Silent MI associated with downstream heart failure risk

Silent heart attacks, which contain few or minor symptoms and may not be diagnosed immediately, leave individuals at increased long-term risk for heart failure, according to a study published Jan. 1 in the Journal of the American College of Cardiology.

Lead researcher Waqas T. Qureshi, MD, and colleagues studied 9,243 participants from the Atherosclerosis Risk in Communities cohort who were free of cardiovascular disease at baseline. Silent myocardial infarction (SMI) was defined as electrocardiographic evidence of MI without clinical MI (CMI) before the fourth follow-up visit. CMI was classified as definite or probable MI as determined by physician review of hospital records.

Over an average of 13 years of follow-up, 976 heart failure events occurred in the study population. The incidence rates per 1,000 person-years were 30.4 for CMI, 16.2 for SMI and 7.8 for patients without MI. When adjusting for demographics and heart failure risk factors, those suffering an SMI had a 35 percent increased risk of developing heart failure compared to individuals with no MI. The risk of heart failure was nearly tripled in those who experienced a CMI.

“Currently, 5.7 million people in the United States have HF, and it is expected that by 2030, (more than) eight million people will have this condition,” wrote Qureshi, with Wake Forest School of Medicine, and coauthors. “Therefore, identifying a new potential mechanism contributing to this pandemic is of enormous importance. Although future research is needed to examine the cost effectiveness of screening for SMI as part of heart failure risk assessment, we believe that our report provides novel insights into an overlooked and potentially addressable contributor to the heart failure pandemic.”

Up to one-third of the approximately one million people in the U.S. who are hospitalized with heart failure each year have a history of MI, according to the authors. SMIs account for roughly half of all MIs, but the risk of heart failure in these patients was previously unclear.

Although the increased risk following SMI is notable, the researchers weren’t surprised to find an even greater risk in those experiencing CMI.

“MI that remains silent is likely small in size or subclinical, and hence, does not affect the myocardium as significantly as CMI, which could explain the stronger risk of HF with CMI than SMI,” Qureshi et al. wrote.

The researchers ran several subgroup analyses based on age, sex, race, smoking status, body mass index, diabetes status, blood pressure and lipid levels. They found the associated risks of heart failure related to MI classification were largely consistent across the subgroups, with a few exceptions.

Of note, younger patients with SMI had a stronger relative risk of heart failure than older patients. In addition, the risk of heart failure following SMI was slightly stronger in women than men, in overweight versus normal weight individuals and in nonsmokers versus current and former smokers.

Some of the subgroups contained a small sample size, the authors acknowledged, limiting the power to detect significant interactions. In addition, only whites and blacks were contained in the study, so the findings may not be applicable to other races and ethnicities. Finally, high-sensitivity troponin assays weren’t available during the study period, which could lead to an underestimation of the prevalence of CMI.

In a related editorial, three physicians from Beth Israel Deaconess Medical Center and Harvard Medical School said this study contributes to “the growing body of evidence on ECG-defined silent MI” and “supports its use as a meaningful clinical endpoint.”

“The addition of ECG-defined silent MI to a composite endpoint may increase the number of events among a population enrolled in a clinical trial,” wrote C. Michael Gibson, MD; Tarek Nafee, MD; and Mathieu Kerneis, MD. “This would increase the statistical power, reduce the required sample size, and thus reduce the duration and cost of a randomized clinical trial.”