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Researchers in the Netherlands have reaffirmed the link between influenza infections and the increased, short-term risk of heart attack. The risk is especially elevated in individuals with no prior diagnosis of heart disease.
The link between the flu and an increased risk of heart attack has been observed by clinicians for some time. However, a 2018 study solidified the data by comparing influenza infections with the rise of hospitalization for acute myocardial infarction (MI), also known as heart attack. The study found that patients were six times more likely to have a heart attack in the week after being diagnosed with flu.
As the Centers for Disease Control and Prevention (CDC) explained, “The [2018] study, which looked at more than 80,000 adult patients hospitalized with flu over eight flu seasons, found that almost 12% of patients, or 1 in 8, had an acute cardiac event, such as acute heart failure or acute ischemic heart disease. Of these, 30% were admitted to the ICU and 7% died while in the hospital.”
A stark warning to patients without risk of heart disease
The Dutch study not only echoed the findings of the 2018 study but also was unique in its stark warning to patients with no history of heart disease.
“Our study results confirm previous findings of an increased risk of MI during or immediately following acute severe flu infection and raises the idea of giving prophylactic anticoagulation to these patients,” said Patricia Bruijning-Verhagen, MD, at University Medical Center Utrecht and senior author of the study, per Medscape.
“Our results also change things—in that we now know the focus should be on people without a history of cardiovascular disease—and highlight the importance of flu vaccination, particularly for this group,” she added.
For the recent 2023 study, Dutch researchers analyzed 158,777 PCR tests for influenza between the years 2008 and 2019. Of these, 26,221 were positive for influenza, constituting 23,405 unique influenza illness episodes.
“A total of 406 episodes were identified with acute [MI] occurring within 1 year before and 1 year after confirmed influenza infection and were included in analysis,” observes the study. “Twenty-five cases of acute [MI] occurred during the risk period versus 394 during the control period.”
The adjusted relative incidence of heart attack during the risk period compared with the control period was 6.16 (which echoes the findings of the 2018 study, which saw an incident of 6.05). However it was the increase in the relative incidence of acute MI in individuals without prior hospitalization for heart attack that drew researchers’ attention. For patients without a history of heart attack or heart disease, their relative incidence jumped up to 16.60 compared with 1.43 for those with prior admission for coronary artery disease.
“Most previous studies of flu and MI didn’t stratify between individuals with and without existing cardiovascular disease. And the ones that did look at this weren’t able to show a difference with any confidence,” Bruijning-Verhagen told Medscape. “There have been suggestions before of a higher risk of MI in individuals with acute flu infection who do not have existing known cardiovascular disease, but this was uncertain.”
“You would think patients with existing cardiovascular disease would be more at risk of MI with flu infection, so this was a surprising result,” said Bruijning-Verhagen. “But I think the result is real. The difference between the two groups was too big for it not to be.”
‘Vaccination is low-hanging fruit’
There may admittedly be a therapeutic reason for this; patients with a history of heart disease are more likely to be on heart medication, for example. But the overall lesson for adult patients is clear: get your flu shot.
“These results should give extra weight to the message to get your flu shot,” Bruijning-Verhagen said. “Even if you do not consider yourself someone at risk of cardiovascular disease, our study shows that you can still have an increased risk of MI as a result of severe flu infection.”
And the cardiovascular burden of respiratory diseases expands past just the flu, having been reported in COVID infections, as well. And indeed the inflammatory nature of these diseases is largely understood to risk a greater long-term burden on the body in a number of patient populations. The best way to mitigate these risks is through preventative medicine like vaccines.
“Vaccination is low-hanging fruit for people at risk of acute myocardial infarction who have not yet had a first event. It is time that we viewed influenza vaccine as a routine preventive measure for ACS and for people with coronary artery disease risk factors, along with statins, blood pressure control, and smoking cessation,” Bruijning-Verhagen told Medscape.
