Prolongation of the electrocardiographic PR interval, known as first-degree atrioventricular block when the PR exceeds 200 milliseconds, is frequently encountered in clinical practice.
To determine the clinical significance of PR prolongation in ambulatory individuals.
Design, Setting, and Participants
Prospective, community-based cohort in Framingham, MA. We studied 7,575 individuals (mean age 46 years, 54% women) who underwent routine 12-lead electrocardiography. The study cohort was followed prospectively from baseline examinations in 1968–1974 through 2007. We used multivariable-adjusted Cox proportional hazards models to examine the relations of PR interval with the incidence of arrhythmic events and death.
Main Outcome Measures
Incident atrial fibrillation (AF), pacemaker implantation, and all-cause mortality.
During follow up, 481 participants developed AF, 124 required pacemaker implantation, and 1,739 died. At the baseline examination, 124 individuals had PR >200 milliseconds. Incidence rates per 10,000 person-years for those with PR >200 milliseconds compared to those with PR ≤200 milliseconds were 140 (95% confidence interval [CI], 95–208) versus 36 (95% CI, 32–39) for AF, 59 (95% CI, 40–87) versus 6 (95% CI, 5–7) for pacemaker implantation, and 333 (95%, CI 260–428) versus 129 (95% CI, 123–135) for death. Corresponding absolute risk increases were 1.04% (AF), 0.53% (pacemaker), and 2.05% (death) per year. In multivariable analyses, each 20-millisecond increment in PR was associated with an adjusted hazards ratio (HR) of 1.12 (95% CI, 1.02–1.22; p=0.018) for AF, 1.22 (95% CI, 1.14–1.30; p<0.001) for pacemaker implantation, and 1.08 (95% CI, 1.02–1.13; p=0.005) for death. Individuals with first-degree atrioventricular block had a two-fold adjusted risk of AF (HR 2.06; 95% CI, 1.36–3.12; p<0.001), three-fold adjusted risk of pacemaker implantation (HR 2.89; 95% CI, 1.83–4.57; p<0.001), and 1.4-fold adjusted risk of death (HR 1.44, 95% C,I 1.09–1.91; p=0.01).
PR prolongation is associated with increased risks of AF, pacemaker implantation, and death.