Prevalence of traditional cardiovascular risk factors in subjects with unrecognized myocardial infarction: a systematic review and meta-analysis

Background Unrecognized myocardial infarction (UMI) is defined as myocardial ischemia (MI) that was not recognized as such during the acute phase, but later identified by pathological Q waves on an electrocardiogram (ECG), myocardial imaging evidence, or pathological findings on autopsy. Previous studies found that UMI accounts for up to 50% of all MIs, especially in women and the elderly. UMI is associated with increased risk of adverse cardiovascular outcomes and mortality, similar to subjects with recognized myocardial infarction (RMI). However, associated risk factors of UMI remain understudied. Purpose We aimed to summarize and combine the evidence on the associations between traditional cardiovascular risk factors and UMI in the general population. We also sought to assess sex differences in these risk factors. Methods A systematic search of general population-based cohort studies investigating UMI and reporting traditional cardiovascular risk factors of subjects with UMI and subjects without MI was performed through Embase, Medline, and Google Scholar up to 7 February 2023. Study selection, data extraction and risk of bias were assessed independently by 2 authors. Pooled standardized mean differences (SMD) or odds ratios (ORs) with 95% confidence intervals (CI) of traditional cardiovascular risk factors were determined, comparing UMI to subjects without MI. Random-effects meta-analyses were performed. If data allowed, analyses were repeated stratified by sex. Results A total of 17 studies were included involving 216,858 individuals, among which 4,717 experienced UMI (mean age 66.1±8.3 year, 49% women). UMI was diagnosed through ECG in 14 studies and MRI in 3 studies. All studies established diagnosis of UMI and risk factors in a cross-sectional manner. Compared to subjects without MI, individuals with UMI demonstrated significantly larger values of BMI (SMD 0.05, 95% CI 0.03-0.08) and SBP (SMD 0.25, 95% CI 0.12-0.39), and higher prevalence of hypertension (OR 1.71, 95% CI 1.07-2.72) and diabetes mellitus (DM) (OR 1.81, 95% CI 1.40-2.34). Risk factors were reported stratified by sex in 3 studies. The relation between hypertension and UMI was stronger in women than in men. In contrast, the association of DM with UMI was weaker in women. However, these differences were statistically non-significant. Conclusion BMI, SBP, hypertension and diabetes mellitus are associated with an increased risk of UMI, similar to RMI. Limited evidence from studies stratified for sex indicate a differential impact of traditional risk factors on UMI in women and men.