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

A swedish population-based study has shown infection COVID-19 to be an risk factor for both myocardial infarction and ischaemic stroke.

Although COVID-19 is a considered to be predominately respiratory infection, a review from the end of 2020, established that infection can also result in adverse cardiovascular outcomes. For example, one study of 3,334 COVID-19 patients in the US, found a 1.6% incidence of ischaemic strokes, and an 8.9% incidence of myocardial infarction. This rate was much 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 was the reason for a study led by a team from the Department of Public Health and Clinical Medicine, Umea University, Umea, Sweden. The researchers 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. The team used two methods of study; the self-controlled case series (SCCS) method and a matched control cohort. In the SCCS method, an individual acts as their own control, so that only those who experience an event are included and serves as an alternative to the cohort or case-controlled study design. For comparative purposes, the researchers also used a more traditional matched cohort study. 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. Since an adverse cardiovascular event could have occurred on the same day as infection with COVID-19, it is possible that the event occurred independently of infection with the virus and the team therefore performed two separate analyses using either day 0 (i.e., day of exposure to COVID-19) and one excluding day 0.

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). In the SCCS study there were 186 acute 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, similar, significant increased risk were 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 acute myocardial infarction and ischaemic stroke.

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