“Inconvenient and Unsettling”: Substantial Silent MI Rates in the United States Prompt Questions for Screening
Silent myocardial infarctions make up almost half of incident heart attacks in the United States, according to a new study, which also found discrepant rates and outcomes based on gender and ethnicity.
When it comes to MI, some can be diagnosed in the clinic through patient symptoms, but others stay hidden often until patients have severe complications or even die. Detecting silent MI is difficult because patients themselves don’t realize what is happening until it is too late, but past research has suggested that various forms of screening may catch these events earlier.
“For practitioners, the main message is that accidental finding of signs of [a] heart attack . . . should be taken more seriously,” senior author Elsayed Z. Soliman, MD (Wake Forest School of Medicine, Winston-Salem, NC), told TCTMD. “If they are in doubt, there are other investigations that could be done to confirm it.”
For the study, researchers led by Zhu-Ming Zhang, MD (Wake Forest School of Medicine), examined 9,498 participants enrolled in the ARIC (Atherosclerosis Risk in Communities) study, which included people from four US communities who were free from cardiovascular disease in the late 1980s and were followed through 2013.
Over a median follow-up of 8.9 years, 3.3% developed a silent MI and 4.1% had a clinically-documented MI. There were substantial differences in event rates between men and women as well as white and black participants. Specifically, rates of both types of MI were higher in men than women (P < 0.0001 for both). The rate of silent MI did not differ significantly between black and white individuals (P = 0.217), but whites were more likely to have a clinically-indicated MI (P = 0.002).
Over a median follow-up of 13.2 years, there were 1,833 cases of all-cause mortality, including 189 coronary heart disease deaths. On multivariate analysis, both silent and clinically-documented MI were associated with increased risk of coronary heart disease-related death (HR 3.06; 95% CI 1.88-4.99 and HR 4.74; 95% CI 3.26-6.90, respectively) and all-cause mortality (HR 1.34; 95% CI 1.09-1.65 and HR 1.55; 95% CI 1.30-1.85, respectively) compared with no MI.
Both silent and clinically-documented MI were linked with higher mortality in men and women, but there were nonsignificant trends toward higher risks of both outcomes in women (P = 0.089 and 0.051, respectively). There were no differences between races for this metric.
‘We Are Different’
Commenting on the study, Harlan Krumholz, MD (Yale School of Medicine, New Haven, CT), told TCTMD in an email that the results are “inconvenient and unsettling.” Inconvenient because “we usually think that screening asymptomatic populations is a low-yield endeavor, but here we are finding that there is a subpopulation with silent MIs,” he said. The unsettling component involves the patients who may have unknowingly suffered myocardial damage and, therefore, may be at elevated risk.
“Universal screening would seem to be an overreaction,” Krumholz commented. “But there may be a role for targeted screening and testing of strategies specific to this population.”
Soliman agreed. Universal screening would be “overkill if you look at the general population,” he said, adding that screening is not easy and could potentially generate many false-positives. Looking closer at who might benefit from screening, Soliman suggested including high-risk patients such as those with hypertension, diabetes, and a history of smoking or coronary heart disease.
Physicians should be more aggressive in doing electrocardiograms for these subgroups, he said, adding that “those types of patients need to be aware that any mild chest discomfort should trigger them to go to the emergency room.”
But it’s also a matter of race and sex, Soliman stressed. “We’re not created the same. We are different,” he explained. “The number of blacks in our study was not [high enough to] make us certain about the conclusions, but there are signs that there are differences.” He added that future studies should include Asian and Hispanic populations to accurately reflect the changing make-up of the United States so that physicians can best screen and treat their patients.
Specifically, these studies should “assess whether genetic background, emerging risk factors, access to healthcare, awareness, and adherence to medications contribute to sex and racial differences,” the authors conclude.
Zhang Z-M, Rautaharju PM, Prineas RJ, et al. Race and sex differences in the incidence and prognostic significance of silent myocardial infarction in the Atherosclerosis Risk in Communities (ARIC) study. Circulation. 2016;Epub ahead of print.
- The study was supported by the National Heart, Lung, and Blood Institute.
- Zhang, Soliman, and Krumholz report no relevant conflicts of interest.