Protection of myocardial function not enhanced by high concentrations of potassium during cardioplegic arrest

Myocardial performance was evaluated intraoperatively in 20 patients undergoing myocardial revascularization when hypothermic potassium cardioplegic arrest was used. High concentrations of potassium (20 mEq/L) were compared to normal concentrations of potassium (5 mEq/L) in hypothermic cardioplegic solutions. The cardioplegic arrest period averaged 53 +/- 3 minutes in the high potassium group and 54 +/- 4 minutes in the low potassium group, Intraoperative calculation of ejection fraction and end-diastolic volume was accomplished by the technique of radiocardiography. All data were grouped according to end-diastolic volume index (EDVI) for both high (HK) and low (LK) potassium comparisons. Comparisons between high and low potassium groups demonstrated no significant differences in ejection fraction (HK = 66%, LK = 61%), cardiac index (HK = 2.74 L/min/m2, LK = 3.0 L/min/m2), stroke work (HK = 36 gm.m/m2, LK = 30 gm.m/m2), oxygen consumption as measured by left heart double product (HK = 9,438; LK = 9,209), and myocardial compliance (HK = 2.8 cc/torr, LK = 4.2 cc/torr at the post-cardioplegic arrest period). The role potassium plays in producing a rapid cardiac arrest is well accepted. Its protective effect on the preservation of high-energy phosphate stores is postulated, but its addition to perfusion hypothermia does not appear to enhance the protective effect observed with perfusion hypothermia alone.