Heart transplantation in donation after circulatory death (DCD) relies on warm perfusion using either in situ normothermic regional perfusion (NRP) or ex situ normothermic machine perfusion. In this study, we explore an alternative: oxygenated hypothermic machine perfusion (HMP) using a novel clinically applicable perfusion system, which is compared to NRP with static cold storage (SCS). In a porcine model, a DCD setting was simulated, followed by either (1) NRP and SCS (2) NRP and HMP with the XVIVO Heart preservation system or (3) direct procurement (DPP) and HMP. After preservation, heart transplantation (HTX) was performed. After weaning from cardiopulmonary bypass (CPB), biventricular function was assessed by admittance and Swan-Ganz catheters. Only transplanted hearts in the HMP groups showed significantly increased biventricular contractility (end-systole elastance) 2 hour post-CPB (left ventricle absolute change: NRP HMP: +1.8 ± 0.56, p = 0.047, DPP HMP: +1.5 ± 0.43, p = 0.045 and NRP SCS: +0.97 ± 0.47 mmHg/ml, p = 0.21; right ventricle absolute change: NRP HMP: +0.50 ± 0.12, p = 0.025, DPP HMP: +0.82 ± 0.23, p = 0.039 and NRP SCS: +0.28 ± 0.26, p = 0.52) while receiving significantly less dobutamine to maintain a cardiac output >4l/min compared to SCS. Diastolic function was preserved in all groups. Post-HTX, both HMP groups showed significantly less increments in plasma troponin T compared to SCS. In DCD HTX, increased biventricular contractility post-HTX was only observed in hearts preserved with HMP. In addition, the need for inotropic support and signs of myocardial damage were lower in the HMP groups. DCD HTX can be successfully performed using DPP followed by preservation with HMP in a preclinical setting.

Background: The ketone body 3‐hydroxybutyrate (3‐OHB) increases cardiac output (CO) by 35% to 40% in healthy people and people with heart failure. The mechanisms underlying the effects of 3‐OHB on myocardial contractility and loading conditions as well as the cardiovascular effects of its enantiomeric forms, D‐3‐OHB and L‐3‐OHB, remain undetermined. Methods and Results: Three groups of 8 pigs each underwent a randomized, crossover study. The groups received 3‐hour infusions of either D/L‐3‐OHB (racemic mixture), 100% L‐3‐OHB, 100% D‐3‐OHB, versus an isovolumic control. The animals were monitored with pulmonary artery catheter, left ventricle pressure‐volume catheter, and arterial and coronary sinus blood samples. Myocardial biopsies were evaluated with high‐resolution respirometry, coronary arteries with isometric myography, and myocardial kinetics with D‐[ ¹¹ C]3‐OHB and L‐[ ¹¹ C]3‐OHB positron emission tomography. All three 3‐OHB infusions increased 3‐OHB levels ( P <0.001). D/L‐3‐OHB and L‐3‐OHB increased CO by 2.7 L/min ( P <0.003). D‐3‐OHB increased CO nonsignificantly ( P =0.2). Circulating 3‐OHB levels correlated with CO for both enantiomers ( P <0.001). The CO increase was mediated through arterial elastance (afterload) reduction, whereas contractility and preload were unchanged. Ex vivo, D‐ and L‐3‐OHB dilated coronary arteries equally. The mitochondrial respiratory capacity remained unaffected. The myocardial 3‐OHB extraction increased only during the D‐ and D/L‐3‐OHB infusions. D‐[ ¹¹ C]3‐OHB showed rapid cardiac uptake and metabolism, whereas L‐[ ¹¹ C]3‐OHB demonstrated much slower pharmacokinetics. Conclusions: 3‐OHB increased CO by reducing afterload. L‐3‐OHB exerted a stronger hemodynamic response than D‐3‐OHB due to higher circulating 3‐OHB levels. There was a dissocitation between the myocardial metabolism and hemodynamic effects of the enantiomers, highlighting L‐3‐OHB as a potent cardiovascular agent with strong hemodynamic effects.

Normothermic regional perfusion (NRP) allows assessment of therapeutic interventions prior to donation after circulatory death transplantation. Sodium-3-hydroxybutyrate (3-OHB) increases cardiac output in heart failure patients and diminishes ischemia–reperfusion injury, presumably by improving mitochondrial metabolism. We investigated effects of 3-OHB on cardiac and mitochondrial function in transplanted hearts and in cardiac organoids. Donor pigs (n = 14) underwent circulatory death followed by NRP. Following static cold storage, hearts were transplanted into recipient pigs. 3-OHB or Ringer’s acetate infusions were initiated during NRP and after transplantation. We evaluated hemodynamics and mitochondrial function. 3-OHB mediated effects on contractility, relaxation, calcium, and conduction were tested in cardiac organoids from human pluripotent stem cells. Following NRP, 3-OHB increased cardiac output (P < 0.0001) by increasing stroke volume (P = 0.006), dP/dt (P = 0.02) and reducing arterial elastance (P = 0.02). Following transplantation, infusion of 3-OHB maintained mitochondrial respiration (P = 0.009) but caused inotropy-resistant vasoplegia that prevented weaning. In cardiac organoids, 3-OHB increased contraction amplitude (P = 0.002) and shortened contraction duration (P = 0.013) without affecting calcium handling or conduction velocity. 3-OHB had beneficial cardiac effects and may have a potential to secure cardiac function during heart transplantation. Further studies are needed to optimize administration practice in donors and recipients and to validate the effect on mitochondrial function.

