Natural history of the PR interval and risk of cardiac events and mortality: a nationwide study

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BACKGROUND: The PR interval is a ubiquitous parameter available to all clinicians. Studies on associated risk have been conflicting, often limited by sample sizes and one ECG per individual. The study aimed to investigate the association between the PR interval and its temporal changes with cardiac events in a nationwide cohort. METHODS: Nationwide hospital ECGs were linked with Danish national registries. Associations between index-PR interval and absolute temporal changes in PR interval (ΔPR), and cardiac events were modelled with multivariable cause-specific Cox models. RESULTS: A total of 9 020 051 ECGs (n=2 234 492; 53% female) were available, with 1 213 073 patients having >1 ECG. Median follow-up was 7.1 years. Median index-PR interval was 158 ms. PR interval <120 or >200 ms was found in 2.9% and 7.4%, respectively. Prevalence of prolonged PR interval increased with age. Median ΔPR was 10 ms and highest among the oldest. Cox models between the index-PR interval and events showed the following HR patterns: U-shaped for risk of atrial fibrillation/flutter, heart failure and ventricular arrhythmias (HR 1.03-1.24, 1.04-1.11, 1.08-1.16, respectively, p<0.05); stepwise increase at PR interval ≥170 ms for syncope (HR 1.08-1.36, p<0.001); linear increasing at PR intervals >160 ms (HR 1.07-2.11, p<0.05) for high-degree atrioventricular block/cardiac device implantation; J-shaped with moderate and marginal increases among the shortest (HR 1.44, p<0.001) and longest PR intervals (HR 1.03, p<0.001), respectively, for all-cause mortality. Models on ΔPR showed stepwise increases in HR for all events. CONCLUSION: Prevalence of PR prolongation and temporal PR changes increased with age. Short, long and temporal changes in the PR interval were all associated with increased risk of cardiac events and all-cause mortality.

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