Quinidine, Serum or Plasma

This Class 1A drug is useful in both supraventricular and ventricular arrhythmias. It major uses are to maintain sinus rhythm after conversion of atrial flutter or fibrillation, to prevent ventricular tachycardia, and for long-term prophylaxis in patients with AV nodal reentrant tachycardia and automatic atrial tachycardia. Quinidine also has been used to prevent symptomatic premature supraventricular and ventricular complexes. Because it slows conduction and prolongs the refractory period of the accessory pathway and suppresses automaticity of ectopic pacemakers, quinidine may prevent recurrences of paroxysmal supraventricular tachycardia caused by reentry over a concealed pathway or AV reciprocating tachycardia associated with the Wolff-Parkinson-White syndrome. It also may slow the ventricular response to atrial flutter or fibrillation in the preëxcitation syndrome. Quinidine is often preferred to procainamide for long-term therapy because elevated antinuclear antibody titers and drug-induced lupus are common during prolonged therapy with procainamide.