Subacute Transient First-Degree AV Block After the Catheter Ablation of a Focal Atrial Tachycardia Originating From the Left Atrium

Atrioventricular (AV) block is a rare but severe complication of the catheter ablation of cardiac arrhythmias. It usually occurs during ablation in the right atrium close to the His bundle and the peri-AV nodal area or the left ventricle in the septal basal area. AV block occurring during the deployment of radiofrequency (RF) energy in the left atrium is much rarer and has only exceptionally been described. We present the case of a subacute transient first-degree AV block occurring late (24 h) after the catheter ablation of a symptomatic incessant focal atrial tachycardia originating from the left atrium. Spontaneous resolution of the AV block with the recovery of normal AV conduction was observed 7 days after the procedure. This case report highlights the fact that care must be exercised while performing RF ablation on the left atrial septum since AV block can occur during the ablation of areas close to the AV node. (Iranian Heart Journal 2023; 24(4): 79-84)