Atrial-Specific KCNQ1 Channelopathy Drives Arrhythmogenesis and Unmasks Amiodarone Proarrhythmia in a Human iPSC Model

Background : While KCNQ1 mutations (I _Ks channel α-subunit) are known to cause long QT syndrome (LQTS) presenting with atrial fibrillation (AF), the underlying mechanisms remain incompletely characterized. Methods : We report a novel KCNQ1 c.625T>C (p.Ser209Pro) mutation identified through whole-exome sequencing and Sanger validation in a LQTS pedigree with atypical AF presentation. Utilizing non-invasive urine-derived epithelial cells, we generated integration-free induced pluripotent stem cells (iPSCs) from patients (S209P-iPSC) and established precise homozygous repair of the mutation via CRISPR/Cas9 to create isogenic controls (GC-iPSC), complemented by healthy control iPSCs (CTRL-iPSC). Critically, we developed an atrial-specific differentiation protocol yielding patient-derived atrial cardiomyocytes (aCMs). Patch-clamp and multi-electrode array electrophysiological analyses revealed prolonged action potential duration and delayed repolarization in mutant aCMs—providing the first direct evidence that KCNQ1 dysfunction drives AF susceptibility through impaired atrial repolarization, resolving a key mechanistic gap in channelopathy-associated arrhythmogenesis. Results : Electrophysiological analysis revealed the KCNQ1 c.625T>C mutation induces a tissue-specific channelopathy: patient-derived aCMs exhibited significantly prolonged field potential duration (FPDc) and reduced I _Ks current versus controls – indicating distinct atrial-selective repolarization impairment. Crucially, antiarrhythmic testing uncovered paradoxical responses: amiodarone, though clinically used for AF prevention, exacerbated atrial pathology by further prolonging FPDc in dose-dependent fashion and inducing torsade de pointes-like arrhythmias in mutant atrial cells, whereas nadolol normalized FPDc. This mechanistic discordance manifested clinically where amiodarone failed to terminate AF but induced long QT in familial patients – providing the first direct evidence of KCNQ1-mediated atrial vulnerability to proarrhythmic drug effects. Conclusion : The KCNQ1 c.625T>C mutation causes atrial-specific delayed repolarization via I _Ks reduction, driving AF in LQTS. We resolve the amiodarone proarrhythmia paradox and establish CRISPR-edited iPSC-atrial myocytes as a transformative platform for precision antiarrhythmic therapy.