Patient information
The study protocol was approved by the ethics committee of Zhengzhou Cardiovascular Hospital, affiliated to Southern Medical University (2020-10-002-F02). Patients in plateau areas who were admitted to the Cardiovascular Surgery Department of Zhengzhou Cardiovascular Hospital] between January 2020 and July 2022 were included. Parents or guardians of all of the patients provided signed informed consent prior to the study. The procedures followed were in accordance with the ethical standards of the relevant institutional committee on human experimentation and with the 1975 Helsinki Declaration, as revised in 2000.