英文原文：
ClassIProarrhythmia
ClassICdrugsarefrequentlyusedinpatientswithatrialfibrillation(AF).TheslowingofconductioninAFcanresultindevelopmentofatrialflutterwithaveryslowfluttercyclelength.Thismayresultinrarecasesin1:1atrioventricularconductionwithfastventricularratesattobpm(seeFigure18.3B).Inmanycases,fastventricularratemaybeassociatedwithmarkedQRSprolongationduetouse-dependentenhancedblockadeoffastsodiumchannelsandfurtherconductionslowing.WideQRStachycardiathuscanmimicventriculartachycardia(VT).Similarly,enhancedslowingofconductionduringsinustachycardiainpatientsreceivingflecainidehasbeenshowntobeassociatedwithdevelopmentofmonomorphicVT.Thiskindofproarrhythmiaismuchmore