Abstract 9138: QT Interval Duration and Incident Mortality in the Framingham Heart Study
Background: The association between QT interval and mortality has been demonstrated in multiple large, prospective population-based studies using Bazett's heart rate correction, but the strength of the association varies considerably among studies. We examined this relationship in the Framingham Heart Study.
Methods and Results: Participants in the first (original cohort, n = 2,415) and second generation (offspring cohort, n = 4,478) cohorts examined in the early 1970s were included in this study. Using Cox proportional hazards regression adjusting for age and sex, a 20 msec increase in QTc (using Bazett's correction; QT/RR1/2 interval) was associated with increased risk of all-cause mortality (HR 1.15, 95% CI 1.12-1.19, p = 7.6x10-17), CHD mortality (HR 1.18, 95% CI 1.08-1.30, p = 0.0003), and sudden cardiac death (HR 1.20, 95% CI 1.04-1.39, p = 0.01). However, additional adjustment for heart rate, either by additional adjustment of the QTc for RR interval, or use of linear regression of QT on RR interval, attenuated the associations with all-cause mortality (HR 1.10, 95% CI 1.06-1.15, p= 3.6x10-6, Figure), CHD mortality (HR 1.11, 95% CI 0.99-1.24, p= 0.07) and SCD (HR 1.16, 95% CI 0.97-1.40, p= 0.11).
Conclusion: In the FHS (mean follow up 27.35 years), there is evidence for a graded relationship between QTc and all-cause mortality, CHD death, and SCD, however, this effect is considerably attenuated by additional adjustment for RR interval. These findings demonstrate that residual confounding by heart rate overestimates the effect on mortality when using Bazett's heart rate correction.
- © 2011 by American Heart Association, Inc.