Systemic light chain cardiac amyloidosis with atrioventricular block

Background: Systemic light-chain (AL) amyloidosis is a rare plasma cell disorder with an annual incidence of approximately 8-12 cases per million population in regions with advanced diagnostic capabilities. Cardiac involvement occurs in 60%-75% of patients, and without treatment, the median survival is only six months. Atrioventricular (AV) conduction block affects approximately 3%-5% of AL patients. Although current therapies can induce deep hematologic remission and often significantly reverse myocardial structural and functional abnormalities, residual amyloid deposits may still trigger delayed, life-threatening conduction system events. Illustrative case: We describe a representative 50-year-old male patient with AL cardiac amyloidosis who achieved deep hematologic remission after standard anti-plasma cell therapy and autologous stem cell transplantation. Echocardiography demonstrated marked improvement in both myocardial structure and systolic/diastolic function. Nevertheless, he presented with syncope. An implantable cardiac monitor (ICM) captured a 7-second episode of asystole. A permanent pacemaker was subsequently implanted, resulting in complete resolution of syncope. Notably, atrial arrhythmias markedly decreased thereafter, and no episodes of paroxysmal atrial fibrillation have been documented on serial ambulatory electrocardiography or remote ICM monitoring during follow-up. Conclusions: This case highlights a crucial principle in the management of AL amyloidosis: improvement in hematologic status and cardiac structure/function does not equate to electrophysiologic stability. In high-risk patients, vigilance for occult conduction disease must persist even after clinical recovery. The ICM serves as a pivotal "bridge" tool to detect intermittent, life-threatening bradyarrhythmias and guide timely, precise device-based intervention. These findings underscore the need for individualized, long-term cardiac electrophysiological monitoring strategies in patients with AL-CA.