Body mass index and cardiovascular clinical outcomes after acute coronary syndromes

Abstract

Obesity, assessed by body mass index (BMI), is considered a major public health problem worldwide. Studies in people without CVD, have shown that BMI between 22.5 to 24.9 kg/m2 is associated with the lowest risk of death in healthy non-smoker populations. However, studies in patients with acute coronary syndrome (ACS) have shown that overweight and obese patients have better survival than those in the normal BMI range. This phenomenon has been called the “obesity paradox”. This thesis has two main components: a systematic review with meta-analysis of the current literature of BMI and ACS, and an individual patient data meta-analysis from 8 randomized trials whose data base was accessible at the PHRI involving ACS patients. The study-level systematic review (35 studies) and meta-analysis (19 studies) demonstrates that there is a statistically significant adjusted 20% risk lower mortality among overweight and obese participants considered normal weight. Nevertheless, there was moderate to high heterogeneity of pooled estimates that could not be explained in subgroup analyses. Also, the systematic review detected major limitations in the current literature, including missing BMI and covariates data, lost to follow-up, enough number of events in high BMI categories, warranting more research in the area. The second component, the individual patient data meta-analysis (n = 81,553), confirmed a 20% lower mortality risk in the overweight and type I obesity categories, compared to the normal the BMI range. This lower risk was robust and remained consistent within several sensitivity analyses. Analysis of secondary outcomes suggests that a reduced risk of bleeding, and probably a reduced risk of ischemia and heart failure related deaths, are the responsible mechanisms. Given the limitations of observational research, prospective randomized interventional trials are required to clarify the optimal range of BMI in those with ACS.