(337) Defining a Post-vaccine Myocarditis Cohort by Applying CDC Case Definition to Structured EHR and Claims Data as a Proxy for Case Adjudication

Background: Rare cases of myocarditis have been identified after mRNA COVID vaccination. Use of population-based secondary data sources allows for meaningful precise analysis of these events. However, clinical adjudication of cases deriving from these source is intensive.

Objectives: To describe clinical characteristics of a post-vaccine myocarditis (PVM) cohort based on an algorithm approximating the CDC acute myocarditis case definition in place of adjudication.

Methods: We screened for cases using ICD-10-CM or SNOMED diagnosis codes for myocarditis between December 18, 2020, and September 14, 2023 (index diagnosis) in a linked dataset of electronic health records (EHR) from Veradigm Network EHR and healthcare claims from Komodo. Post-vaccination screening cases required a record of a marketed Moderna vaccine targeting SARS-CoV-2 in the 30 days prior to/on the index diagnosis. As a proxy for case adjudication, we applied an algorithm based on the CDC definition of probable or confirmed myocarditis, which included both a clinical symptom of myocarditis (chest pain, dyspnea, palpitations, or syncope) and evidence of a cardiac test (troponin lab, electrocardiogram, echocardiogram, or cardiac magnetic resonance imaging) within 7 days of the index diagnosis. Characteristics and initial care of the cases were reported.

Results: Patients in the proxy PVM cohort (N = 250) were mostly males (61.6%), and on average, 42.0 (SD: 17.6) years old. Males comprised 72.7% of those 18-24 years old and 82.1% of those 30-39 years old. Diagnoses recorded among patients during the 12 months preceding index diagnosis included cardiovascular disease other than hypertension (59.2%), primary hypertension (34.0%), prior myocarditis (14.4%), and pericarditis (10.0%). In addition, 15.6% had a diagnosis of COVID-19 in the preceding 180 days. Common baseline medications included antihypertensives (42.8%), anti-inflammatories (36.4%), and statins (21.2%). Among the 223 patients with claims coverage at index, the most commonly dispensed medications within 30 days after the index event were beta-blockers (30.5%), diuretics (15.7%), and corticosteroids (15.7%). Chest pain (81.2%) was the most frequent myocarditis symptom, followed by dyspnea (48.0%), palpitations (12.1%), and syncope (3.6%).

Conclusions: While full case adjudication is the gold standard, a proxy definition based on the CDC criteria for myocarditis can provide an estimate of patients with a higher likelihood of meeting the adjudication criteria of vaccine-associated myocarditis. Case adjudication by cardiologists, leveraging structured data supplemented with clinical notes, is ongoing. Patients will be followed for up to 5 years to assess long-term outcomes.