Intra-atrial block after COVID-19 vaccination-induced fulminant myocarditis: a case report.

Background: Myocarditis is associated with an increased risk of conduction disturbances during the acute phase, which recovers in most cases but rarely recurs during the chronic phase. Case summary: A 50-year-old man who developed fulminant myocarditis after COVID-19 mRNA vaccination was discharged 24 days after admission. He was readmitted for heart failure associated with two P waves: one P wave (P1) had a normal amplitude and was dissociated from the QRS, and the other (P2) had a very low amplitude and was associated with the QRS. The patient was referred for pacemaker implantation. Before implantation, an electrophysiological study was conducted using electro-anatomical mapping (EAM). During the P1 wave activation, the sinus rhythm spread to the right atrium but was blocked in the atrioventricular (AV) node area. During P2 activation, the activation originated from the right superior pulmonary vein (RSPV), spread to the left atrium and AV node area through the interatrial septum, and was conducted to the right ventricle, exhibiting a complete intra-atrial block with two discrete rhythms. An atrial lead was successfully placed in a narrow area in the right atrial septum where the pacing captured the left atrium and AV node area under the guidance of EAM findings. Discussion: The EAM technology has demonstrated intra-atrial block and two types of atrial rhythms, sinus and RSPV. Electro-anatomical mapping findings were also useful for identifying the ideal pacemaker implantation site. Synchrony between the left atrium and ventricle via His-Purkinje conduction, which was achieved with EAM-guided atrial septal pacing, was prioritized.