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2-adrenoceptors in
Purkinje?
Division of Cardiovascular Diseases, Department of Internal Medicine, University of Iowa College of Medicine; and Veterans Administration Medical Center, Iowa City, Iowa 52242
Recent studies have shown the presence of postjunctional
2-adrenergic receptors on canine Purkinje fibers but not
muscle cells. Stimulation of these receptors results in prolongation of
the action potential duration and the Purkinje relative refractory period. We studied the effect of 2-adrenergic agonists
on inducible ischemic ventricular tachycardia (VT) of both
Purkinje fiber and myocardial origin. Open-chest dogs in whom VT was
induced with extrastimuli after occlusion of the anterior descending
coronary artery were studied. A mapping system, incorporating Purkinje signals, characterized the mechanisms of VT. The
2-adrenergic agonists clonidine (0.5-4.0
µg/kg) or UK 14,304 (4-5 µg/kg) versus saline were given
intravenously after reproducibility of inducible sustained monomorphic
VT had been demonstrated. Eighteen dogs were given clonidine, eleven of
which had focal Purkinje VT. Of these 11 dogs, clonidine blocked VT
induction in 9 (81.9%) and rendered VT nonsustained in 1 (9.1%), and
VT remained inducible in 1 dog (9.1%), although this was focal
midmyocardial VT only. In the seven dogs with VT of myocardial origin,
six (85.6%) remained inducible with clonidine, whereas one dog
(14.4%) had only nonsustained VT after clonidine. Of the six dogs, UK
14,304 blocked VT induction in four (66.6%) and rendered VT
nonsustained in one (16.7%), and VT remained inducible in one dog
(16.7%). In four dogs with VT of myocardial origin, VT remained
inducible. In the eight control dogs that were given saline, focal
Purkinje VT was repeatedly inducible. Pharmacological stimulation of
postjunctional 2-adrenoceptors on Purkinje fibers may
selectively prevent induction of VT of Purkinje fiber origin in the
ischemic canine ventricle.
ischemia; mapping; autonomics
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