Tags: Disease.
First-degree 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.In first-degree AV block the impulse conducting from atria to ventricles through the 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.