QTc interval length and QT dispersion as predictors of mortality in patients with non-insulin-dependent diabetes

Abstract

Patients with non-insulin-dependent diabetes (NIDDM) are at independent risk of cardiovascular death. The reason is only partially understood. The aim of our study was therefore to evaluate the impact of corrected QT interval length (QTc) and QT dispersion (QT-disp) on mortality in a cohort of 324 Caucasian NIDDM patients. A resting 12-lead ECG was recorded at baseline. Maximum (QT-max) and minimum QT (QT-min) intervals were measured, and QT-max was corrected for heart rate (QTc-max). QT-disp was defined as the difference between QT-max and QT-min. QTc-max was 454 (376-671) ms(1/2) (median (range)) and QT-disp 61 (0-240) ms. Prolonged QTc interval (PQTc), defined as QTc-max > 440 ms(1/2), was present in 67% of the patients and prolonged QT-disp (PQT-disp), defined as QT-disp > 50 ms, was present in 51%. During the 9-year follow-up period, 100 patients died (52 from cardiovascular diseases). Thirty-seven percent of the patients with PQTc died compared with 17% with normal QTc interval (p<0.001). The Cox proportional hazard model, including putative risk factors at baseline, revealed the following independent predictors of all cause mortality; QTc-max (p<0.05), age (p<0.0001), albuminuria (p<0.01), retinopathy (p<0.01), HbA1c (p<0.05), insulin treatment (p<0.01), total cholesterol (p<0.01), serum creatinine (p<0.05) and presence of cardiac heart disease based on Minnesota coded ECG (p<0.001). Whereas QT-disp was not a predictor, QTc-max interval was an independent predictor of cardiovascular mortality. Our study showed a high prevalence of QTc and QT-disp abnormalities and indicated that QTc-max but not QT-disp is an independent predictor of all cause and cardiovascular mortality in NIDDM patients.

QTc interval and resting heart rate as long-term predictors of mortality in type 1 and type 2 diabetes mellitus: a 23-year follow-up

“…In addition to findings of previous reports, we also observed a relation between elevated rHR and both cardiac mortality and mortality due to ischaemic heart disease. On the other hand, the present analysis did not confirm an association between QT c and any of the endpoints in type 2 diabetes as has been reported previously [6,7,9,10,35]. Given previous hypotheses that prolongation of QT c as a marker of cardiac autonomic neuropathy could be of greater importance in type 1 than in type 2 diabetes [5], our findings on this count are intriguing, and it can only be speculated on the underlying mechanisms.…”

“…Compared with previous publications reporting an association of QT c with mortality in type 2 diabetes [9,10,35], subjects with type 2 diabetes were substantially younger in the present study. It should also be noted that some earlier reports revealing an association between QT c and mortality were cross-sectional [35] or based on a case-control design [9] and in the case of prospective trials [6,7,10] had a considerably shorter follow-up. In type 2 diabetes hyperglycaemia is often associated with a pro-inflammatory state including obesity, dyslipidaemia and hypertension, thereby promoting the development of atherosclerosis [41].…”

“…However, the association between QT c and cardiovascular mortality in type 2 diabetes is controversial. Some reports suggest that QT c correlates with an increase in cardiovascular mortality [6][7][8][9]. Others have indicated that QT dispersion might more accurately predict cardiovascular mortality in this patient group [10][11][12].…”

The case for hypoglycaemia as a proarrhythmic event: basic and clinical evidence

“…The change in QT interval corresponds to the fact that, at a cellular level, diabetes lengthens action potentials [24,52] and reduces repolarising of K + currents [52] in a way similar to proarrhythmic medications. QT prolongation predicts mortality in type 1 [53] and type 2 [54][55][56][57][58] diabetes. In the case of type 1 diabetes, QT prolongation conferred an odds ratio for death of 24.6 (95% CI 6.52-92.85) [53].…”

Hyperbaric Oxygen Therapy Decreases QT Dispersion in Diabetic Patients

“…QT dispersion, which is the difference between the longest and shortest QT interval, is an index of myocardial electrical activity. It was demonstrated that an increase in QT dispersion is associated with the malignant ventricular arrhythmias and sudden death in diabetic patients (Christensen et al 2000).…”