Prevalence and spectrum of electroencephalogram-identified epileptiform activity among patients with long QT syndrome

BACKGROUND Congenital long QT syndrome (LQTS) is a heritable cardiac disease whereby patients are at an increased risk for LQTS-triggered syncope, seizures, and sudden cardiac arrest. Seizure episodes are common in LQTS and most often seen in patients with type 2 LQTS (LQT2). OBJECTIVE To determine the prevalence of electroencephalogram (EEG)-identified epileptiform activity among patients with LQTS. METHODS A retrospective electronic medical record review of 610 patients with LQTS (250 [41%] men), evaluated between 2000 and 2012, was performed to identify (1) all patients with LQTS who presented with seizures/seizure-like episodes, (2) patients with LQTS who underwent a subsequent neurologic evaluation and EEG study, and (3) patients with LQTS and abnormal EEG recordings that showed epileptiform activity during sinus rhythm, confirming a seizure independent from cardiac arrhythmia. RESULTS Overall, seizures/seizure-like episodes were recorded in 68 of 610 (11%) patients with LQTS. Ten patients were diagnosed with a seizure disorder by an epileptologist on the basis of the clinical findings and EEG studies, giving a prevalence of 10 of 610 (1.6%; 95% confidence interval 0.8%-3%) among patients with LQTS. A diagnosis of epilepsy was overrepresented in patients with LQT2 (7 of 190 [3.7%]) in comparison to all other LQT subgroups (3 of 420 [0.7%]; P = .0126). CONCLUSIONS While the overall prevalence of epilepsy among patients with LQTS is low, 10 of 68 (15%) of the patients who presented with seizures/seizure-like episodes had EEG-identified epileptiform activity. Confirming earlier observational reports, epilepsy is more common in patients with LQT2, further supporting the shared pathogenetic link hypothesis of this KCNH2-encoded potassium channel that is expressed in both the heart and the brain.