A hidden heart attack can leave damage beyond the heart. Researchers found that even silent myocardial infarctions are associated with faster cognitive decline over time, raising new questions about how heart health shapes long-term brain function.
Study: History of myocardial infarction and cognitive decline: REGARDS cohort. Image credit: PeopleImages/Shutterstock.com
Recent research published in journals stroke They found that people with a self-reported history of past myocardial infarction or electrocardiogram (ECG) evidence had a faster decline in overall cognitive function.
Hidden cardiovascular risks and brain health
Vascular disease is a major potentially modifiable risk factor for cognitive impairment and dementia. Previous research has linked acute myocardial infarction (AMI), commonly known as a heart attack, to an increased risk of long-term cognitive decline.
In clinical practice, prior MI is often identified using a patient’s self-reported medical history and electrocardiogram (ECG) findings such as Q waves. However, it remains unclear whether these routinely used measures can reliably identify people at high risk of future cognitive decline.
An estimated 22% to 44% of myocardial infarctions go undiagnosed clinically and leave a characteristic Q-wave pattern on the ECG, a condition known as silent MI. Despite having no symptoms, silent MI is associated with a higher risk of dementia, white matter disease, and silent cerebral infarction. Previous evidence of this association is primarily limited to studies of older men, highlighting the need for validation in more diverse populations.
To investigate this question, researchers used data from the REGARDS cohort, a large prospective study in the United States aimed at examining blood vessels that contribute to brain health. This cohort included a detailed cardiovascular evaluation along with standardized cognitive tests repeated over many years.
Using these data, the researchers examined whether self-reported or electrocardiogram-detected evidence of a previous myocardial infarction was associated with more rapid cognitive decline in a diverse population of black and white American adults.
Testing for cognitive decline related to MI history
In the current study, REGARDS participants were stratified into four subgroups.
- Non-myocardial infarction: No history or ECG evidence of self-reported myocardial infarction.
- Self-reported MI: patient reported diagnosis of MI to physician, but no ECG evidence was found
- Clinical MI: The patient had a history of MI and the ECG showed Q waves.
- Silent myocardial infarction: The patient did not report a history of myocardial infarction, but the electrocardiogram showed Q waves
Global cognitive function was assessed by telephone-based screening. The scores were tracked over time to examine whether changes in the scores were related to previous myocardial infarction.
Cognitive decline due to previous MI
The baseline cohort included 20,923 people with a median follow-up of 10.1 years. During this period, 4,884 participants, or approximately 23%, died. The mortality rate for the previous MI subgroup was 44.4% compared to 21% for the non-MI subgroup.
At baseline, there were 2,183 participants with a history of previous MI. Of these, 1,098 had a self-reported history of previous myocardial infarction, 281 had clinical myocardial infarction, and 804 had silent myocardial infarction. Participants who had a previous myocardial infarction were more likely to have cardiovascular risk factors.
The odds of developing cognitive impairment per year increased slightly by 4% to 9% in participants with MI across all subcategories. Severe cognitive impairment was also more likely to occur among participants with MI, silent MI, and self-reported MI, although clinical MI showed a similar trend that was not statistically significant.
The researchers found that previous MI was associated with a faster annual decline in cognitive function by 0.016 points on the study’s Global Cognitive Scale compared to patients without previous MI. Similar accelerated rates of decline were observed for all MI subcategories, including self-reported MI (0.016 points per year), clinical MI (0.020 points per year), and silent MI (0.015 points per year). Although numerically small, these differences can accumulate over time.
Accelerated cognitive decline was observed in both black and white MI participants and gender. In women, silent cardiomyopathy and self-reported myocardial infarction were associated with accelerated overall cognitive decline, whereas in men, all subtypes showed this association. Clinical MI in women showed a similar association, but it did not reach statistical significance.
Association with domain-specific cognitive decline
The specific areas of cognitive impairment tested here included executive function (the mental skills needed to plan, organize, pay attention, control impulses, solve problems, and adapt to new demands), learning, and memory.
Participants with self-reported MI showed faster declines in all these domains, whereas the clinical MI group showed a significant decline only in memory. Silent MI was not associated with declines in any of these regions. The authors noted that these domain-specific findings should be considered exploratory given the small sample size and infrequency with which these assessments were performed.
Shared vascular damage may cause brain dysfunction
These findings are consistent with the increased risk of cognitive impairment and dementia in patients with coronary ischemia reported in previous studies. The mechanisms underlying this association are still at the hypothetical stage.
For example, both have common risk factors. However, even after adjusting for new-onset cardiovascular events, the risk of cognitive decline continued to accelerate. Other possibilities include silent infarcts in the brain, decreased removal of waste products from brain tissue, microvascular disease, poor cerebral perfusion, and systemic inflammation.
The different patterns of decline across cognitive domains in MI subtypes may reflect differences in the mechanisms underlying cognitive decline, despite atherosclerosis being a common cause.
Asymptomatic MI and cognitive decline
A key finding of this study is the association between accelerated cognitive decline and silent MI, a subgroup often overlooked in previous population-based studies. This may have contributed to inconsistent results in previous studies. Notably, almost 37% of MI participants in the REGARDS cohort at baseline belonged to this subcategory.
The authors suggest that “silent MI may represent a cardiac manifestation of broader systemic microvascular disease.” People with silent myocardial infarction are less likely to have large-vessel atherosclerosis and more likely to have extensive small-vessel disease. This is consistent with previous findings that this subgroup is at increased risk for ischemic stroke, possibly due to repeated silent cerebral infarctions.
Simple cognitive function screening may miss subtle declines
The authors note that this study has several limitations. Because biological age does not necessarily correlate with chronological age, we may have underestimated the effect of age on cognition in participants with a history of MI. The increased mortality in the MI group may have reduced the observable effects of previous MI on cognitive impairment.
The ECG criteria for MI used here were inconsistent across studies, limiting generalizability. Self-reported MI history has moderate sensitivity when compared with medical records. The cognitive screening tools used here are not comprehensive assessments, may miss small changes in cognition, and are nonspecific across dementia subtypes.
Regular electrocardiograms may identify future cognitive risks
This is one of the earliest studies to investigate the association between different forms of prior MI and future cognitive impairment. Overall, cognitive function declined more rapidly in patients with a previous myocardial infarction, whether clinically recognized or silent.
The use of a simple and clinically viable tool to identify these individuals is an important advantage that supports further studies to validate these results.
This finding supports further research into whether routine screening for myocardial infarction with electrocardiogram and self-reported medical history can help identify individuals at increased risk for long-term cognitive impairment.
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