Class III antiarrhythmics

Class III antiarrhythmics

Class III antiarrhythmics act by blocking potassium channels, prolonging the repolarization. Overall, they prolong the duration of the action potential without affecting the resting potential and depolarization. On the ECG, these drugs produce a prolonged QT interval. As these agents do not affect the sodium channel, conduction velocity is not decreased. The prolongation of the action potential duration and refractory period, combined with the maintenance of normal conduction velocity, prevent reentrant arrhythmias. Amiodarone unifies effects of all antiarrhythmic drug classes. It slows down

the SA node, it delays the refractory period, and it delays the conduction through the AV node and bundle of His. Amiodarone is indicated for the treatment of refractory VT or VF, particularly in the setting of acute ischaemia. Amiodarone is also safe to use in individuals with cardiomyopathy and atrial fibrillation, in order to maintain normal sinus rhythm. The plasma half-life measures 20–100 days, which means that the action of amiodarone is maintained even after stopping therapy. The cardiovascular adverse effects of amiodarone are bradycardia and heart block; other adverse effects can be more severe and require close monitoring: thyroid abnormalities, corneal deposits, pulmonary disorders, liver problems, and skin pigmentation. Sotalol is indicated for the treatment of atrial or ventricular tachyarrhythmias, and for AV nodal reentrant arrhythmias.


Known adverse effects of amiodarone include all of the following EXCEPT:


Correct statements concerning sotalol include all EXCEPT:


Appropriate monitoring parameters for a patient on amiodarone therapy include