Myocardial Protection in Heart Surgery

Abstract

One of the unmet clinical needs in heart surgery is the prevention of myocardial stunning and necrosis that occurs as a result of ischemia-reperfusion. Myocardial stunning, a frequent consequence after heart surgery, is characterized by a requirement for postoperative inotropic support despite a technically satisfactory heart operation. In high-risk patients with marginal cardiac reserve, stunning is a major cause of prolonged critical care and may be associated with as much as a 5-fold increase in mortality. In contrast, the frequency of myocardial necrosis (myocardial infarction [MI]) after cardiac surgery is less appreciated and its consequences are much more subtle. The consequences may not be apparent for months to years. While we now have a much better understanding of the molecular mechanisms underlying myocardial stunning and MI, we still have no effective way to prevent these complications, nor a consistently effective means to engage the well-studied endogenous mechanisms of cardioprotection. The failure to develop clinically effective interventions is multifactorial and can be attributed to reliance on findings obtained from subcellular and cellular studies, to drawing conclusions from preclinical large animal studies that have been conducted in a disease-free state, and to accepting less than robust surrogate markers of injury in phase II clinical trials. These factors also explain the disappointing failure to identify effective adjuvant therapy in the setting of percutaneous coronary revascularization for acute MI (AMI) and reperfusion injury. These issues have contributed to the disappointing outcomes of large and costly phase III trials, resulting in a lack of enthusiasm on the part of the pharmaceutical industry to engage in further drug development for this indication. The purpose of this review is to (1) define the scope of the clinical problem; (2) summarize the outcomes of selected phases II and III clinical trials; and (3) identify the gap that needs to be closed in order to address the unmet clinical need.