An Investigation Into the Influence of the pH of a Cardioplegic Solution on Markers of Myocardial Damage

Although crystalloid cardioplegic solutions are generally buffered to be alkalotic, some workers have advocated the use of an acidotic solution. In order to evaluate the influence of the pH of a crystalloid cardioplegic solution on post-ischaemic markers of myocardial injury, we studied 30 rat hearts using an isolated perfused heart model, with a one hour ischaemic arrest at 20°C following single dose cardioplegia. The pH of the cardioplegic solution was varied by adjusting the pCO2. Six pH levels were studied with five hearts at each level, (group 1 pH = 7.0102 ±0.0106 (±SEM) group 2 = 7.2044 ±0.0077, group 3 = 7.4074 ±0.0068, group 4 = 7.6082 ±0.0071, group 5 = 7.8010 ±0.0082, group 6 = 8.0352 ±0.0129). Pre-arrest (control) and post-arrest coronary effluent enzyme levels, heart rate, coronary vascular resistance and ECG score were determined. In addition, times to spontaneous defibrillation were noted. There were no statistically significant differences between the control values. The mean time in seconds from institution of reperfusion to spontaneous defibrillation in groups 1 to 6 respectively were 67.6 ±2.379, 62 ±1.949, 62 ±1.483 52.4 ±3.326, 58.6 ±1.631 and 55 ±2.55 (p<0.01 Kruskal-Wallis Test). Post-arrest mean heart rates were 190 (one heart only), 203.33 ±26.034, 217.5 ±17.017, 235 ±26.552, 214 ±16 and 208 ±15.29 (NS). The post-arrest mean ECG scores were 2.4 ±0.5099, 1.2 ±0.5831, 1.2 ±0.7348, 0.2 ±0.2, 0.6 ±0.2449 and 0.6 ±0.2449. (NS). Of note is that ECG scores of two or more were only seen in groups 1, 2 and 3. Post-arrest mean coronary vascular resistances were 134.6 ±18.819, 118.6 ±6.653, 78 ±4.461, 65.8 ±2.01, 68 ±1.342 and 72.2 ±5.774 (p<0.001). Post-arrest coronary effluent mean creatine phosphokinase levels were 703.21 ±149.97, 152.34 ±27.959, 141.11 ±12.67 ,80.568 ±16.025, 88.854 ±17.391 and 88.108 ±17.225 (p<0.005). Post-arrest coronary effluent mean lactate dehydrogenase levels were 244.02 ±60.516, 192.46 ±68.234, 141.66 ±56.317, 25.55 ±10.974, 41.366 ±4.428 and 35.2 ±8.473 (p