Electrophysiological effects of propafenone studied with programmed electrical stimulation of the heart in patients with recurrent paroxysmal supraventricular tachycardia

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Abstract
Propafenone is an antiarrhythmic which possesses the properties of a class I agent. Its electrophysiological effects were studied with programmed electrical stimulation of the heart in 12 patients suffering from recurrent episodes of reentrant supraventricular tachycardia (atrioventricular nodal tachycardia:five cases; circus movement tachycardia involving an accessory pathway: six cases; atrial flutter and fibrillation with the Wolff-Parkinson- White syndrome: one case). Propafenone was perfused intravenously at a dose of 2 mg/kg over W min. It lengthened the transnodal conduction time, the H V interval, the VA conduction time (over the A V node) and the refractory period of right atrial muscle. The effects of the drug on accessory pathways used in the anterograde direction were measurable in four cases. Complete blockade along the bypass was seen in one instance and prolongation of the effective refractory period in the other three. In the retrograde direction, four patients out of six showed prolongation of the refractory period of the accessory pathway, after drug injection. Perfused intravenously during episodes of tachycardia, the drug interrupted the rhythm disorder in 10 out of 11 cases, but on three occasions, this was achieved by spontaneous ventricular premature beats which were not present prior to initiation of treatment. Tachycardia could still be initiated in six patients after propafenone (five out of six with circus movement tachycardia, one out of five with AV nodal tachycardia). The effects of chronic oral propafenone administration (300 mg t.d.s.) were assessed in five patients; they were similar to those observed after acute intravenous injection. Propafenone is a promising drug for the treatment of A V nodal tachycardia and might be useful for protection against high ventricular rates in patients with the preexcitation syndrome.