Association between obesity and infarct size: insight into the obesity paradox.

Background: In patients with coronary heart disease, being overweight or obese is associated with better outcomes, a phenomenon known as the 'obesity paradox'. Despite the high prevalence of obesity in the United Sates, its effects on infarct size are largely unexplored. Methods: Prospective cross-sectional study of 102 consecutive patients admitted with acute myocardial infarction (MI). Standardized forms were used to collect data on body mass index (BMI), waist circumference (WC), cardiovascular risk factors, and medications. Peak troponin I and creatinine phosphokinase (CPK) were used to estimate infarct size. Epicardial and pericardial fat were measured by echocardiography. We used univariate and multivariate analyses to assess whether obesity was associated with infarct size. Correlations between BMI, WC and cardiac fat with cardiac biomarkers were also performed. Results: Mean age was 62±12 years, and 55% were men. Obesity was diagnosed in 69%. On multivariate analysis, obesity was associated with greater infarct size in non-ST elevation MI (p=0.02). A positive correlation was observed between BMI and peak troponin I (rho=0.24, p=0.03), and both, BMI and WC had a positive correlations with CPK levels (rho=0.28, & rho=0.28, both p=0.02). However, in ST elevation MI, obesity was associated with smaller infarct size (p=0.05). Epicardial fat + pericardial fat had a negative correlation with peak CPK levels (rho=-0.36, p=0.05). Conclusions: We observed an opposite association between obesity and infarct size depending on the type of MI. These results were unexpected and may provide insight into the pathophysiology of the obesity paradox. (Word count: 244)