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Elevated QT interval variability (QTV) has been associated with increased cardiac mortality, but the underlying mechanisms are incompletely understood. Sympathetic activity is thought to be a main contributor to QTV. The aim of this study was to investigate the relation between cardiac sympathetic integrity and QTV in 15 patients with type 2 diabetes mellitus and varying degrees of cardiac autonomic neuropathy. Cardiac sympathetic innervation was assessed by 123I-mIBG scintigraphy based on heart-to-mediastinum ratio of 123I-mIBG uptake 4 hours after infusion. To assess QTV high resolution ECGs (1000 Hz) were recorded during standing. Beat-to-beat QT intervals were calculated over a period of 5 minutes, using a template-stretching algorithm. QTV was quantified using time and frequency domain measures as well as non-linear approaches (symbolic dynamics, fractal dimension). The group mean and standard deviation of HMR values were 1.07 ± 0.48. Time and frequency domain QTV parameters were significantly increased in subjects with sympathetic dysinnervation and inversely correlated with HMR (r = -0.7, p <; 0.001). In conclusion, there is a clear link between sympathetic dysinnervation and elevated QTV in patients with type 2 diabetes mellitus during sympathetic activation. Sympathetic dysinnervation is associated with increased ventricular repolarization lability.