Extremely Small Body Size, Not Biological Sex, as a Mortality Risk Factor in Coronary Artery Bypass Grafting: A Nationwide Study in Japan
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Background
Coronary artery disease is a significant health concern and can lead to death. Coronary artery bypass grafting (CABG) is the primary surgical treatment for this disease. However, the long-standing hypothesis that women face higher surgical mortality than men after CABG remains controversial. The universal healthcare system and the established national cardiovascular surgery registry of Japan provide a unique oppotunity to assess this supposition. This study aimed to re-evaluate this long-standing hypothesis.
Methods
This nationwide observational retrospective study analyzed 40,796 primary elective CABG procedures performed in Japan between January 2019 and December 2023. It included 33,202 men (81%) and 7,594 women (19%). Data were sourced from the Japan Cardiovascular Surgery Database. Preoperative, intraoperative, and postoperative variables were analyzed to assess sex differences in operative mortality. The impact of the yearly procedure volume at each facility was evaluated.
Results
Operative mortality for elective CABG was 1.25% in men and 1.63% in women ( P =0.01), supporting higher operative mortality in women in Japan. Preoperatively, women had lower body surface area and smoking rates. No notable sex differences were observed in the choice of surgical procedure, cardiopulmonary bypass use, or graft selection. Postoperative mediastinitis occurred more frequently in women than in men. After adjusting for body surface area, the difference in mortality became insignificant. A multivariable logistic regression analysis controlling for age, body mass index, preoperative comorbidities, preoperative status, and the facility’s annual CABG procedure volume confirmed that a body surface area of <1.4 m 2 was a significant mortality risk factor, irrespective of sex. The higher proportion of women with a body surface area of <1.4 m 2 explained the higher mortality in this group compared to the cases in men. These findings support that extremely small body size is a mortality risk factor for CABG.
Conclusions
Nationwide registry data from Japan revealed that female sex is not an independent predictor for CABG mortality. Higher mortality in women primarily reflects the overrepresentation of female patients with very small body sizes. These findings suggest that surgical procedures and anastomosis strategies for small coronary arteries can improve outcomes in all patients when optimized.
