J. Patel et al., ANTIARRHYTHMIC EFFICACY OF BETA-ADRENERGIC-BLOCKADE DURING ACUTE-ISCHEMIA IN MYOCARDIUM WITH SCAR, The American journal of the medical sciences, 307(4), 1994, pp. 259-263
Ventricular arrhythmia production in the ischemic heart is considered
to be influenced by prior infarction. Although beta-adrenergic blockad
e is known to have beneficial effects during acute ischemia, its anti-
arrhythmic efficacy during post-infarction ischemia is not known. To e
xplore this question, we have used a model with a relatively high inci
dence of ischemic arrhythmias. Mongrel dogs 2 to 3 years of age were s
tudied intact under anesthesia. An irreversible injury of the infero-p
osterior myocardium was produced with an electrode catheter 1 week ear
lier. The arrhythmic response to acute ischemia was assessed using ser
ial, transient 15-minute occlusions of the left-anterior descending co
ronary artery with a balloon catheter. During ischemia alone, the inci
dence of ventricular fibrillation in animals who underwent all phases
of the study was 6 of 9; with atenolol (0.2 mg/kg intravenously) and i
schemia, 1 of 9 (p < 0.05). To assess the role of the bradycardic resp
onse, the latter was repeated 1 week subsequently during atrial pacing
at the heart rate that existed before ischemia. Fibrillation occurred
in 8 of 9, a significant reversal of the therapeutic effect. To exclu
de the potential artifact of a fixed intervention protocol, a study wa
s undertaken with the short-acting esmolol, in which three ischemic pe
riods were alternated at 1-hour intervals: (A) ischemia without treatm
ent, (B) ischemia with continuous infusion of 150 mu g/kg/min esmolol,
and (C) same as B except that heart rate was maintained by atrial pac
ing. Ventricular fibrillation occurred in 7 of 10 in period A, 1 of 10
(p < 0.03) in period B, and 8 of 10 in period C (p < 0.02). Therefore
, despite the high incidence of fibrillation without treatment, beta-a
drenergic blockade was effective in reducing the incidence of ventricu
lar fibrillation during early ischemia.