Clinically Suspected Myocarditis Temporally Related to COVID-19 Vaccination in Adolescents and Young Adults: Suspected Myocarditis After COVID-19 Vaccination
Authors: Truong Dongngan T. , Dionne Audrey , Muniz Juan Carlos , McHugh Kimberly E. , Portman Michael A. , Lambert Linda M. , Thacker Deepika , Elias Matthew D. , Li Jennifer S. , Toro-Salazar Olga H. , Anderson Brett R. , Atz Andrew M. , Bohun C. Monique , Campbell M. Jay , Chrisant Maryanne , D’Addese Laura , Dummer Kirsten B. , Forsha Daniel , Frank Lowell H. , Frosch Olivia H. , Gelehrter Sarah K. , Giglia Therese M. , Hebson Camden , Jain Supriya S. , Johnston Pace , Krishnan Anita , Lombardi Kristin C. , McCrindle Brian W. , Mitchell Elizabeth C. , Miyata Koichi , Mizzi Trent , Parker Robert M. , Patel Jyoti K. , Ronai Christina , Sabati Arash A. , Schauer Jenna , Sexson Tejtel S. Kristen , Shea J. Ryan , Shekerdemian Lara S. , Srivastava Shubhika , Votava-Smith Jodie K. , White Sarah , Newburger Jane W. 
Published: December 2021

Background:
Understanding the clinical course and short-term outcomes of suspected myocarditis after the coronavirus disease 2019 (COVID-19) vaccination has important public health implications in the decision to vaccinate youth.

Methods:
We retrospectively collected data on patients <21 years old presenting before July 4, 2021, with suspected myocarditis within 30 days of COVID-19 vaccination. Lake Louise criteria were used for cardiac MRI findings. Myocarditis cases were classified as confirmed or probable on the basis of the Centers for Disease Control and Prevention definitions.

Results:
We report on 139 adolescents and young adults with 140 episodes of suspected myocarditis (49 confirmed, 91 probable) at 26 centers. Most patients were male (n=126, 90.6%) and White (n=92, 66.2%); 29 (20.9%) were Hispanic; and the median age was 15.8 years (range, 12.1–20.3; interquartile range [IQR], 14.5–17.0). Suspected myocarditis occurred in 136 patients (97.8%) after the mRNA vaccine, with 131 (94.2%) after the Pfizer-BioNTech vaccine; 128 (91.4%) occurred after the second dose. Symptoms started at a median of 2 days (range, 0–22; IQR, 1–3) after vaccination. The most common symptom was chest pain (99.3%). Patients were treated with nonsteroidal anti-inflammatory drugs (81.3%), intravenous immunoglobulin (21.6%), glucocorticoids (21.6%), colchicine (7.9%), or no anti-inflammatory therapies (8.6%). Twenty-six patients (18.7%) were in the intensive care unit, 2 were treated with inotropic/vasoactive support, and none required extracorporeal membrane oxygenation or died. Median hospital stay was 2 days (range, 0–10; IQR, 2–3). All patients had elevated troponin I (n=111, 8.12 ng/mL; IQR, 3.50–15.90) or T (n=28, 0.61 ng/mL; IQR, 0.25–1.30); 69.8% had abnormal ECGs and arrhythmias (7 with nonsustained ventricular tachycardia); and 18.7% had left ventricular ejection fraction <55% on echocardiogram. Of 97 patients who underwent cardiac MRI at a median 5 days (range, 0–88; IQR, 3–17) from symptom onset, 75 (77.3%) had abnormal findings: 74 (76.3%) had late gadolinium enhancement, 54 (55.7%) had myocardial edema, and 49 (50.5%) met Lake Louise criteria. Among 26 patients with left ventricular ejection fraction <55% on echocardiogram, all with follow-up had normalized function (n=25).

Conclusions:
Most cases of suspected COVID-19 vaccine myocarditis occurring in persons <21 years have a mild clinical course with rapid resolution of symptoms. Abnormal findings on cardiac MRI were frequent. Future studies should evaluate risk factors, mechanisms, and long-term outcomes.