Relationship between atrioventricular arrhythmias and the concentration of K⁺ ion in cardioplegic solution

The use of potassium cardioplegia during cardiac operation is associated with various types of arrhythmias such as a complete heart block or junctional rhythm following the resumption of coronary blood flow. The purpose of this study was twofold: (I) to determine if a relationship exists between the atrioventricular (AV) dissociation arrhythmias and the quantity of potassium used in cardioplegic solutions and (2) to determine whether reducing the quantity of potassium ion infused would result in depletion of high-energy phosphates (HEPs) during the period of cardioplegic arrest. Patients undergoing myocardial revascularization made up the study group, which consisted of three groups of 20 patients each. Group I was perfused with 20 mEq/L K⁺ cardioplegic solution both initially and after each distal anastomosis. Group II was perfused with 5 mEq/L K⁺ both initially and after each distal anastomosis. Group III was perfused initially with 20 mEq/L K⁺ and then with 5 mEq/L K⁺ for subsequent anastomoses. There was a statistical difference in the incidence of arrhythmias both at hypothermic (28°C) and normothermic temperatures among the groups. In Group I an average of 29 mEq K⁺ was infused and 85% incidence of arrhythmias was noted at 28°C. In Group II 8 mEq K⁺ was infused and a 15% incidence of arrhythmia (P<0.001) was observed. Group III had an average of 21 mEq K⁺ infused, and six of 15 patients had arrhythmias (p<0.01). At 37°C, Group I patients had a 45% incidence of arrhythmias as compared to Group II (10%) and Group III (10%) (p<0.05). The level of HEPs, including both adenosine triphosphate (ATP) and creatine phosphate (CP), was 61.2 μmoles/gm and fell to 53.5 μmoles/gm (13%) in Group I (p = NS). By comparison, in Group II the HEP level was 62.7 μmoles/gm at control and fell to 59.7 μmoles/gm (5%) (p = NS). In group III, the HEP level was 58.9 μmoles/gm at control and fell to 49.4 μmoles/gm (16%) after cardioplegic arrest (p = NS). There was essentially no change in HEPs in any group. This study indicates that excellent myocardial preservation can be obtained with the use of either high concentrations of potassium (20 mEq/L K⁺) or normal concentrations of potassium (5 mEq/L K⁺). Significant AV dissociation arrhythmias can be avoided by using an initial infusion of 20 mEq/L K⁺, followed by repeated infusions with normal concentrations of potassium, while still preserving HEPs during the arrest period.