Funding for this research was provided by:
National Natural Science Foundation of China (No. 81670315)
Text and Data Mining valid from 2019-07-04
Received: 13 March 2019
Accepted: 24 June 2019
First Online: 4 July 2019
Ethics approval and consent to participate
: Ethical approval was obtained from Beijing Friendship Hospital ethics committee (certification number: 2018-P2–051-01). This retrospective study was conducted without informed consent for some objective reasons and was approved by the ethics committee. All study procedures were performed in accordance with Declaration of Helsinki.
: Not applicable.
: The authors declare that they have no competing interests.