Cardiac hypothermia: 31P and 1H NMR spectroscopic studies of the effect of buffer on preservation of human heart atrial appendages.

31P and 1H nuclear magnetic resonance spectroscopy has been used to follow noninvasively the time course of energetic metabolite levels in human heart atrial appendages preserved under various temperatures and buffer conditions. From sample harvest up to the normal 5-h time limit for heart preservation, ATP levels in human atrial appendages are much better maintained in 0.9% saline and PIPES-buffered preservation solutions at 12 degrees C than at 4 degrees C. Furthermore, preservation at 12 degrees C can be improved considerably by using high extracellular buffer concentrations. The increased buffer concentration allows better maintenance of the intracellular pH and leads to a faster glycolytic rate as measured by lactate production. At 4 degrees C, ATP levels decline rapidly during the first 5 h but reached a stable plateau, which is well maintained over 15-20 h. At this temperature, the rate of lactate production is similar at all buffer concentrations (20, 60, and 100 mM PIPES). As a consequence of these observations, we postulate that the mechanisms of ATP production and utilization at 4 degrees C and at 12 degrees C are different. At 4 degrees C, the rate of glycolysis is temperature limited whereas at 12 degrees C, low intracellular pH inhibits glycolysis.