are those that increase the refractory time of the AV node, thereby slowing AV conduction. These include calcium channel blockers, beta-blockers, cardiac glycosides, and anything that increases cholinergic activity such as cholinesterase inhibitors. Digitalis is a sodium/potassium ATPase inhibitor and also prolongs AV conduction.

Diagnosis

In normal individuals, the AV node slows the conduction of electrical impulse through the heart. This is manifest on a surface electrocardiogram (ECG) as the PR interval. The normal PR interval is from 120 ms to 200 ms in length. This is measured from the initial deflection of the P wave to the beginning of the QRS complex.

In first-degree heart block, the diseased AV node conducts the electrical activity more slowly. This is seen as a PR interval greater than 200 ms in length on the surface ECG. It is usually an incidental finding on a routine ECG.

First-degree heart block does not require any particular investigations except for electrolyte and drug screens, especially if an overdose is suspected.

Treatment

The management includes identifying and correcting electrolyte imbalances and withholding any offending medications. This condition does not require admission unless there is an associated myocardial infarction. Even though it usually does not progress to higher forms of heart block, it may require outpatient follow-up and monitoring of the ECG, especially if there is a comorbid bundle branch block. If there is a need for treatment of an unrelated condition, care should be taken not to introduce any medication that may slow AV conduction. If this is not feasible, clinicians should be very cautious when introducing any drug that may slow conduction; and regular monitoring of the ECG is indicated.

Prognosis

Isolated first-degree heart block has no direct clinical consequences. There are no symptoms or signs associated with it. It was originally thought of as having a benign prognosis. In the Framingham Heart Study, however, the presence of a prolonged PR interval or first degree AV block doubled the risk of developing atrial fibrillation (irregular heart beat), tripled the risk of requiring an artificial pacemaker, and was associated with a small increase in mortality. This risk was proportional to the degree of PR prolongation.[2]

A subset of individuals with the triad of first-degree heart block, right bundle branch block, and either left anterior fascicular block or left posterior fascicular block (known as trifascicular block) may be at an increased risk of progression to complete heart block.

See also

References

  1. ^ "Lesson VI - ECG Conduction Abnormalities". Retrieved 2009-01-07. 
  2. ^ Cheng S, Keyes MJ, Larson MG, McCabe EL, Newton-Cheh C, Levy D, Benjamin EJ, Vasan RS, Wang TJ (2009). "Long-term outcomes in individuals with prolonged PR interval or first-degree atrioventricular block". JAMA 301 (24): 25712577.  
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.