Cardiogenic shock (CS) is associated with high mortality and medical therapies have failed to improve survival. Treatment with lactate is associated with improved cardiac function which may benefit this condition. Comprehensive hemodynamic assessment of lactate administration in CS is lacking, and the mechanisms underlying the cardiovascular effects of lactate in CS have not yet been elucidated. In this study we aimed to study the cardiovascular and cardiometabolic effects of treatment with lactate in experimental ischemic CS. In a randomized, blinded design, 20 female pigs (60 kg) were studied. Left main coronary artery microsphere injections were used to cause CS, defined as a 30% reduction in CO or mixed venous saturation (SvO2). Subjects were randomized to receive either intravenous exogenous lactate or euvolemic, equimolar saline (control) for 180 min. Positive inotropic control with dobutamine was administered on top of ongoing treatment after 180 min. Extensive hemodynamic measurements were obtained from pulmonary artery and left ventricular (LV) pressure–volume catheterization. Furthermore, endomyocardial biopsies were analyzed for mitochondrial function and arterial, renal vein, and coronary sinus blood samples were collected. The primary endpoint was change in CO during 180 min of treatment. Arterial lactate levels increased from 2.4 ± 1.1 to 7.7 ± 1.1 mmol/L (P < 0.001) during lactate infusion. CO increased by 0.7 L/min (P < 0.001) compared with control, due to increased stroke volume (P = 0.003). Notably, heart rate and mean arterial pressure did not differ significantly between treatments. End-systolic elastance (load independent contractility) was enhanced during lactate infusion (P = 0.048), together with LV ejection fraction (P = 0.009) and dP/dt(max) (P = 0.041). Arterial elastance (afterload) did not differ significantly (P = 0.12). This resulted in improved ventriculo-arterial coupling efficiency (P = 0.012). Cardiac mechanical efficiency (P = 0.003), diuresis (P = 0.016), and SvO2 (P = 0.018) were increased during lactate infusion. Myocardial mitochondrial complex I respiration was enhanced during lactate infusion compared with control (P = 0.04). Concomitant administration of dobutamine on top of lactate resulted in further hemodynamic improvements compared with control. Lactate infusion improved cardiac function and myocardial mitochondrial respiration in a porcine model of CS. The hemodynamic effects included increased CO mediated through stroke volume increase. These favorable cardiovascular effects may benefit patients with CS.

Cardiogenic shock (CS) is characterized by reduced cardiac output (CO), reduced end-organ perfusion, and high mortality. Medical therapies have failed to improve survival. The ketone body 3-hydroxybutyrate (3-OHB) enhances cardiac function in heart failure and CS. We aimed to elucidate the cardiovascular and cardiometabolic effects of 3-OHB treatment during CS. In a randomized, assessor-blinded crossover design, we studied 16 female pigs (60 kg, 5 months of age). CS was induced by left main coronary artery microsphere injections. Predefined criteria for CS were a 30% reduction in CO or mixed venous saturation (SvO₂). Intravenous 3-OHB infusion and a matching control solution were administered for 120 min in random order. Hemodynamic measurements were obtained by pulmonary artery catheterization and a left ventricular (LV) pressure–volume catheter. Myocardial mitochondrial function was assessed using high resolution respirometry. During CS, infusion with 3-OHB increased CO by 0.9 L/min (95%CI 0.4–1.3 L/min) compared with control infusion. SvO₂ (P = 0.026) and heart rate (P < 0.001) increased. Stroke volume (P = 0.6) was not altered. LV contractile function as determined by LV end-systolic elastance improved during 3-OHB infusion compared with control infusion (P = 0.004). Systemic and pulmonary vascular resistance decreased, and diuresis increased. LV mitochondrial function was higher after 3-OHB infusion compared with control. We conclude that 3-OHB infusion enhances cardiac function by increasing contractility and reducing vascular resistance, while also preserving myocardial mitochondrial respiratory function in a large animal model of ischemic CS. These novel findings support the therapeutic potential of exogenous ketone supplementation in CS management. Graphical abstract

Background.: Thoracoabdominal normothermic regional perfusion (NRP) is a new method for in situ reperfusion and reanimation of potential donor organs in donation after circulatory death by reperfusion of the thoracic and abdominal organs with oxygenated blood. We investigated effects of high oxygenation (HOX) versus low oxygenation (LOX) during NRP on donor heart function in a porcine model. Methods.: Pigs (80 kg) underwent a 15-min anoxic cardiac arrest followed by cardiac reanimation on NRP using a heart-lung bypass machine with subsequent assessment 180 min post-NRP. The animals were randomized to HOX (FiO₂ 1.0) or LOX (FiO₂ 0.21 increased to 0.40 during NRP). Hemodynamic data were obtained by invasive blood pressure and biventricular pressure-volume measurements. Blood gases, biomarkers of inflammation, and oxidative stress were measured. Results.: Eight of 9 animals in the HOX group and 7 of 10 in the LOX group were successfully weaned from NRP. Right ventricular end-systole elastance was significantly improved in the HOX group compared with the LOX group, whereas left ventricular end-systole elastance was preserved at baseline levels. Post-NRP cardiac output, mean arterial, central venous, and pulmonary capillary wedge pressure were all comparable to baseline. Creatinine kinase-MB increased more in the LOX group than the HOX group, whereas proinflammatory cytokines increased more in the HOX group than the LOX group. No difference was found in oxidative stress between groups. Conclusions.: All hearts weaned from NRP showed acceptable hemodynamic function for transplantation. Hearts exposed to LOX showed more myocardial damage and showed poorer contractile performance than hearts reperfused with high oxygen.