Inflammatory infiltration of the cardiac conduction system in acute lymphocytic myocarditis.

A 53-year-old man with prior history of bone marrow transplant after acute myeloblastic leukaemia was admitted in the acute cardiac care unit due to suspected acute myocarditis. At admission, his electrocardiogram (ECG) showed right bundle branch block and left anterior fascicular block (Panel A). Previously, he had been assessed regularly in a dedicated cardio-oncology clinic, with normal ECG and transthoracic echocardiography (see Supplementary material online, Videos S1 and S2). Despite high-dose pulses of methylprednisolone, he developed both complete atrio-ventricular (AV) block and progressive left ventricular systolic dysfunction (see Supplementary material online, Videos S3 and S4), leading to cardiogenic shock requiring temporary transvenous pacing and mechanical circulatory support with VA-ECMO. However, he died on day 9 due to multiorgan failure. Gross examination of the heart (Panel B) was normal, but histopathology and immunohistochemistry showed significant infiltration of the ventricular myocardium (Panel C), AV node (Panel D) left anterior fascicle (Panel E), and right bundle branch (Panel F) by mononuclear CD3 + T cells, consistent with the diagnosis of lymphocytic myocarditis. High-definition images S1-S8 are included in the Supplementary material online.