[1] Korea Univ, Guro Hosp, Coll Med, Dept Thorac & Cardiovasc Surg, Seoul 02841, South Korea
[2] Korea Univ, Ansan Hosp, Coll Med, Dept Thorac & Cardiovasc Surg, Ansan 15355, South Korea
[3] Korea Univ, Anam Hosp, Coll Med, Dept Thorac & Cardiovasc Surg, Seoul 02841, South Korea
[4] Korea Univ, Coll Med, Dept Biostat, Seoul 02841, South Korea