Interpreting low body mass index outcomes after coronary artery bypass grafting: The need for mechanistic data and stratified analyses

To the Editor:

The study carried out by Kuroda and colleagues¹ evaluating the influence of body mass index (BMI) on outcomes following coronary artery bypass grafting (CABG) from the Coronary Revascularization Demonstrating Outcome Study in Kyoto Registry is extremely relevant to clinical practice. The finding that patients with low BMI (<18.5) face increased risk of both early and late mortality provides valuable evidence, yet several considerations remain important when interpreting the findings.

Firstly, internal thoracic artery (ITA) use was marginally lower in the low-BMI group (93% vs 95%-97%), but the reasons for this were not examined. The lower ITA use in low-BMI patients may reflect either technical issues during harvesting or patient-related factors, such as smaller or more fragile ITAs and coronary targets of poorer quality. The resultant use of vein grafts could have predisposed these patients to early graft failure and postoperative myocardial infarction. In the absence of data on graft selection rationale, it remains uncertain whether lower ITA utilization was causally linked to early myocardial infarction, or whether both represent independent consequences of low BMI.

Secondly, approximately half the patients underwent off-pump CABG, but outcomes were not stratified by pump status. Given that on-pump and off-pump procedures differ in hemodynamic parameters, inflammatory response, and embolic risk, particularly in frail or malnourished patients, this is an important omission. Within the low-BMI group, a comparison of outcomes by surgical technique could have provided valuable insights, especially regarding perioperative myocardial infarction, stroke, and early cardiovascular mortality. Such an analysis might have clarified whether the excess early risk in low-BMI patients was attributable, at least in part, to operative approach rather than BMI alone.

Finally, at 5 years, low-BMI group patients exhibited a significantly higher incidence of noncardiovascular death compared with those of normal BMI (15.1% vs 8.1%). The authors suggest that this may reflect sarcopenia, malnutrition, or infection; however, these remain unproven hypotheses. The study did not assess sarcopenia, nutritional biomarkers, infection rates, or provide detailed cause-of-death categories. In the absence of such data, it is not possible to determine whether the observed excess mortality was indeed driven by these mechanisms or by other competing risks, such as malignancy, chronic pulmonary disease, or renal failure.

Although this study makes a valuable contribution by highlighting the vulnerability of low-BMI patients undergoing CABG, its clinical implications could be further strengthened by additional mechanistic data on conduit choice, surgical strategy (on-vs off-pump), and more granular cause-of-death information.

Conflict of Interest Statement

The authors reported no conflicts of interest.

The Journal policy requires editors and reviewers to disclose conflicts of interest and to decline handling or reviewing manuscripts for which they may have a conflict of interest. The editors and reviewers of this article have no conflicts of interest.