Importance The BNT162b2 (Pfizer-BioNTech) messenger RNA COVID-19 vaccine was authorized on May 10, 2021, for emergency use in children aged 12 years and older. Initial reports showed that the vaccine was well tolerated without serious adverse events; however, cases of myocarditis have been reported since approval.

Objective To review results of comprehensive cardiac imaging in children with myocarditis after COVID-19 vaccine.

Design, Setting, and Participants This study was a case series of children younger than 19 years hospitalized with myocarditis within 30 days of BNT162b2 messenger RNA COVID-19 vaccine. The setting was a single-center pediatric referral facility, and admissions occurred between May 1 and July 15, 2021.

Main Outcomes and Measures All patients underwent cardiac evaluation including an electrocardiogram, echocardiogram, and cardiac magnetic resonance imaging.

Results Fifteen patients (14 male patients [93%]; median age, 15 years [range, 12-18 years]) were hospitalized for management of myocarditis after receiving the BNT162b2 (Pfizer) vaccine. Symptoms started 1 to 6 days after receipt of the vaccine and included chest pain in 15 patients (100%), fever in 10 patients (67%), myalgia in 8 patients (53%), and headache in 6 patients (40%). Troponin levels were elevated in all patients at admission (median, 0.25 ng/mL [range, 0.08-3.15 ng/mL]) and peaked 0.1 to 2.3 days after admission. By echocardiographic examination, decreased left ventricular (LV) ejection fraction (EF) was present in 3 patients (20%), and abnormal global longitudinal or circumferential strain was present in 5 patients (33%). No patient had a pericardial effusion. Cardiac magnetic resonance imaging findings were consistent with myocarditis in 13 patients (87%) including late gadolinium enhancement in 12 patients (80%), regional hyperintensity on T2-weighted imaging in 2 patients (13%), elevated extracellular volume fraction in 3 patients (20%), and elevated LV global native T1 in 2 patients (20%). No patient required intensive care unit admission, and median hospital length of stay was 2 days (range 1-5). At follow-up 1 to 13 days after hospital discharge, 11 patients (73%) had resolution of symptoms. One patient (7%) had persistent borderline low LV systolic function on echocardiogram (EF 54%). Troponin levels remained mildly elevated in 3 patients (20%). One patient (7%) had nonsustained ventricular tachycardia on ambulatory monitor.

Conclusions and Relevance In this small case series study, myocarditis was diagnosed in children after COVID-19 vaccination, most commonly in boys after the second dose. In this case series, in short-term follow-up, patients were mildly affected. The long-term risks associated with postvaccination myocarditis remain unknown. Larger studies with longer follow-up are needed to inform recommendations for COVID-19 vaccination in this population.

重要性 BNT162b2 (Pfizer-BioNTech) 信使 RNA COVID-19 疫苗于 2021 年 5 月 10 日获得授权，可用于 12 岁及以上儿童的紧急使用。初步报告显示，疫苗耐受性良好，没有严重的不良事件；然而，自批准以来已报告了心肌炎病例。

目的 回顾COVID-19疫苗接种后心肌炎患儿的综合心脏影像学检查结果。

设计、设置和参与者 本研究是一组病例系列，涉及在 BNT162b2 信使 RNA COVID-19 疫苗接种 30 天内因心肌炎住院的 19 岁以下儿童。该设置是一个单中心儿科转诊机构，入院时间为 2021 年 5 月 1 日至 7 月 15 日。

主要结果和措施 所有患者都接受了心脏评估，包括心电图、超声心动图和心脏磁共振成像。

结果 15 名患者（14 名男性患者 [93%]；中位年龄，15 岁 [范围，12-18 岁]）在接受 BNT162b2（辉瑞）疫苗后住院治疗心肌炎。接种疫苗后 1 至 6 天出现症状，包括 15 名患者 (100%) 的胸痛、10 名患者 (67%) 的发热、8 名患者 (53%) 的肌痛和 6 名患者 (40%) 的头痛. 所有患者入院时肌钙蛋白水平均升高（中位数，0.25 ng/mL [范围，0.08-3.15 ng/mL]），入院后 0.1 至 2.3 天达到峰值。通过超声心动图检查，3 名患者 (20%) 出现左心室 (LV) 射血分数 (EF) 降低，5 名患者 (33%) 出现异常的整体纵向或周向应变。没有患者出现心包积液。13 名患者 (87%) 的心脏磁共振成像结果与心肌炎一致，包括 12 名患者 (80%) 的晚期钆增强，2 名患者 (13%) 的 T2 加权成像区域高信号，3 名患者的细胞外体积分数升高(20%)，以及 2 名患者 (20%) 的 LV 整体天然 T1 升高。没有患者需要入住重症监护病房，住院时间中位数为 2 天（范围 1-5）。在出院后 1 至 13 天的随访中，11 名患者 (73%) 的症状得到缓解。一名患者 (7%) 的超声心动图显示左室收缩功能持续临界低 (EF 54%)。3 名患者 (20%) 的肌钙蛋白水平保持轻度升高。1 名患者 (7%) 在动态监护仪上出现非持续性室性心动过速。

结论和相关性 在这项小型病例系列研究中，儿童在接种 COVID-19 后诊断出心肌炎，最常见于第二次接种后的男孩。在这个病例系列中，在短期随访中，患者受到轻微影响。与疫苗接种后心肌炎相关的长期风险仍然未知。需要进行更大规模、随访时间更长的研究来为该人群中的 COVID-19 疫苗接种提供建议。