Effects of ketone body 3-hydroxybutyrate on cardiac and mitochondrial function during donation after circulatory death heart transplantation.

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.

Abnormal mitochondrial function and morphology in heart transplanted patients with cardiac allograft vasculopathy.

BACKGROUND: Cardiac allograft vasculopathy (CAV) remains the Achilles' heel of long-term survival of HTx patients. Mitochondrial dysfunction has been reported in both arteriosclerotic coronary disease and heart failure. However, myocardial mitochondrial function has not been examined in HTx patients with CAV. METHODS: 43 HTx patients (21 patients with CAV and 22 patients without CAV) ≥12 months after HTx were enrolled. Endomyocardial biopsies were analyzed using high-resolution respirometry for glucose-coupled mitochondrial respiration. Number and area of mitochondria profiles as well as cristae morphology were assessed by transmission electron microscopy. Echocardiography and coronary angiography were used to measure global longitudinal strain (GLS) and grade CAV. RESULTS: Complex I+II-linked respiration was reduced in patients with CAV compared with patients without CAV (82.7 ± 31.9 pmol O2/(s•mg) vs 116 ± 35.9 pmol O2/(s•mg), p = 0.003). Mitochondrial respiratory function measured as oxidative phosphorylation coupling efficiency was positively associated with left ventricular GLS (r = 0.49, p = 0.002) and negatively associated with elevated biomarkers (Troponin T: r=-0.33, p = 0.04 and NT-proBNP: r = -0.41, p = 0.009). Mitochondrial profile number and area did not differ. However, patients with CAV had a larger proportion of mitochondria with abnormal cristae morphology (p < 0.001). CONCLUSIONS: Myocardial mitochondrial respiration is impaired in patients with CAV and is associated with an abnormal cristae morphology. The mitochondrial dysfunction appears to be associated with reduced myocardial contractile function and elevated biomarkers. These results highlight that mitochondrial targeted treatment in patients with CAV should be assessed in future clinical studies.

Burden of arrhythmia and silent ischemia in heart transplant patients with cardiac allograft vasculopathy.

BACKGROUND: The incidence of sudden cardiac death (SCD) following heart transplantation (HTx) accounts for approximately 10% of post-HTx deaths. Ischemia, brady- and tachy-arrhythmias caused by rejection and cardiac allograft vasculopathy (CAV) seem related to SCD. Hence, we aimed to investigate the relation between CAV, arrhythmias and silent ischemia in long-term HTx patients. Methods. 49 HTx patients were included. Patients were CAV classified in accordance with guidelines from the International Society of Heart and Lung Transplantation. Patients were divided into predefined CAV groups (CAV 0, CAV 1, CAV 2 + 3). Incidences of arrhythmia and silent ischemia were detected by 48-h electrocardiogram monitoring and analyzed blinded to CAV-status. Results. Median time since transplantation was 9 years [IQR 4-14]. We observed a higher incidence of non-sustained ventricular tachycardia (NSVT) in CAV 2 + 3 patients than CAV 0 and 1 patients (p = .01). Likewise, isolated premature ventricular complexes (PVC) (p = .01) and PQ-interval prolongation (p = .01) were more frequent in CAV 2 + 3 patients than CAV 0 and 1 patients. Silent ischemia was only observed among CAV 3 patients (p = .04). We saw no significant difference in the incidence of supraventricular tachycardia among CAV groups (p = .21). Likewise, no difference in the right bundle branch block was observed (p = .68). Conclusion. NSVT was associated with CAV status in long-term HTx patients. Patients with moderate to severe CAV showed higher incidences of PVCs and PQ-interval prolongation than patients with mild or no CAV. Silent ischemia was only seen in patients with severe CAV.

Platelet aggregation and response to aspirin therapy in cardiac allograft vasculopathy.

