A diagnosis of influenza increased the risk of subsequent atrial fibrillation by about 18%, investigators reported online in Heart Rhythm.

Clinicians therefore should consider atrial fibrillation (AF) in patients with influenza-like symptoms who report palpitations or experience an ischemic stroke, said Dr. Ting-Yung Chang of Taipei Veterans General Hospital in Taiwan and his associates. Influenza vaccination might help prevent AF, and high-risk patients should be encouraged to receive the vaccination annually, they said. However, a large prospective study is needed to clarify whether influenza vaccination reduces the risk of AF and subsequent ischemic stroke and systemic thromboembolic events, they added.

Atrial fibrillation increases the risk of stroke about fivefold, triples the risk of heart failure, and doubles the chances of dementia and death, the researchers noted. Mounting evidence implicates inflammation and sympathetic nervous system dysregulation in the pathogenesis of AF, raising questions about whether influenza might underlie or contribute to some cases of AF. To explore relationships among AF, influenza, and influenza vaccination, the investigators analyzed data for 11,374 patients with AF who were enrolled in the Taiwan National Health Insurance Research Database between 2000 and 2010. They matched each patient with AF to four controls based on age, sex, enrollment date, and the Charlson comorbidity index ( Heart Rhythm. 2016 Feb. doi: 10.1016/j.hrthm.2016.01.026 ).

Unvaccinated patients with influenza were 18% more likely to develop AF than unvaccinated patients without influenza (odds ratio, 1.18; 95% confidence interval, 1.01-1.38; P = .032), even after adjusting for demographic factors, medical history, and use of relevant health care services, the researchers reported. In contrast, vaccinated patients who later developed influenza were about as likely to develop AF as unvaccinated patients who did not develop influenza, both in the overall analysis and in subgroups stratified by age, sex, and comorbidities. Moreover, vaccinated patients without influenza were even less likely to develop AF than unvaccinated patients without influenza (OR, 0.88; 95% CI, 0.84-0.93; P less than .001).

The registry database excluded relevant data on smoking history, body mass index, and physical activity level, the researchers said. “Influenza infection was diagnosed using ICD-9 codes with concomitant use of antiviral agents, and was not further confirmed based on the results of viral culture with throat swab,” they added. “The diagnostic accuracy of influenza infection cannot be fully ascertained.”

The National Science Council and the Taipei Veterans General Hospital funded the study. The researchers had no disclosures.