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COVID-19 is an independent risk factor for myocardial infarction and ischaemic stroke

Researchers have found that infection with COVID-19 to be an independent risk factor for both myocardial infarction and ischaemic stroke.

While COVID-19 is largely a respiratory infection, a review in 2020 established that infection can also result in adverse cardiovascular outcomes. In one study of 3,334 COVID-19 patients in the US for example, researchers observed an incidence of 1.6% for ischaemic strokes, and 8.9% for myocardial infarction. In fact, this rate was considerably higher than in a Danish observational study of 5119 patients, of whom, only 0.3% experienced an acute myocardial infarction. However, many of the adverse cardiovascular outcomes have reported among those hospitalised with COVID-19 and there is a lack of data on this disease burden following infection with the virus at the population level.

This led by a team from the Department of Public Health and Clinical Medicine, Umea University, Umea, Sweden to examine the incidence of both cardiovascular outcomes at the population level. The team sought to quantify the relative risk of both ischaemic stroke and myocardial infarction following infection with COVID-19, using a large, nationwide register within Sweden. As both myocardial infarction and ischaemic stoke could occur independently of infection with COVID-19, the team used two different methods of study; the self-controlled case series (SCCS) and a matched control cohort. In the SCCS method, an individual acts as their own control and hence only those who experience an event are included in the analysis. The period of study was February to September 2020 and the researchers calculated the incidence rate ratio (IRR) of both cardiovascular events following onset of COVID-19. As mentioned earlier, since either adverse cardiovascular outcome could have occurred on the same day as infection with COVID-19, to try and account for this, the team performed two separate analyses using either day 0 (i.e., day of exposure to COVID-19) and one excluding day 0 and compared the IRRs using both analyses.

Findings
Using the national registry, a total of 86,742 individuals were diagnosed with COVID-19 during the period of study with a median age of 48 years (43% male). There were 186 myocardial infarctions, of whom 39 patients died. When day 0 was excluded, the IIR for acute myocardial infarction was 2.89 (95% CI 1.51 – 5.55) for the first week, 2.53 (95% CI 1.29 – 4.94) for the second week, although not significant for weeks 3 and 4 (IIR = 1.60, 95% CI 0.84 – 3.04). However, when day 0 was included, the IIR was significantly higher (IIR = 8.44, 95% CI 5.45 – 13.08) for the first and second weeks, but again, not significant for the third and fourth weeks. The corresponding values for ischaemic stroke were also significantly increased during the first week when day 0 was excluded (IIR = 2.97, 95% CI 1.71 – 5.15) and when day 0 was included (IIR = 6.18, 95% CI 4.06 – 9.42).

In the matched cohort analysis, a similar and significant increased risk was observed for both acute myocardial infarction and ischaemic stroke, irrespective of whether day 0 was included.
Based on these findings from two independent methods, the authors concluded that COVID-19 is an independent risk factor for both myocardial infarction and ischaemic stroke.

Citation
Katsoularis I et al. Risk of acute myocardial infarction and ischaemic stroke following COVID-19 in Sweden: a self-controlled case series and matched cohort study. Lancet 2021



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