QT Interval Variability in Type 2 Diabetic Patients with Cardiac Sympathetic Dysinnervation Assessed by 123I-Metaiodobenzylguanidine Scintigraphy

Authors


  • This work was supported in part by the National Health and Medical Research Council (Centre of Clinical Research Excellence award) and Australian Research Council (Discovery Project grant, 110102049) of Canberra, Australia. M. Baumert was supported by a fellowship from the Australian Research Council.

Julian W. Sacre, Ph.D., School of Human Movement Studies, The University of Queensland, Brisbane, Qld. 4072, Australia. Fax: +61 7 3365 6877; E-mail: julian.sacre@uqconnect.edu.au

Abstract

QT Variability and Sympathetic Dysinnervation. Introduction: The mechanism of adverse prognosis attributable to proarrhythmic cardiac sympathetic dysinnervation in patients with type 2 diabetes is incompletely understood. This study sought the association of cardiac sympathetic dysinnervation with temporal instability of ventricular repolarization assessed by beat-to-beat QT interval variability.

Methods and Results:123I-metaiodobenzylguanidine (123I-MIBG) scintigraphy was analyzed in 31 type 2 diabetic patients for cardiac sympathetic dysinnervation (4-hour heart-to-mediastinum ratio <1.8) and regional sympathetic integrity and washout rate (from 15-minute 123I-MIBG uptake). Relative QT variability was defined from a continuous 5-minute ECG in the supine position (n = 31) and standing position (subgroup; n = 15) by the log ratio of absolute QT variability (QT variance divided by the mean QT interval squared) to heart rate (HR) variability (HR variance divided by the mean HR squared). Patients with (n = 16; 52%) versus without cardiac sympathetic dysinnervation demonstrated higher relative QT variability in the supine position (P < 0.001), owing to lower HR variability. However, on standing, absolute QT variability was significantly raised in these patients (P = 0.009) despite similar HR variability in the 2 groups. Correlations of heart-to-mediastinum ratio with standing QT variability (relative [r =−0.63, P = 0.013] and absolute [r =−0.79, P = 0.001]) were superior to corresponding supine measures (relative [r =−0.47, P = 0.008] and absolute [P = NS]). No associations of QT variability with washout rate or regional 123I-MIBG uptake were identified.

Conclusion: Elevated QT variability is associated with cardiac sympathetic dysinnervation in type 2 diabetes and may contribute to adverse prognosis. Moreover, QT variability may be more specific for cardiac sympathetic innervation when measured in the context of sympathetic activation. (J Cardiovasc Electrophysiol, Vol. 24, pp. 305-313, March 2013)

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