Optimization of techniques for cardiac preservation: Phosphorus-31 NMR spectroscopic and functional studies in isolated rat and pig hearts.

Abstract

The effects of cardioplegic and reperfusion conditions on energy metabolites and cardiac function were investigated in order to define better conditions for heart preservation (4 or 8 hrs). Myocardial energy metabolites (ATP, PCr and inorganic phosphate), intracellular pH and contractile function were followed using $\sp{31}$P NMR spectroscopy and left intra-ventricular balloon, respectively, during preservation and reperfusion in isolated pig and rat hearts. These hearts were subjected to various conditions of cardioplegia and reperfusion which involved re-arrest perfusion following ischemic preservation, increased concentrations of buffer and Mg$\sp{++}$ in cardioplegic and reperfusion solutions, and an intracellular-type cardioplegic solution. The effect of re-arrest perfusion was tested by comparing the recovery of energy metabolites and contractile function between pig hearts subjected to a secondary cardioplegic solution (S-C-S) prior to Krebs-Henseleit (K-H) solution and those reperfused with K-H solution alone after 8 hours of ischemic preservation at 12$\sp\circ$C. The levels of ATP and PCr during reperfusion in both groups of hearts were comparable whereas the left ventricular developed pressure was significantly higher in the hearts reperfused with S-C-S than in those reperfused only with K-H solution. The reperfusion-induced ventricular fibrillation that occurred in K-H reperfused hearts was prevented by re-arrest perfusion. A cardioplegic solution containing 150 mmol/L MOPS (higher buffer cardioplegic solution) helped to maintain intracellular pH during 8 hours of ischemic preservation. However, it did not affect the levels of energy metabolites during preservation and contractile function during reperfusion. The effects of 16 mmol/L Mg$\sp{++}$ in cardioplegic and reperfusion solution were evaluated using both rat and pig hearts. In working rat hearts, 16 mmol/L Mg$\sp{++}$ in cardioplegic solution did not alter myocardial oxygen consumption and contractile function following 30 minutes of normothermic preservation. Moreover, Langendorff pig hearts preserved with either 0 or 16 mmol/L Mg$\sp{++}$ cardioplegic solution showed similar decrements in energy metabolites during 4 hours of ischemic preservation at 12$\sp\circ$C and recovery of contractile function during reperfusion while 16 mmol/L Mg$\sp{++}$ in K-H solution resulted in a dramatic decline of contractile function. Furthermore, 16 mmol/L Mg$\sp{++}$ in S-C-S also did not affect the levels of high energy phosphates and contractile function during reperfusion. At 4$\sp\circ$C the pig hearts stored with either University of Wisconsin solution (UW, an intracellular-type cardioplegic solution) or St Thomas' solution (an extracellular-type cardioplegic solution) showed comparable changes in energy metabolites during 8 hours of preservation and a similar recovery of contractile function during reperfusion. However, at 12$\sp\circ$C, hearts stored in UW solution showed rapid decrease in ATP and PCr during preservation and significantly poorer functional recovery during reperfusion; four of eight hearts stored in UW solution at 12$\sp\circ$C showed the "stone heart" phenomenon with disappearance of PCr and ATP upon reperfusion. The addition of 0.5 mmol/L Ca$\sp{++}$ to UW solution significantly improved contractile function and prevented the occurrence of the "stone heart" phenomenon with stable levels of high energy phosphates. (Abstract shortened by UMI.)