In the 1950s, the consensus among cardiac surgeons was that the results of the surgical methods at that time were satisfactory (22). Yet, numerous reports described low cardiac output syndrome occurring after surgical correction of congenital anomalies (23). Unfortunately, at that time, no definitive connection was provided between the lack of proper myocardial protection during surgery and the potential for postoperative cardiac dysfunction or high mortality rates.

Not until the advent of coronary bypass in the late 1960s and early 1970s were intraoperative myocardial infarctions or deaths attributed to poor protection of the myocardium (24,25). At that time, several reports also noted that the levels of cardiac enzymes after surgery were significantly elevated, indicating that additional myocardial damage had occurred during the operations (25).

As a result, surgeons of that era showed an increasing interest in attempting to protect the heart during the period of global ischemia (cross-clamping) via infusions of cold perfusates into the coronary circulation. Cold infusion is one of the methods known collectively as cardioplegia. Other modes for inducing cessation of cardiac activity employ chemical additions to perfusates or shocking the heart with electrical stimuli. After continued demonstration of its effectiveness, the use of hypo-thermic cardioplegia became quite widespread.

Yet, today many issues still need to be investigated concerning optimizing cardioplegic methodologies, such as which type of solution to use, how much to inject, how often to reinfuse, how long to extend global ischemia safely using cardioplegia approaches, and how well a specific solution might protect the energy reserves of the myocardium.

Operative settings that require cardioplegia involve aortic cross-clamping and coronary infusion (Fig. 5), usually of cold chemical solutions (26-30). Some surgeons prefer to inject warm (31,32) or tepid (33) solutions that have been mixed with chemical components (e.g., high-potassium concentrations). Ideally, normal myocardial cells require uninterrupted coronary perfusion. Therefore, the principles of applying cardioplegia are aimed at: (1) conserving energy through the rapid induction of diastolic arrest; (2) slowing the metabolic demands and the degenerative processes that inevitably follow global myocardial ischemia; and (3) preventing unfavorable ischemic changes.

Research over the past 30-plus years has provided several formulations of chemical components that have been used with or without cooling to obtain these three goals. Interestingly, these solutions still vary widely, likely because they have been independently developed at several separate institutions.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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