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Myocardial protection in the operating room refers to strategies and methods used to attenuate or prevent perioperative infarction and/or postischemic ventricular dysfunction. In the setting of an acute myocardial infarction (MI) it refers to adjuvant therapy administered before, during or after reperfusion therapy. In transplantation it refers to the methods used to preserve the donor heart. Although the clinical situations are different, the goal of protection is the same, that is, to prevent or treat myocardial stunning and infarction. The underlying pathophysiology in all three settings is the same and relates to the etiology and consequences of ischemia/reperfusion (I/R) injury. After surgery the injury may manifest as low cardiac output, hypotension, and the need for postoperative inotropic support and ultimately mechanical circulatory support. I/R injury may be reversible (stunning) or irreversible (infarction) and is differentiated by electrocardiographic abnormalities (presence of a new Q-wave), elevations in the levels of specific plasma enzymes or proteins such as creatine kinase-MB and troponin I or T and/or the presence of regional or global echocardiographic wall motion abnormalities. Depending upon the criteria used, the incidence of postoperative MI in patients undergoing coronary artery bypass grafting (CABG) with cardiopulmonary bypass (CPB) ranges between 3% and 18%.1-4 While the majority of these are non-Q wave infarctions, they still are independently associated with adverse outcomes and prolonged aortic cross-clamp time and duration of CPB. Despite advances in techniques and cardioprotective strategies, the incidence of severe ventricular dysfunction, heart failure and death postoperatively ranges between 1% and 15%. The higher mortality rates are generally associated with high-risk patients with minimal cardiac reserve. These complications have an enormous impact on both families and society. From an economic standpoint alone, procedures for cardiovascular diseases are costly.
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According to Heart Disease and Stroke Statistics–2015 Update,5 in 2010 an estimated 954,000 percutaneous interventions (PCIs), 397,000 CABG operations, 1,029,000 diagnostic cardiac catheterizations, 97,000 defibrillator implants and 370,000 pacemaker procedures were performed on inpatients in the United States. The estimated cost was $204.4 billion. Between 2013 and 2030, medical costs of coronary heart disease alone are projected to increase by 100%. Cardiovascular disease costs more than any other diagnostic group. Therefore, a reduction in perioperative complications associated with heart surgery would have a significant impact on resource utilization and overall operative costs.6-8 Since I/R injury is a major cause of morbidity and mortality after heart surgery, the purpose of this chapter is to review its underlying mechanisms, review the history of myocardial protection, update the reader regarding the current protective techniques and discuss new strategies under investigation.
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ISCHEMIA/REPERFUSION INJURY
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The etiology of perioperative myocardial necrosis and postischemic myocardial dysfunction after cardiac surgery is multifactorial. Myocardial necrosis and elevation of associated cardiac biomarkers may arise as a result of ischemia due to intrinsic coronary disease unrelated to revascularization, anesthetic factors, atrial cannulation, suturing of heart muscle, plaque rupture or platelet embolism, and graft ...