A 62-year-old man is hospitalized for chest pain and palpitations. His past medical history is significant for coronary artery disease, ischemic cardiomyopathy, paroxysmal atrial fibrillation, and hypertension. Blood pressure on admission is 135/78 mm Hg and pulse is 78/min. During hospitalization, the patient has 2 episodes of brief loss of consciousness. ECG recording during the episodes shows polymorphic QRS complexes that change in amplitude and cycle length. Between the episodes, his ECG shows QT interval prolongation but is otherwise unremarkable. Which of the following medications is most likely responsible for this patient's condition?

Question

A 62-year-old man is hospitalized for chest pain and palpitations.  His past medical history is significant for coronary artery disease, ischemic cardiomyopathy, paroxysmal atrial fibrillation, and hypertension.  Blood pressure on admission is 135/78 mm Hg and pulse is 78/min.  During hospitalization, the patient has 2 episodes of brief loss of consciousness.  ECG recording during the episodes shows polymorphic QRS complexes that change in amplitude and cycle length.  Between the episodes, his ECG shows QT interval prolongation but is otherwise unremarkable.  Which of the following medications is most likely responsible for this patient's condition?

Quizplus · Accepted Answer

This patient's presentation (syncope and ECG findings) is suggestive of long QT syndrome with associated torsades de pointes (TdP, "twisting of points"). TdP is a form of polymorphic ventricular tachycardia characterized by QRS complexes of varying amplitude and cycle length giving the appearance that the tip of the QRS complex is "twisting" around the ECG baseline. TdP is differentiated from other forms of polymorphic ventricular tachycardia because it is always associated with a prolonged QT interval. It may terminate spontaneously or can degenerate into ventricular fibrillation and sudden cardiac death. QT prolongation may be acquired or congenital. Acquired QT prolongation is most frequently caused by electrolyte imbalances (hypokalemia, hypomagnesemia) and pharmacologic agents such as class IA and III antiarrhythmics (eg, quinidine, sotalol), antibiotics (eg, macrolides, fluoroquinolones), methadone, and antipsychotics (eg, haloperidol). Sotalol is a class III antiarrhythmic agent (K⁺ channel blocking) used for treatment of atrial fibrillation. It prolongs action potential duration, resulting in QT interval prolongation. (Choice A) Digoxin slows conduction through the atrioventricular node by augmenting vagal parasympathetic tone, and it increases cardiac contractility by inhibiting Na⁺/K⁺-ATPase (increasing intracellular calcium). It also decreases the action potential duration and can cause QT interval shortening. (Choices B and D) Diltiazem (nondihydropyridine calcium channel blocker) and metoprolol (beta-1 selective antagonist) slow the sinus node discharge rate and atrioventricular nodal conduction. These agents prolong the PR interval but do not affect the QT interval. (Choice C) Lidocaine is a class IB antiarrhythmic drug that acts by blocking sodium channels and inhibiting phase 0 depolarization. It does not prolong the QT interval. Educational objective: Torsades de pointes (TdP) refers to polymorphic ventricular tachycardia that occurs in the setting of a congenital or acquired prolonged QT interval. TdP is most commonly precipitated by medications that prolong the QT interval such as certain antiarrhythmics (sotalol, quinidine), antipsychotics (haloperidol), and antibiotics (macrolides, fluoroquinolones).

A 62-Year-Old Man Is Hospitalized for Chest Pain and Palpitations