Inclusion Criteria:  Male or female patients with 18≤age≤65 VVS as the cause of TLOC ≥2 episodes of VVS during the last year The capability of giving informed consent Signed written informed consent  Exclusion Criteria:  Other causes of TLOC including orthostatic hypotension, postural tachycardia, carotid sinus hypersensitivity, or seizure Cardiac rhythm disorders including ventricular tachycardia, long QT syndrome, Brugada syndrome, ARVC, CHB, and any conduction abnormality on ECG Severe valvular heart disease Hypertrophic cardiomyopathy Cardiac systolic dysfunction (ejection fraction≤40%) Obstructive coronary artery disease Renal failure stage≥3 Other non-cardiovascular chronic illnesses Urinary retention Pheochromocytoma Thyrotoxicosis Glaucoma