Impact of body mass index on short-term outcome after acute myocardial infarction: does excess body weight have a paradoxical protective role?

Obesity is a risk factor for acute myocardial infarction (AMI), due in part to obesity-related conditions. However, the relation between BMI (body mass index) and outcome in patients with AMI has not been completely clarified. The aim of our study was to assess the impact of BMI on short-term outcome after AMI. METHODS: We retrospectively studied 717 consecutive patients admitted to our Intensive Coronary Care Unit for AMI. The end-point of the study was all-cause mortality. RESULTS: The mean age was 64+/-12 years. Mean BMI was 26+/-3.5 kg/m2. During follow-up 15 patients died. Non-survivors were significantly older than survivors (p<0.0001); BMI (p = 0.0027) and weight (p = 0.0002) were significantly lower in non-survivors than survivors; left ventricular dimensions (end-diastolic diameter: p = 0.0023; end-systolic diameter: p = 0.0019), the number of akinetic segments (p<0.0001) and contractile efficiency (p<0.0001) were also significantly lower in non-survivors. At Cox proportional univariate analysis low BMI (p = 0.0019), female sex (p = 0.0041), age (p<0.0001), left ventricular dimensions (end-diastolic diameter = 0.0040, end-systolic diameter = 0.0053), number of akinetic segments (p = 0.0001) and degree of left ventricular dysfunction (p = 0.0002) were significant predictors of prognosis. The prognostic power of BMI remained after adjustment for age (p<0.05), left ventricular dimensions (end-diastolic diameter: p<0.0042; end-systolic diameter p = 0.04), contractile efficiency (p = 0.0045) or number of akinetic segments (p = 0.0070). CONCLUSION: Low BMI is an independent predictor of poor prognosis in the short-term outcome after AMI. The underlying mechanisms remain to be investigated.