Interstitial pH during myocardial preservation: Assessment of five methods of myocardial preservation

We investigated changes in myocardial pH during cardioplegic arrest with five methods of preservation at 15 ° ± 1 °C. Twenty-five dogs were subjected to cardiopulmonary bypass for 150 minutes. Group I (control) had hypothermia only. Group II received THAM-buffered blood cardioplegia, group III a bicarbonate-buffered blood cardioplegic solution, group IV infusions of hyperkalemic blood, and group V oxygenated St. Thomas 2 solution. After 120 minutes of ischemia, interstitial pH in group I was markedly depressed (6.4 ± 0.07; p < 0.01). The pH in groups II and IV was well maintained (7.23 ± 0.05 and 7.27 ± 0.07) and differed significantly ( p < 0.05) from that of the remaining groups. The pH in groups III and V was less well maintained (7.14 ± 0.02 and 7.01 ± 0.05), with no significant difference ( p > 0.05) between these two groups. Postreperfusion functional recovery after 45 minutes was 24% ± 6% in group I, 92% ± 3% in group II, 82% ± 5% in group III, 84% ± 4% in group IV, and 66% ± 6% in group V. Creatine kinase levels were significantly ( p < 0.01) increased and ultrastructural damage was more prominent in group I compared with the remaining groups. Myocardial water content significantly increased in all groups. We conclude that a strongly buffered blood-based cardioplegic solution is more effective in preventing interstitial acidosis during moderate hypothermia and that maintenance of an optimal tissue pH plays an important role in postischemic functional recovery.