PROARRHYTHMIC EFFECTS OF CLASS IC DRUGS

Three cases managed with class Ic antiarrhythmic drugs but with subseq uent 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 posto perative condition of tetralogy of Fallot who received 300-mg doses of flecainide for sustained ventricular tachycardia had spontaneous sust ained ventricular tachycardia. A 74-year-old man given 150 mg of propa fenone for atrial tachycardia developed sustained ventricular tachycar dia. The present cases illustrate that class Ic drugs may exacerbate v entricular arrhythmias, and their use may reveal concealed sinus node dysfunction. This may be due to marked slowing of conduction and prolo nged ventricular refractoriness, which are characteristic of the class Ic drugs; also, it is probable that the patients' underlying cardiac conditions served as contributing factors.