MYOCARDIAL PROTECTION DURING PROLONGED ISCHEMIC CARDIAC-ARREST - EXPERIMENTAL EVALUATION OF 3 CRYSTALLOID CARDIOPLEGIC SOLUTIONS

The aim of this study is to define the cardioprotective effects (funct ional and metabolic) of our modified ''extracellular'' cardioplegic so lution (MBS: containing glucose, aspartate and lactobionate), St. Thom as' Hospital No. 2 (STH) and Bretschneider's No. 3 (Bret) solutions du ring prolonged hypothermic ischaemia (20-degrees-C, 6 hours) in the is olated working rat heart. Hearts (n = 9-10 in each group) were arreste d with, and exposed to, multidose reinfusion (2 minutes every 40 minut es interval) throughout the ischaemic period with cold (4-degrees-C) M BS, STH or oxygenated (95% O2: 5% CO2) Bret. All MBS treated hearts re sumed spontaneous regular sinus rhythm (0.51 +/- 0.01 minutes) of cont raction during post-ischaemic reperfusion for 30 minutes at 37-degrees -C with the complete recovery of all the functional indices (aortic fl ow: 87.4 +/- 3.4%, cardiac output: 94.1% +/- 3.3%, coronary flow: 101. 8 +/- 4.1%, heart rate: 99.8 +/- 2.8% and aortic pressure: 105.7 +/- 4 .6% of prearrest control values). In contrast, hearts protected with e ither STH or Bret showed the poor or no post-ischaemic recovery of car diac pump function (aortic flow: 7.2 +/- 4.8%, and 0%, respectively). Recovery of all other left ventricular function indices were also sign ificantly (p < 0.001) decreased with increasing more hearts failing to regain function (MBS: 0/10, STH: 7/9 and Bret: 9/9). The efflux of la ctate during 6 hours ischaemic arrest was increased [52.40 +/- 1.50 v 36.8 +/- 1.70 (STH) or 14.45 +/- 0.70 (Bret) mumol/heart, p<0.001] and the progressive increase in the coronary vascular resistance was comp letely abolished in MBS treated hearts. These improvements were associ ated with the reduction in the decline of the myocardial adenosine tri phosphate (23.44 +/- 1.08 v 3.79 +/- 1.08 or 4.51 +/ 0.71 mumol/g dry wt), creatine phosphate (30.23 +/- 1.52 v 8.01 +/- 2.21 or 5.41 +/- 0. 03 mumol/g dry wt) and guanosine triphosphate (2.26 +/- 0.23 v 0.24 +/ - 0.11 or 0.59 +/- 0.07 mumol/g dry wt) during ischaemia, and total re synthesis after reperfusion (ATP: 92% v 36% or 25% and CP: 126% v 92% or 59% of control). These results indicate that the new cardioplegic s olution, MBS can meet the metabolic demand of the ischaemic myocardium because of the greater synthesis of intramyocardial ATP and CP during cardioplegic arrest, provide substantially improved protection of hea rts from injury and thus increase (double) the safe duration of cardia c arrest.