Which of the following can cause prolongation of the QT interval due to medication effects?

• A. A congenital condition
• B. Amiodarone (and other antiarrhythmics)
• C. Acute myocardial infarction
• D. Drug-drug interactions

Answer: (B)

Prolongation of the QT interval happens when ventricular repolarization is delayed. This most often occurs when a drug blocks the delayed rectifier potassium current (IKr) that helps reset heart cells between beats, extending the action potential duration. Amiodarone and other antiarrhythmic drugs are classic examples because they block potassium channels as part of their effect, which lengthens the QT interval on the ECG. While a congenital long QT condition and acute myocardial infarction can also show a longer QT, those are not caused by a drug’s direct effect. Drug–drug interactions can sometimes raise levels of QT‑prolonging drugs, but the primary medication‑related cause here is the antiarrhythmic action. So, amiodarone (and other antiarrhythmics) best fits the idea of QT prolongation due to medication effects.