The cardiac conduction system: History, development, and disease.

The heart is the first organ to form during embryonic development, establishing the circulatory infrastructure necessary to sustain life and enable downstream organogenesis. Critical to the heart's function is its ability to initiate and propagate electrical impulses that allow for the coordinated contraction and relaxation of its chambers, and thus, the movement of blood and nutrients. Several specialized structures within the heart, collectively known as the cardiac conduction system (CCS), are responsible for this phenomenon. In this review, we discuss the discovery and scientific history of the mammalian cardiac conduction system as well as the key genes and transcription factors implicated in the formation of its major structures. We also describe known human diseases related to CCS development and explore existing challenges in the clinical context.

An integrated program to expand donor utilization in pediatric heart transplantation: Case report of successful transplant with multiple donor risk factors.

BACKGROUND: Pediatric heart transplantation (HT) continues to be limited by the shortage of donor organs, distance constraints, and the number of potential donor offers that are declined due to the presence of multiple risk factors. METHODS: We report a case of successful pediatric HT in which multiple risk factors were mitigated through a combination of innovative donor utilization improvement strategies. RESULTS: An 11-year-old, 25-kilogram child with cardiomyopathy and pulmonary hypertension, on chronic milrinone therapy and anticoagulated with apixaban, was transplanted with a heart from a Hepatitis C virus positive donor and an increased donor-to-recipient weight ratio. Due to extended geographic distance, an extracorporeal heart preservation system (TransMedics™ OCS Heart) was used for procurement. No significant bleeding was observed post-operatively, and she was discharged by post-operative day 15 with normal biventricular systolic function. Post-transplant Hepatitis C virus seroconversion was successfully treated. CONCLUSIONS: Heart transplantation in donors with multiple risk factor can be achieved with an integrative team approach and should be taken into consideration when evaluating marginal donors in order to expand the current limited donor pool in pediatric patients.

Cord blood DNA methylation signatures associated with preeclampsia are enriched for cardiovascular pathways: insights from the VDAART trial.

BACKGROUND: Preeclampsia has been associated with maternal epigenetic changes, in particular DNA methylation changes in the placenta. It has been suggested that preeclampsia could also cause DNA methylation changes in the neonate. We examined DNA methylation in relation to gene expression in the cord blood of offspring born to mothers with preeclampsia. METHODS: This study included 128 mother-child pairs who participated in the Vitamin D Antenatal Asthma Reduction Trial (VDAART), where assessment of preeclampsia served as secondary outcome. We performed an epigenome-wide association study of preeclampsia and cord blood DNA methylation (Illumina 450 K chip). We then examined gene expression of the same subjects for validation and replicated the gene signatures in independent DNA methylation datasets. Lastly, we applied functional enrichment and network analyses to identify biological pathways that could potentially be involved in preeclampsia. FINDINGS: In the cord blood samples (n = 128), 263 CpGs were differentially methylated (FDR <0.10) in preeclampsia (n = 16), of which 217 were annotated. Top pathways in the functional enrichment analysis included apelin signaling pathway and other endothelial and cardiovascular pathways. Of the 217 genes, 13 showed differential expression (p's < 0.001) in preeclampsia and 11 had been previously related to preeclampsia (p's < 0.0001). These genes were linked to apelin, cGMP and Notch signaling pathways, all having a role in angiogenic process and cardiovascular function. INTERPRETATION: Preeclampsia is related to differential cord blood DNA methylation signatures of cardiovascular pathways, including the apelin signaling pathway. The association of these cord blood DNA methylation signatures with offspring's long-term morbidities due to preeclampsia should be further investigated. FUNDING: VDAART is funded by National Heart, Lung, and Blood Institute grants of R01HL091528 and UH3OD023268. HMK is supported by Jane and Aatos Erkko Foundation, Paulo Foundation, and the Pediatric Research Foundation. HM is supported by K01 award from NHLBI (1K01HL146977-01A1). PK is supported by K99HL159234 from NIH/NHLBI.

Recurrent Mild Acute Rejections and Donor-specific Antibodies as Risk Factors for Cardiac Allograft Vasculopathy in a National Pediatric Heart Transplant Cohort.

