First-degree AV block associated with increased risk of adverse outcomes

Clinical Question

Is first-degree atrioventricular block associated with an increased risk for adverse cardiovascular events?

Bottom Line

First-degree atrioventricular (AV) block, defined as a PR interval exceeding 200 milliseconds, is associated with a significantly increased risk of atrial fibrillation, pacemaker insertion, and all-cause mortality. (LOE = 1b)


Cheng S, Keyes MJ, Larson MG, et al. Long-term outcomes in individuals with prolonged PR interval or first-degree atrioventricular block. JAMA 2009;301(24):2571-2577.  [PMID:19549974]

Study Design

Cohort (prospective)






Although commonly seen in clinical practice, the significance of first-degree AV block (PR interval exceeding 200 milliseconds) is unknown. These investigators analyzed data from the well-known Framingham Heart Study, a community-based cohort identified in 1968-1974, including 7575 individuals (mean age = 47 years; 54% women) prospectively followed through 2007. Three individuals reviewed medical histories, physical examinations from hospitalizations, and personal physician records for all patients with suspected new events. A cardiologist evaluated all electrocardiograms. At baseline, first-degree AV block occurred in 124 participants. Compared with individuals having a normal PR interval, adverse outcomes including atrial fibrillation (number needed to treat to harm [NNTH] = 96), pacemaker implantation (NNTH = 189), and all-cause mortality (NNTH = 49) occurred significantly more often in those having baseline first-degree AV block. An additional 161 individuals with an initially normal PR interval at baseline who developed first-degree AV block during follow-up also had a significantly increased occurrence of atrial fibrillation and pacemaker insertion, but not all-cause mortality.