Abstract

BACKGROUND: Although abnormalities of the QT interval are associated with atrial fibrillation (AF), it is unclear whether ventricular depolarization (QRS duration) or repolarization (JT interval) is a more important marker of AF risk. METHODS: This analysis included 4,181 (95% white; 59% women) participants from the Cardiovascular Health Study (CHS) who were free of baseline AF and major intraventricular delay. A linear scale was used to compute heart rate adjusted QT (QTa), QRS (QRS_a ), and JT (JT_a ) intervals. Prolonged QT_a , QRS_a , and JT_a were defined by values greater than the sex-specific 95th percentile for each measurement. AF events were ascertained during the annual study electrocardiograms and from hospitalization discharge data. Cox regression was used to compute hazard ratios (HR) and 95% confidence intervals (CI) for the associations of prolonged QT_a , QRS_a , and JT_a with AF, separately. RESULTS: Over a mean follow-up of 12.1 years, a total of 1,236 (30%) AF events were detected. An increased risk of AF (HR = 1.50. 95% CI = 1.20, 1.88) was observed with prolonged QT_a . When we examined the association between individual components of the QT_a interval and AF, the risk of AF was limited to prolonged JT_a (HR = 1.31, 95% CI = 1.04, 1.65) and not prolonged QRS_a (HR = 1.00, 95% CI = 0.77, 1.30). Similar results were obtained per 1-SD increase in QT_a (HR = 1.07, 95% CI = 1.01, 1.13), QRS_a (HR = 0.99, 95% CI = 0.94, 1.06), and JT_a (HR = 1.07, 95% CI = 1.01, 1.13). CONCLUSIONS: The JT interval is a more important marker of AF risk in the QT interval among persons who do not have ventricular conduction delays.