Comparison of single-dose and multiple-dose crystalloid and blood potassium cardioplegia during prolonged hypothermic aortic occlusion

Abstract

Blood potassium cardioplegia (BCP) has recently been advocated as a superior method of myocardial protection, but it has not been compared to a crystalloid potassium cardioplegia solution (KCP). This study was undertaken to compare the protective effect of single (SD) and multiple dose (MD) BCP and KCP during 120 minutes of hypothermic (22° C) aortic occlusion. Thirty-five dogs were divided into four groups: Group I, SD-KCP; Group II, SD-BCP; Group III, MD-KCP; Group IV, MD-BCP. Both perfusates contained 25 mEq/L of potassium chloride at pH 7.4. Change in left ventricular function was defined as the arithmetic difference in the center of mass between prearrest and post-arrest left ventricular function curves and was expressed as percent recovery of left ventricular stroke work. Regional myocardial flow was measured with microspheres. Ventricular biopsies were serially obtained for measurement of myocardial water, adenosine triphosphate (ATP) creatine phosphate, and calcium and for electron microscopy. Percent recovery of left ventricular function was as follows: Group I, 63%; Group II, 48%; Group III, 64%; Group IV, 75%; and 57% of dogs in Group II had incomplete arrest. Endocardial/epicardial flow ratio increased immediately after reperfusion in Groups I and III with rapid return to baseline. Group II had prolonged return to baseline, and in Group IV the flow ratio remained at control levels throughout reperfusion. ATP and creatine phosphate were best preserved in Group IV, although in all groups ATP remained greater than 75% of control. No significant uptake of calcium was noted on reperfusion in any group. Electron microscopy demonstrated intracellular edema and minimal ischemic injury in all groups, but Group II biopsies revealed extravasated red blood cells in the interstitium. Careful MD-BCP results in superior myocardial protection, whereas suboptimal BCP results in a depressed and damaged myocardium. KCP appears to be more sustained and consistent and therefore may offer greater assurance of reproducible, effective cardioplegia.