First-degree atrioventricular block: risk marker or innocent finding?

First-degree atrioventricular (AV) block is a relatively common electrocardiographic finding, defined as PR interval >200 ms. Traditionally, isolated first-degree AV block or PR prolongation had been considered as a benign phenomenon, but this perception has been challenged by a report from the Framingham Heart Study, suggesting that first-degree AV block was associated with increased risk of atrial fibrillation, pacemaker implantation and all-cause mortality in this population.1 This, together with the ongoing search for non-invasive risk markers for prediction of cardiovascular disease, has sparked a renewed interest in first-degree AV block, resulting in the publication of a dozen studies on its prognostic significance during the last 7–8 years. However, results have been mixed, and the clinical significance of PR prolongation has remained elusive. Consequently, the current meta-analysis on the prognostic significance of prolonged PR interval by Kwok et al in Heart 2 is a welcome addition to the literature. Their analysis was conducted from 14 studies published between 1972 and 2011, the majority in recent years, with >400 000 participants. Some of the individual studies included in the meta-analysis demonstrated increased risk of adverse outcomes associated with prolonged PR interval, while others suggested no clinical significance. When studies performed in the general population and adjusted for potential confounders were combined, PR prolongation …