Myocardial protection by warm blood cardioplegia. A ³¹P nuclear magnetic resonance spectroscopy study of an isolated perfused rat heart

Objective: A study of the protective efficiency imparted by intermittent warm blood cardioplegia (WBCP) using perfused rat heart model. Methods: Hemodynamic parameters were monitored simultaneously with metabolic changes in high-energy phosphates using ³¹P-NMR spectroscopy. Following 30 min perfusion with Krebs-Henseleit (KH) buffer, all hearts were arrested for one hour (G1 and G2) and then reperfused with KH for 30 minutes. A warm oxygenated crystalloid cardioplegia (WCCP, modified St Thomas' hospital solution) was used for the control group (G1). The second group of hearts (G2) were arrested with oxygenated WBCP (K+=15 mM; Hct=15-20%) and the third group (G3), was subjected to a protocol consisting of 4 periods (10 min each) of WBCP interspersed by 10 min of global ischaemia. Results: The post-arrest percentage recoveries of LVDP, +dP/dt and HR were respectively: 88, 93 and 90 for G1 (n=8); 97, 100 and 98 for G2 (n = 10); 76, 79 and 91 for G3 (n=12). The corresponding metabolic recoveries of ATP and PCr were respectively, 85 and 90 for G1; 91 and 98 for G2 and 73 and 85 for G3. The PCr level declined during the arrest period in G1 contrasting with elevated PCr level (> 140%) during the WBCP arrest in G2. After an initial rise to ~140%, PCr level gradually decreased during the intermittent WBCP interval (G3). Conclusions: At normothermia, with equal CF rates, continuous WBCP provides better myocardial protection, through an effective oxygen supply, compared with WCCP. During the intermittent periods of ischaemia, certain metabolic and hemodynamic dysfunction occurs.