TRC: Class III drugs

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:

Extra info: Amiodarone has diverse side effects, which should be monitored.

Option explanation:

worsening of the existing arrhythmia

corneal microdeposits

blue-grey skin discoloration

equilibrium disorders

Correct statements concerning sotalol include all EXCEPT:

Option explanation:

prolongs action potential duration and effective refractory period by blocking sodium channels.

prolongs cell repolarization by blocking potassium channels.

prolongs Q-T interval

increases effective refractory period

Appropriate monitoring parameters for a patient on amiodarone therapy include

Extra info: These parameters need to be monitored because amiodarone can cause pulmonary fibrosis, hypothyroidism, and increased levels of liver enzymes.

Option explanation:

baseline chest X-ray, liver function test and thyroid function test

baseline pulmonary function test, and BUN

baseline thyroid function test, WBC, and platelets

baseline liver function test, WBC, and platelets