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 m2 was a significant mortality risk factor, irrespective of sex. The higher proportion of women with a body surface area of <1.4 m2 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.

The authors have declared no competing interest.

This is a nationwide, retrospective observational study, not a clinical trial or a prospective interventional study.

Sources of Funding: None

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The Institutional Review Board of Iwate Prefectural Central Hospital approved this nationwide observational retrospective study (approval number: 1839), which conforms to the principles of the Declaration of Helsinki. The requirement for informed consent from patients was waived by adopting an opt-out method.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

All data are not available because the data access of Japan Cardiovascular Surgery Database is strictly limited.