<prompt> Which one of the following drugs is most likely to block K channels in the heart responsible for the delayed rectifier current?AmiodaroneEncainideLidocainePhenytoin  <response>: Amiodarone is a highly effective antiarrhythmic drug, in part because of its multiple actions, which include Na channel block, beta adrenoceptor block, K channel block, and Ca channel block. Drugs that block K channels which include class IA and class III antiarrhythmics prolong APD and ERP and predispose toward torsades de pointes ventricular arrhythmias. Encainide is a class IC drug, lidocaine and phenytoin are class IB, and verapamil is class IV, none of which inhibits the delayed rectifier K current responsible for membrane repolarization during the cardiac action potential. 