Category: membrane
Ventricular AP has 5 phases. Phase 0 (rapid depolarization): voltage-gated Na+ channels (Nav1.5) — CLASS I antiarrhythmics block (Ia quinidine + procainamide; Ib lidocaine + mexiletine; Ic flecainide + propafenone). Phase 1 (early repolarization): Ito1 transient outward K+. Phase 2 (plateau): L-type Ca2+ current — CLASS IV CCBs (verapamil + diltiazem) block here. Phase 3 (repolarization): IKr (hERG, KCNH2 = Kv11.1) + IKs (KCNQ1) — CLASS III (sotalol + dofetilide + ibutilide + amiodarone) block IKr → QT prolongation. Phase 4 (resting potential): inward rectifier IK1 maintains. SA + AV node: β1-AR controls If "funny current" pacemaker — β-BLOCKERS (CLASS II) slow rate. Genetic LQTS: KCNH2 LOF (LQT2, drug-induced TdP susceptibility), KCNQ1 LOF (LQT1), SCN5A GOF (LQT3).