According to a new study published in the Journal of American Medical Association, unrecognized myocardial infarction (UMI) detected by cardiac magnetic resonance (CMR) was associated with equivalent all-cause mortality as compared to recognized myocardial infarction (RMI) at 10 years of follow-up. Individuals with UMI also had a higher risk of nonfatal MI, heart failure, and death than those without any evidence of MI.
Differences noted at the mid- and long-term follow-up
This population-based, prospective, cohort study followed 935 individuals between the age of 67 and 93 years for 13 years, after characterization by CMR. The primary outcome was all-cause mortality while the secondary outcome was major adverse cardiac events (MACE) defined as death, nonfatal MI, and heart failure. After 3 years of follow-up, the rates of mortality were similar between the individuals with UMI and no MI (3%) and both were lower than the mortality rate in the RMI group (9%). At 5 years, the mortality rate was higher in the UMI group (13%) compared with the “no MI” group (8%) but was lower than the mortality rate in the RMI group (19%). At 10 years of follow-up, there was no significant difference in the mortality rate between the UMI and the RMI groups (49% vs 51%) and both were significantly higher than this of the “no MI” group (30%).
“While screening with CMR is clearly not recommended, identification of risk factors certainly is, as borne out once more by these novel observations.” -Dr. Robert O. Bonow, MD, MS
After adjusting for confounders such as diabetes, age, and sex, UMI still had an increased risk of death compared to no MI (HR 1.61; 95% CI, 1.27-2.04) and a higher risk of MACE (HR 1.56; 95% CI, 1.26-1.93). However, the difference in the risk of death and MACE between the UMI and the RMI groups did not reach statistical significance with hazard ratios (HR 0.99; 95% CI 0.71-1.38) and (HR 0.99; 95% CI 0.71-1.38) respectively. Dr. Robert O. Bonow (Northwestern University Feinberg School of Medicine, Chicago, Illinois) commented in an accompanying editorial, “A unique aspect of this long-term study is the 100% completeness of follow-up, with data available in all 935 participants of the elderly Icelandic cohort.”
Why was the association with unfavorable outcomes found only on the long-term follow-up?
The study suggested that UMI could have similar outcomes to RMI on the long-term follow-up, after being relatively quiescent in the short- to middle-term follow-up. The authors offered two possible explanations for this finding. The first was that UMI represented a different category of ischemic heart disease with more involvement of the small vessels and lower epicardial plaque burden at the baseline. The second explanation was that the individuals with RMI had more chance of receiving medical treatment with aspirin, statins, and B blockers which may have attenuated their mortality in the long-term.
Dr. Bonow added, “The smaller infarct size and better LV function appear to explain the lower short-term mortality rates associated with UMI compared with RMI. However, patients with RMI appear to have better recognition of risk factors and thus better control of smoking, hypertension, and hypercholesterolemia.” “While screening with CMR is clearly not recommended, identification of risk factors certainly is, as borne out once more by these novel observations,” he concluded.