Electrophysiology of Tiapamil in Concealed Accessory Pathways

Abstract

The effect of 2 mg/kg intravenous tiapamil was studied by programmed stimulation of the heart in 6 patients. Before tiapamil, sustained tachycardias were initiated in 5, and only atrial echoes in 1. In all patients, the reentrant circuit involved an accessory pathway conducting only in the ventriculoatrial direction. When administered during tachycardia, tiapamil promptly terminated the arrhythmia in 5 cases. Tiapamil lengthened the atrio-His (A-H) interval and the effective refractory period of the A-V node. As a result of these changes, it was not possible to initiate the tachycardia in 1 patient. In 1 case, tiapamil permitted the induction of sustained tachycardia, while only echoes had been initiated before the drug. In 2 cases, the tachycardia zone narrowed, in 2 others it widened following tiapamil. The ability to sustain the arrhythmia was lost in 1 patient. Tiapamil may be useful for the termination of reentrant supraventricular tachycardia involving concealed accessory pathways. Whether tiapamil prevents or favors the initiation of tachycardia in these patients depends on the interplay between the prolongation of the effective A-V nodal refractory period and the prolongation of the transnodal conduction time in individual patients.

Electrophysiologic Changes after Tiapamil in Coronary and Noncoronary Patients

“…in the dose of 1.5 mg/kg i.v.. the HR. These findings confirm those obtained by other investigators in different patients [1][2][3]. The effects of the 1.5 mg/kg dose are more marked than those of the lower dose (1 mg/kg), showing a correlation be tween the dose and the effect.…”

“…Seipel and Breithardt [1] have re viewed the electrophysiological properties of calcium antagonists. Other authors have de scribed the electrophysiological effects of tia pamil in patients with concealed accessory' pathways [2] and also in patients with differ ent cardiac diseases [3].…”

Effect of Tiapamil in the Preexcitation Syndrome

“…a congener of verapamil, has been shown to be useful in the management of paroxysmal reentrant supraventricular ta chycardia 11,2], The present study extends 1 Supported by the Fonds zur Förderung der wissen schaftlichen Forschung in Österreich, project 4011.…”

“…Our first study on the elec trophysiology of this calcium antagonist in normal subjects showed a prolongation of the functional and effective refractory' periods of the A-V node [4], On this basis one may pre dict that tiapamil could well be as potent in terminating A-V nodal reentrant tachycar dias as verapamil which is regarded as the most potent drug available for this purpose [6,8,9]. All tachycardias due to reentry in the A-V node alone or in the A-V node and a concealed accessory connection were inter rupted within 2 min [1,2], The present re sults extend this favorable action to circus movement tachycardia in the overt antegrade preexcitation syndrome. Both orthodromic and antidromic (limited data) tachycardias responded favorably.…”

“…Our methods of stimulation and record ing techniques have been described elsewhere [1,2]. In brief, three or four catheters were positioned in the high right atrium, below the tricuspid valve, and at the apex of the right ventricle.…”