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 scintig raphic evidence of cardiac sympathetic neuronal dysinnervation is pres ent 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 sympathet ic innervation of the heart caused by lower-than-normal right cardiac sympathetic activity. Although the majority of clinical features of th e long QT syndrome can be understood according to this hypothesis, its validity has never been shown. Noninvasive scintigraphic evaluation o f the pattern of sympathetic innervation of the heart has recently bec ome possible with catecholamine analogues that can be taken up by symp athetic 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 enr olled in this study (three men, six women; mean age, 39+/-16 years). S cintigraphic evaluation of the pattern of cardiac sympathetic innervat ion in each patient was performed with HED in conjunction with positro n emission tomography. The results of scintigraphic imaging in these p atients were compared with those obtained in 14 asymptomatic volunteer s. 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. Conclu sions. Patients with the long QT syndrome have normal cardiac sympathe tic innervation as assessed by HED. This finding, although not incompa tible with the sympathetic imbalance hypothesis of the long QT syndrom e, suggests that if a decrease in right sympathetic activity is presen t in patients with familial long QT syndrome, it is unlikely to be att ributed to an abnormal distribution of cardiac sympathetic nerves.