Comparison of the effects of intravenous and oral betaxolol on antegrade and retrograde conduction in patients with atrioventricular nodal reentrant and atrioventricular reentrant tachycardia.

The electrophysiologic effects of intravenous (0.15 mg kg-1) and oral (20 mg day-1) betaxolol have been investigated in 11 patients with atrioventricular (A-V) nodal reentrant tachycardia and eight patients with orthodromic A-V reentrant tachycardia. Betaxolol significantly (P greater than 0.01) prolonged sinus cycle length, sinus node recovery time, intranodal conduction time, and the antegrade functional refractory period of the A-V node. When the effective refractory period of the A-V node could be determined it was increased by betaxolol, whereas no significant electrophysiologic effects were observed in the atrium, the ventricle or the accessory pathway. Intravenous betaxolol prevented tachycardia in 8 out of 11 patients with A-V nodal reentrant tachycardia, whereas oral betaxolol was effective in 10 patients, primarily by acting on the antegrade limb in two patients and on the retrograde limb in eight patients. In those with A-V reentrant tachycardia, intravenous betaxolol did not prevent tachycardia in any patient, while it was effective after oral treatment in two patients. When the tachycardia remained inducible, cycle length of the tachycardia increased in all patients, due to prolongation of the antegrade and retrograde conduction time in patients with A-V nodal reentrant tachycardia, and due to an increase in the antegrade conduction time, i.e. the A-V node, in the patients with A-V reentrant tachycardia. In conclusion, betaxolol proved to be effective in the treatment of supraventricular tachycardia; for chronic treatment, a single oral dose (20 mg) seems to suffice.