Free oxygen radicals contribute to high incidence of reperfusion-induced arrhythmias in isolated rat heart

Early period of reperfusion of ischemic myocardium is associated with a hig h incidence of severe tachyarrhythmias including ventricular tachycardia an d fibrillation (VT and VF). Free oxygen radicals (FOR) have been identified as one of the principal factors responsible for reperfusion-induced events . However, their role in arrhythmogenesis is not clear. In the present stud y, in isolated Langendorff-perfused rat hearts subjected to 30 min global i schemia, the onset of reperfusion induced 100% incidence of both VT and VF with their gradual cessation over 5 min of reperfusion. Generation of H2O2 in the myocardium in the first minutes of reperfusion was visualized by mea ns of cerium cytochemistry and confirmed by Xray microanalysis. The mechani sm of the arrhythmogenic effect of FOR may involve inhibition of the sarcol emmal Na+/K+-ATPase, as demonstrated in the rat heart sarcolemmal fraction subjected to FOR-generating system (H2O2 + FeSO4).