The risk of total mortality, cardiovascular mortality, and myocardial infarction is highest among underweight patients, while cardiovascular mortality is lowest among overweight patients, according to a report, ‘Relationship of Body Mass Index With Total Mortality, Cardiovascular Mortality, and Myocardial Infarction After Coronary Revascularization: Evidence From a Meta-analysis’, published in the Mayo Clinic Proceedings.

Currently more than two-thirds of adult Americans are classified as overweight or obese, and obesity is considered a risk factor for worst clinical outcomes following cardiovascular procedures however, emerging data suggest that higher BMI protects against adverse outcomes in many acute and chronic disease states.

In a meta-analysis of 36 studies, Dr Abhishek Sharma, Cardiology Fellow at the State University of New York Downstate Medical Center in Brooklyn, New York, and colleagues determined that low BMI (<20) in tens of thousands of patients with coronary artery disease who underwent coronary revascularization procedures was associated with a 1.8- to 2.7-fold higher risk of myocardial infarction and all-cause and cardiovascular mortality over a mean follow up period of 1.7 years.

"At this stage we can only speculate on the reasons for this ‘paradox’” said Sharma. “One explanation may be that overweight patients are more likely to be prescribed cardioprotective medications such as beta blockers and statins and in higher doses than the normal weight population. Further, obese and overweight patients have been found to have large coronary vessel damage, which might contribute to more favourable outcomes. This population may have a higher metabolic reserve, which might act protectively in chronic conditions like CAD. Also, there could be a difference in the pathophysiology of cardiovascular disease in over- and underweight patients. A non-modifiable genetic predisposition may also play a role in underweight patients."

Conversely, overweight and obese patients had more favourable outcomes. Cardiovascular mortality risk was lowest among overweight patients with a BMI 25-30 compared to people with a BMI 20-25. Indeed, in obese and severely obese patients with a BMI in the 30-35 and >35 range, all-cause mortality was 27% and 22% lower than people with normal BMI.

"However, this is still speculation,” he concludes. “Further prospective studies are needed to investigate this association and explore potential underlying mechanisms."