Shattering the myth: Obesity paradox in cardiac arrest
Mortality is lower and outcomes are better among overweight patients following cardiac surgery, but when considering other preoperative variables, in-hospital and 1-year mortality do not appear to be independently influenced by body mass index (BMI), thus casting doubt on the “obesity paradox,” according to a study presented at the European Society of Cardiology Congress 2019 (ESC 2019).
The effect of BMI on mortality “could be indirect, being mediated through other comorbidities,” the researchers explained.
A total of 5,419 patients (mean age, 65.8±12.1 years; 72 percent male) were included. Presurgical variables were significantly different across the BMI groups, with underweight patients showing statistically more comorbid and severe clinical presentation.
The underweight group were also more likely to experience low cardiac output syndrome, medical and surgical bleeding, and longer hospital stay (p<0.05), while the obese group more frequently had mediastinitis, hyperglycaemia and prolonged mechanical ventilation (p<0.05). [ESC 2019, abstract N81074]
In univariable regression analysis, the following factors predicted in-hospital mortality: age, female sex, nonelective surgery, nonisolated coronary surgery, vascular periphery disease, chronic obstructive pulmonary disease, severe left ventricular fraction ejection, chronic renal disease, anaemia, stroke, myocardial infarction, heart failure and BMI categories (p<0.05).
Those with normal weight had a higher risk of mortality (odds ratio [OR], 1.49, 95 percent CI, 1.09–1.9; p=0.01), whereas overweight patients had a significantly lower risk of death (OR, 0.66, 0.5–0.88; p=0.005). No statistical significance was observed in the underweight and obese categories.
However, BMI as a continuous variable did not independently predict in-hospital mortality after adjusting for other risk factors in the multivariate analysis.
Ninety-five perfect of patients completed the 1-year follow-up period, during which 223 (4.12 percent) died. There was no significant difference between BMI categories in the analysis of unadjusted long-term mortality (p-log rank=0.16).
An earlier study also reported a survival benefit in obese patients after stroke, but no obesity paradox was observed in patients with intravenous thrombolysis. The investigators then suggested the need for well-designed trials to examine the effects of weight reduction on stroke risk in obese patients. [PLoS One 2017;12:e0171334]
The current retrospective cohort study included consecutive patients undergoing cardiac surgery from January 2007 to January 2019 and categorized them into four groups based on their BMI: underweight (≤18.5 kg/m2; 0.5 percent; n=27), normal weight (18.5–25 kg/m2; 25.7 percent; n=1,393) overweight (>25–30 kg/m2; 44.7 percent; n=2,423) and obese (>30 kg/m2; 29.1 percent; n=1,576).
Early and late clinical outcomes among the different BMI groups were compared using multivariable analyses. The Kaplan-Meier method was used to determine the overall 1-year survival, which was then compared across the BMI categories using the log-rank test.
“Obesity has been considered a risk factor for cardiovascular death and for poor outcomes from a variety of surgical procedures,” the researchers said. “Recent studies suggest that overweight and obese patients may paradoxically have a better prognosis in cardiac surgery compared with patients with normal BMI.”