The many faces of atrioventricular block in myocarditis: a case series and proposed clinical strategy highlighting cardiovascular magnetic resonance-guided diagnosis, device selection, and disease monitoring.

Background: Atrioventricular (AV) conduction disorders are a relatively rare complication in acute myocarditis. Although frequently transient in nature, persistent AV block has been reported. Cardiac magnetic resonance (CMR) imaging is critical in the diagnostic work-up and follow-up of myocarditis. This case series describes the use of CMR imaging to guide diagnosis, device selection, and disease monitoring. Case Summary: Four patients with complete AV block due to acute myocarditis underwent serial CMR imaging for diagnosis, disease monitoring, and device timing and selection. Recovery of AV conduction was variable in the presented cases. Cardiac magnetic resonance imaging was able to identify two distinct clinical scenarios of disease progress and subsequent AV conduction recovery: first, two patients (Cases 1 and 2) in which resolution of myocardial inflammation was paralleled by resolution of AV conduction disorders and, second, a patient (Case 3) in which AV block persisted even after resolution of inflammation due to the development of myocardial fibrosis. However, in one patient (Case 4), CMR was unable to adequately detect the disease progress, i.e. a patient with persistent AV block despite resolution of inflammation and no signs of myocardial fibrosis. Discussion: This case series illustrates the variable clinical course of AV conduction disorders in the context of acute myocarditis. Cardiac magnetic resonance imaging was essential in the identification of underlying myocarditis, offering insights in the disease course, and may therefore be used as an adjunctive tool for device selection. However, mismatch between CMR findings and AV conduction disorders may occur and warrants further investigation.