A gender-based analysis of the obesity paradox in cardiac surgery: height for women, weight for men?

OBJECTIVES

In cardiac surgery, obesity is associated with a lower mortality risk. This study aims to investigate the association between body mass index (BMI) and operative mortality separately in female patients and male patients undergoing cardiac surgery and to separate the effects of weight and height in each gender-based cohort of patients.

METHODS

A retrospective cohort study including 7939 consecutive patients who underwent cardiac surgery was conducted. The outcome measure was the operative mortality.

RESULTS

In men, there was a U-shaped relationship between the BMI and the operative mortality, with the lower mortality rate at a BMI of 35 kg/m2. In women, the relationship is J-shaped, with the lower mortality at a BMI of 22 kg/m2. Female patients with obesity class II-III had a relative risk for operative mortality of 2.6 [95% confidence interval (CI) 1.37-4.81, P = 0.002]. The relationship between weight and mortality rate is a U-shaped bot in men and women, with the lower mortality rate at 100 kg for men and 70 kg for women. Height was linearly and inversely associated with the operative mortality in men and women. After correction for the potential confounders, height, but not weight, was independently associated with operative mortality in women (odds ratio 0.949, 95% CI 0.915-0.983; P = 0.004); conversely, in men, this association exists for weight (odds ratio 1.017, 95% CI 1.001-1.032; P = 0.034), but not height.

CONCLUSIONS

Contrary to men, in women obesity does not reduce the operative mortality in cardiac surgery, whereas the height seems to be associated with a lower mortality.