Which class does Quinidine belong to?

Which class does Quinidine belong to?

• A. Type 1A
• B. Type 1B
• C. Type 2
• D. Type 3

Answer: (A)

Quinidine is a class IA antiarrhythmic agent. It blocks fast sodium channels in cardiac tissue, which slows the phase 0 upstroke and conduction velocity. At the same time, it prolongs repolarization by delaying potassium efflux, lengthening the action potential duration and increasing the refractory period. This combination—slowed conduction plus longer repolarization—defines the IA group and sets it apart from the other sodium channel blockers, which either shorten the action potential (class IB) or have a strong block with little effect on repolarization (class IC). The other major classes, such as beta-blockers (class II) and potassium channel blockers (class III), act through different mechanisms. Remember the clinical caveat: quinidine can prolong the QT interval and carry proarrhythmic risk, so its use is carefully considered.

Quinidine is a class IA antiarrhythmic agent. It blocks fast sodium channels in cardiac tissue, which slows the phase 0 upstroke and conduction velocity. At the same time, it prolongs repolarization by delaying potassium efflux, lengthening the action potential duration and increasing the refractory period. This combination—slowed conduction plus longer repolarization—defines the IA group and sets it apart from the other sodium channel blockers, which either shorten the action potential (class IB) or have a strong block with little effect on repolarization (class IC). The other major classes, such as beta-blockers (class II) and potassium channel blockers (class III), act through different mechanisms. Remember the clinical caveat: quinidine can prolong the QT interval and carry proarrhythmic risk, so its use is carefully considered.