A 54-year-old man is evaluated for paroxysmal atrial fibrillation. During the episodes, the patient experiences palpitations, chest tightness, light-headedness, and shortness of breath. Medical history is significant for asthma, hypertension, and diet-controlled diabetes mellitus. Prior testing showed normal left ventricular ejection fraction, no evidence of valvular disease, and no obstructive coronary artery disease. It is decided to proceed with dofetilide therapy. Initiation of this therapy increases this patient's risk for which of the following?

Question

A 54-year-old man is evaluated for paroxysmal atrial fibrillation.  During the episodes, the patient experiences palpitations, chest tightness, light-headedness, and shortness of breath.  Medical history is significant for asthma, hypertension, and diet-controlled diabetes mellitus.  Prior testing showed normal left ventricular ejection fraction, no evidence of valvular disease, and no obstructive coronary artery disease.  It is decided to proceed with dofetilide therapy.  Initiation of this therapy increases this patient's risk for which of the following?

Quizplus · Accepted Answer

11ec160b_3ba2_f81f_9249_754750b95972_MD0001_00 Relatively young patients with symptomatic paroxysmal atrial fibrillation are often treated with a rhythm-control strategy to restore and maintain normal sinus rhythm and to eliminate symptoms. Antiarrhythmic drugs commonly used for rhythm control of atrial fibrillation include class IC (eg, flecainide, propafenone) and class III (eg, ibutilide, dofetilide) agents. Dofetilide and ibutilide selectively block the rapid component of the delayed-rectifier potassium current. This slows repolarization and prolongs action potential duration and the effective refractory period in cardiomyocytes, suppressing the electrical foci that lead to atrial fibrillation. As a result, the QT interval is prolonged, leading to an increased risk of torsade de pointes, a form of polymorphic ventricular tachycardia that can cause syncope and sudden cardiac death. To minimize this risk, dofetilide or ibutilide therapy is started only in the hospital with temporary cardiac monitoring. (Choice A) Adenosine can trigger bronchospasm, likely by stimulating the release of histamine and leukotrienes from mast cells. Class III antiarrhythmics are not associated with bronchospasm. (Choice B) Beta blockers (via inhibition of beta-1 receptor-driven chronotropy) and nondihydropyridine calcium channel blockers (via blockade of L-type atrioventricular [AV] node calcium channels) slow AV node conduction and in overdose can cause complete AV block. Digoxin (via enhanced vagal tone) and adenosine can also cause AV block. Although some class III antiarrhythmics (ie, sotalol, amiodarone) have negative chronotropic effects and may slow AV node conduction, dofetilide and ibutilide have no significant effect on AV node conduction. (Choice D) Amiodarone can disrupt thyroid function and lead to hyper- or hypothyroidism, but dofetilide and other class III antiarrhythmics do not affect thyroid function. Compared with other class III antiarrhythmics, amiodarone is associated with a lower risk of torsade de pointes. (Choice E) Most antiarrhythmic drugs, including class III, are not associated with an increased risk of venous thromboembolism. (Choice F) Digoxin toxicity can cause visual disturbances consisting of blurred or yellow vision, but visual disturbance is not an adverse effect of class III antiarrhythmics. Educational objective: Dofetilide and ibutilide are class III antiarrhythmics that treat atrial fibrillation by blocking the rapid component of the delayed-rectifier potassium current to slow repolarization and increase the effective refractory period. As a result, the QT interval is prolonged, creating an increased risk of polymorphic ventricular tachycardia (torsade de pointes). __________ References: 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society. (http://www.ncbi.nlm.nih.gov/pubmed/24685669) Safety of oral dofetilide for rhythm control of atrial fibrillation and atrial flutter. (http://www.ncbi.nlm.nih.gov/pubmed/26063741)

A 54-Year-Old Man Is Evaluated for Paroxysmal Atrial Fibrillation