Effects of cardiac sympathetic innervation on regional wall motion abnormality in patients with long QT syndrome

Aim - To assess the spatial relation between regional cardiac sympathetic innervation and regional ventricular repolarisation indicated by ventricular wall motion abnormality in patients with congenital long QT syndrome. Design - Regional percentage uptake and washout rate of ¹²³I metaiodobenzylguanidine (MIBG) were measured to assess cardiac sympathetic innervation in septum, anterior wall, lateral wall, and posterior wall. Left ventricular short axis images on echocardiography were digitised to reconstruct digitised M mode echocardiograms, from which left ventricular wall thickness curves were obtained. The wall thickening time (ThT) was defined as the period in which the instantaneous wall thickness exceeded 90% of the maximum wall thickness. The ThT was measured from the ventricular wall thickness curve at the same segments where regional percentage uptake and washout rate of ¹²³I MIBG were measured. Patients - Seven patients with long QT syndrome. Results - The regional washout rate (mean (SD)) of ¹²³I MIBG in patients with long QT syndrome was greater in the segments with decreased percentage uptake of ¹²³I MIBG than in those without (17.4 (10.6)% v 9.7 (16.5)%, p < 0.03). ThT in segments both with and without decreased percentage uptake of ¹²³I MIBG was longer than in control subjects (p < 0.0001). ThT was longer in the segments with decreased percentage uptake of ¹²³I MIBG than in those without (199 (70) ms v 150 (66) ms, p = 0.0018). Conclusions - Activation of regional cardiac sympathetic terminals is likely to participate in additional regional prolongation of ventricular repolarisation in patients with long QT syndrome.