Doctors need to take concerted action to ensure that people who are at risk of heart disease receive the influenza vaccine every autumn, according to the authors of a new report published in the European Heart Journal.
Their research shows that influenza epidemics are associated with a rise in deaths from heart disease and that flu can actually trigger the heart attacks that result in death.
However, only about 60% of people in the USA who ought to have a flu jab actually have one and this percentage is even smaller in Europe, said Professor Mohammad Madjid, the lead author of the report.
"Our research has shown that influenza epidemics are associated with a rise in coronary deaths. This calls for more intensive efforts to increase the vaccination rate in people at risk of coronary heart disease. This may be especially important in an influenza pandemic when we would expect to see high mortality amongst the elderly and those suffering from heart problems or who have multiple coronary risk factors," he said. "Between 10 and 20% of people catch flu every year, and I have estimated that we can prevent up to 90,000 coronary deaths a year in the USA if every high risk patient received an annual flu vaccination."
Prof Madjid, who is assistant professor of medicine at the University of Texas-Houston, and a senior research scientist at the Texas Heart Institute in Houston, USA, worked with colleagues in the US and in St Petersburg in the Russian Federation to investigate deaths between 1993 and 2000 in St Petersburg that had been shown by autopsy reports to be due to coronary heart disease.
"This was a population where only a small minority were receiving flu vaccines or statin drugs, so this enabled us to see what happened naturally in the absence of these medicines," said Prof Madjid. "Relying on autopsy reports rather than death certificates enabled us to be much more accurate about the cause of death, because doctors often neglect to list flu on a death certificate if their patients have died from a heart attack and, conversely, heart attack symptoms can be missed in patients suffering from flu and pneumonia."
They found that 11,892 people died from acute myocardial infarction (AMI) (47.8% men and 52.2% women), and 23,000 died from chronic ischaemic heart disease (IHD) (40.1% men and 59.9% women). The peaks in deaths from both AMI and IHD coincided with the times when influenza epidemics and acute respiratory disease (ARD), which often accompanies flu, were at their height. They found that the chances of dying from AMI increased by a third in epidemic weeks, compared to non-epidemic weeks, and the chances of dying from IHD increased by a tenth. This was the same for both men and women and in different age groups.
Researchers believe that flu causes an acute and severe inflammation in the body, which, in some patients, can destabilise atherosclerotic plaques in coronary arteries and cause heart attacks.
Prof Madjid said: "Most people develop atherosclerotic lesions in their coronary arteries in early childhood and these lesions grow over time. Inflammation plays a pivotal role in development and growth of these lesions. Most people in Western countries live with different stages of atherosclerosis and many will never show any clinical manifestations of the atherosclerosis. However, in some patients the quiescent, stable atherosclerotic plaques undergo sudden changes, mainly due to exaggerated inflammation, leading to rupture of these vulnerable plaques and subsequent formation of clots resulting in heart attacks.
"This study shows that flu is an important trigger of heart attacks because flu is a severe infection, with high incidence rates and is readily preventable. Therefore, our results give us a new tool for preventing heart attacks.