Alpha-2 adrenergic antagonism enhances risk of ventricular tachycardia during acute ischemia.
OBJECTIVE
In this study we tested the hypothesis that alpha-2 adrenergic antagonism could facilitate induction of previously non-inducible ventricular tachycardia (VT) during acute ischemia. Previous reports suggest that VT during ischemia may be modulated by (alpha-2 adrenergic agonists.


METHODS
The left anterior descending artery was occluded after instrumentation of the ischemic risk zone with 21 multipolar plunge needles, each recording 6 bipolar electrograms. Three dimensional mapping characterized the mechanism of VT induced with extrastimuli.


RESULTS
Of 16 non-inducible dogs included, eight which were given the alpha-2 adrenergic antagonist yohimbine all had inducible VT, while all eight in the control group remained non-inducible (p < 0.05). Six of the VTs were of focal Purkinje origin. The cycle length of the VTwas 119 +/- 4 ms. Mean arterial pressure (81+/- 8 to 82 +/- 8 mmHg, p = ns), ventricular effective refractory period (146 +/- 6 to 144 +/- 5 ms, p = ns) and ischemic zone size (55 +/-6% vs. 61 +/- 4%, p = 0.45) were not altered by yohimbine indicating minimal central or pre-junctional effects of the drug.


CONCLUSIONS
Yohimbine facilitates induction of VT, especially those with focal Purkinje fiber origin, suggestive of an effect mediated through antagonism of post-junctional alpha-2 adrenoceptors on Purkinje fibers.
Arnar
David O
DO
Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA.
Xing
Dezhi
D
Martins
James B
JB
D000317:Adrenergic alpha-Antagonists / Q000009:adverse effects*; D000818:Animals; D004195:Disease Models, Animal; D004285:Dogs; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D008297:Male; D017202:Myocardial Ischemia / Q000188:drug therapy*; D011690:Purkinje Fibers / Q000187:drug effects / Q000503:physiopathology; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects; D017180:Tachycardia, Ventricular / Q000139:chemically induced* / Q000503:physiopathology; D015016:Yohimbine / Q000009:adverse effects*
D000317:Adrenergic alpha-Antagonists; D018341:Receptors, Adrenergic, alpha-2; D015016:Yohimbine