Scintigraphic pattern of regional cardiac sympathetic innervation in patients with familial long QT syndrome using positron emission tomography.

BACKGROUND

The purpose of this study was to determine whether scintigraphic evidence of cardiac sympathetic neuronal dysinnervation is present in patients with the familial long QT syndrome. The "sympathetic imbalance" hypothesis for the familial long QT syndrome proposes that the long QT syndrome results from a congenital imbalance of sympathetic innervation of the heart caused by lower-than-normal right cardiac sympathetic activity. Although the majority of clinical features of the long QT syndrome can be understood according to this hypothesis, its validity has never been shown. Noninvasive scintigraphic evaluation of the pattern of sympathetic innervation of the heart has recently become possible with catecholamine analogues that can be taken up by sympathetic nerve terminals: radioiodinated metaiodobenzyl guanidine or C-11 hydroxyephedrine (HED).

METHODS AND RESULTS

Nine affected patients, each from a separate family with familial long QT syndrome, were enrolled in this study (three men, six women; mean age, 39 +/- 16 years). Scintigraphic evaluation of the pattern of cardiac sympathetic innervation in each patient was performed with HED in conjunction with positron emission tomography. The results of scintigraphic imaging in these patients were compared with those obtained in 14 asymptomatic volunteers. Scintigraphic evaluation demonstrated that HED retention index and HED uptake normalized to blood flow were no different in patients with the familial long QT syndrome than in normal control patients.

CONCLUSIONS

Patients with the long QT syndrome have normal cardiac sympathetic innervation as assessed by HED. This finding, although not incompatible with the sympathetic imbalance hypothesis of the long QT syndrome, suggests that if a decrease in right sympathetic activity is present in patients with familial long QT syndrome, it is unlikely to be attributed to an abnormal distribution of cardiac sympathetic nerves.