Treatment of ectopic atrial arrhythmias and premature atrial complexes in adults with encainide.

Few studies of the antiarrhythmic effects of encainide have included patients with primary atrial tachycardias and premature atrial contractions (PACs). In this review, 11 patients with primary atrial tachycardia and 10 patients with symptomatic PACs were abstracted from all studies known to have been performed. These patients had been shown to be highly resistant to prior antiarrhythmic treatments. Intravenous encainide terminated a primary atrial tachycardia in 4 of 4 patients, 3 of whom had an incessant arrhythmia, and oral encainide was effective or partially effective in 6 of 10 patients treated for an average of 2.9 years with a mean dosage of 156 mg/day. Intravenous encainide was effective or partially effective in 8 of 10 patients with symptomatic PACs, and oral encainide was effective or partially effective in 6 of 9 patients treated for an average of 1.8 years with a mean dosage of 114 mg/day. The median number of PACs per hour on Holter recording was reduced from a baseline rate of 1,139/hour to 166/hour at 3 to 5 months of treatment (p = 0.001). Adverse effects were modest. The mechanism of action of encainide in these arrhythmias appears to be depression of ectopic pacemaker activity.