Which Vaughan Williams class prolongs the action potential and effective refractory period?

Which Vaughan Williams class prolongs the action potential and effective refractory period?

• A. Class 1a
• B. Class 2
• C. Class 1b
• D. Class 3

Answer: (D)

Class III antiarrhythmics slow repolarization by blocking outward potassium currents, which lengthens the action potential duration and the effective refractory period. By delaying phase 3 of the action potential, the heart tissue remains refractory for a longer time after each beat, reducing the likelihood of re-entrant circuits that cause tachyarrhythmias. This mechanism also manifests on the ECG as QT interval prolongation. Drugs in this class, such as amiodarone, sotalol, dofetilide, and ibutilide, are used to treat various tachyarrhythmias, but they carry a risk of proarrhythmia like torsades de pointes and require careful monitoring. Other classes focus more on slowing conduction or automaticity rather than extending repolarization, so they do not robustly prolong the action potential duration and ERP in the way Class III does.

Class III antiarrhythmics slow repolarization by blocking outward potassium currents, which lengthens the action potential duration and the effective refractory period. By delaying phase 3 of the action potential, the heart tissue remains refractory for a longer time after each beat, reducing the likelihood of re-entrant circuits that cause tachyarrhythmias. This mechanism also manifests on the ECG as QT interval prolongation. Drugs in this class, such as amiodarone, sotalol, dofetilide, and ibutilide, are used to treat various tachyarrhythmias, but they carry a risk of proarrhythmia like torsades de pointes and require careful monitoring. Other classes focus more on slowing conduction or automaticity rather than extending repolarization, so they do not robustly prolong the action potential duration and ERP in the way Class III does.