[Anti-arrhythmia and electrophysiological effects of encainide in supraventricular tachycardias]

In order to assess the electrophysiologic effects and anti-arrhythmia effects of encainide after acute IV injection and chronic oral therapy, a group of 10 patients (mean age 54) with recurrent supraventricular tachycardia was studied. Seven patients had more than 2 attacks per month, and supraventricular tachycardia (SVT) resulted in severe symptoms in the three remaining SVT was due to AV nodal re-entry in 6 patients and to concealed accessory pathway in 4. After a control study, SVT was initiated, and encainide (0.75 mg/kg) was infused intravenously in attempt to stop the tachycardia. A second study was achieved. After 4 days of oral therapy (25 or 50 mg T.I.D.) a third study was performed, including SVT initiation attempts. Encainide depressed conduction in all cardiac tissues, and this effect was more evident after oral administration. Antegrade I:I conduction cycle length increased of 13.9% (p less than 0.05), and the same parameter in retrograde conduction increased of 30.03% (p less than 0.05). IV injection interrupted 2 of 10 SVT only. However, after 30 minutes, 5 re-initiated SVT were nonsustained, and mean cycle length increased from 326 +/- 21 to 397 +/- 51 (p less than 0.01). After oral therapy, SVT was initiated in 4 of 10 patients, nonsustained in 3. During long term follow-up (one year or more), no severe adverse effect has been reported. Three patients are still experiencing short events of well-tolerated SVT. Hence, moderate or low doses or oral encainide may safely control recurrent supraventricular tachycardia.