Review 1: "Post-Acute Cardiovascular Outcomes of COVID-19 in Children and Adolescents: An EHR Cohort Study from the RECOVER Project"

RR\ID Evidence Scale rating by reviewer:

• Reliable. The main study claims are generally justified by its methods and data. The results and conclusions are likely to be similar to the hypothetical ideal study. There are some minor caveats or limitations, but they would/do not change the major claims of the study. The study provides sufficient strength of evidence on its own that its main claims should be considered actionable, with some room for future revision.

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Review: This manuscript is interesting from different perspectives and provides robust data on cardiovascular disorders during the post-acute SARS-CoV-2 infection in children and adolescents, a group of complications previously described but not described with so much detail. 

The study has some strengths to comment:

1. The number of individuals included from different US medical centers is vast, with the advantage of various racial, social, and economic backgrounds. The sample size probably represents the US pediatric population in different medical systems.

2. It also includes patients with and without congenital heart disease, enhancing the conclusions of the increased risk of cardiovascular disorders after COVID-19, even in healthy populations, which could be, in turn, a solid argument to regularly vaccinate children against SARS-CoV-2. The authors could consider the latter point for the discussion. 

3. The study presents a statistically solid analysis, with a cautious selection of covariates, stratification, and congenital heart disease analysis. They also performed a sensitivity analysis. 

4. Strengths and limitations are widely mentioned.

5. A strong fact of this investigation is that they extended the follow-up of these patients up to 6 months after the SARS-CoV-2 infection, which is higher than many of the studies published today. Also, they were able to include patients from March 2020 to March 2023 with the possibility of analyzing the impact of the corresponding dominant virus variants and their outcomes. Their findings show the highest risk of any cardiovascular outcome in the pre-Delta period, showing a consistent decline after Delta. I suggest the authors further discuss this finding in the discussion section, as it can have important clinical implications, mainly for children and adolescents with congenital heart disease. 

Other comments:

• The introduction needs to be reviewed. To introduce this information better, provide more focused data with some objective support (e.g., the frequency of cardiovascular disorders after COVID-19 in children and adolescents) and utilize some of the published data. 

• Delete the study's strengths from the introduction, as they are discussed in the discussion. 

• The definition of documented SARS-CoV-2 infections is a bit confusing. A diagnosis of COVID-19 or PASC is accepted, but it is not clear if a confirmatory test was available at some point. Since this is a research study, patients in this cohort should have a confirmatory COVID-19 test to avoid confounding with other viral or inflammatory disorders. If it is only a wording confusion, please consider changing it.