ISCHEMIA-INDUCED AND REPERFUSION-INDUCED VENTRICULAR ARRHYTHMIAS IN DOGS - EFFECTS OF ESTROGEN

The purpose of this investigation was to determine if exogenous estrog en could attenuate the ventricular arrhythmias caused by myocardial is chemia and reperfusion. Conjugated equine estrogen, administered as an intravenous bolus injection (100 mu g) to anesthetized, instrumented beagles of both genders, significantly attenuated the incidence of ven tricular arrhythmias during a 20-min period of ischemia (2 +/- 1 vs. 1 9 +/- 16% ectopy) and in the first 5 min of reperfusion (15 +/- 9 vs. 69 +/- 20% ectopy). By 15-20 min of ischemia, ventricular salves and n onsustained ventricular tachycardia were frequently observed in nontre ated dogs. One dog in this group fibrillated during ischemia. In contr ast, estrogen-treated dogs exhibited only an occasional ventricular pr emature beat during the same period of ischemia. When compared with ba seline values, the percent ectopy during ischemia in estrogen-treated dogs was insignificant. During reperfusion, nontreated dogs displayed severe, life-threatening arrhythmias such as sustained ventricular tac hycardia. In two of these dogs ventricular tachycardia deteriorated to ventricular fibrillation. In comparison, estrogen-treated dogs displa yed only innocuous ventricular arrhythmias during reperfusion, i.e., v entricular premature beats, ventricular salves, and ventricular bigemi ny. In addition to the effect of estrogen on arrhythmias, there was a gradual increase in coronary blood flow on reperfusion in estrogen-tre ated dogs. This effect of estrogen was preceded by a significantly hig her coronary perfusion pressure during ischemia (31 +/- 2 vs. 18 +/- 4 mmHg, P < 0.05). In conclusion, our findings suggest that antiarrhyth mic effects of estrogen treatment might stabilize ventricular rhythmic ity during ischemia and reperfusion.