Hiroko Matsuda

Effects of verapamil on accessory pathway properties and induction of circus movement tachycardia in patients with the Wolf-Parkinson-White syndrome.

Summary: The electrophysiological effects of 0.2 mg/kg of intravenously administered verapamil (mean plasma level, 51.3 ng/ml) were evaluated using intracardiac recordings and electrical stimulation in 10 patients with the concealed or manifest Wolff-Parkinson-White syndrome. Verapamil produced a minimal effect on both the antegrade and retrograde effective refractory periods of the accessory pathway and the retrograde conduction time over the accessory pathway. but significantly lengthened the intranodal conduction time as well as the effective and functional refractory periods of the atrioventricular (AV) node. Reproducible sustained circus movement tachycardia was initiated in 8 patients before administration of verapamil and in 2 after verapamil. The sustained tachycardia could no longer be initiated in 6 patients because of an increase in AV nodal refractoriness. In 4 patients. atrial echoes were induced at longer premature beat intervals due to a greater AV conduction delay of the atrial impulse. The cycle length of the tachycardia was lengthened in 2 patients, reflecting an increase in the A-H interval after verapamil administration.-In conclusion, these results show that verapamil has no apparent effect on either antegrade or retrograde accessory pathway properties and suggest that verapamil does indeed prevent sustained circus movement tachycardia by increasing the AV nodal refractoriness in some patients with the Wolff-Parkinson-White syndrome.

Effects of perhexiline maleate on the refractory periods of isolated atrial muscle and atrioventricular node of the rabbit.

Summary The electrophysiologic effects of perhexiline maleate were studied with glass microelectrodes in three types of isolated rabbit heart preparations: (a) sinoatrial node preparation; (b) left atrial free-wall preparation; and (c) atrioventricular node preparation. The spontaneous firing rate of the sinoatrial node was decreased by 10–15% at a concentration of 10−5 g/ml. The sinus node recovery time after atrial overdrive was prolonged by about 50%. The effective refractory period of the left atrial free wall showed concentration-dependent prolongation at concentrations above 10−7 g/ml. Although this period was shortened after washing with perhexiline-free Tyrode solution, it did not return to the control level. The effective refractory period of the right atrium was prolonged by 15% at a concentration of 10−5 g/ml, but the functional refractory period did not change. The conduction time, effective refractory period, and functional refractory period of the atrioventricular node were significantly increased. Previous reports had claimed that perhexiline had pharmacologic effects on Purkinje fibers and ventricular myocardium at lower concentrations than on the atrium, but we found significant actions on the atrium and the atrioventricular node in therapeutic concentrations.