An isolated, blood perfused pig heart model was adapted for metabolic studies using 31 P NMR spectroscopy during continuous normothermic blood cardioplegia (CNBC). The experiment comprised two groups: In Group I (n=5) the hearts were subjected to 1 hour of CNBC. In Group II (n=5) a 20 min period of ischemia was introduced in the middle of the period of CNBC. Left ventricular function was assessed, in the beating heart, prior to the period of CNBC and after 60 min of cardioplegia, using an intra-ventricular balloon. During the entire period of the experiment, spectra were obtained using a 4.7 T/30 cm bore BrukerTM Biospec 31P NMR spectrometer with 2 min of resolution. At the end of the experiments myocardial biopsies were taken for ATP and phosphocreatine (PCr) analyses using high performance liquid chromatography (HPLC). ATP and PCr were maintained after the period of cardioplegic arrest (Group I). However the Group II, complete loss of PCr was shown after 14 ± 2 min of normothermic ischemia, followed by an increase of inorganic phophate (Pi) and decrease of intracellular pH. Following reperfusion after CNBC, PCr, pH and Pi returned normal values in 3 min. Left ventricular function, assessed by end-systolic elastance, was maintained at 100±10% of control in Group I. In the Group II, left ventricular function was 88 ± 7% (p<0.05) of the control. HPLC analyses of the myocardial biopsies showed normal values for Group I, ATP (24 ± 3 µmol/g dry weight) and PCr (55 ± 14 µmol/g dry weight), but in Group II, despite normal levels of PCr after reperfusion, the ATP levels decreased to 21 ± 3 µmol/g dry weight at the end of the experiments. These results showed that cardiac metabolism was seriously compromised after 14 min of normothermic ischemia and left ventricular function had decreased (Group II). However in Group I, in which CNBC was used without interruptions, function and metabolism were preserved, suggesting this is the ideal technique to protect the heart during cardiac surgery.
nuclear magnetic ressonance; cardioplegia