Question:
Q-T prolongation is most characteristically seen with which drug?
Q-T prolongation is most characteristically seen with which drug?
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Which class IA antiarrhythmic is the classic cause of Torsades de Pointes?
Updated On: Jun 24, 2026
- Quinidine
- Amiodarone
- Magnesium sulfate
- Lignocaine
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The Correct Option is A
Solution and Explanation
Step 1: Recall the concept. Class IA antiarrhythmics block potassium channels, prolonging repolarization and the QT interval, which can trigger Torsades de Pointes.
Step 2: Identify the drug. Quinidine is the classic class IA agent and the most common cause of drug-induced QT prolongation and Torsades among the options.
Step 3: Conclude. Option A (quinidine) is correct.
Step 4: Exclude distractors. Lignocaine (class IB) shortens or does not prolong QT, magnesium sulfate is actually used to TREAT Torsades, and although amiodarone prolongs QT it rarely causes Torsades and is not the best single answer here.
Step 2: Identify the drug. Quinidine is the classic class IA agent and the most common cause of drug-induced QT prolongation and Torsades among the options.
Step 3: Conclude. Option A (quinidine) is correct.
Step 4: Exclude distractors. Lignocaine (class IB) shortens or does not prolong QT, magnesium sulfate is actually used to TREAT Torsades, and although amiodarone prolongs QT it rarely causes Torsades and is not the best single answer here.
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