Proarrhythmic effects of class Ic drugs.

Three cases managed with class Ic antiarrhythmic drugs but with subsequent aggravation of arrhythmias are reported herein. A 58-year-old man given 300 mg of flecainide for atrial flutter developed sinus arrest and transient ventricular fibrillation. A 42-year-old man with a postoperative condition of tetralogy of Fallot who received 300-mg doses of flecainide for sustained ventricular tachycardia had spontaneous sustained ventricular tachycardia. A 74-year-old man given 150 mg of propafenone for atrial tachycardia developed sustained ventricular tachycardia. The present cases illustrate that class Ic drugs may exacerbate ventricular arrhythmias, and their use may reveal concealed sinus node dysfunction. This may be due to marked slowing of conduction and prolonged ventricular refractoriness, which are characteristic of the class Ic drugs; also, it is probable that the patients' underlying cardiac conditions served as contributing factors.