Which of the following is NOT known to prolong the QT interval and carry a risk of torsades de pointes?

• A. Sotalol
• B. Ibutilide
• C. Procainamide
• D. Lidocaine

Answer: (D)

The key idea is how drugs affect the heart’s repolarization and the risk of torsades de pointes. Drugs that block potassium channels and delay repolarization tend to lengthen the QT interval and can trigger torsades de pointes, especially with electrolyte disturbances or other QT-prolonging drugs.

Sotalol and ibutilide are both class III antiarrhythmics that markedly slow repolarization by blocking potassium channels, so they reliably prolong the QT interval and carry a risk of torsades de pointes. Procainamide, a class IA drug, also lengthens the QT by delaying repolarization, so it can contribute to torsades, though its risk profile differs and is generally linked to its QT prolongation effect.

Lidocaine, on the other hand, is a class IB sodium channel blocker. It primarily acts on depolarized/ischemic tissue and has little to no effect on the overall QT interval; it does not prolong repolarization and is not associated with torsades de pointes.