Protection of the ischemic myocardium: cold chemical cardioplegia, coronary infustates and the importance of cellular calcium control.

Crystalloid cardioplegic infusates with "extracellular" and "intracellular" ionic formulation were compared in the isolated working rat heart under hypothermic conditions of coronary infusion (4 min, 4 degrees C) and ischemia (100 min, 20 degrees C) and with the postischemic recovery of various parameters of cardiac function for the assessment of efficacy. With the St. Thomas' Hospital (ST) solution the recovery was superior to that observed with the Bretschneider (BR) solution no 3. In further experiments it was found that the ST solution owed its efficacy to the content of potassium (16.0 mM) and magnesium (16.0 mM) and its safety and stability to the presence of nearly normal extracellular concentrations of calcium (1.2 mM) and sodium (116.6 mM). The efficacy of the BR solution was totally dependent upon its content of procaine (7.4 mM), and the ionic composition with low sodium (12.0 mM) and zero calcium was of little value without the use of additional protective measures. The results emphasized the importance of an optimal cellular calcium homeostasis during coronary infusion of cardioplegic solutions, during ischemia, and initially during reperfusion after ischemia. Cardioplegic infusates which are to afford a stable cellular calcium control should preferably be based on an extracellular ionic composition.