In the treatment of chronic
ectopic atrial tachycardia, standard antiarrhythmic
therapy has been shown to be ineffective in the majority of patients. The intravenous and oral effects of two class IC
antiarrhythmic drugs,
encainide and
flecainide, in five patients with chronic
ectopic atrial tachycardia were studied using exercise testing, 24 hour long-term electrocardiography and programmed electrical stimulation. All patients had been treated unsuccessfully with at least four
antiarrhythmic drugs. In two patients
tachycardia was persistent, and in three patients
tachycardia occurred intermittently for more than 12 hours/day. Intravenous
encainide and
flecainide at doses ranging from 0.3 to 2.0 mg/kg and from 0.5 to 1.5 mg/kg
body weight, respectively, terminated
atrial ectopic tachycardia in all patients. Oral
encainide, 150 to 225 mg/day, completely suppressed ectopic atrial activity in four patients during a mean follow-up period of 8 +/- 3 months. In the remaining patient
encainide markedly reduced the number of episodes of
tachycardia. In three patients
encainide had to be withdrawn because of intolerable side effects. These patients were well controlled with oral
flecainide, 200 to 300 mg/day, without side effects. On the basis of these results, the efficacy of
encainide and
flecainide in the treatment of chronic
ectopic atrial tachycardia appears to be not
drug-specific but rather a general class IC property.