A patient with atrial fibrillation started on sotalol for rhythm control presents two weeks later with presyncope. ECG shows a corrected QT interval of 540 ms with runs of polymorphic ventricular tachycardia. Which property of sotalol most accounts for this presentation?
- A It accumulates only in patients with hepatic impairment
- B It shortens the action potential duration through potassium channel activation
- C Its incidence of torsades de pointes rises steeply with dose and is highest among class III agents ✓
- D Its beta-blocking component directly triggers triggered activity in the sinus node
Correct answer: C. Its incidence of torsades de pointes rises steeply with dose and is highest among class III agents
Explanation
Sotalol combines nonselective beta-blockade with class III IKr (rapid delayed rectifier potassium current) blockade, producing dose-dependent QT prolongation. Torsades de pointes occurs in roughly 2 to 4 percent of patients, with risk rising sharply above total daily doses of 320 mg and with renal impairment, since sotalol is almost entirely renally cleared. It lengthens rather than shortens repolarization. The beta-blocking moiety is protective against sudden death but does not cause torsades itself.
Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.
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