L.M. West

Machine perfusion for cardiac allograft preservation

Purpose of reviewThe current cardiac preservation strategy for cardiac transplantation involves arresting hearts with a crystalloid preservation solution and storing them in this solution in an ice chest. This technique has allowed good results in heart transplantation, but has limited the transport interval, and has not encouraged major efforts to expand the donor pool. Machine perfusion of explanted organs, a technique used clinically in kidney transplantation, is now under active investigation in the cardiac arena. This review examines the current status of this technology. Recent findingsRecent experimental studies in animals have tested machine perfusion for cardiac preservation. This technique appears to reduce the allograft ischemic burden, may permit longer preservation times, and improves early ventricular function upon reperfusion of the donor heart. The metabolic profile of the stored heart appears better preserved with machine perfusion; however, investigators have noted a risk of edema development in perfused cardiac grafts. SummaryEarly experimental results are encouraging and suggest that machine perfusion may offer superior cardiac performance after transplantation. In the future, this technology may lead to an expansion of the donor pool through greater use of expanded-criteria donors, resuscitation of ischemically injured hearts, or procurement of hearts that are donated after cardiac death.

Myocardial perfusion characteristics during machine perfusion for heart transplantation.

BACKGROUND Optimal parameters for machine perfusion preservation of hearts prior to transplantation have not been determined. We sought to define regional myocardial perfusion characteristics of a machine perfusion device over a range of conditions in a large animal model. METHODS Dog hearts were connected to a perfusion device (LifeCradle, Organ Transport Systems, Inc, Frisco, TX) and cold perfused at differing flow rates (1) at initial device startup and (2) over the storage interval. Myocardial perfusion was determined by entrapment of colored microspheres. Myocardial oxygen consumption (MVO(2)) was estimated from inflow and outflow oxygen differences. Intra-myocardial lactate was determined by (1)H magnetic resonance spectroscopy. RESULTS MVO(2) and tissue perfusion increased up to flows of 15 mL/100 g/min, and the ratio of epicardial:endocardial perfusion remained near 1:1. Perfusion at lower flow rates and when low rates were applied during startup resulted in decreased capillary flow and greater non-nutrient flow. Increased tissue perfusion correlated with lower myocardial lactate accumulation but greater edema. CONCLUSIONS Myocardial perfusion is influenced by flow rates during device startup and during the preservation interval. Relative declines in nutrient flow at low flow rates may reflect greater aortic insufficiency. These factors may need to be considered in clinical transplant protocols using machine perfusion.

Importance of Organ Preservation Solution Composition in Reducing Myocardial Edema during Machine Perfusion for Heart Transplantation

OBJECTIVE Machine perfusion preservation has been used experimentally to extend the storage interval of donor hearts. We previously demonstrated that machine perfusion with glucose-supplemented Celsior preservation solution led to superior reperfusion function but resulted in increased myocardial edema compared with conventional static preservation. We hypothesized that other solutions that contain an oncotic agent, such as University of Wisconsin Machine Perfusion Solution (UWMPS), might reduce graft edema development while maintaining myocardial oxidative metabolism during long-term storage. METHODS Canine hearts were stored and perfused in a perfusion preservation device (LifeCradle; Organ Transport Systems) after cardioplegic arrest and donor cardiectomy. Hearts were perfused either with glucose-supplemented Celsior (which lacks an oncotic agent) or UWMPS (which contains hydroxyethyl starch) at 5 degrees C in the perfusion device over 10 hours. Oxygen consumption (MVO(2)), lactate accumulation, regional flow distribution, and myocardial water content were measured. RESULTS Hearts in both groups continued to extract oxygen over the entire perfusion interval. Lactate accumulation was minimal in both groups. Both solutions delivered perfusate evenly to all regions of myocardium. Heart weight increase (Celsior 31.3 +/- 4.3%, UWMPS -3.3 +/- 1.9%) and final myocardial water content (Celsior 80.2 +/- 1.3%, UWMPS 75.9 +/- 0.3%) were higher in the Celsior group (P < .005). CONCLUSIONS Donor hearts can be supported by a perfusion device over relatively extended storage intervals. These organs continue to undergo oxidative metabolism with little lactate accumulation. An oncotic agent appears to be important in limiting increases in myocardial water content. UWMPS appears to be superior for perfusion preservation of myocardium by reducing edema development during storage.

