The symptoms of a heart attack are well known, but a significant number of heart attacks go undiagnosed. According to the Mayo Clinic, so-called silent heart attacks can masquerade as the flu or indigestion, but are still caused by blocked blood flow to the heart, just like a symptomatic heart attack. A person usually won’t know they’ve had a silent heart attack until hints of heart attack damage show up on a scan or test.
Preliminary research presented at the American Stroke Association (ASA) International Stroke Conference 2021 on March 17, 2021, found that symptomless heart attacks increase a person’s risk of stroke, but not quite as much as symptomatic heart attacks.
Researchers retroactively analyzed data from 4,200 participants in the Cardiovascular Health Study, which took place from 1989 to 1999. All the patients included in the preliminary research were at least 65 years old, and the majority were white men. Since all participants in the Cardiovascular Health Study were followed and screened for stroke risk for an average of 10 years, the researchers were able to compare people who did not have evidence of a silent heart attack or classic heart attack with those who had one of these. After adjusting for comorbidities that also increase a person’s risk of stroke, the team found that having a silent heart attack independently increased a person’s risk of ischemic stroke by about 45 percent in the long term, whereas having an overt heart attack increased a person’s long-term risk by 60 percent.
According to Alexander Merkler, MD, an assistant professor of neurology at Weill Cornell Medicine in New York City, doctors have long recognized that classic heart attacks — which cause chest pain, shortness of breath, and other hallmark signs of a heart attack — are associated with raising a person’s risk of stroke.
“What we found is that silent heart attacks that go unnoticed, and which are already associated with arrhythmia and an increased risk of those classic, chest-crushing heart attacks, are also associated with stroke,” says Dr. Merkler.
Merkler established a link between silent heart attack and stroke in a study published in May 2019 in JAMA Neurology. He and his team used Icelandic data and found that having a silent heart attack doubled a person’s risk of having a stroke from an unknown cause.
“It adds to the body of evidence that silent heart attack is not an innocent bystander, that it’s associated with other heart effects and potentially brain effects. This study shows that the heart injury is happening first, and that it puts patients at risk for future classic strokes,” says Merkler, adding that more research is needed to confirm the initial study’s findings.
According to Christine Holmstedt, DO, the codirector of the comprehensive stroke and cerebrovascular center at the Medical University of South Carolina in Charleston, who was not involved in the study, the initial evidence that directly credits the heart injury with causing a stroke later on is strong.
“What is really interesting is that these were not small-vessel strokes, which means ultimately they look like embolic strokes, which tells us that they most likely did come from the heart,” says Dr. Holmstedt.
According to the ASA, when an embolism, or blood clot, forms in the heart or a major blood vessel, the clot can travel to the brain and cause an embolic ischemic stroke. Ischemic strokes account for almost 90 percent of all strokes, the ASA reports. If future research confirms the association that this initial study found, silent heart attack could become a recognized risk factor for stroke. This may prompt physicians to more aggressively screen patients who have had a silent heart attack for other stroke risk factors, says Merkler. Future studies are also needed to determine how silent heart attacks may impact younger people and Black, Indigenous, and People of Color (BIPOC) communities.
“The patients in this study were all over 65 years of age and the majority were white, so future studies are necessarily to evaluate whether or not the findings will hold true in other age groups and other races,” says Merkler.