Neonatal myocardial oxygen consumption during ventricular fibrillation, hypothermia, and potassium arrest

Background. Many investigators have examined oxygen consumption in adult hearts under conditions that simulate those encountered during cardiac operations and those that approximate basal metabolism. Few studies, however, have addressed this issue in neonatal myocardium. Methods. Hearts from 3- to 9-day-old piglets were studied in a blood-perfused isolated heart preparation in working, empty beating, fibrillating, potassium chloride-arrested (at 37°C and 15°C), and hypothermic (15°C) states. Results. Oxygen consumption (expressed in milliliters of O₂ per 100 g of ventricular tissue per minute; mean ± standard deviation) was 6.69 ± 1.91 for working hearts and fell to 3.19 ± 1.08 for empty-beating hearts, 3.72 ± 0.84 for fibrillating hearts, 1.30 ± 0.34 for potassium-arrested hearts at 37°C, 0.37 ± 0.18 for hypothermic (15°C) hearts, and 0.32 ± 0.10 for potassium-arrested hearts at 15°C. All values were significantly different except the two obtained at 15°C. Conclusions. Vented fibrillating hearts used more oxygen than empty beating hearts. The addition of an arresting concentration of KCl did not lower oxygen consumption below that observed with hypothermia alone at 15°C. If potassium-based cardioplegia is incrementally beneficial in neonatal myocardial protection over that afforded by hypothermia alone, its effects cannot be explained by reduction in oxygen demand.