Limitations of this study
A major limitation of this study is the small number of patients. We used the Calgary score as the reference standard for diagnosis of VVS; however, this is controversial. In addition, performing the combination of a TET and the HUTT is complicated and time consuming, and many not be useful in clinical practice. A simplification in which a TET is performed, and then a HUTT is performed within 10 min after the TET may also increase the diagnosis rate of VVS, and would be simpler and less time-consuming to perform.