Every year, hundreds of thousands of people have a heart attack. New research suggests that both mild and severe respiratory infections might make some people more susceptible to heart attacks.
A team of researchers from the University of Sydney in Australia set out to investigate the link between respiratory infections and the risk of heart attack.
In Australia, approximately 56,000 people have a heart attack each year, and nearly 9,300 die from it.
The new study - published in the Internal Medicine Journal - found that respiratory infections such as pneumonia, the common influenza, and bronchitis all seem to increase the chances of having a heart attack.
The research looked at 578 patients who had a heart attack due to a blockage in their coronary arteries. The patients reported on their history of respiratory infection, including bronchitis and pneumonia, and they gave information on their most recent infections and how often they tend to get an infection.
The patients were admitted to the Royal North Shore Hospital in New South Wales, Australia. The diagnosis of a heart attack was confirmed by coronary angiography, a special X-ray test used to detect whether or not coronary arteries are blocked and to what extent.
Risk of heart attack 17 times higher in first 7 days after an infection
The study suggests that respiratory infections can trigger heart attacks.
Overall, 17 percent of the patients said they had symptoms of a respiratory infection up to 7 days before the heart attack, and 21 percent had had a respiratory infection within 31 days.
Although lower on the whole, the risk of having a heart attack among patients with mild upper respiratory infection was still 13 times higher than usual.
"Although upper respiratory infections are less severe, they are far more common than lower respiratory tract symptoms. Therefore it is important to understand their relationship to the risk of heart attacks," comments the study's lead author, Dr. Lorcan Ruane.
The senior author of the research, Prof. Geoffrey Tofler - who is also a cardiologist at the University of Sydney, Royal North Shore Hospital, and Heart Research Australia - explains that, according to the results, the risk of a heart attack does not occur only at the onset of a respiratory infection.
Rather, the risk is at its highest during the first 7 days, then decreases slightly, only to remain steadily high for as much as a month.
Associate professor and study investigator Thomas Buckley, from Sydney Nursing School, weighs in on the significance of these findings, saying, "The incidence of heart attacks is highest during winter in Australia. This winter peak is seen not only in Australia but also in other countries around the world is likely due in part to the increased incidence of respiratory infections. People should take measures to reduce exposure to infection, including flu and pneumonia vaccines where appropriate."
Prof. Tofler also comments on the results, venturing some possible explanations for the association found:
"Possible reasons for why respiratory infection may trigger a heart attack include an increased tendency towards blood clotting, inflammation and toxins damaging blood vessels, and changes in blood flow.
Our message to people is while the absolute risk that any one episode will trigger a heart attack is low, they need to be aware that a respiratory infection could lead to a coronary event. So consider preventative strategies where possible, and don't ignore symptoms that could indicate a heart attack."
Prof. Tofler also suggests that the next step should be to identify preventive therapies for the people who are more prone to having a heart attack.