Malignant neurocardiogenic vasovagal syncope associated with chronic exaggerated vagal tone

A head-up tilt test was performed in a 23-year-old woman with a history of two syncopal episodes. The patient developed abrupt syncope with 48 seconds of sinus arrest. Analysis of the high frequency (HF) power of heart rate v ariability over 24 hours before and after metoprolol therapy showed a signi ficantly elevated HF power in this patient compared to age- and sex-matched healthy subjects. It is suggested that an exaggerated resting vagal tone m ight be associated with the pathogenesis of prolonged asystole in our patie nt.