There is a strong association between BMI and acute coronary syndrome (ACS) outcomes, according to new research published in the American Journal of Cardiology.
Obese patients experienced the best outcomes six months after hospitalization for ACS, the study’s authors reported, and underweight patients experienced the worst outcomes. These findings represent a striking example of what is known among researchers as the “obesity paradox”—though even the paradox has its limits.
The study’s authors focused on six-month outcomes related to all-cause and cardiovascular mortality for more than 8,000 patients treated from 1999 to 2018. All patients received care in Australia, the mean patient age was 64 years old and 72% were male.
For the sake of this study, a healthy BMI was considered anything from 18.5 to 24.9. An underweight BMI was anything below 18.5, an overweight BMI was 25 to 29.9 and an obese BMI was 30 to 39.9.
Overall, after six months, underweight patients had an all-cause mortality rate of 11%. That number was 1% for obese patients and 4% for patients with a healthy BMI. Where the obesity paradox fades, the researchers noted, was when it comes to extremely obese patients with a BMI greater than 40; their all-cause mortality rate jumped back up to 2%, higher than it is for other obese patients.
Similar statistics were seen for cardiovascular mortality after six months. The rates were 7% for underweight patients, 1% for patients with a healthy BMI, 0.4% for obese patients and 0.7% for extremely obese patients.
So why do underweight patients face these poorer outcomes? The authors provided a few possible explanations.
“Our study shows that patients in the underweight group were older, with more prevalent co-morbidities including peripheral vascular disease, prior heart failure, anemia and were smokers all of which can lead to disease-induced cachexia, which may contribute to their higher mortality,” wrote lead author Seshika Ratwatte, BMed, department of cardiology at Concord Repatriation General Hospital in Australia, and colleagues. “In some cases we may be observing reverse causality whereby pre-existing illness may lead to unintended weight loss and higher mortality in low-BMI groups. For example, it has been suggested that being underweight can be a marker of a nutritional disorder, making patients more prone to infection and post-procedural complications.”
Diving deeper into the data, the authors also noted that underweight patients were less likely to undergo percutaneous coronary intervention (PCI) or coronary artery bypass surgery (CABG) than those with a healthy BMI. And obese patients were less likely to undergo thrombolysis than those with a healthy BMI—but more likely to undergo CABG.
Michael has more than 16 years of experience as a professional writer and editor. He has written at length about cardiology, radiology, artificial intelligence and other key healthcare topics.