Exploring the Relationship Between the Flu and Heart Attacks
Influenza is a contagious viral respiratory disease that infects the nose, throat, and potentially the lungs. The flu season occurs annually every fall and winter, spanning roughly from October to March. As the peak of flu season approaches, it is important to understand the risks associated with infection. Those with pre-existing conditions, like diabetes, asthma, or cancer, may be more vulnerable to influenza complications such as myocardial infarctions (MIs), also known as heart attacks. Recent research has shown that the onset of influenza may increase an individual’s risk for MI and how the increased risk may be prevented by vaccination.
Heart attacks are caused by blockages in coronary arteries; when plaque builds up, it narrows arteries and prevents them from delivering blood and oxygen to the rest of the body. The most common cause of heart attacks is coronary heart disease, specifically acute coronary syndrome (ACS), which is the leading cause of death worldwide. As the flu is one of the most common infections, a relationship between the two has been suspected for years. It wasn’t until recently, however, that the relationship was studied more deeply. Researchers were interested in determining whether the flu is associated with type 1 MI—a heart attack due to coronary plaque rupture and thrombosis, the blockage of blood vessels by blood clots—or type 2 MI, which is not due to any coronary artery complication. A wide-scale, five-year regional analysis of over 8,000 patients in Madrid, Spain examined the link between influenza infection and adverse cardiac events.
The study found that patients had an increased risk of death by ACS during the fall and winter months, which overlap with the flu season. Although past studies have not been able to show the relative risks of cold weather and flu infection separately on MI incidence, this study established an independent relationship between type 1 acute MI and influenza. Peaks during the flu season were generally associated with an increased risk for a type 1 MI, with the greatest risk within the week following initial infection.
Heart attacks are caused by blockages in coronary arteries; when plaque builds up, it narrows arteries and prevents them from delivering blood and oxygen to the rest of the body. The most common cause of heart attacks is coronary heart disease, specifically acute coronary syndrome (ACS), which is the leading cause of death worldwide. As the flu is one of the most common infections, a relationship between the two has been suspected for years. It wasn’t until recently, however, that the relationship was studied more deeply. Researchers were interested in determining whether the flu is associated with type 1 MI—a heart attack due to coronary plaque rupture and thrombosis, the blockage of blood vessels by blood clots—or type 2 MI, which is not due to any coronary artery complication. A wide-scale, five-year regional analysis of over 8,000 patients in Madrid, Spain examined the link between influenza infection and adverse cardiac events.
The study found that patients had an increased risk of death by ACS during the fall and winter months, which overlap with the flu season. Although past studies have not been able to show the relative risks of cold weather and flu infection separately on MI incidence, this study established an independent relationship between type 1 acute MI and influenza. Peaks during the flu season were generally associated with an increased risk for a type 1 MI, with the greatest risk within the week following initial infection.
Receiving the flu vaccine greatly reduces the risk for infection and subsequent flu-related complications.
Image Source: CDC
Biologically, this could be explained by the fact that an initial immune response mechanism against influenza is controlled in the body by communication between platelets and neutrophils. Neutrophils are the “first responders” at infection sites, and were previously thought to be primarily responsible for the immune system’s initial response. But, platelets, which are disc-shaped cells that circulate within the blood and bind together upon recognition of damaged blood vessels, may play an equally critical role. Upon infecting the body, the influenza virus is initially recognized by a structure on platelets called Toll-like receptor 7 (TLR7) and engulfed. TLR7 releases a protein that causes nearby neutrophils to release their DNA, activating thrombotic processes that may contribute to an increased risk of MI.
Vaccination against influenza, however, has shown to be effective in lessening this risk of flu infection and may be effective in preventing consequent acute MI. Flu vaccination was associated with a highly reduced risk for a type 1 MI, specifically in patients older than 59. The vaccine may even mediate inflammation in those with cardiovascular risk factors, thereby preventing thrombotic events.
Overall, it is important to recognize the risks associated with certain diseases and infections. Though the results from the study are correlative and not causal, vaccination was shown to decrease risk for infection and subsequent complications. For those at risk for cardiac events, especially those with pre-existing conditions, it is important to recognize the risk reduction associated with receiving the flu vaccine. You should discuss the pros and cons of receiving the flu vaccine with a medical professional.
Vaccination against influenza, however, has shown to be effective in lessening this risk of flu infection and may be effective in preventing consequent acute MI. Flu vaccination was associated with a highly reduced risk for a type 1 MI, specifically in patients older than 59. The vaccine may even mediate inflammation in those with cardiovascular risk factors, thereby preventing thrombotic events.
Overall, it is important to recognize the risks associated with certain diseases and infections. Though the results from the study are correlative and not causal, vaccination was shown to decrease risk for infection and subsequent complications. For those at risk for cardiac events, especially those with pre-existing conditions, it is important to recognize the risk reduction associated with receiving the flu vaccine. You should discuss the pros and cons of receiving the flu vaccine with a medical professional.
Featured Image Source: Andrea Piacquadio
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