Supplementary Material for: Optimal QT correction formula for older Chinese: Guangzhou Biobank Cohort Study

Introduction: To identify the optimal QT correction formula for generating corrected QT (QTc) and cutoffs for prolonged QTc, and examine the associations with mortality and cardiovascular disease (CVD) in older Chinese. Methods: A prospective study included 24,611 Chinese aged 50+ years and without CVD at 2003-2008 from Guangzhou Biobank Cohort Study. QT interval was corrected by Bazett, Fridericia, Framingham and Hodges formulas. The slope and R2 of the QTc and heart rate regression were used to determine the optimal correction formula. The 95th percentile of QTc was used to defined prolonged QTc. Cox regression was used to examine associations of prolonged QTc with mortality and CVD. The net reclassification index was calculated to assess risk reclassification. Results: During an average follow-up of 15.3 years, 5,261 deaths and 5,539 CVD occurred. Optimal heart correction was observed for the Hodges formula, and Bazett formula performed the worst. Prolonged QTc corrected by Fridericia, Framingham and Hodges formulas had similar association strength with all-cause mortality, CVD mortality and incident CVD (especially coronary heart disease, myocardial infarction and ischemic stroke), with hazard ratios approximately being 1.25, 1.40 and 1.15, respectively. They also improved risk reclassification for all-cause mortality, CVD mortality and incident CVD by approximately 5%, 10% and 6%, respectively. However, prolonged QTc corrected by Bazett formula was not associated with incident CVD and did not improve risk reclassification. Conclusions: Hodges formula outperformed other formulas for heart rate correction. Fridericia, Framingham and Hodges formulas can be used for death and cardiovascular risk prediction.