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Respiratory infection can trigger acute myocardial infarction

By Nicole MacKee
The risk of having a heart attack is 17 times higher in the seven days after a respiratory infection, according to Australian research published in the Internal Medicine Journal

Senior author Professor Geoffrey Tofler, a cardiologist from Royal North Shore Hospital, The University of Sydney and Heart Research Australia, said the findings confirmed suggestions from previous studies that respiratory infection could act as a trigger for myocardial infarction. 

‘This link may also contribute to the seasonal variation and winter peak of heart attack,’ Professor Tofler told Cardiology Today

The study used coronary angiography to investigate the link between respiratory infections, such as pneumonia, bronchitis and influenza, and increased risk of a myocardial infarction. The researchers noted that absence of angiographic data was a limitation in previous registry- and record-based studies because elevated troponin levels and ECG changes may also occur in myocarditis due to respiratory infection. 

In an analysis of the Triggers and Modifiers of Acute Myocardial Infarction (TAMAMI) study, researchers investigated 578 consecutive patients with myocardial infarction due to coronary artery blockage at Royal North Shore hospital. The patients, who had an average age of 59.5 years and were mostly men (84%), provided information on recent and usual occurrence of symptoms of respiratory infection. 

Patients were interviewed about their symptoms and their activities before the onset of symptoms, including if they experienced a ‘flu-like illness with fever and sore throat.’ They were considered affected if they reported sore throat, cough, fever, sinus pain, flu-like symptoms, or if they reported a diagnosis of pneumonia or bronchitis. 

Among the patients, 100 (17%) reported symptoms of respiratory infection within seven days, and 123 (21%) within 31 days of the myocardial infarction. 

A second analysis was among those with symptoms restricted to the upper respiratory tract, which included the common cold, pharyngitis, rhinitis and sinusitis. Lead author Dr Lorcan Ruane said: ‘For those participants who reported upper respiratory tract infection symptoms the risk increase was less, but was still elevated by 13-fold.’ 

‘Possible mechanisms for why respiratory infection may trigger a heart attack include platelet activation and a prothrombotic state, inflammation, cytokine release and coronary plaque disruption, and haemodynamic effects such as tachycardia and vasoconstriction,’ Professor Tofler said. The increased risk of a heart attack peaked in the first seven days and gradually reduced, but remained elevated for one month.

While the absolute risk of any one episode of respiratory infection triggering a heart attack is low, the researchers said awareness of the link provides an opportunity to emphasise preventive measures such as influenza and pneumonia vaccination, particularly for those at increased risk or who have contact with susceptible individuals. 
Internal Med J 2017; 47: 522-529. 

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