The impact of body mass index on clinical outcomes after acute myocardial infarction.

Background: Several studies indicated that an elevated body mass index (BMI) is associated with a lower rate of mortality in patients with acute myocardial infarction (AMI). However, the existence of the obesity paradox in AMI patients remains controversial.

Methods: We examined the association of BMI and clinical outcomes in 2157 patient with AMI (mean follow-up of 26 months). BMI was categorized into 9 groups (<18.5, 18.5 to 20.9, 21.0 to 23.4, 23.5 to 24.9, 25.0 to 26.4, 26.5 to 27.9, 28.0 to 29.9, 30.0 to 34.9, and ≥35.0 kg/m2). Cox regression was used to calculate hazard ratios (HR) for the various BMI categories, adjusting for the clinical variables, left ventricular ejection fraction, and hemoglobin level.

Results: BMI had a U-shaped association with mortality. Relative to the lowest mortality group (BMI of 26.5 to 27.9 kg/m2), the adjusted HRs for mortality were increased only in the lower (HR 2.3; 95% CI 1.3-4.2) and upper (HR 1.8; 95% 1.2-2.9) BMI categories. There was a significant interaction between BMI and anemia (P=0.0003) such that the U-shaped relationship between BMI and mortality was present mainly in patients with anemia. Patients in the lower and upper BMI categories and concomitant anemia had a striking increase in mortality (adjusted HR 5.1, 95% CI 1.9-11.7 and 3.2, 95% CI 1.5-7.0, respectively).

Conclusion: Both obesity and underweight are associated with increased mortality in patients with AMI. The risk of mortality is particularly high among underweight and obese patients with anemia.