Data Sources
We evaluated patients with VVS who presented to the syncope unit12, 13, 25 of Tehran Heart Center,26 Tehran, Iran, for a head-up tilt table test (HUTT) from February 2020 to February 2021 as the case group. The control group was selected from the population-based Tehran Cohort Study (TeCS) on adult inhabitants of Tehran.27 The demographic and baseline data were retrieved from the syncope registry of Tehran Heart Center25 for the case group and the database of TeCS27 for the control group. The protocol of this study was designed according to the Declarations of Helsinki 2013 and approved by the ethics committee of Tehran University of Medical Sciences (IR.TUMS.MEDICINE.REC.1397.856). Informed consent was obtained from all participants after a detailed discussion on the study protocol and before inclusion.