QT interval and the risk of myocardial infarction and all-cause death: A cohort study

Methods: All male residents aged 20–61 years and female residents aged 20–56 years were invited to the Tromsø Study in 1986–1987. A total of 15,558 participants free of heart disease were prospectively followed over 20 years for myocardial infarction and death. QT interval at baseline was measured on lead I of the electrocardiogram. Hazard ratios (HRs) with 95% confidence intervals (CIs) per standard deviation change in QT interval were calculated using a Cox regression model. Results: We identified 756 cases of myocardial infarction and 1,183 all-cause deaths. Prolonged QT interval was present in 792 (5%) participants. QT interval was not associated with increased risk of myocardial infarction (HR: 0.95, 95% CI: 0.84–1.07, after adjustment for potential confounders). Heart-rate-corrected QT interval was a significant predictor for all-cause death in men (HR: 1.15, 95% CI: 1.03–1.29), but not in women (HR: 1.04, 95% CI: 0.91–1.18), after adjustment for potential confounders. Conclusions: The findings suggest that the previously observed relationship between QT interval and increased risk of cardiovascular death is not mediated by increased risk of myocardial infarction. The clinical utility of the QT interval to identify individuals at high risk for coronary events is limited in a general population without prior heart disease.