1. Division of Cardiovascular Surgery, Second Affiliated Hospital of Harbin Medical University, Key Laboratory of Education Ministry for Myocardial Ischemia, Harbin, Heilongjiang 150086, P.R. China
2. Division of Thoracic Surgery, Tang Du Hospital of Fourth Military Medical University, Xi'an, Shaanxi 710032, P.R. China
3. Division of Epidemiology and Biostatistics, School of Public Health, Harbin Medical University, Harbin, Heilongjiang 150086, P.R. China