Treatment Strategy of Vasovagal Syncope

The left atrium model was established under the guidance of three-dimensional mapping. Atrial septum puncture、left atrium mapping and right atrium mapping will be performed according to standard EP lab protocol. The location of GPs will be detected with HAFE potential (duration ≥ 50ms， deflections ≥ 4 times， amplitude ≥ 0.7mV) and high frequency stimulation (HFS; 30 Hz, 20 mV, pulse width 2ms) through positive vasovagal response (transient ventricular asystole, atrioventricular block, or R-R interval increased by 30%) . Saline Irrigated-tip catheter with pressure monitoring will be applied for the procedure, and radiofrequency energy is limited to 40W and 43℃ for at least 30s at each site. The ablation endpoint for each GP is defined as the complete elimination of all targeted HAFE potential and elimination of positive vasovagal response. The endpoint of the procedure was that the heart rate reach 75% of the maximum heart rate in atropine test.

Midodrine will start dosing with 5 mg of the study drug 3 times daily, 4 hours apart, during daylight hours.Dose with be adjusted within a range of 2.5 mg twice daily, 4 hours apart, up to 10 mg, 3 times daily, every 4 hours. The optimal dose ranging be completed within the first 2 weeks. If intolerable symptoms persisted despite dose reductions, the drug will be withdrawn, and the patient was released from the study.