by egpat Posted on 09-06-2017
Yes. Class Ia agents like quinidine, procainamide, disopyramide are proarrhythmic agents that can increase QT interval predisposing to torsade de pointes.These agents show major action by blocking voltage gated sodium channels.That's why they are classified as class I agents.
At the same time, they also show potassium channel blocking activity. Since they have class III activity , the effective refractory period increases leading to increased QT interval in ECG and may precipitate torsade de pointes.
Procainamide is a class Ia antiarrhythmic agent that also shows class III activity by blocking the potassium channels.
Procainamide is metabolized by N-acetylation forming an active metabolite N-acetyl procainamide which shows class III activity.