BACKGROUND: Long-term survival after heart transplantation (HTx) is compromised by cardiac allograft vasculopathy (CAV) characterized by coronary macro- and microvascular disease. The pathogenesis of CAV is unclear and may involve coronary thrombosis. We investigated whether HTx patients with CAV had higher platelet aggregation and turnover than HTx patients without CAV and healthy controls. Furthermore, we investigated the anti-platelet effect of low-dose aspirin in HTx patients. METHODS: We included 57 patients who had undergone HTx (median 8.3 years from HTx) and 57 healthy controls. Platelet aggregation was measured on-aspirin and off-aspirin using impedance aggregometry with adenosine diphosphate (ADP) and arachidonic acid (AA). We evaluated platelet turnover by flow cytometry, CAV burden by coronary angiography and echocardiography, and microvascular function by echocardiographic coronary flow velocity reserve (CFVR). RESULTS: Off-aspirin, HTx patients with CAV (n = 21) had higher ADP-induced platelet aggregation than healthy controls (p < 0.01) and HTx patients without CAV (n = 36) (p < 0.05). Aspirin treatment reduced AA-induced platelet aggregation in both HTx groups, but HTx patients with CAV had higher platelet aggregation on-aspirin than HTx patients without CAV (p < 0.05). Platelet turnover did not differ between HTx patients with CAV and HTx patients without CAV (p > 0.34). HTx patients with lower CFVR values had higher platelet aggregation than HTx patients with higher CFVR values (p < 0.05). CONCLUSIONS: Off-aspirin, platelet aggregation was higher in HTx patients with CAV than in HTx patients without CAV and healthy controls. On-aspirin, platelet aggregation was higher in HTx patients with CAV than in HTx patients without CAV. Aspirin monotherapy may not provide sufficient platelet inhibition in HTx patients with CAV.

Survival, graft function, and incidence of allograft vasculopathy in heart transplant patients receiving adverse risk profile donor hearts.

AIM: To clarify if use of adverse cardiovascular risk profile (ARP) grafts is associated with impaired long-term outcomes after heart transplantation (HTx). METHODS: Survival was obtained from Scandia Transplant and a local database. ARP DONOR INCLUSION CRITERIA: ≥55 years, diabetes mellitus, arterial hypertension, hypoxemia-induced death, impaired left ventricular (LV) ejection fraction. ARP donors were compared to donors not meeting the eligibility criteria. Sub-analyses were made for donor age. RESULTS: In total, 302 HTxs were performed in 296 patients from 31 December 1992 to 11 August 2016. Median survival was 16.5 years (95% CI, 14.3-22.9), there was no difference between profiles (HR 0.63 (95% CI, 0.33-1.19), P = 0.15). LV systolic function was significantly better in ARP donors (P < 0.05). Freedom from cardiac allograft vasculopathy (CAV) was comparable between profiles, HR 0.9 (95% CI 0.5-1.5). Donor age predisposes to CAV (high to low age: HR 2.8 (95% CI 1.7-4.5), P < 0.0001). Median survival was comparable in patients receiving allograft ≥55 and <55 years (HR 0.77 (95% CI 0.4-1.4), P = 0.38). CONCLUSION: Long-term survival and graft function were excellent in patients receiving ARP grafts. Older grafts were associated with CAV but did not influence survival. Thus, the strategy of expanding availability using ARP grafts seems safe.

Detection of early changes in the coronary artery microstructure after heart transplantation: A prospective optical coherence tomography study.

BACKGROUND: Optical coherence tomography (OCT) enables in-vivo cardiac allograft vasculopathy (CAV) microstructure characterization. Early coronary artery microstructure changes after heart transplantation (HTx) may provide valuable mechanistic information regarding CAV development. Our in this study was to describe and characterize changes in the coronary artery microstructure during the first year after HTx using serial OCT scans. METHODS: Twenty-six patients were enrolled at routine baseline coronary angiography 3 months after HTx. Coronary OCT scans were performed on all 3 major vessels at baseline and were repeated 12 months after HTx. We contoured the vessel layers for absolute and relative measurements. Lipid plaques, calcified plaques, layered fibrotic plaques (LFPs) and bright spots were analyzed by delineating circumferential borders and measuring angulation of total circumference. RESULTS: A total of 8,789 frames from 71 vessels were analyzed after 3 and 12 months (vessel length 79 ± 24 mm vs 82 ± 23 mm, respectively, p = 0.39). Mean intima area increased by 20% from 3 months to 12 months (1.6 [1.2 to 2.7] mm2 vs 1.9 [1.3 to 3.2] mm2, p < 0.0001). Mean lumen area decreased by 2% (9.1 [7.5 to 11.6] mm2 vs 8.9 [6.9 to 10.9] mm2, p < 0.01). LFPs showed an almost 5-fold increase at follow-up (1.0% [0% to 6.5%] vs 4.8% [0% to 24.5%], p < 0.0001). Bright spots were also detected more frequently at 12 months (0% [0% to 2.8%] vs 0.8% [0% to 6.8%], p < 0.001). We found no significant difference in extent of lipid plaque (p = 0.78) or calcified plaque (p = 0.37) during follow-up. The intima area change and LFP progression during follow-up correlated strongly (r2 = 0.51, p < 0.0001). CONCLUSIONS: Early CAV formation during the first year after HTx is characterized by a pronounced intima layer thickening strongly associated with LFP progression. In contrast, the extent of lipid plaque and calcifications remained stable. LFP formation may be a key mechanism in CAV.