PREVENTION BY DEXAMETHASONE OF THE MARKED ANTIARRHYTHMIC EFFECTS OF PRECONDITIONING INDUCED 20-H AFTER RAPID CARDIAC PACING

Dogs were paced, via a pacing electrode in the right ventricle, for fo ur 5 min periods at a rate of 220 beats min(-1). On the following day they were reanaesthetized, thoracotomized and the left anterior descen ding coronary artery occluded for 25 min. Pacing markedly reduced the severity of ischaemia-induced arrhythmias (e.g. reduction in VF from 4 5% in unpaced dogs to 10% in paced dogs; P < 0.05), an effect reversed by dexamethasone (4 mg kg(-1) i.v., 45 min prior to,pacing). This pro tection may be due to the induction of nitric oxide synthase or cyclo- oxygenase.