Differences in regional myocardial perfusion, metabolism, MVO2, and edema after coronary sinus machine perfusion preservation of canine hearts.

Machine perfusion improves solid organ preservation for transplantation. We have demonstrated that antegrade perfusion preservation of hearts is superior to cold storage but may be limited by aortic valve incompetence. We hypothesized that retrograde perfusion (RP) through the coronary sinus may provide more reliable perfusate delivery to the heart. This study was designed to determine the optimal perfusion parameters and evaluate regional flow after RP of canine hearts. After donor cardiectomy, canine hearts (n = 6) were established in a perfusion device (LifeCradle, Organ Transport Systems, Inc., Frisco, TX) through a coronary sinus catheter. Hearts were perfused at 5°C over flow rates from 10 to 35 ml/100 g myocardium/min for 20 minutes at each flow rate. Colored microspheres were used to quantify tissue perfusion. Oxygen consumption (MVO2) and perfusion parameters were measured. At end-perfusion, tissue was collected for proton magnetic resonance spectroscopy (1H MRS), microsphere analysis, and determination of myocardial edema. MVO2 increased up to flow rates of 20 ml/100 g/min. Right ventricular (RV) perfusion was reduced at all flow rates. Increased lactate/alanine ratios by 1H MRS and reduced myocardial water content were noted in RV samples. RP results in excellent left ventricular (LV) perfusion. RV perfusion is reduced and oxidative metabolism in the right ventricle may not be maintained by RP. Further studies to evaluate effects of reduced RV perfusion by RP on functional recovery after transplantation are warranted.

Metabolic characteristics of human hearts preserved for 12 hours by static storage, antegrade perfusion, or retrograde coronary sinus perfusion

OBJECTIVE Machine perfusion of donor hearts is a promising strategy to increase the donor pool. Antegrade perfusion is effective but can lead to aortic valve incompetence and nonnutrient flow. Experience with retrograde coronary sinus perfusion of donor hearts has been limited. We tested the hypothesis that retrograde perfusion could support myocardial metabolism over an extended donor ischemic interval. METHODS Human hearts from donors that were rejected or not offered for transplantation were preserved for 12 hours in University of Wisconsin Machine Perfusion Solution by: (1) static hypothermic storage; (2) hypothermic antegrade machine perfusion; or (3) hypothermic retrograde machine perfusion. Myocardial oxygen consumption (MVO2), and lactate accumulation were measured. Ventricular tissue was collected for proton and phosphorus 31 magnetic resonance spectroscopy (MRS) to evaluate the metabolic state of the myocardium. Myocardial water content was determined at the end of the experiment. RESULTS Stable perfusion parameters were maintained throughout the perfusion period with both perfusion techniques. Lactate/alanine ratios were lower in perfused hearts compared with static hearts (P<.001). Lactate accumulation (antegrade 2.0±0.7 mM, retrograde 1.7±0.1 mM) and MVO2 (antegrade 0.25±0.2 mL, retrograde 0.26±0.3 mL O2/min/100 g) were similar in machine-perfused groups. High-energy phosphates were better preserved in both perfused groups (P<.05). Left ventricular myocardial water content was increased in retrograde perfused hearts (80.2±0.8%) compared with both antegrade perfused hearts (76.6±0.8%, P=.02) and static storage hearts (76.7±1%, P=.02). CONCLUSIONS Machine perfusion by either the antegrade or the retrograde technique can support myocardial metabolism over long intervals. Machine perfusion seems promising for long-term preservation of human donor hearts.

