Prevalence of QT prolongation and associated LVEF changes in diabetic patients over a four-year retrospective time period
We evaluated the association of QT interval corrected for heart rate (QTc) and resting heart rate (rHR) with mortality (all-causes, cardiovascular, cardiac, and ischaemic heart disease) in subjects with type 1 and type 2 diabetes. We followed 523 diabetic patients (221 with type 1 diabetes, 302 with type 2 diabetes) who were recruited between 1974 and 1977 in Switzerland for the WHO Multinational Study of Vascular Disease in Diabetes. Duration of follow-up was 22.6 ± 0.6 years. Causes of death were obtained from death certificates, hospital records, post-mortem reports, and additional information given by treating physicians. In subjects with type 1 diabetes QTc, but not rHR, was associated with an increased risk of: (1) all-cause mortality (hazard ratio [HR] 1.10 per 10 ms increase in QTc, 95% CI 1.02–1.20, p = 0.011); (2) mortality due to cardiovascular (HR 1.15, 1.02–1.31, p = 0.024); and (3) mortality due to cardiac disease (HR 1.19, 1.03–1.36, p = 0.016). Findings for subjects with type 2 diabetes were different: rHR, but not QTc was associated with mortality due to: (1) all causes (HR 1.31 per 10 beats per min, 95% CI 1.15–1.50, p < 0.001); (2) cardiovascular disease (HR 1.43, 1.18–1.73, p < 0.001); (3) cardiac disease (HR 1.45, 1.19–1.76, p < 0.001); and (4) ischaemic heart disease (HR 1.52, 1.21–1.90, p < 0.001). Effect modification of QTc by type 1 and rHR by type 2 diabetes was statistically significant (p < 0.05 for all terms of interaction). QTc is associated with long-term mortality in subjects with type 1 diabetes, whereas rHR is related to increased mortality risk in subjects with type 2 diabetes.