Chronic active myocarditis with spatially and temporally heterogeneous lesions causing severe heart failure and intractable atrial arrhythmia: An autopsy case report

The pathogenesis of chronic active myocarditis remains unclear. A 65-year-old man underwent permanent pacemaker implantation for sick sinus syndrome and pulmonary vein isolation for paroxysmal atrial fibrillation. Four years later, the left ventricular ejection fraction decreased from 51 % to 35 %, and the apical left ventricular inferior wall developed akinesis. Isolated cardiac sarcoidosis was suspected; however, prednisolone and optimal medical therapy failed to improve the symptoms. Even after cardiac resynchronization therapy followed by atrioventricular junction ablation for untreatable atrial tachycardia, the patient died of heart failure eight years after referral. An autopsy revealed inflammatory cell infiltration accompanied by cardiac myocytolysis in both atria and ventricles. He was diagnosed with chronic active myocarditis based on pathological findings and a persistent increase in the blood high-sensitivity cardiac troponin levels before death. The myocardium around the sinus node showed extensive and severe fibrosis with mild inflammation, suggesting a chronic inflammatory phase. In contrast, the left atrium and both ventricles showed active myocardial inflammation with fibrosis, suggesting a persistently active inflammatory phase. This case demonstrated that atrial inflammation caused intractable atrial arrhythmia, while ventricular inflammation led to biventricular heart failure, and highlighted the presence of spatially and temporally heterogeneous inflammation in chronic active myocarditis. Learning objective We describe a case of chronic active myocarditis with spatially and temporally heterogeneous lesions throughout the four cardiac chambers. Inflammatory cell infiltration was observed in both atria and ventricles. Extensive fibrosis replaced the myocardium around the sinus node, suggesting a chronic phase. The left atrium and ventricles showed active inflammation, suggesting an active phase. Atrial and ventricular inflammation led to atrial arrhythmia and heart failure, respectively.