Originally published by 2 Minute Medicine^® (view original article). Reused on AccessMedicine with permission.

1. Risk of acute myocardial infarction and ischemic stroke was increased during the first two weeks following a COVID-19 infection compared to the general population.

2. The risk of developing acute myocardial infarction and ischemic stroke decreased in weeks 3-4 following a COVID-19 infection compared to the first two weeks.

Evidence Rating Level: 3 (Average)

Study Rundown:

Inflammatory states, such as those precipitated by COVID-19 infection, are known to transiently increase risk of acute myocardial infarction (MI) and ischemic stroke. This Swedish self-controlled case study (SCCS) and matched cohort study analyzed the risk of acute MI and stroke in individuals during an active COVID-19 infection. In the SCCS, incidence rate of acute MI and stroke was calculated during week 1-4 of acute COVID-19 infection and compared to a control period (pre- and post-infection). The incidence rate ratio of acute MI or stroke was shown to be much higher during the month following COVID-19 infection, especially within the first two weeks. The matched cohort portion of this study compared the incidence of an acute event in the COVID-19 population to a matched cohort. This showed that the risk of acute MI and stroke was higher in the two weeks following a COVID-19 infection and decreased in the third and fourth weeks. Limitations of this study include those caused by health registry data, such as the inability to define the exact date of COVID-19 infection and having to use an estimate. Nonetheless, this is a large-scale study that suggests COVID-19 infection is a risk factor for the development of acute MI or stroke.

Click to read the study in the Lancet

Click to read an accompanying editorial in the Lancet

Relevant Reading: The COVID-19 pandemic and the incidence of acute myocardial infarction

In-Depth [case-control study]:

This study analyzed the risk of acute MI and ischemic stroke following COVID-19 infections in 86 742 individuals in Sweden. The Swedish health registry and public health data was used to create the sample. Analysis was done in two parts: 1) incidence rate ratio (IRR) was calculated from first MI or stroke event following a COVID-19 infection compared to a control period for that individual (self-controlled) before infection; 2) a cohort matched based on sex, age and county of Sweden was used to determine risk of MI or stroke compared to the general population. To control for comorbidities, the weight Charlson Comorbidity Index (wCCI) was used to determine health status.

Each individual had to be assigned a “COVID-19 date”, as date of infection was not always known. Therefore, the earliest date related to COVID-19 on their health records was used (ex. disease onset, admission, diagnosis). The control period used in the self-controlled case study (SCCS) was the study period from Feb 1 to Sep 14, 2020, excluding 28 days pre- and post- the COVID-19 date. The researchers noted during their analysis that often the “COVID-19 date” and MI/stroke were the same day (day 0). It is possible patients only received a positive result for COVID-19 when they were admitted for MI/stroke and were infected at an earlier date. Therefore, to control for bias caused by infection and event occurring on the same day, two calculations were done including and excluding day 0.

The results of the SCCS showed the IRR for acute MI was 8.44 (5.45-13.08) for week 1, 2.56 (1.31-5.01) for week 2, and 1.60 (0.84-3.04) for weeks 3 and 4 following day 0. When day 0 was excluded, the IRR for acute MI was found to be 2.89 (1.51-5.55) for week 1. For ischemic stroke, the IRR with day 0 included was 6.18 (4.06-9.42) for week 1, 2.85 (1.64-4.97) for week 2, and 2.14 (1.36-3.38) for weeks 3 and 4. If day 0 is excluded, the IRR lowers to 2.97 (1.71-5.15). In the matched cohort study including day 0, the ORs for acute MI and ischemic stroke were 6.61 (3.56-12.20) and 6.74 (3.71-12.20) for the two weeks following a COVID-19 infection, respectively. The ORs when day 0 was excluded were 3.41 (1.58-7.36) and 3.63 (1.69-7.80) for acute MI and stroke, respectively.

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