1. Department of Cardiovascular Surgery; Japan Labor Health and Welfare Organization Osaka Rosai Hospital; Osaka Japan
2. Department of Cardiovascular Surgery; Osaka University Graduate School of Medicine; Suita, Osaka 565-0871 Japan
3. Osaka Cardiovascular Surgery Research (OSCAR) Group; Osaka Japan
4. Department of Biostatistics; Hyogo College of Medicine; Nishinomiya Hyogo Japan