An Apparent Obesity Paradox in Cardiac Surgery

I n this issue of Circulation, Mariscalco and colleagues 1 report findings from 2 separate analyses that describe lower in-hospital mortality rates in overweight and obese (class I and class II) patients undergoing cardiac surgery in comparison with leaner patients.Obesity paradoxes are not new to the field of cardiovascular disease and have been observed in heart failure, 2 acute coronary syndromes, 3 and chronic kidney disease.4 Rather, the novelty of the present study is the authors' interpretation that the common practice of recommending weight loss before surgery may not be warranted, and that refusing surgery to patients who are morbidly obese should be reconsidered.Although such strong clinical recommendations contradict the extensive body of research describing the risk of significant perioperative complications for obese patients undergoing any type of surgery, the methodologies they used to generate their findings are appropriate and the provocative findings warrant continued discussion.With the use of both a clinical registry and a meta-analysis, patients in the overweight and class I and class II obesity groups had unadjusted in-hospital and 30day mortality rates that were half those of patients who were normal weight and almost two-thirds lower than those who were underweight.Two of the most common arguments in opposition to the obesity paradox are that patients who are leaner are sicker and have a higher burden of comorbidities that independently contribute to mortality, or their health behaviors, namely cigarette smoking, contribute directly to mortality and leaner body habitus.However, even when these measured characteristics are taken into account by using multivariable modeling, mortality remains 15% to 20% lower in patients who are overweight and obese.Not only were the findings robust but they were consistent across analyses.When 26 studies conducted in 13 countries including >500 000 patients were meta-analyzed, leaner patients had higher 30-day mortality than patients who were overweight and obese.Although the effect estimates across the studies varied according to the types of surgeries included, overall study quality, and other methodologic differences, the summary effect estimates from the meta-analysis mirrored those from the cohort study.As presented in an extensive set of supplementary analyses, 1 findings in subgroups of patients defined by baseline disease were consistent and oftentimes stronger among those without preexisting comorbidities.It is notable that the paradox was apparent in never smokers, and former and current smokers, as well.However, the primary and subgroup analyses did not include some of the highest-risk patients, because patients who underwent cardiac surgery despite hemodynamic instability, respiratory failure, or end-stage renal disease on dialysis were excluded by the authors in their analysis of the registry, which lends itself to selection bias.Similarly, patients with obesity and significant comorbidities are less likely to be considered An Apparent Obesity Paradox in Cardiac Surgery