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European Heart Journal 1986 7(7):576-583;
Copyright © 1986 by the European Society of Cardiology.
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© 1986 The European Society of Cardiology

Clinical cardiac electrophysiology of indoramin, a post-synaptic alpha blocker

G.S. BUTROUS and A.J. CAMM

Department of Cardiology, St Bartholomew's Hospital London, U.K.

Received 25 October 1985; revised 22 January 1986; .

Dr G. S. Bulrous, Department of cardiology, St. Bartholomew's Hospital, London ECIA 7BE, England.

Abstract

Indoramin is a selective post-synaptic alpha blocker. Animal experiments had shown that it has antiarrhythmic effects, but whether this is due to its alpha blocking effect or some other mechanism is not known. Fifteen patients (10 males) underwent electrophysiological investigations before and 15 minutes after intravenous indoramin injection (0.2-0.5 mg kg–l). The plasma level of indoramin was measured and the patients were divided into two groups: group 1 (8 patients) whose plasma level was less than 100 µg ml–1 (average 72 µg ml–l) and group 2 (7 patients) whose plasma level was more than 100 µg ml–1 (average 151 µ ml–1). In both groups there was a significant drop in the systolic blood pressure after indoramin (129±22 to 111 ±23 mmHg, P<0.001). There was a marked improvement in the sinus node recovery time in group 1 only (253±92 to 163±40ms, P<0.01). Similarly there was a decrease in AH interval during fixed rate atrial pacing in group 1 only (128 ±33 to 100 ±37 ms, P<005) and a significant decrease in the Wenckebach cycle length after indoramin in group 1 only (372 ±85 to 347 ± 74 ms, P<005). At the atrial level there were no significant effects in either group but there was a significant increase in the ventricular effective refractory period in group 2 (231 ± 35 to 264 ± 64 ms, P< 0.05) but no change in group 1. The QTc prolonged significantly in group 2 (407 ±87 to 438 ±67 ms, P>0-05) but not in group 1. These findings suggest that indoramin has dual electrophysiological effects: (1) an ‘excitatory’ effect as seen in group 1 which is probably due to alpha blockade or enhanced beta stimulation, and (2) a ‘depressive’ effect: seen in group 2, which may be due to a direct effect.

Key Words: Alpha adrenoceptors, • indoramin, • cardiac electrophysiology.


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