A 56-year-old man arrives at the emergency department after experiencing palpitations and lightheadedness for the past two hours. He has a history of hypertension but no other cardiac conditions, and he has never previously experienced similar symptoms. The patient consumes 1 to 2 alcoholic beverages per day but does not smoke or use illegal drugs. The blood pressure is 132/76 mm Hg, and the pulse rate is 116 bpm, which is irregular. Except for tachycardia, the cardiopulmonary examination is normal. The resting ECG reveals atrial fibrillation. Transesophageal echocardiography is performed on the patient, which reveals normal cardiac anatomy and no intracardiac thrombi. Electrical cardioversion is carried out. Sinus rhythm is restored following the intervention, and amiodarone therapy is started to maintain normal sinus rhythm. Which of the following cardiac electrophysiologic changes are most likely to occur in this patient due to the medication?

Question

Quizplus · Accepted Answer

Eductional Objective: Amiodarone works primarily as a class III antiarrhythmic, slowing ventricular repolarization and prolonging the QT interval by inhibiting the delayed rectifier potassium current. It also inhibits fast sodium channels (class I effect) to slow ventricular depolarization and prolong the duration of the QRS complex. Beta blockade (class II effect) and slow L-type calcium channel inhibition (class IV effect) slow conduction in the sinus node and atrioventricular node, resulting in a lower sinus rate and a longer PR interval.

A 56-Year-Old Man Arrives at the Emergency Department After Experiencing