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1 University of Adelaide
2 Baker Heart Research Institute
3 Baker Medical Research Institute
4 University of Newcastle
* To whom correspondence should be addressed. E-mail: eugene.nalivaiko{at}newcastle.edu.au.
Suggestions were made that increased myocardial sympathetic activity is reflected by elevated QT variability (dynamic changes in the QT-interval duration). It is however unknown what is the relationship between QT variability and the amount of noradrenaline released from the cardiac sympathetic terminals. We thus attempted to assess this relationship. The study was performed in 17 subjects (12 with major depression disorder and 5 with panic disorder). Cardiac noradrenaline spillover (measured with direct catheter technique coupled with norepinephrine isotope dilution methodology) was assessed before and 4 months after treatment with SSRI antidepressants. The distribution of the cardiac noradrenaline spillover was bimodal, with the majority of patients having values of 10 ng/min or less. There was a positive correlation between cardiac noradrenaline spillover and QTc (r = 0.7, p = 0.03), but not with any of QT variability measures. However, in a subgroup of 5 patients that had high levels of cardiac noradrenaline spillover (>20 ng/min), a tendency for a strong positive correlation with QTvar (r = 0.9, p = 0.08) was observed. There were significant correlations between the severity of depression and QT variability indices normalized to the heart rate (QTVi, and QT/RR coherence), and between the severity of anxiety and the QT/RR residual and regression coefficient, respectively. Treatment with SSRI antidepressants substantially reduced depression score, but did not affect any of QT variability indices. We conclude that in depression/panic patients with near-normal cardiac noradrenaline levels, QT variability is not correlated with cardiac noradrenaline spillover, and is not affected by treatment with SSRI.
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