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Study Linking Flu to Sudden Heart Troubles Highlights Need for Flu Shots

CardioSmart News

If you haven’t already rolled up your sleeve to get your flu shot this year, new research gives you another reason to do so. About 1 out of 8 individuals who were hospitalized with the flu (influenza) also had a serious, sudden heart complication during their stay, a study published in the Annals of Internal Medicine found.

Earlier studies have suggested a link between influenza and these events. But the authors said theirs shows just how common these heart troubles are and sheds light on the factors that may make these events more likely.

The study used the U.S. Centers for Disease Control and Prevention’s Influenza Hospitalization Surveillance Network (FluSurv-NET). It included 80,261 adults (median age of 69) who were hospitalized with influenza across 17 states over eight flu seasons from 2010-2011 through 2017-2018. Of these, nearly 12% developed an acute cardiovascular event, with acute heart failure and reduced blood flow to the heart (ischemic heart disease) being the most common.

Older adults, people with preexisting heart conditions, and those who used tobacco, or had diabetes or kidney disease appeared to be at greatest risk. In fact, among those who were hospitalized with influenza and had an acute cardiovascular event, 20.6%— or 1 in 5—had chronic cardiovascular disease, 19.3% had chronic kidney disease, and 14.8% had diabetes.

The findings also highlight how severe these cardiovascular complications can be in someone with influenza. Among people hospitalized with the flu who had a sudden cardiac event, nearly 1 out of 3 were admitted to the intensive care unit, 14% needed to be placed on a ventilator, and 7% died.

The analysis prompted researchers to encourage clinicians to “consider an influenza diagnosis when a patient is hospitalized with an exacerbation of or new onset cardiovascular event” during the flu season to be able to give appropriate treatment as early as possible.

Similar to trends seen in the U.S. population, less than half of patients included in the study (47.2%) received a flu shot during the current influenza season, while 39.2% had not (whether someone got a flu shot was unknown for 13.6%). But vaccination helps. Data showed that people who were vaccinated against the flu at least two weeks before hospitalization had a significantly lower risk of new or worsening heart failure compared with those who were unvaccinated.

Researchers included only patients with confirmed influenza, so there could have been many others. Also, as the study looks back at patient data, it shows only a relationship between influenza infection (defined as a positive test result within 14 days before or three days after hospital admission) and heart complications. It cannot say whether one causes the other.

These findings are a timely reminder of the importance of getting an annual flu shot to help prevent complications, especially in people with heart disease and others considered at high risk of developing serious health problems.

The CDC recommends that everyone 6 months and older get a flu vaccine every year. This year’s flu shot is more important than ever amid escalating COVID-19 cases, experts say. Getting a flu shot can prevent illness from another respiratory threat and ease the burden on hospitals.

Visit CardioSmart.org/Flu for more information.

Acute Cardiovascular Events Associated With Influenza in Hospitalized Adults,” Annals of Internal Medicine, Oct. 20, 2020.  Learn about CardioSmart's editorial process. Information provided for educational purposes only. Please talk to your health care professional about your specific needs.