People suffering from the flu may be at higher risk for having a heart attack, especially those with heart disease and diabetes, British researchers report.
"Influenza is most concerning because of its secondary complications," said Dr Marc Siegel, an associate professor of medicine at New York University School of Medicine in New York City, US.
"Most of the time with influenza, death or hospitalisation isn't because of the influenza, it's because influenza puts you in a weakened state - it's a stress on the system," he said. "So, it is not surprising that you would have the increased risk of a myocardial infarction during or right after an influenza infection."
Virus bad for heart
In addition, the flu virus may have a negative effect directly on the heart, Siegel said. "Flu stresses and strains the system," he added.
To determine the risk of heart attack among those with flu, a research team led by Andrew C Hayward, a senior lecturer in infectious disease epidemiology at the UCL Centre for Infectious Disease Epidemiology in London, looked at 39 studies conducted between 1932 and 2008.
The studies showed an increase in deaths from heart disease and more heart attacks during flu season. In fact, excess deaths because of heart disease averaged 35% to 50%, according to the report in The Lancet Infectious Diseases.
Flu shot lowers risk
But the studies also showed that getting a flu shot reduced the risk of dying from heart disease or suffering a heart attack, Hayward's group found.
"We believe influenza vaccination should be encouraged wherever indicated, especially in those people with existing cardiovascular disease. Further evidence is needed on the effectiveness of influenza vaccines to reduce the risk of cardiac events in people without established vascular disease," Hayward's team concluded.
Dr Gregg C. Fonarow, a professor of cardiology at the University of California, Los Angeles, agreed that flu shots appear to reduce the risk of heart attacks.
"It has long been hypothesised that influenza infection results in an acute inflammatory response that can also trigger the onset of cardiovascular events, such as heart attack and stroke in vulnerable individuals," Fonarow said.
Annual vaccination recommended
A number of observational studies have suggested more cardiovascular events occur in patients with influenza than otherwise expected, and that individuals who receive annual flu shots are much less likely to have fatal or non-fatal cardiovascular events, or be hospitalised for heart failure, he said.
"Guidelines from the American Heart Association and American College of Cardiology strongly recommend that all individuals with cardiovascular disease receive annual influenza vaccination," Fonarow said.
However, Dr Pascal James Imperato, dean and distinguished service professor at the School of Public Health at the State University of New York Downstate Medical Centre in Brooklyn, said the role of flu shots in preventing heart attack has not been proven conclusively.
"The role of severe respiratory infections in precipitating myocardial infarctions in vulnerable individuals is well-established," Imperato said. "However, the role of influenza vaccines in protecting such individuals is less clear from the limited scientific evidence available." - (Steven Reinberg/HealthDay News, September 2009)