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Small, silent infarcts found only on cardiac MRI were associated with a mortality risk that crept up over 10 years to match that of patients with a clinically detected MI, according to longer follow-up of the ICELAND MI cohort study.

Those unaware of MI until baseline cardiac MRI had the same 3% risk of all-cause mortality at 3 years as peers without any MI, while both groups were at lower risk than patients with a known history of MI (9% at 3 years).

Yet the picture was different at 10 years, Andrew Arai, MD, of the National Heart, Lung, and Blood Institute in Bethesda, Maryland, and colleagues reported in .

At that point, 30% of patients who had no MI at baseline had died, compared with 49% of those who had unrecognized MI and 51% of those with a recognized MI.

"Being more prevalent than recognized MI, unrecognized MI constitutes an underappreciated public health problem," the researchers wrote. "Whether early detection of unrecognized MI by cardiac MRI could allow for the institution of risk factor management and thus reduce the associated long-term risks merits further investigation."

"Although [the study] is important, until such time as we have studies that show that treating patients with unrecognized MI changes outcome, it is not clear that routine screening CMR [cardiac MRI] would be indicated," cautioned Christopher Kramer, MD, of the University of Virginia in Charlottesville, who was not involved in the study.

Elsayed Soliman, MD, MSc, of Wake Forest School of Medicine in Winston-Salem, North Carolina, agreed, saying it "should be considered very carefully in the context of cost-benefit and the possibility of false positive results."

Nevertheless, the study contributes to mounting evidence that unrecognized MI is not benign and "should be taken as seriously as any MI," Soliman told 番茄社区app. He also was not involved in the study.

The study comprised 935 community-dwelling older people in Iceland (48.3% men; mean age 76 years). There was no loss to follow-up, as outcomes were gathered from a national database of death and healthcare records.

Unrecognized MI was associated with worse outcomes at 10 years compared with MI on multivariate analysis for the following:

• Death: HR 1.61, 95% CI 1.27-2.04
• Combined death, non-fatal MI, heart failure: HR 1.56, 95% CI 1.26-1.93
• MI: HR 2.09, 95% CI 1.45-3.03
• Heart failure: HR 1.52, 95% CI 1.09-2.14

Unrecognized MI carried as high a 10-year risk of death (HR 0.99, 95% CI 0.71-1.38) and major adverse cardiac events (HR 1.23, 95% CI 0.91-1.66) as recognized MI.

There are two potential reasons for the eventual convergence between the mortality curves of unknown and known MI, the investigators suggested.

It may be that unrecognized MI represents a different coronary disease phenotype with more small-vessel involvement and atrial fibrillation, thus charting a different natural course. The other possibility is that patients with recognized MI lowered their risk through preventive therapy and changed risky behaviors, such as smoking.

Patients with MI, recognized or not, tended to have more cardiovascular risk factors.

The group with unrecognized MI had coronary artery calcium scores and left ventricular ejection fractions that fell between those of the recognized- and no-MI cohorts. Previously-undetected infarcts were also significantly smaller than those in recognized MI.

In subgroup analysis, men, people with diabetes, and those under age 70 actually had a higher risk of death from unrecognized MI but comparatively lower mortality risk with recognized MI, the researchers reported.

"These directionally opposite stratified outcomes of unrecognized MI and recognized MI may be due to distinct pathophysiological mechanisms or may represent a treatment effect," Arai and colleagues noted, though they cautioned that these are hypothesis-generating findings.

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