A 45-year-old man arrives at the clinic with recurrent palpitations, chest discomfort, and shortness of breath. He was diagnosed with paroxysmal atrial fibrillation a year ago and was treated with rate control with a beta blocker. For hypertension and obesity, previous medical history is also important. An echocardiogram reveals left atrial enlargement, normal left ventricular ejection fraction, and no evidence of valvular disease. Holter monitoring over 24 hours reveals bursts of atrial fibrillation associated with the patient's symptoms. To maintain normal sinus rhythm, he is started on dofetilide. This medication exerts its main effect on which portion of the action potential curve?

Question

Quizplus · Accepted Answer

Eductional Objective: During phase 3 of the cardiac action potential, Class III antiarrhythmic drugs (amiodarone, sotalol, dofetilide) primarily block potassium channels and inhibit outward potassium currents, thereby prolonging repolarization and total action potential duration.

A 45-Year-Old Man Arrives at the Clinic with Recurrent Palpitations