In the Literature: Research You Need to Know

Clinical question: Does PR prolongation have any clinical significance in ambulatory adults?

Background: Several studies have suggested that first-degree atrio-ventricular block (AVB) is associated with a benign prognosis. However, these studies were based on young, active men in the military. Another study, which was based on middle-aged men, has suggested that AVB may be associated with coronary artery disease. Little is known about AVB prognosis in ambulatory individuals older than 20 years of age.

Study design: Prospective cohort study.

Setting: Community-hospital-based patients.

Synopsis: A subset population of 7,575 individuals older than 20 from the Framingham Heart Study showed that a prolonged PR interval of more than 200 msec is associated with an increased risk of atrial fibrillation/flutter, pacemaker implantation, and all-cause mortality.

When adjusted for age, sex, cardiovascular disease status, body mass index, hypertension, smoking, diabetes, and ratio of total to high-density lipoprotein cholesterol, individuals with first-degree AVB had a twofold adjusted risk of atrial fibrillation (HR, 2.06; 95% CI, 1.36-3.12; P<0.001), a threefold adjusted risk of pacemaker implantation (HR, 2.89; 95% CI, 1.83-4.57; P<0.001), and 1.4-fold adjusted risk of all-cause mortality (HR, 1.44, 95% CI, 1.09-1.91; P=0.01).

This study was confounded by the usual limitations of the Framingham Study Database. Most notably, this study focused specifically on ambulatory patients with prolonged PR interval demonstrated on routine electrocardiogram and, therefore, does not account for factors commonly related to the inpatient setting, such as electrolyte abnormalities. Hospitalists should neither prognosticate nor plan more frequent follow-up for patients based on a prolonged PR interval based on an EKG obtained during acute illness.

Bottom line: PR prolongation is associated with increased risks of atrial fibrillation/flutter, pacemaker implantation, and all-cause mortality in ambulatory adults.

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

—Reviewed for The Hospitalist by Robert Chang, MD; Nabil Alkhoury-Fallouh, MD; Anita Hart, MD; Hae-won Kim, MD; Francis McBee-Orzulak, MD; Helena Pasieka, MD; Division of General Medicine, University of Michigan, Ann Arbor

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