Myocardial Substrate Oxidation and Tricarboxylic Acid Cycle Intermediates During Hypothermic Machine Perfusion.

BACKGROUND: The optimal substrate for hypothermic machine perfusion preservation of donor hearts is unknown. Fatty acids, acetate, and ketones are preferred substrates of the heart during normothermic perfusion, but cannot replete the tricarboxylic acid (TCA) cycle directly. Propionate, an anaplerotic substrate, can replenish TCA cycle intermediates and may affect cardiac metabolism. The purpose of this study was to determine myocardial substrate preferences during hypothermic machine perfusion and to assess if an anaplerotic substrate was required to maintain the TCA cycle intermediate pool in perfused hearts. METHODS: Groups of rat hearts were perfused with carbon-13 (13C)-labeled substrates (acetate, ß-hydroxybutyrate, octanoate, with and without propionate) at low and high concentrations. TCA cycle intermediate concentrations, substrate selection, and TCA cycle flux were determined by gas chromatography/mass spectroscopy and 13C magnetic resonance spectroscopy. RESULTS: Acetate and octanoate were preferentially oxidized, whereas ß-hydroxybutyrate was a minor substrate. TCA cycle intermediate concentrations except fumarate were higher in substrate-containing perfusion groups compared with either the no-substrate perfusion group or the no-ischemia control group. CONCLUSIONS: The presence of an exogenous, oxidizable substrate is required to support metabolism in the cold perfused heart. An anaplerotic substrate is not essential to maintain the TCA cycle intermediate pool and support oxidative metabolism under these conditions.

Successful transplantation in canines after long-term coronary sinus machine perfusion preservation of donor hearts.

BACKGROUND: Machine perfusion is a promising strategy for donor heart preservation, but delivery of perfusate through the aorta may be limited by aortic valve incompetence. We hypothesized that retrograde machine perfusion preservation through the coronary sinus avoided this issue and allowed for recovery of donor hearts after long-term storage. METHODS: Canine hearts were procured after arrest with 1 liter University of Wisconsin Machine Perfusion Solution (UWMPS) and preserved for 14 hours by static hypothermic storage (Static group, n = 5) or retrograde machine perfusion through the coronary sinus (RP group, n = 5). Myocardial oxygen consumption (MVo2) and lactate were monitored in perfused hearts. Hearts were implanted and reperfused for 6 hours. The pre-load recruitable stroke work was determined as a measure of myocardial function. Cardiac enzyme release was quantified. Cell death was evaluated by TUNEL (terminal deoxynucleotidyltransferase-mediated deoxy uridine triphosphate nick-end label). RESULTS: MVo2 decreased initially then stabilized. Lactate accumulation was low in RP hearts. All RP hearts separated from cardiopulmonary bypass. All Static hearts required a return to bypass (p < .05). Pre-load recruitable stroke work in RP hearts was increased (55 ± 7 mm Hg) compared with Static (20 ± 11 mm Hg, p < .05) and did not differ from baseline values. Creatine kinase release was greater in Static group hearts (102 ± 16 IU/liter/g) than in RP hearts (51 ± 8 IU/liter/g, p < .05). The fraction of TUNEL-positive cells was higher in the Static group, but this difference was not significant. CONCLUSIONS: Retrograde machine perfusion can preserve donor hearts for long intervals. Cardiac function after implantation suggested excellent myocardial protection. Retrograde machine perfusion appears promising for extending the donor ischemic interval and improving results of heart transplantation.

Characterizing cardiac donation after circulatory death: implications for perfusion preservation.

BACKGROUND: Donation after circulatory determination of death (DCDD) involves variable definitions of death among hospitals, and DCDD hearts are not generally considered for transplantation. The definition can affect ischemic times, and machine perfusion preservation appears promising for recovery of DCDD hearts. The purpose of the current study was to investigate the agonal phase of DCDD donors and evaluate retrograde perfusion preservation of DCDD donor hearts in a large animal model of cardiac transplantation. METHODS: Ten canines were anesthetized and then disconnected from mechanical ventilation. Time to loss of pulse (systolic blood pressure <50 mm Hg), loss of pressure, and asystole or fibrillation were recorded. Five minutes after asystole, hearts were exposed and arrested with 1 L of University of Wisconsin Machine Perfusion Solution. Eight hearts were cold preserved for 4 hours by retrograde machine perfusion or static storage (n = 4/group), then reimplanted and reperfused for 6 hours. The preload recruitable stroke work was used to measure myocardial function. RESULTS: The agonal phase was similar between groups. Loss of pulse and pressure were consistent between animals (7.9 ± 0.5 minutes [range, 5 to 11 minutes], 10.2 ± 0.4 minutes [range, 9 to 13 minutes], respectively). Electrical silence was variable at 26.9 ± 3.8 minutes (range, 11 to 43 minutes). All perfused hearts separated and remained off cardiopulmonary bypass. Three of four static hearts initially separated from cardiopulmonary bypass, but two returned by the end of the reperfusion period. The preload recruitable stroke work was significantly higher in perfused hearts. CONCLUSIONS: Protocols for DCDD have implications on ischemic times of donor hearts. Machine perfusion preservation can recover DCDD hearts more consistently than static storage.