40-HOUR PRESERVATION OF THE RABBIT HEART - OPTIMAL OSMOLARITY, [MG2+], AND PH OF A MODIFIED UW SOLUTION

The University of Wisconsin solution modified with 2,3-butanedione mon oxime and calcium experimentally extends the limits of ischemic preser vation of the heart. This study evaluates other characteristics of thi s modified solution that may further enhance preservation: osmolarity, Mg2+ concentration ([Mg2+]), and pH. Rabbit hearts were hushed with t he modified University of Wisconsin solution and stored for 40 hours a t 4 degrees C. Maximal left ventricular developed pressure (LVDP), lef t ventricular end-diastolic volume (LVEDV), maximum rate of increase o f left ventricular pressure (dP/dt), heart rate, and coronary now were measured during 60 minutes of isolated crystalloid reperfusion with a n isovolumic left ventricular balloon at constant end-diastolic pressu re. Creatine kinase release and myocardial adenine nucleotide content were measured at completion of reperfusion. Solution osmolarity was te sted at 357, 327, 297, and 277 mOsm/T, by reducing K+, Na+, and lactob ionate concentrations. [Mg2+] was assessed at 5 and 16 mmol/L. Solutio n pH was studied at 7.0, 7.4, and 7.8. A control group of hearts was f lushed and immediately reperfused to establish baseline function. Hear ts stored in either hypertonic (357 mOsm/L) or hypotonic (277 mOsm/L) solutions functioned poorly, reaching 58% and 50% of control LVDP (p < 0.001), 49% (p < 0.01), and 58% (p = not significant) of LVEDV, 56% a nd 49% of +dP/dt (tt < 0.001), respectively, and released substantiall y more creatine kinase (p < 0.001 versus control). Hearts stored in ne ar-isotonic solutions (327 and 297 mOsm/L) functioned better, attainin g 79% and 72% of control LVDP (p < 0.05), 94% and 110% of LVEDV (p = n ot significant), 89% and 85% of +dP/dt (p = not significant), respecti vely, and released less creatine kinase (p = not significant versus co ntrol). An increase in [Mg2+] to 16 mmol/L further improved LVDP to 84 % (p < 0.05), and dP/dt to 91% of control (p = not significant). Adeno sine triphosphatase regeneration also returned to control levels. Rais ing or lowering the solution pH resulted in significantly worsened ven tricular function and a greater creatine kinase release (p < 0.001). W e conclude that hearts preserved in this modified University of Wiscon sin solution regain substantial ventricular function, even after 40 ho urs of cold ischemia, when the solution osmolarity is kept between 297 and 327 mOsm/L, [Mg2+] is elevated to 16 mmol/L, and pH is maintained at 7.4.