Anaerobic metabolism in heart muscle plays a role in maintenance of myocardial preservation only during
ischemia or
hypoxia. In an ischemic state, such as during a
heart attack or even during the induced
ischemia of open heart surgery, there is impairment of blood flow to the myocardium. The major energy-yielding process in the heart is through the metabolism of
glucose and
lipids by oxidative reactions. Under anaerobic conditions,
oxygen is not available to accept the electrons in the metabolic degradation of substrates and anaerobic glycolysis becomes important in the preservation of myocardial viability during the ischemic process. Unfortunately, the accumulated products of glycolysis, namely
protons and
lactate, work to inhibit glycolysis, ultimately resulting in a depression of anaerobic metabolism.
Cardioplegia, as utilized during open heart surgery, has the effect of inducing instantaneous induction of myocardial mechanical and electrical arrest with a maximal inhibition of the energy utilizing metabolic processes. This effectively reduces substrate utilization and prevents the deleterious consequences of the ischemic process.
Cardioplegia is most effective when combined with the additive properties of
hypothermia, which plays a significant role in decreasing myocardial metabolism. However, during prolonged hypothermic cardioplegic arrest, sufficient
ATP cannot be maintained for cellular integrity and anaerobic glycolysis becomes of increasing importance for maintenance of myocardial preservation. This presentation deals with the mechanics of aerobic versus anaerobic metabolism during the ischemic process of open heart surgery.