Glucose is an Ineffective Substrate for Preservation of Machine Perfused Donor Hearts

BACKGROUND Machine perfusion with oxygenated preservation solution can support donor heart metabolism but the preservation solution should contain an oxidizable substrate to improve cellular energetics. We hypothesized that myocardial metabolism can be influenced by exogenous substrates in the preservation solution. METHODS Eight groups of isolated rat hearts (n = 4/group) were perfused with University of Wisconsin Machine Perfusion Solution containing carbon 13 ((13)C) labeled glucose (2.5 mM, 5 mM, 10 mM, or 20 mM) or pyruvate (5 mM, 10 mM, 20 mM, or 40 mM). Hearts were perfused at 0.5 mL/min for 6 h at 8°C, and myocardial oxygen consumption (MVO(2)) was measured. At end-perfusion, magnetic resonance spectroscopy was performed on ventricular extracts to determine the contribution of exogenous, labeled substrate to glycolysis and oxidative metabolism by (13)C incorporation into metabolic intermediates. RESULTS MVO(2) and perfusion conditions did not differ amongst groups. Exogenous glucose was metabolized by anaerobic glycolysis and contributed little to oxidative metabolism as measured by (13)C incorporation into metabolic intermediates. Pyruvate led to greater lactate enrichment via the lactate dehydrogenase reaction. Enrichment of tricarboxylic acid (TCA) cycle intermediates was also greater in all pyruvate groups compared with glucose-containing groups (P < 0.05). Anaplerosis was increased in all pyruvate groups (P < 0.05). CONCLUSIONS The preservation solution substrate composition influences myocardial substrate metabolism during machine perfusion preservation of donor hearts. Exogenous glucose is a minor substrate in machine perfused myocardium, is primarily metabolized by glycolysis and does not contribute appreciably to oxidative metabolism. Pyruvate appears more effective in supporting myocardial metabolism. Further experiments examining the influences of substrate modifications on reperfusion function are warranted.

Effects of Antegrade and Retrograde Machine Perfusion Preservation on Cardiac Function After Transplantation in Canines

INTRODUCTION Most studies investigating machine perfusion preservation for heart transplantation perfuse through the aortic root (antegrade), but the coronary sinus (retrograde) is a potential option. We hypothesized that retrograde machine perfusion provides better functional protection than static storage, while avoiding the potential irregular perfusion seen when aortic insufficiency occurs with antegrade perfusion. MATERIALS AND METHODS Eighteen canine donor hearts were arrested, procured, and stored in modified Celsior solution for 4 hours by using either static storage at 0°C to 4°C (n = 6) or machine perfusion preservation at 5°C via the aortic root (antegrade, n = 6) or coronary sinus (retrograde, n = 6). Lactate and myocardial oxygen consumption were measured in perfused hearts. Hearts were reimplanted and reperfused for 6 hours with hourly function calculated by using the preload recruitable stroke work (PRSW) relation. Myocardial water content was determined at the end of the experiment. RESULTS Storage lactate levels and myocardial oxygen consumption were comparable in both perfused groups. The PRSW was increased immediately after bypass in the antegrade group (120.6 ± 19.1 mm Hg) compared with the retrograde (75.0 ± 11.3 mm Hg) and static (78.1 ± 10.5 mm Hg) storage groups (P < .05). At the end of reperfusion, PRSW was higher in the retrograde group (69.8 ± 7.4 mm Hg) compared with the antegrade (40.1 ± 6.8 mm Hg) and static (39.9 ± 10.9 mm Hg) storage groups (P < .05). Myocardial water content was similar among groups. CONCLUSIONS Both antegrade and retrograde perfusion demonstrated excellent functional preservation, at least equivalent to static storage. Initial function was superior in the antegrade group, but the retrograde hearts displayed better function late after reperfusion. Neither perfused group developed significant edema. Machine perfusion preservation is a promising technique for improving results of cardiac transplantation.