Rare pattern of subendocardial injury and papillary muscle involvement in a pediatric patient with acute myocarditis. (QF_TH_062)

A previously healthy eleven-year-old girl was air-transferred in ventricular tachycardia and severe cardiogenic shock following two days of high fever, emesis and diarrhea without known sick contacts. She was intubated and placed on Veno-Arterial Extracorporeal Membrane Oxygenation (V-A ECMO), broad-spectrum antibiotics and anticoagulation per protocol. Laboratory workup revealed a blood culture (+) for Neisseria meningitidis with no other end-organ involvement. ECMO course was uneventful, and the patient tolerated weaning from mechanical support to inotropic infusions on day#5. Following hemodynamic stabilization, the patient underwent a scheduled cardiac magnetic resonance (CMR) for presumed acute myocarditis evaluation.

Diagnostic Techniques and Their Most Important Findings:

A combination of breath-holds and free-breathing acquisitions was performed uneventfully. A bolus dose of Gadobutrol (0.15ml/kg) was injected 15 minutes prior to the end. The study revealed a dilated left ventricle (LV) with globally diminished systolic function, [LV ejection fraction (EF) 25%] and apical akinesis, while the right ventricular (RV) free wall function was preserved (RV EF 31%). There was diffuse signal increase in Short TI Inversion Recovery (STIR) and native T2 time consistent with edema. Early Gadolinium enhancement with TI time of 600ms demonstrated a 5 x 3 mm hypointense lesion consistent with a thrombus along the septal apical wall. Late gadolinium enhancement (LGE) imaging demonstrated extensive linear subepicardial and mid-wall fibrosis with ring-like distribution at the basal and mid-cardiac levels. Additionally, there was transmural LGE with involvement of the subendocardial layer at the mid-septum, and all the apical segments, best visualized with dark-blood LGE sequences. Interestingly, there was significant enhancement at the base of the anterolateral papillary muscle raising concerns regarding potential left anterior descending coronary pattern ischemia. The family opted for no further invasive workup via diagnostic catheterization or endomyocardial biopsy. Eventually, a computed tomography angiography (CTA) did not demonstrate coronary obstruction. However, in the presence of an LV thrombus, the patient continued anticoagulants at a therapeutic target. Serial follow-up via echocardiography has shown mild improvement of lateral LV wall contractility, persistent apical hypokinesis and moderate mitral valve regurgitation while on optimal heart failure regimen.

Learning Points from this Case:

Despite the signature LGE pattern of non-ischemic inflammatory injury, acute myocardial inflammation may present with atypical, infract-like picture leading to diagnostic and management ambiguity. Acute myocarditis with subendocardial involvement is an underrecognized phenotype associated with worse clinical prognosis. Risk factors such as septicemia and shock, severe myocardial dysfunction, ventricular arrhythmia, ECMO exposure and diffuse immune response should raise clinical suspicion of the diagnosing CMR team.