Aims: Syncope in long QT syndrome (LQTS) is expected to be due to Torsades de Pointes ventricular tachycardia (TdP). Often these patients faint in situations with emotional stress. The aim of the present study was to evaluate whether neurocardiogenic syncope occurs in LQTS.
Methods and results: Ten untreated consecutive LQTS patients (age 11-72 years, median 37.5 years, five males and five females from five different families (one KvLQT1 mutation, two HERG mutations in three families and one without established genetic background)) were examined by a head-up tilt-table test (HUT). If syncope did not occur within 25 min, the patient received 0.25 mg nitroglycerine sublingually and the HUT was continued for 20 min. Nine out of 10 patients had a positive HUT. The syncope resulted from a combined vasodepressor and bradycardiac response. There were no cases of TdP. No syncope occurred in a 42-year-old asymptomatic male LQTS patient with a borderline prolonged QTc of 0.45 s and a HERG mutation. In 11 of 21 patients referred for syncope without LQTS a positive HUT was found (P < 0.10).
Conclusion: Syncope in LQTS can be of neurocardiogenic origin and is not necessarily due to TdP. The reason for neurocardiogenic syncope in LQTS is unknown, but involvement of the autonomic nervous system outside the heart is possible.