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tachycardia episodes markedly but had to be withdrawn because of intolerable side effects.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.