Encainide versus flecainide for chronic atrial and junctional ectopic tachycardia.

For treatment of chronic atrial and junctional ectopic tachycardia, standard antiarrhythmic therapy has been shown to be ineffective in most patients. Both the intravenous efficacy and the oral efficacy of 2 class IC antiarrhythmic drugs, encainide and flecainide, were studied in 16 patients with atrial ectopic tachycardia and in 3 patients with junctional ectopic tachycardia, using exercise testing, 24-hour long-term electrocardiography and programmed electrical stimulation. All patients had been previously treated unsuccessfully with several antiarrhythmic drugs. In 5 patients, tachycardia was persistent; in the remaining patients, it occurred intermittently for more than 12 hours/day. Intravenous encainide, in doses ranging from 0.3 to 2.0 mg/kg body weight, was given to 5 patients with atrial ectopic tachycardia, and it terminated atrial ectopic tachycardia in all patients. Intravenous flecainide was given to 9 patients, and it terminated atrial tachycardia in 4 and slowed the tachycardia rate in 2. It terminated junctional tachycardia in 2 patients and slowed tachycardia rate in 1. During a follow-up period of 10 +/- 5 months, oral encainide, in dosages between 150 and 225 mg/day, completely suppressed atrial ectopic activity in 4 patients. In the remaining patient, encainide reduced the number of tachycardia episodes markedly but had to be withdrawn because of intolerable side effects. During a 12 +/- 11-month (median 6) follow-up, oral flecainide at dosages between 200 and 300 mg/day, completely suppressed ectopic activity in 7 patients and improved symptoms in 5. Only 1 patient failed to respond to oral flecainide. The results of this study indicate that both encainide and flecainide are effective in the treatment of chronic ectopic atrial and junctional tachycardia.