In-hospital outcomes of acute myocardial infarction patients without standard modifiable cardiovascular risk factors across varying body mass index

Abstract Background Individuals who present with acute myocardial infarction (AMI) in the absence of standard modifiable cardiovascular risk factors (i.e., SMuRF-less) seem to have a significantly increased risk of mortality; however, it remains unclear whether the ‘SMuRF paradox’ would be influenced by patients’ baseline body mass index (BMI) status. Purpose To assess the disparities in the prevalence and prognostic implications of SMuRF-less among patients with newly diagnosed AMI across varying body mass index (BMI). Methods Using data from the Improving Care for Cardiovascular Disease in China–Acute Coronary Syndrome (CCC–ACS) project, we retrospectively analyzed AMI patients with and without SMuRFs and categorized their baseline BMI as underweight (<18.5kg/m2), normal weight (18.5-24kg/m2), overweight (24-28kg/m2), and obese (>28kg/m2). The primary outcome was in-hospital all-cause mortality. Multivariable logistic regression models were used to estimate BMI-stratified associations between SMuRF-less and each outcome, sequentially adjusting for demographic, clinical characteristics, and prevention strategies. Results Between 2014 and 2019, 44,538 adult patients hospitalized for first-presentation AMI were included, of which 4,454 (10.0%) were SMuRF-less. The incidence of SMuRF-less declined from 16.2% to 6.5% as BMI increased by category, and it prevailed more frequently among females and elders regardless of their BMI status. During the median hospital stay of 9 days, SMuRF-less patients had a significant increase in in-hospital mortality than patients with one or more SMuRF (2.1% vs. 1.0%, adjusted odds ratio [OR], 1.750 [95% CI 1.057–2.896], P<0.001). The highest mortality rate was observed in the SMuRF-less underweight group (3.5%). Took ≥1 SMuRF and obese as the reference group as they presented the finest outcome, SMuRF-less underweight group exhibited the highest increase in mortality (3.5% vs 0.5%, adjusted odds ratio [OR], 3.854 [95% CI 2.130–6.973], P<0.001). However, interaction analyses provided no evidence that BMI significantly modifies SMuRF-less’s association with in-hospital mortality (P for interaction=0.247). Conclusion Approximately one-tenth of first-presentation AMI patients had no SMuRF, who were more frequently women, elders, and underweight. Compared with those with at least one SMuRF, SMuRF-less patients have a significantly higher risk of in-hospital mortality, especially in those underweight, while in-hospital survival was the most favorable among ≥1 SMuRF and obese patients.