Aim: The Bremen Diabetes Study is an observation study to characterise type 2 diabetic patients at high risk for death and cardiovascular complications by routine metabolic and cardiovascular tests. The aim of the present analysis was to evaluate the prediction of QTc interval prolongation and/or heart rate for cardiovascular mortality in comparison to traditional cardiovascular risk factors.
Methods: We followed 475 type 2 diabetic patients (age 55 - 75 years; 304 women, 171 men) from a defined residential area, seen in our clinic primarily for metabolic control. Patients with coexisting micro- or macroangiopathic complications were not excluded. Outcome data were obtained for 423 subjects. QT intervals were measured in a 12 lead ECG and corrected for heart rate with Fridericia's equation [QTc = QT/RR1/3].
Results: During the 5 year observation period 57 patients (13.5 %) died due to cardiovascular causes. In multivariate analysis we found that QTc interval prolongation (p = 0.0008), elevated heart rate (p = 0.0001), serum creatinine (p = 0.0260), smoking (p = 0.0056) and peripheral arterial disease (p = 0.0127) at baseline were independent predictors for cardiovascular death. The odds ratio was 2.7 (95 % CI 1.07 - 4.11) for QTc interval prolongation (> 421 ms) and 3.3 (95 % CI 1.33 - 8.19) for elevated heart rate (> 75/min).
Conclusion: Easily established ECG criteria such as prolonged QTc time and elevated heart rate obviously are powerful predictors of cardiovascular death in type 2 diabetic patients and are possibly superior to the traditional cardiovascular risk factors. As heart rate itself is an independent risk indicator, QTc time should be calculated by a formula (e.g. Fridericia's equation) that more accurately corrects QT for heart rate than the widely used Bazett's formula.