A patient on sotalol for maintenance of sinus rhythm after cardioversion of atrial fibrillation develops syncope. ECG shows QTc of 560 ms followed by polymorphic ventricular tachycardia. Which property of sotalol best explains this event?
- A Strong sodium channel blockade causing wide QRS tachycardia
- B Dose-dependent IKr block prolonging repolarization, compounded by its beta-blocking action masking warning palpitations ✓
- C Muscarinic antagonism producing tachycardia and ischemia
- D Coronary vasospasm secondary to alpha receptor blockade
Correct answer: B. Dose-dependent IKr block prolonging repolarization, compounded by its beta-blocking action masking warning palpitations
Explanation
Sotalol combines nonselective beta-blockade with class III IKr (rapid delayed rectifier potassium current) blockade that prolongs the action potential and QT interval. Torsades de pointes risk rises with dose, hypokalemia, bradycardia, and renal impairment, so sotalol needs hospital initiation with QT monitoring. Its beta-blocking component slows heart rate, itself a torsades risk factor, and can mask prodromal palpitations. Sodium channel blockade causes QRS widening, not QT prolongation.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
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