Is Influenza Infection a Risk Factor for Atrial Fibrillation?

A retrospective analysis of records from more than 55,000 patients indicates that influenza infection increases the risk of developing atrial fibrillation (AF) and that increased vaccination could reduce AF onset.

Investigators used the Taiwan National Health Insurance Research Database to identify 11,374 patients with newly diagnosed AF between 2000 and 2010 and matched each of those patients by age and sex with 4 controls who had no AF. The investigators then gathered data on the preceding year for each subject and that subject’s controls, looking for information about influenza vaccination and infection.

After adjustment for baseline differences, the 1,369 patients who got no vaccinations and subsequently sustained infections had a significantly higher risk of developing AF than the 38,353 patients who got no vaccinations but escaped infection (odds ratio [OR], 1.182; p=0.032).

The analysis also found that vaccinations were associated with a lower risk of developing AF, independent of any documented infection. The 16,452 people who received vaccinations and sustained no infections were significantly less likely to develop AF than the patients who sustained no infection despite receiving no vaccination (OR, 0.881; p <0.001). Even when investigators looked at the 696 who received vaccinations but still sustained infection, they found that their risk of developing AF was statistically no different than the risk of people who received no vaccination and sustained no infection (OR, 1.136, p=0.214).

“Influenza infection was significantly associated with the development of AF, with an 18% increase in the risk, which could be reduced through influenza vaccination,” the study authors wrote in Heart Rhythm. “The lower risk of AF with vaccination was consistently observed in subgroup analyses.”

The investigators later argued that their findings have several practical implications.

“According to the findings presented here, the possibility of AF should be kept in mind when patients with influenza infection complain of palpitations or experience ischemic stroke,” they wrote. “Influenza vaccination should be encouraged for patients, especially those who have a high risk of AF, to try to prevent the occurrence of AF and subsequent stroke. However, a further prospective study is necessary to confirm our findings.”

An accompanying editorial written by Northwestern University cardiologists Nishant Verma, MD, MPH, and Bradley P. Knight, MD, FHRS, reached much the same conclusion.

“Although the flu vaccine is already recommended for many patient groups, this study suggests that there are even more potential public health benefits of the vaccine,” they wrote. “The results of this study beg the question as to whether the acute treatment of the influenza infection itself, or addressing the inflammatory response associated with infection, may help prevent secondary episodes of AF. Beyond the prospective trial mentioned by the authors, we look forward to future studies into these and other areas that may help confirm and validate the observed findings.”

The new study complements prior research that has shown that preexisting heart disease, including AF, is associated with a higher risk of developing influenza and with increased disease severity among people who do develop influenza. The Centers for Disease Control and Prevention report that about half of all people hospitalized with influenza during the 2014-2015 flu season suffered from some form of heart disease.