Text and Data Mining valid from 2019-06-08
Received: 14 November 2018
Accepted: 29 May 2019
First Online: 8 June 2019
Ethics approval and consent to participate
: This study was carried out in accordance with the Declaration of Helsinki. In view of the retrospective nature of our study, it was difficult to obtain consent from all patients. None recognizable patient information was used in this study. And we acquired an exemption from ethics approval conferred by the Subcommittee on Biomedical Ethics of West China Hospital.
: Not applicable.
: The authors declare that they have no competing interests.