Zhonghua Xu1, Xiaomei Li1, Qingyu Wu2, Hongyin Li1, Guangyu Pan1. 1. Department of Cardiac Surgery, First Hospital of Tsinghua University, Beijing 100016, China. 2. Department of Cardiac Surgery, First Hospital of Tsinghua University, Beijing 100016, China. Email: wuqingyu@mail.tsinghua.edu.cn.