Cardioplegic protection of hearts with pre-arrest ischaemic injury: effect of glucose, aspartate, and lactobionate.

This study compared the cardioprotective effects of three oxygenated "extracellular" crystalloid cardioplegic solutions. These were MBS (containing glucose, aspartate, and lactobionate [GAL]), St. Thomas' Hospital No. 2 (STH), and modified STH (added glucose, aspartate, and lactobionate) (STHGAL). Isolated working rat hearts (45) were initially injured with 10 min of global normothermic ischaemia and then arrested for 4 hr at (30 degrees C) with multidose cardioplegia (2 min every 30 min). The hearts (n = 9 per group) were then reperfused for 7 min in the non-working mode and for a further 23 min in the working mode. MBS-treated hearts rapidly resumed spontaneous sinus rhythm (0.69 +/- 0.06 minutes) with nearly complete recovery of function (aortic flow 93.3 +/- 5.4%, cardiac output 95.7 +/- 3.6%, stroke volume 95.3 +/- 3.7%, heart rate 102.2 +/- 3.7%, and aortic pressure 88.3 +/- 3.2% of pre-ischaemic control values). With either STH or STHGAL these indices were significantly (p < 0.01) lower (aortic flow 25.5 +/- 10.4% or 69.5 +/- 6.5%, cardiac output 30.1 +/- 11.1% or 67.6 +/- 6.6%, aortic pressure 36.5 +/- 7.7% or 63.9 +/- 8.0%, respectively). Total lactate efflux (indicating glycolysis) during cardioplegia was increased (p < 0.01) by inclusion of GAL (MBS 63.7 +/- 1.8, STHGAL 68.7 +/- 2.2, STH 28.5 +/- 1.3 mumol/heart). Progressive increase in coronary vascular resistance was observed during STH-based cardioplegia but not during MBS-based. The improved recovery of function was associated with reduced depletion of adenosine triphosphate (MBS 9.44 +/- 0.79, STHGAL 8.21 +/- 1.00, STH 1.02 +/- 0.10 mumol/g dry wt), total adenine nucleotide pool (14.61 +/- 0.83, 16.81 +/- 0.85, 7.33 +/- 0.52 mumol/g dry wt) and energy charge (0.767 +/- 0.019, 0.620 +/- 0.037, 0.248 +/- 0.012) during arrest, and significantly (p < 0.01) better resynthesis during reperfusion (ATP: 66%, 16%, 40%; TAN: 64%, 22%, 43% of control respectively). These findings indicate that the novel cardioplegic solution MBS (US Pat. No. 5,290,766) provides better myocardial protection than STH in hearts with pre-arrest ischaemic injury not only by providing metabolic substrates but also because of its more appropriate balance of cations.