The electrophysiologic effects of oral
encainide (75 to 150 mg daily) were evaluated in 14 patients (6 male and 8 female, aged 49 +/- 9 years) with atrioventricular (AV) node reentrant
tachycardia of the slow-fast type. The patients were studied in control conditions and after 2 to 12 days of treatment.
Encainide increased the AH interval from 67 +/- 10 to 82 +/- 23 ms (p less than 0.02). Anterograde Wenckebach cycle length was increased in three patients, reduced in four, unchanged in one; it was not measurable in the remaining patients because
tachycardia was induced. Retrograde Wenckebach periodicity increased from 307 +/- 71 to 401 +/- 92 ms (p less than 0.005) in all nine patients in whom it was measurable; complete retrograde block was observed in one patient. At the control study,
tachycardia was induced in all patients, with a mean cycle length of 341 +/- 50 ms; after
encainide,
tachycardia was inducible in only 1 patient, with an increase in cycle length from 270 to 320 ms; in the other patients,
tachycardia was not inducible because of a lack of retrograde (11 patients) or anterograde (2 patients) conduction. The mean plasma concentrations of
encainide and its metabolites O-demethyl-
encainide and
3-methoxy-O-demethyl-encainide measured in 13 patients during the repeat study were 161 +/- 304, 128 +/- 100 and 95 +/- 85 ng/ml, respectively; three poor metabolizers who presented a high concentration of the parent compound were observed in this series. All patients were discharged on
encainide at a mean daily dose of 112 +/- 39 mg.(ABSTRACT TRUNCATED AT 250 WORDS)