Flu increases risk for acute myocardial infarction

Issue: March 2018

Patients with respiratory infections, particularly influenza, have an increased risk for acute myocardial infarction, according to a study published in The New England Journal of Medicine.

Perspective from Scott D Solomon, MD

“Our findings are important because an association between influenza and acute myocardial infarction (MI) reinforces the importance of vaccination,” Jeffrey C. Kwong, MD, a scientist at the Institute for Clinical Evaluative Sciences and Public Health Ontario, said in a press release.

Researchers analyzed data from 364 hospitalizations for acute MI between May 2008 and May 2015 in 332 patients (median age, 77 years; 48% women) who were tested for and diagnosed with influenza between May 2009 and May 2014. Patients were excluded if the positive influenza specimen was collected during their hospitalization for acute MI.

The risk interval was defined as the first 7 days after the respiratory specimen was obtained. The control interval was other times within the observation period, which was the interval from 1 year before and 1 year after the specimen was collected.

Twenty admissions per week for acute MI occurred during the risk interval, and there were 3.3 admissions per week during the control interval (incidence ratio = 6.05; 95% CI, 3.86-9.5).

On days 8 through 14, there was no significant increase in acute MI (incidence ratio = 0.6; 95% CI, 0.15-2.14). This was also seen on days 15 through 28 (incidence ratio = 0.75; 95% CI, 0.31-1.81).

Within 7 days, the incidence ratios were 5.17 for influenza A (95% CI, 3.02-8.84), 10.11 for influenza B (95% CI, 4.37-23.38), 3.51 for respiratory syncytial virus, or RSV (95% CI, 1.11-11.12), and 2.77 for other viruses (95% CI, 1.23-6.24).

“Our findings, combined with previous evidence that influenza vaccination reduces cardiovascular events and mortality, support international guidelines that advocate for influenza immunization in persons older than 65 years of age to protect against ischemic coronary events,” Kwong and colleagues wrote. “Other strategies to mitigate the cardiovascular risk associated with respiratory infections include maximizing the uptake of existing vaccines against other respiratory pathogens, developing more effective influenza vaccines and vaccines against other burdensome respiratory pathogens (eg, RSV) and promoting established infection prevention practices such as hand hygiene, respiratory etiquette and social distancing.” – by Darlene Dobkowski

Reference:
Kwong JC, et al. N Engl J Med. 2018;doi:10.1056/NEJMoa1702090.

Disclosures: Kwong reports no relevant financial disclosures. Please see the study for a list of all other authors’ relevant financial disclosures.

Perspective

Scott D Solomon, MD

This confirms what prior studies have suggested, that there was indeed a temporal association between influenza and MI. It is still not clear why there is this association, although several mechanisms, including increased metabolic demands in the setting of influenza in an at-risk patient and potential pro-inflammatory effects of influenza, can trigger acute plaque rupture and prothrombotic effects of influenza.

This does raise the possibility that strategies that both increase the proportion of individuals who receive influenza vaccine and improve the effectiveness of the vaccine might reduce MI. Unfortunately, we have shown that the prevalence of influenza vaccination is low, even in high-risk individuals with heart disease.

I am currently leading, along with Orly Vardeny, PharmD, MS, from the University of Minnesota, a nearly 10,000-patient, NIH-funded trial called INVESTED, which is directly testing whether a high-dose influenza vaccine would reduce CV events to a greater extent than a standard vaccine in high-risk individuals.

Scott D Solomon, MD

Director, noninvasive cardiology

Disclosures: Disclosure: Solomon reports that his institution has received supplemental grant support from Sanofi-Pasteur for performing the INVESTED trial.