Opioid antagonist modulation of ischaemia-induced ventricular arrhythmias:A peripheral mechanism

Ventricular arrhythmias are an important cause of death after myocardial is chaemia. Animal studies have generated conflicting data on the potentiating or attenuating effects of opioid agonists and antagonists on cardiac rhyth m during acute myocardial ischaemia and coronary artery reperfusion. Whethe r these effects of opioid antagonists are mediated by central or peripheral nervous system mechanisms remains unclear. We examined (a) the effects of peripheral opioid receptor blockade on ischaemia-induced arrhythmia by usin g methylnaltrexone (MNTX), a navel quaternary derivative of naltrexone (NTX ) that does not cross the blood-brain barrier, and (b) whether MNTX would m odulate morphine effects during acute coronary artery ligation and reperfus ion in the rabbit. The incidence and severity of cardiac arrhythmias were a ssessed during 40 min of coronary artery occlusion and reperfusion and summ arised in an arrhythmia score (AS). MNTX reduced the incidence of ventricul ar fibrillation (VF) and arrhythmia score during coronary artery occlusion when compared with vehicle (p < 0.05). Naltrexone reduced the incidence of VF (p < 0.05). Although morphine alone had no significant effects, its coad ministration blunted the antiarrhythmic properties of MNTX. The data sugges t that blockade of opiate receptors outside the central nervous system may protect against ischaemia-induced arrhythmias.