Abstract
Myocardial ischemia/reperfusion injury has come to be a serious phenomenon in clinical practice as the progression of interventional recanalization to salvage ischemic myocardium. Brief coronary occlusion lasting<20 minutes produces depression of myocardial contractile function for several hours. This reversible injury is referred to as “myocardial stunning”. Coronary blood flow to stunned myocardium is restored to normal or near normal. Myocardial Stunning may occur in a number of clinical settings including cardiac surgery, cardiac transplantation, percutaneous transluminal coronary angioplasty, and angina pectoris. Thoracic epidural anesthesia (TEA) increases subendocardial blood flow before ischemia and enhances functional recovery of left ventricular contractility after reperfusion. The possible mechanisms of this cardioprotection are improvement of subendocardial blood flow due to suppression of excessive excitation of cardiac adrenergic system, or decrease in myocardial oxygen consumption. Though details have not been clarified, elevated concentration of cardiac interstitial norepinephrine (NE) release has been observed during myocardial ischemia. We investigated the effects of NE administration for TEA induced cardioprotection on stunned myocardium in dogs. NE administration during ischemia and early reperfusion period suppressed functional recovery after reperfusion under cardiac sympathetic nerve blockade by TEA. Cardioprotective effects of TEA would be produced through suppression of cardiac NE release during ischemia. The anti-ischemic effect of TEA might be influenced with co-existing general anesthetics. Halogenated anesthetics improve myocardial functional recovery in myocardial stunning. Sevoflurane protects stunned myocardium through activation of mitochondrial ATP-sensitive potassium channels. TEA has no additional protective effect on recovery of stunned myocardium during sevoflurane anesthesia. Propofol, an intravenous anesthetic, can not improve functional recovery of myocardial contractility. TEA does not improve functional recovery of stunned myocardium during propofol anesthesia. Although cardioprotective effects of TEA might be influenced by general anesthetics, TEA can exert beneficial effects to prevent lethal cardiac event for patients with coronary artery disease especially in perioperative period which increases risk of myocardial ischemia.
