First-Degree Atrioventricular Block: A Finding Not Always Benign!

First-degree atrioventricular block (AVB) is characterized by sinus rhythm, AV conduction 1:1 and PR interval > 200ms. The prevalence varies according to age group, relatively rare in the population 60 years. The reported prevalence in the general population ranges from 2 to 14%. In most cases (75%), it is due to a proximal or nodal block that tends to improve conduction with a reduction in the PR interval with maneuvers that lead to an increase in adrenergic tone and/or atropine infusion.

Usually considered a benign finding, PR interval prolongation or first-degree AV block has its prognosis more recently questioned due to emerging evidence that it is the independent factor in the increased risk of atrial fibrillation (AF), cardiac pacemaker implantation and all-cause mortality. In the Framingham cohort, the presence of first-degree AV block is considered a risk factor for the development of AF, a fact confirmed in subsequent studies in other community-based cohort with the demonstration of the association between PR prolongation and heart failure and/or AF.

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