Cardioplegic infusion: the safe limits of pressure and temperature.

In patients with coronary artery disease, infusion of very cold cardioplegic solutions at elevated pressures may facilitate homogeneous cooling and cardioplegia. This study was designed to determine if very high infusion pressures or very low temperatures of the cardioplegic solution damages normal myocardium. In a hemodynamically controlled canine right heart bypass preparation, a crystalloid solution (Plasma-Lyte 148 with 30 mEq/L potassium chloride, 0 degree to 2 degrees C) was infused with separate control of the infusion pressures in the left anterior descending and circumflex arteries. A sonomicrometer measured regional myocardial function in each area. During a 100 minute arrest period, cardioplegic solution was reinfused every 20 minutes and reduced myocardial temperatures to an average of 9.4 degrees +/- 2.2 degrees C. In a comparison of infusion pressures of 50 versus 100 mm Hg and 100 versus 150 mm Hg, postarrest regional myocardial function was unchanged from prearrest. However, in a comparison of infusion pressures of 150 to 200 mm Hg, a significant fall in regional myocardial function was noted with the higher pressures (106% and 64% recovery, respectively, p less than 0.02, n = 6). Excluding the areas perfused at 200 mm Hg, comparison of regions cooled to less than 8 degrees C and to greater than 8 degrees C demonstrated no difference in recovery of regional myocardial function. In this study, elevation of cardioplegic infusion pressures to 150 mm Hg and lowering of myocardial temperatures to less than 8 degrees C caused no impairment of regional myocardial function.