Watch Out – Flu Can (Rarely) Trigger an MI

It’s known that influenza can have cardiac complications, including myocarditis, an inflammation of the heart muscle.  But it’s not been clear whether flu has a direct effect on the risk of heart attack (myocardial infarction, or MI).  A report in the journal Lancet tries to remedy this.   

British researchers reviewed 42 medical publications describing 39 studies done since 1932 on flu, flu-like illness, and acute respiratory infection and the occurrence of an MI. 

There were 17 so-called ‘ecological studies’ that looked at populations or communities; all of them revealed an association between circulating flu viruses and cardiovascular deaths and MIs.  The association was statistically ‘medium to strong’.  There was an average of 35% to 50% excess deaths attributable to heart disease, but results varied considerably between studies.

Of 7 studies that examined the possible relationship of acute respiratory infection and occurrence of an MI, 5 showed a significant association, with more than a doubling of the likelihood or risk; the other 2 showed no statistical association, but a trend towards one.  Three of 5 studies showed an association between influenza-like symptoms and MI, again roughly a doubling of the risk.

There were only two studies examining a possible protective effect of vaccination on the risk of MI.  One small trial found such a protective effect against cardiovascular death (a reduction to a quarter of the rate in an unvaccinated group), while another found a protective effect against MI.

These findings are not dramatic, but then the individual studies were not adequately designed to show clear-cut, large effects.  One expert asked replied that the review doesn’t “show that vaccination is protective against MI.”  However, he went on: “it is prudent to vaccinate high-risk patients, including those with existing heart disease”.  I think it’s prudent for just about everyone over 65 to get a seasonal flu vaccination . . .