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Influenza increases risk for AF
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Influenza infection is associated with an 18% increased risk for atrial fibrillation, which may be reduced through influenza vaccination, according to new research published in Heart Rhythm.
Researchers conducted an observational study to determine whether influenza infection is a risk factor for AF and whether vaccination could reduce that risk. From 2000 to 2010, they identified 11,374 patients with newly diagnosed AF from the Taiwan National Health Insurance Research Database who were then matched by age and sex to four control (without AF) patients each. The reference group consisted of patients without influenza infection and vaccination.
The total study population consisted of 56,870 patients. The mean age was 71 years and 56% were men.
The primary outcome was the relationship between AF and influenza infection/vaccination 1 year before enrollment.
According to the findings, patients with influenza who were not vaccinated (n = 1,369) had an 18% higher risk for AF compared with the control group (OR = 1.182; P = .032). The risk for AF, however, was lower for patients who received the influenza vaccination without developing influenza infection (n = 16,452; OR = 0.881; P < .001). In addition, those who were vaccinated but still developed influenza (n = 696) had a similar risk for AF compared with the reference group (OR = 1.136; P = .214).
Subgroup analyses revealed a lower risk for AF with vaccination, according to the results.
“Although the precise mechanisms of AF are not well understood, accumulating evidence indicates that inflammation and the autonomic nervous system are involved in the development of AF,” Tze-Fan Chao, MD, and Su-Jung Chen, MD, of Taipei Veterans General Hospital, Taiwan, said in a press release.
The researchers concluded that although more research on these mechanisms are needed, physicians should be mindful of the possibility of AF when patients with influenza experience ischemic stroke or complain of palpitations. They also recommended that high-risk patients receive the influenza vaccination each year.
In a related editorial, Nishant Verma, MD, MPH, and Bradley P. Knight, MD, FHRS, both from the division of cardiology, department of medicine at Northwestern University, wrote, “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.”
Verma and Knight called for future research to investigate whether the acute treatment of the influenza infection with neuraminidase inhibitors or the addressing of the infection’s inflammatory response in some way may help reduce this influenza-associated AF risk. – by Tracey Romero
Disclosure: The researchers and Verma and Knight report no relevant financial disclosures.
Perspective
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John D. Day , MD, FHRS, FACC
It has long been recognized clinically that respiratory infections can trigger AF. This study quantifies the possible AF risk from influenza. It also reports on the possible protective aspect of the influenza vaccine.
These same findings were recently published on MI (Barnes M, et al. Heart. 2015;doi:10.1136/heartjnl-2015-307691). In that study, the findings were nearly identical: Influenza may cause a MI and a vaccine may reverse that risk.
I suspect the mechanism for both of these studies is the same. Influenza causes an inflammatory reaction and also activates the sympathetic nervous system. This inflammatory response and sympathetic nervous system activation can cause both AF and MI. This study adds to the growing body of data that the influenza vaccine may be protective in preventing CV complications of influenza.
A limitation of this research is that it is an observational study. Thus, we don’t really know if influenza causes AF or that the vaccine prevents AF. All we know is that influenza is associated with more AF and that the influenza vaccine is associated with less AF.
Ideally, a randomized study could be performed to see if there really is a causation here. However, this study will likely never be done, as it would be considered unethical to withhold a vaccine that clearly decreases the risk for influenza.
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