These are described in detail in the Methods section.
ReviewInfluenza as a trigger for acute myocardial infarction or death from cardiovascular disease: a systematic review
Introduction
During influenza epidemics there are many deaths and serious complications in vulnerable populations. People with underlying chronic medical disorders such as cardiovascular disease are particularly at risk.1 However, the association between influenza infection and acute myocardial infarction is unclear. Early studies reported seasonal patterns of cardiovascular deaths that were similar to patterns of influenza circulation.2, 3, 4, 5 Clinical findings in patients with influenza revealed characteristic systemic effects such as high fever, myalgia, and fatigue, but also revealed frequent myocardial involvement.6, 7, 8, 9 These findings led to the hypothesis that influenza might act as an acute inflammatory stimulus triggering cardiovascular events. Markers of systemic inflammation have been used to predict the risk of vascular disease in people,10 and inflammatory cells are an important component of atherosclerotic plaques.11 The influenza virus has extensive effects on inflammatory and coagulation pathways,12 which might lead to destabilisation of vulnerable atherosclerotic plaques and thus coronary artery occlusion—the major cause of acute myocardial infarction.13 In this systematic review, we examine the association between influenza infection and acute myocardial infarction or cardiovascular death, including the protection against cardiovascular events provided by influenza vaccines.
Section snippets
Search strategy
Searches were done using PubMed (up to February, 2009) and EmBase (from 1980 to February, 2009), without language limits. We used the following PubMed MeSH search terms: “‘influenza human’ or ‘influenza vaccines’ or ‘viruses[Majr]’ or ‘respiratory tract infections[Majr]’ and ‘myocardial infarction’”. The search was repeated with the MeSH terms “‘influenza human’ or ‘influenza vaccines’ and ‘cardiovascular diseases[Majr]’”. Keyword searches were done in both databases with combinations of the
Results
The search yielded 1869 articles, of which 99 were deemed relevant and 37 fulfilled inclusion criteria (figure 1). An additional five articles were identified by scanning reference lists of included studies and relevant reviews. 42 papers were included in our analysis, published between 1932 and 2008. Of these, 17 described ecological studies, 15 reported case–control studies, three were prospective cohort studies, two were case only studies (incorporating one self-controlled case series study
Discussion
A range of observational studies done in different settings have generally tended to support the hypothesis that acute respiratory infections—influenza in particular—can trigger acute myocardial infarction. There is also more limited evidence for an adverse effect on cardiovascular death. Two relatively small randomised trials suggest that influenza vaccination reduces the risk of cardiovascular death and some coronary ischaemic events.
This Review used a systematic, transparent search strategy,
Search strategy and selection criteria
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