Final answer:
Procainamide, a potassium channel blocker, is indicated for the treatment of stable wide complex tachycardias such as ventricular tachycardia because it prolongs the refractory period of cardiac cells by slowing down phase 3 of the cardiac action potential (repolarization).
Step-by-step explanation:
Procainamide is a medication used in the treatment of certain types of wide complex tachycardias, particularly those due to ventricular tachycardia. As a potassium channel blocker, procainamide slows down the repolarization phase of the cardiac action potential, effectively lengthening the refractory period of cardiac cells. This helps in reducing abnormal rapid rhythms by decreasing the excitability of cardiac tissues. Potassium channel blockers like procainamide specifically impact the phase 3 of the cardiac action potential, which is the repolarization phase.
By impeding the movement of K+ through voltage-gated K+ channels, these medications increase the duration of the action potential and hence the refractory period. This action makes them effective in treating conditions like ventricular tachycardia which is a type of wide complex tachycardia that is stable and where procainamide is indicated as a treatment option.