Changes in myocardial free amino acids during pediatric cardiac surgery: a randomised controlled trial of three cardioplegic techniques.

Objective: The developing heart has a much greater dependence on amino acid (AA) metabolism than the adult heart in determining its ischemic tolerance. Blood cardioplegia preserves myocardial free AAs in adult hearts but no clinical studies have looked at the effect of different cardioplegic techniques on intracellular free AAs in the pediatric heart.
Methods: Pediatric patients were randomised to receive intermittent antegrade cold crystalloid (CC), cold blood (CB) or cold blood cardioplegia with a 'hot shot' (CB+HS). Right ventricular biopsies were collected prior to ischemia, at the end of ischemia and 20 min after reperfusion. Amino acid levels were analysed as repeated measures, adjusting for baseline levels. Data were analysed separately for acyanotic and cyanotic patients.
Results: Of 103 patients recruited, 32 (22 acyanotic and 10 cyanotic), 36 (24/12) and 35 (25/10), respectively were allocated to CC, CB and CB+HS groups. Cyanotic patients were significantly younger with longer cross-clamp times. In acyanotic patients, there were no significant effects of cardioplegic method on aspartate, glutamine, taurine, alanine or branched chain AA levels (all p>0.05). However, in cyanotic patients, there were significant interactions of cardioplegic method and time (all p<0.05) for all amino acids, with patients allocated to CB+HS having higher levels after reperfusion compared with CC, and patients allocated to CB having intermediate levels.
Conclusions: For cyanotic patients (younger, longer cross-clamp times), CB+HS preserves myocardial free AAs better than CC; CB gives an intermediate effect. In acyanotic patients, AA levels (all p>0.15) and group means were similar both at the end of ischemia and after reperfusion.