Clinical Implication of 'Obesity Paradox' in Elderly Patients With Acute Myocardial Infarction

Background The clinical impact of body mass index (BMI), especially in the elderly with acute myocardial infarction (AMI), has not been sufficiently evaluated. The purpose of this study was to elucidate the clinical impact BMI in very old patients (>80 years) with AMI. Methods The study analysed 2,489 AMI patients aged >80 years from the Korea Acute Myocardial Infarction Registry and the Korea Working Group on Myocardial Infarction (KAMIR/KorMI) registries between November 2005 and March 2012. The study population was categorised into four groups based on their BMI: underweight (n=301), normal weight (n=1,150), overweight (n=890), and obese (n=148). The primary endpoint was major adverse cardiovascular event (MACE), a composite of cardiac death, myocardial infarction, target lesion revascularisation, and target vessel revascularisation. Results Baseline characteristics among the four groups were similar, except for hypertension (45.1 vs 58.4 vs 66.2 vs 69.9%, respectively; p<0.001) and diabetes (16.6 vs 23.6 vs 30.7 vs 35.1%, respectively; p<0.001). Coronary care unit length of stay was significantly different among the four groups during hospitalisation (5.3 +/- 5.9 vs 4.8 +/- 6.8 vs 4.2 +/- 4.0 vs 3.5 +/- 2.1 days; p=0.007). MACE (16.9 vs 14.9 vs 13.7 vs 8.8%; p=0.115) and cardiac death (10.3 vs 8.4 vs 7.9 vs 4.1%; p=0.043) less frequently occurred in the obese group than in other groups during the 1-year follow-up. A multivariate regression model showed obese status (BMI >27.5 kg/m(2)) as an independent predictor of reduced MACE (hazard ratio [HR], 0.20; 95% confidence interval [CI], 0.06-0.69; p=0.010) along with reduced left ventricular ejection fraction (<40%) as a predictor of increased MACE (HR,1.87; 95% CI, 1.31-2.68; p=0.001). Conclusion Body mass index in elderly patients with acute myocardial infarction was significantly associated with coronary care unit stay and clinical cardiovascular outcomes.