Parametric Mapping Cardiac Magnetic Resonance Imaging for the Diagnosis of Myocarditis in Children in the Era of COVID-19 and MIS-C

Abstract

Myocarditis comprises many clinical presentations ranging from asymptomatic to sudden cardiac death. The history, physical examination, cardiac biomarkers, inflammatory markers, and electrocardiogram are usually helpful in the initial assessment of suspected acute myocarditis. Echocardiography is the primary tool to detect ventricular wall motion abnormalities, pericardial effusion, valvular regurgitation, and impaired function. The advancement of cardiac magnetic resonance (CMR) imaging has been helpful in clinical practice for diagnosing myocarditis. A recent Scientific Statement by the American Heart Association suggested CMR as a confirmatory test to diagnose acute myocarditis in children. However, standard CMR parametric mapping parameters for diagnosing myocarditis are unavailable in pediatric patients for consistency and reliability in the interpretation. The present review highlights the unmet clinical needs for standard CMR parametric criteria for diagnosing acute and chronic myocarditis in children and differentiating dilated chronic myocarditis phenotype from idiopathic dilated cardiomyopathy. Of particular relevance to today's practice, we also assess the potential and limitations of CMR to diagnose acute myocarditis in children exposed to severe acute respiratory syndrome coronavirus-2 infections. The latter section will discuss the multi-inflammatory syndrome in children (MIS-C) and mRNA coronavirus disease 19 vaccine-associated myocarditis.

Keywords: COVID-19; cardiac MRI; children; mRNA COVID-19 vaccine; multisystem inflammatory syndrome in children; myocarditis.

Figure 1

T1 mapping demonstrates a global increase in myocardial T1 relaxation times at the base (A), mid-ventricular level (B), and the apex (C). The average left ventricular myocardial T1 relaxation time is prolonged (1067 ms), and myocardial extracellular volume is elevated (32%).

Figure 2

T2 mapping demonstrating the regional increase in myocardial T2 relaxation times at the basal anteroseptal and anterolateral segments (A), with normal T2 times at the mid-ventricular level (B) and the apex (C). Clinical vignette: A 20-month-old female with myocarditis associated with rhino/enterovirus, rapid left ventricular ejection fraction recovery from 24% to 48%, elevated troponin, and diffuse low voltage QRS complexes on electrocardiogram. There was no evidence of myocardial delayed enhancement after gadolinium contrast emphasizing the additional utility of T1 and T2 mapping in the evaluation of myocarditis.

Figure 3

Late gadolinium enhancement (LGE) imaging allows the noninvasive visualization of areas affected by myocardial scar, conferring clinicians the unique ability to differentiate ischemic from nonischemic lesions based on typical LGE patterns.

Figure 4

CMR in an adolescent with acute myocarditis: (A) Shows subepicardial early gadolinium enhancement (EGE) (white arrow); (B) Shows subepicardial LGE (white arrow).

Figure 5

T1 mapping demonstrating the global increase in myocardial T1 relaxation times at the base (A), mid-ventricular level (B), and the apex (C). The average left ventricular myocardial T1 relaxation time is mildly prolonged (1077 ms).

Figure 6

T2 mapping demonstrating normal myocardial T2 relaxation times at the base (A), mid-ventricular level (B), and at the apex (C). Clinical vignette: 12-year-old female with possible chronic myocarditis associated with Parvovirus B19, dilated LV with decreased LVEF 22%.

Figure 7

Several putative mechanisms of myocarditis due to SARS-CoV-2 and other common cardiotropic viruses.

Figure 8

LGE in the mid myocardium of the inferior and lateral wall (white arrows). Clinical vignette: 15-year-old-female soccer player with COVID-19-associated myocarditis. This subject reported shortness of breath and chest pain with activity and was found to have ventricular ectopy and non-sustained runs of ventricular tachycardia on Holter monitoring.

Figure 9

CMR shows no LGE (A) but diffusely elevated T1 time (B).

Figure 10

A 16-year-old-male with mRNA COVID-19 vaccine-associated myocarditis. (A) subepicardial LGE (white arrow); (B) subepicardial LGE (white arrow); (C) early gadolinium enhancement (EGE) (white arrow); and (D) shows enhanced T2 signal (white arrow).