Abstracts

Rationale: Cerebral potassium ion channel dysfunction may lead to idiopathic epilepsies. In the heart, cardiac potassium channel dysfunction encoded by the HERG gene, is linked to the long QT-syndrome type 2 (LQTS-2) predisposing to ventricular arrhythmias and sudden cardiac death. This potassium channel is co-expressed in the heart and in the brain. Accordingly, it has been suggested that some cases of losses of consciousness in patients with LQTS-2 may be caused by a coexisting cerebral channelopathy. We aimed to describe the semiology of loss of consciousness in LQTS-2 patients and explore electroencephalographic (EEG) alterations in these patients.Methods: We studied 15 patients (mean age: 43 (21-72), 12 women) with a genotyped diagnosis of LQTS-2. We assessed a standardized medical history with emphasis on the semiology of previous syncopes and a clinical neurological examination. A 1hr 64-channel awake EEG was analysed by visual assessment. In addition, brain connectivity was quantified by Direct Transfer Function (DTF) from the current source density estimate within the theta band (4-7 Hz) using the mean of all 10 sec epochs for 1 h.Results: Of the 15 patients, 11 (73%) had experienced syncopes, of which 6 (55%) had experienced tonic-clonic activity or spells and urine incontinence. One of the 11 (9%) had experienced urine incontinence in absence of tonic-clonic activity or spells. Two patients (13%) had been diagnosed with epilepsy and received anti-epileptic medication prior to their LQTS-2 diagnosis. A visual examination of EEGs showed an increased frequency of theta activity fronto-centrally in 5 of the 15 examined patients, including one patient with epileptic activity. The mean source connectivity strength was 0.0548 over all patients and channels. The highest source connectivity was seen in Pz (central parietal electrode position)(0.1460). Data thus indicates a low connectivity value.Conclusions: Syncopes in LQTS-2 patients were frequently associated with tonic-clonic activity, spells and urine incontinence, which could also be consistent with epilepsy. In addition, 2/15 had co-existing diagnoses of epilepsy and LQTS-2. The majority of the EEGs showed minor to moderate changes with intermittent theta activity. EEG pathology was confirmed by the quantitative analysis demonstrating connectivity between 0.0188 and 0.1460, indicating a low connectivity value. Our study underlines the difficulties in differentiating between cardiac syncopes and epileptic seizures clinically. However, our results may also indicate overlapping causative mechanisms in the two conditions.