Abstract
BACKGROUND: Prolongation of the QT interval is associated with an increased risk of atrial fibrillation (AF) and stroke. OBJECTIVES: The purpose of this analysis was to determine if AF explains the association between prolonged QT and stroke. METHODS: A total of 6305 participants (mean age 62 ± 10 years; 54% women; 38% whites; 27% blacks; 23% Hispanics; 12% Chinese-Americans) from the Multi-Ethnic Study of Atherosclerosis (MESA) were included in this analysis. A linear scale was used to compute heart rate-adjusted QT (QT(a)). Prolonged QT(a) was defined as ≥ 460 ms in women and ≥ 450 ms in men. Incident AF cases were identified using hospital discharge records and Medicare claims data. Vascular neurologists adjudicated stroke events by medical record review. Cox regression was used to examine the association between prolonged QT(a) and stroke with and without AF. RESULTS: A total of 216 (3.4%) of study participants had prolonged QT(a). Over a median follow-up of 8.5 years, 280 (4.4%) participants developed AF and 128 (2.0%) participants developed stroke. In a multivariable Cox regression analysis adjusted for socio-demographics, cardiovascular risk factors, and potential confounders, prolonged QT(a) was associated with an increased risk of AF (HR = 1.7, 95% CI 1.1, 2.6) and stroke (HR = 2.3, 95% CI 1.3, 4.1). When AF was included as a time-dependent covariate, the association between prolonged QT(a) and stroke was not substantively altered (HR = 2.4, 95% CI 1.3, 4.3). CONCLUSION: The increased risk of stroke in those with prolonged QT potentially is not explained by documented AF. Further research is needed to determine if subclinical AF explains the association between the QT interval and stroke.