People with unrecognized myocardial infarction (UMI) carry a lower short-term risk of death but an equal 10-year risk of mortality compared to those with clinically diagnosed heart attacks, according to an analysis of the ICELAND MI study published in JAMA Cardiology.
Cardiac magnetic resonance (CMR) imaging can detect more UMIs than electrocardiograms, with previous evidence showing that UMI by CMR is more prevalent among older adults than recognized MI (RMI). However, the long-term prognosis of UMI isn’t well-studied, wrote authors led by Andrew E. Arai, MD, with the National Institutes of Health in Bethesda, Maryland.
The researchers analyzed 935 individuals from an Icelandic cohort study who were a mean 76 years old at the time of enrollment. Each participant received CMR at baseline and was followed for up to 13.3 years.
Baseline evaluations revealed 17 percent of the cohort had experienced UMI while 10 percent had a clinically recognized MI before study enrollment.
The three-year mortality rate in the UMI group (3 percent) matched that of individuals with no history of MI, but was significantly lower than the 9 percent observed in the RMI cohort. At five years, mortality rates associated with UMI (13 percent) represented a middle ground between no MI (8 percent) and RMI (19 percent).
Importantly, though, the death rates between UMI and RMI leveled out at 10 years of follow-up, with 49 and 51 percent of patients dying in each of those groups, respectively.
“Being more prevalent than RMI, UMI constitutes an underappreciated public health problem,” Arai and colleagues wrote. “Whether early detection of UMI by CMR could allow for the institution of risk factor management and thus reduce the associated long-term risks merits further investigation.”
After adjusting for age, sex and diabetes status, UMI was associated with a 61 percent increase in all-cause mortality at 10 years compared to no MI, plus double the risk of a subsequent MI and 1.52 times the risk of heart failure. However, the adjusted differences for mortality and major adverse cardiac events weren’t significantly different for UMI and recognized MI.
The authors noted smoking rates were lower in the RMI group, which also had more prescriptions for guideline-based medical therapy and lower cholesterol rates. This suggests having a clinically recognized heart attack could trigger risk factor modification and more intense treatment, whereas patients with UMI might not receive those interventions.
Arai et al. said the different disease courses of UMI and RMI could be another explanation for the late convergence of mortality between those two groups.
“UMI may represent a different coronary disease phenotype with more small-vessel involvement and atrial fibrillation than RMI and thus chart a different natural course,” they wrote. “Because of a lower epicardial plaque burden than RMI at baseline, UMI event rates may lag behind RMI and increase after a delay. It is also plausible that additional UMI events over time accelerate the mortality rate in this group.”
Commenting on the study, JAMA Cardiology editor Robert O. Bonow, MD, MS, noted the smaller infarct size associated with UMI versus RMI (4 percent versus 9.6 percent of the left ventricle) likely explains the difference in short-term outcomes. Also, baseline left ventricular ejection fractions were higher in the UMI group—60 percent compared to 53 percent.
While Bonow doesn’t believe widespread screening with CMR has a role in routine practice, he said the study is a reminder of the importance of risk factor recognition.
“Patients with RMI appear to have better recognition of risk factors and thus better control of smoking, hypertension, and hypercholesterolemia,” wrote Bonow, with Northwestern University Feinberg School of Medicine. “Because those with UMI are not recognized as candidates for cardiovascular prevention interventions, they ultimately have an acceleration of incidence MI and heart failure, with an associated increase in mortality over time. While screening with CMR is clearly not recommended, identification of risk factors certainly is, as borne out once more by these novel observations.”
Daniel joined TriMed’s Chicago editorial team in 2017 as a Cardiovascular Business writer. He previously worked as a writer for daily newspapers in North Dakota and Indiana.