Progressive Conduction System Disease in Hydroxychloroquine Cardiotoxicity: A Call for Early Vigilance.

Hydroxychloroquine (HCQ) cardiotoxicity is increasingly recognized, yet progressive conduction system disease remains underappreciated and may represent a lethal phenotype. We report a 67-year-old female on chronic HCQ who developed progressive conduction abnormalities culminating in cardiogenic shock and sudden death despite initial stabilization with isolated atrial pacing. Autopsy revealed extensive sinoatrial and atrioventricular nodal lysosomal toxicity and fibrosis confirming irreversible conduction injury. This case highlights the lysosomal basis of HCQ toxicity and reframes conduction disease as a primary, irreversible manifestation. Vigilant ECG surveillance and early consideration of dual-chamber pacing may prevent catastrophic outcomes in patients on chronic HCQ therapy.