Reperfusion injury might occur in patients with acute ST segment elevation myocardial infarction undergoing the primary percutaneous coronary intervention(P-PCI),characterized by myocardial stunning, reperfusion-induced arrhythmia, microvascular dysfunction and injury of cardiac sympathetic nerve, etc.~Nicorandil is an antianginal agent with a dual mechanism of action: nitrate and K+ATP channel opener. The nitrate action causes vasodilation of systemic veins and epicardial coronary arteries, while the adenosine triphosphate (ATP)-sensitive potassium channel opener action causes vasodilation of peripheral and coronary resistance arterioles. Nicorandil not only decreases preload and afterload but also increases coronary blood flow.~The study will compare the effectiveness between nicorandil and placebo of preventing the reperfusion injury especially injury of cardiac sympathetic nerve in patients with acute ST segment elevation myocardial infarction undergoing the P-PCI.It is intended that before reperfusion injury ,nicorandil which was early used by intracoronary injection could prevent and release the microcirculatory spasm, release the coronary microvascular endothelial swelling,decrease embolism of atherosclerotic debris and thrombus formation,moreover,it could reduces the release of norepinephrine from sympathetic endings of the heart directly.So,it could decrease the phenomenon of no-reflow/slow reflow,reperfusion-induced arrhythmia and injury of cardiac sympathetic nerve.
The investigators evaluate the effects of intracoronary and intravenous administration of nicorandil on cardiac sympathetic nerve activity and distribution in patients with acute myocardial infarction undergoing primary percutaneous coronary intervention