Relation between QT interval variability and cardiac sympathetic innervation in patients with diabetes mellitus

Abstract

Elevated QT interval variability (QTV) has been asso- ciated with increased cardiac mortality, but the underlying mechanisms are incompletely understood. Sympathetic ac- tivity is thought to be a main contributor to QTV. The aim of this study was to investigate the relation between car- diac 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 inter- vals 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 parame- ters were significantly increased in subjects with sympa- thetic 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.