The Journal of Thoracic and Cardiovascular Surgery, Vol 95, 263-270, Copyright © 1988 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
The effects of verapamil on left ventricular function in the presence of beta-adrenergic blockade
TP Barragry, JW Blatchford, IC Tuna and WS Ring
Department of Surgery, University of Minnesota, Minneapolis.
Supraventricular tachyarrhythmias frequently complicate myocardial
revascularization. Intravenous administration of verapamil has been
effective in terminating these arrhythmias. To determine the effects of
verapamil on left ventricular systolic function, we implanted ultrasonic
dimension transducers in dogs and, after they had recovered from the
operation, studied them while they were awake and unsedated. Intravenous
administration of verapamil (0.2 mg/kg) resulted in an elevation of cardiac
output above baseline because of reflex-induced tachycardia. Contractility,
as measured by the load-independent end- systolic pressure-volume
relationship, remained unchanged. When the animals were pretreated with
atropine and propranolol, verapamil resulted in a fall in cardiac output
and contractility. The intact animal responded to the vasodilatory effect
of verapamil by releasing catecholamines to maintain cardiac output and
hemodynamic stability. Only when this compensatory mechanism was blocked by
a beta-adrenergic blocker do the inherently negative inotropic and
chronotropic effects of verapamil become apparent. The clinical
ramifications of this finding are of greater importance to the surgeon as
more patients receive beta-adrenergic blocking agents up to the time of the
immediate preoperative period. We conclude that verapamil should be
administered with caution to patients with supraventricular
tachyarrhythmias who have been receiving beta-adrenergic blocking agents.
