The association of QT interval components with atrial fibrillation.

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 (QRSa ), and JT (JTa ) intervals. Prolonged QTa , QRSa , and JTa 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 QTa , QRSa , and JTa 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 QTa . When we examined the association between individual components of the QTa interval and AF, the risk of AF was limited to prolonged JTa (HR = 1.31, 95% CI = 1.04, 1.65) and not prolonged QRSa (HR = 1.00, 95% CI = 0.77, 1.30). Similar results were obtained per 1-SD increase in QTa (HR = 1.07, 95% CI = 1.01, 1.13), QRSa (HR = 0.99, 95% CI = 0.94, 1.06), and JTa (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.