A hidden heart attack can leave behind more than just heart damage. Researchers have found that even silent heart attacks are associated with faster cognitive decline over time, raising new questions about how heart health shapes long-term brain function.
Study: Previous myocardial infarction and cognitive decline: The REGARDS cohort. Image credit: PeopleImages/Shutterstock.com
A recent study published in the journal Rap found that subjects with a self-reported history or electrocardiogram (ECG) evidence of previous myocardial infarction experienced faster decline in global cognitive function.
Hidden cardiovascular risks and brain health
Vascular disease is an important and potentially modifiable risk factor for cognitive decline and dementia. Previous studies have 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 or electrocardiogram (ECG) findings such as Q waves. However, it remains unclear whether these routinely used measures can reliably identify individuals at higher risk of future cognitive decline.
An estimated 22%-44% of myocardial infarctions are never diagnosed clinically but leave characteristic Q-wave patterns on the EKG, a condition known as silent MI. Despite the absence of recognized symptoms, silent MI has been associated with a higher risk of dementia, white matter disease, and silent cerebral infarctions. Previous evidence for this association has been largely 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 US designed to examine vascular factors that contribute to brain health. The cohort includes detailed cardiovascular assessments alongside standardized cognitive tests repeated over several years.
Using these data, researchers examined whether self-reported or EKG-detected evidence of prior myocardial infarction was associated with faster cognitive decline in a diverse population of Black and White American adults.
Examination of cognitive decline in relation to history of MI
In the present study, REGARDS participants were divided into four subgroups:
- Non-MI: no self-reported history or ECG evidence of MI
- Self-reported myocardial infarction: patient reported a physician diagnosis of myocardial infarction, but no ECG evidence was found
- Clinical myocardial infarction: patient had history of MI and ECG showed Q wave
- Silent MI: the patient reported no history of MI, but the EKG showed a Q wave
Global cognitive function was assessed by telephone screening. Scores were monitored over time and change was examined for association with previous MI.
Cognitive impairment with previous MI
The core cohort included 20,923 subjects, with a median follow-up of 10.1 years. During this period, 4,884 participants died, about 23%. The mortality rate in the prior MI subgroup was 44.4%, compared with 21% in the non-MI subgroup.
At baseline, there were 2,183 participants with a history of prior MI. Of these, 1,098 had a self-reported history of previous MI, 281 had clinical myocardial infarction, and 804 had silent myocardial infarction. Participants with a previous MI were more likely to have cardiovascular risk factors.
The odds of experiencing cognitive impairment per year were slightly increased by 4%–9% in participants with MI across all subcategories. Severe cognitive impairment was also more likely among participants with any MI, silent MI, and self-reported MI, while clinical MI showed a similar trend that was not statistically significant.
The researchers found that prior 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 prior MI. Similar rates of accelerated decline were seen across MI subtypes, 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 could accumulate over time.
Accelerated cognitive decline was observed in both black and white MI participants in both sexes. Among women, silent and self-reported MI was associated with accelerated global cognitive decline, whereas for men, all subtypes showed this association. Clinical EM in women showed a similar direction of association, but this did not reach statistical significance.
Association with domain-specific cognitive decline
The specific domains of cognitive impairment examined here included executive functioning (mental skills needed for planning, organizing, paying attention, regulating impulses, solving problems, and adapting to new demands), learning, and memory.
Participants with self-reported MI showed faster decline in all these domains, whereas the clinical MI group showed significant decline only in memory. Silent MI was not associated with a reduction in any of these domains. The authors noted that these domain-specific findings should be considered exploratory given the small sample size and infrequent administration of these assessments.
Common vascular damage can lead to brain decline
These findings are consistent with the increased risk of cognitive impairment and dementia among people with coronary ischemia, as reported by previous studies. The mechanisms underlying this association remain hypothetical.
For example, both have common risk factors. However, after adjusting for new-onset cardiovascular events, the risk of cognitive decline continued to accelerate. Other possibilities include silent infarcts in the brain, impaired clearance of waste products from brain tissue, microvascular disease, poor cerebral perfusion, and systemic inflammation.
Variable patterns of decline in cognitive domains with MI subtype may reflect different underlying mechanisms of cognitive deterioration despite a common atherosclerotic origin.
Silent MI and cognitive decline
An important finding of this study is the association between accelerated cognitive decline and silent MI, a subgroup often overlooked in previous population-based studies. This could have contributed to inconsistent results in past research. Specifically, 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 MI 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 higher risk of ischemic stroke, perhaps due to recurrent silent cerebral infarctions.
Brief cognitive control can miss the subtle decline
The authors note several limitations of the study. Since biological age does not always correlate with chronological age, they may have underestimated the effect of age on cognition in participants with prior MI. The increased mortality in the MI group may have reduced the observed effect of prior MI on cognitive impairment.
The ECG criteria for EM used here are not consistent across studies, limiting their generalizability. Self-reported myocardial history is moderately sensitive compared with medical records. The cognitive screening tool used here is not a comprehensive assessment, may miss small changes in cognitive function, and is not specific for dementia subtypes.
Regular EKGs may identify future cognitive risk
This is one of the first studies to investigate the association between different forms of prior MI and future cognitive impairment. Overall, cognitive function declined more rapidly in patients with prior MI, regardless of whether it was clinically recognized or silent.
The use of simple, clinically feasible tools to identify these individuals is a significant benefit that supports further research to validate these results.
The findings support further study of whether routine myocardial infarction screening via EKG and self-reported history could help identify people at higher risk of long-term cognitive decline.
