Although uncommon, incessant
supraventricular tachycardia (the daily presence of
supraventricular tachycardia for more than 50% of the day) is a major therapeutic problem. Using programmed electrical stimulation of the heart, long-term electrocardiographic monitoring and exercise testing, the effect of intravenous and oral
encainide for termination and prevention of incessant
supraventricular tachycardia was assessed in 11 patients (aged 25 to 58 years). All patients had received 3 to 12 drugs (mean 6) without control of their
arrhythmia. Eight patients suffered from incessant
supraventricular tachycardia using an accessory pathway in retrograde direction (three with overt
Wolff-Parkinson-White syndrome, one with a concealed accessory atrioventricular [AV] pathway of the fast type, three with a concealed accessory AV pathway of the slow type and one with a nodo-ventricular accessory pathway). Three patients had incessant atrial
tachycardia, one of whom also had the
Wolff-Parkinson-White syndrome. Intravenous
encainide (1.5 mg/kg in 15 minutes) terminated incessant
supraventricular tachycardia in seven of nine patients. In four of nine patients,
supraventricular tachycardia could thereafter still be reinitiated by pacing. Oral
encainide (100 to 325 mg/day, mean 180) completely suppressed the incessant
supraventricular tachycardia in eight patients in a follow-up period of 5 to 20 months (mean 11). In two patients, episodes of
tachycardia were markedly reduced with the administration of
encainide in combination with
sotalol (one patient) and
amiodarone (one patient).
Encainide failed to control incessant
tachycardia in one patient. Mild central nervous system side effects developed in two patients, but both could continue taking oral
encainide.
Encainide proved to be a very useful agent to control incessant
supraventricular tachycardia resistant to other antiarrhythmic agents.