A 55-year-old woman started on sotalol for paroxysmal atrial fibrillation presents with syncope. ECG shows QTc of 560 ms with polymorphic ventricular tachycardia. The property of sotalol most responsible for this complication is:
- A Strong sodium channel blockade with marked QRS widening
- B Selective atrial potassium channel blockade
- C Dose-related IKr blockade that prolongs action potential duration, combined with beta-blockade masking warning palpitations ✓
- D Calcium channel blockade causing bradycardia
Correct answer: C. Dose-related IKr blockade that prolongs action potential duration, combined with beta-blockade masking warning palpitations
Explanation
Sotalol is a racemic mixture: the d-isomer blocks the rapid component of the delayed rectifier potassium current (IKr), prolonging repolarization and the QT interval in a dose-related fashion, while the l-isomer provides beta-blockade. Torsades de pointes risk rises with higher doses, hypokalemia, and renal impairment, since sotalol is renally cleared. It has no significant sodium or calcium channel blocking activity.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.