123I-metaiodobenzylguanidine scintigraphy in the detection of irregular regional sympathetic innervation in long QT syndrome

Twelve patients with the long QT syndrome were studied to determinethe usefulness of ¹²³I-metaiodobenzylguanidine (MIBG) single-photonemission tomography (SPECT) at 2 h and 6 h after injection;the results were compared to 10 healthy volunteers (controls).Uptake of MIBG in the left ventricle at 2 h after injectionwas significantly reduced in patients with the long QT syndrome(1.43±0.13) vs 1.66±0.15 in controls, heart-to-mediastinumratio, P <0.002) and washout after 6 h was faster on a planarview image. Decreased MIBG uptake could be observed preferentiallyin the anterior and lateral walls near the apex. The half-timevalues of MIBG washout from the left ventricle were significantlyreduced in the long QT syndrome (6.4±1.5 h) comparedto controls (16.7±15.3 h, P <0.002). In three cases,the same pattern of disturbed activity distribution was maintainedeven after surgical left cardiac sympathetic denervation. Thepresent results strongly support the hypothesis that an inhomogenousregional distribution of sympathetic nerve terminals accompaniedby an overall reduction in their absolute number may play animportant role in the pathogenesis of the long QT syndrome.Additional functional disturbances, possibly related to theuptake of catecholamines in the left ventricle may coexist withregional inhomogeneity of nerve terminals. The differences observedfrom one case to the other may be related to the variation inseverity of the disease. MIBG SPECT imaging seems an interestingnew tool for the quantitative assessment of presynaptic sympatheticnerve terminal disturbances in the left ventricle of patientswith the long QT syndrome.