Unexplained Syncope in Patients With Congenital Long QT Syndrome　- Role of Implantable Loop Recorders in Diagnostic Evaluation.

BACKGROUND: Syncope is common in patients with congenital long QT syndrome (LQTS). However, not all episodes of syncope or loss of consciousness are caused by torsades de pointes (TdP); some are attributable to bradycardia or non-cardiac causes. This study investigated the clinical utility of implantable loop recorders (ILRs) in patients with LQTS presenting with unexplained syncope. METHODS AND RESULTS: We retrospectively studied 18 patients with LQTS (7 with LQTS type (LQT) 1, 3 with LQT2, 1 with LQT3, and 7 genotype-negative LQTS) who underwent ILR implantation for recurrent syncope. Multiple causes of syncope were suspected in each patient; there were 14 cases of arrhythmia, 4 of epilepsy, 8 of neurally mediated syncope (NMS), and 9 of unknown cause. During a mean (±SD) follow-up of 37±22 months after ILR implantation, 8 (44%) patients experienced recurrent syncope. Four episodes were caused by TdP and the remaining 4 episodes were attributed to epilepsy or NMS (cardioinhibitory type). No significant difference was observed in baseline clinical characteristics between patients with and without TdP following ILR implantation, but female sex (P=0.051) and a higher Schwartz score (P=0.08) tended to be associated with TdP. CONCLUSIONS: Syncope in patients with LQTS is not always attributable to TdP, and non-arrhythmic causes should be considered. Although ILRs may aid in diagnostic evaluation, careful risk stratification remains essential in patients with suspected arrhythmic syncope.