Background: Immune-mediated factors such as acute cellular rejections and donor-specific antibodies (DSAs) are risk factors for cardiac allograft vasculopathy (CAV). We studied a national cohort with a unified setting and thorough protocol endomyocardial biopsy (EMB) data for an association between cellular rejections, especially when mild and recurrent, and DSAs with CAV in pediatric heart transplant (HTx) patients. Methods: This is a retrospective, national cohort study of 94 pediatric HTxs performed between 1991 and 2019 and followed until December 31, 2020. Diagnosis of CAV was based on reevaluation of angiographies. Protocol and indication EMB findings with other patient data were collected from medical records. Associations between nonimmune and immune-mediated factors and CAV were analyzed with univariable and multivariable Cox regression analyses. Results: Angiographies performed on 76 patients revealed CAV in 23 patients (30%). Altogether 1138 EMBs (92% protocol biopsies) were performed on 78 patients (83%). During the first posttransplant year, grade 1 rejection (G1R) appeared in 45 patients (58%), and recurrent (≥2) G1R findings in 14 patients (18%). Pretransplant DSAs occurred in 13 patients (17%) and posttransplant DSAs in 37 patients (39%). In univariable analysis, pretransplant DSAs, appearance and recurrence of G1R findings, and total rejection score during the first posttransplant year, as well as recurrent G1R during follow-up, were all associated with CAV. In multivariable analysis, pretransplant DSAs and recurrent G1R during the first posttransplant year were found to be associated with CAV. Conclusions: Our results indicate that pretransplant DSA and recurrent G1R findings, especially during the first posttransplant year, are associated with CAV after pediatric HTx.

Prescription medication use after congenital heart surgery.

BACKGROUND: Improvements in mortality after congenital heart surgery have necessitated a shift in focus to postoperative morbidity as an outcome measure. We examined late morbidity after congenital heart surgery based on prescription medication use. METHODS: Between 1953 and 2009, 10,635 patients underwent congenital heart surgery at <15 years of age in Finland. We obtained 4 age-, sex-, birth-time, and hospital district-matched controls per patient. The Social Insurance Institution of Finland provided data on all prescription medications obtained between 1999 and 2012 by patients and controls. Patients were assigned one diagnosis based on a hierarchical list of cardiac defects and dichotomised into simple and severe groups. Medications were divided into short- and long-term based on indication. Follow-up started at the first operation and ended at death, emigration, or 31 December, 2012. RESULTS: Totally, 8623 patients met inclusion criteria. Follow-up was 99.9%. In total, 8126 (94%) patients required prescription medications. Systemic anti-bacterials were the most common short-term prescriptions among patients (93%) and controls (88%). Patients required betablockers (simple hazard ratio 1.9, 95% confidence interval 1.7-2.1; severe hazard ratio 6.5, 95% confidence interval 5.3-8.1) and diuretics (simple hazard ratio 3.2, 95% CI 2.8-3.7; severe hazard ratio 38.8, 95% CI 27.5-54.7) more often than the general population. Both simple and severe defects required medication for cardiovascular, gastrointestinal, psychiatric, neurologic, metabolic, autoimmune, and infectious diseases more often than the general population. CONCLUSIONS: The significant risk for postoperative cardiovascular and non-cardiovascular disease warrants close long-term follow-up after congenital heart surgery for all defects.

Inhibition of Vascular Endothelial Growth Factor Receptors 1 and 2 Attenuates Natural Killer Cell and Innate Immune Responses in an Experimental Model for Obliterative Bronchiolitis.

Obliterative bronchiolitis (OB) after lung transplantation is a nonreversible, life-threatening complication. Herein, the role of vascular endothelial growth factor receptor (Vegfr)-1 and -2 was investigated in the development of obliterative airway disease (OAD), an experimental model for OB. The nonimmunosuppressed recipients underwent transplantation with fully major histocompatibility complex mismatched heterotopic tracheal allografts and received Vegfr1 and -2-specific monoclonal antibodies either alone or in combination, or rat IgG as a control. The treatment with Vegfr1- or -2-blocking antibody significantly decreased intragraft mRNA expression of natural killer cell activation markers early after transplantation. This was followed by reduced infiltration of Cd11b+ cells and Cd4+ T cells as well as down-regulated mRNA expression of proinflammatory chemokines and profibrotic growth factors. However, blocking of both Vegfr1 and -2 was necessary to reduce luminal occlusion. Furthermore, concomitant inhibition of the calcineurin activation pathway almost totally abolished the development of OAD. This study proposes that blocking of Vegf receptors blunted natural killer cell and innate immune responses early after transplantation and attenuated the development of OAD. The results of this study suggest that further studies on the role of Vegfr1 and -2 blocking in development of obliterative airway lesions might be rewarding.

Long-term Social Outcomes After Congenital Heart Surgery.

BACKGROUND: Patients are surviving decades after congenital heart surgery (CHS), raising the importance of postoperative quality of life as an outcome measure. We determined the long-term social outcomes after CHS performed during childhood. METHODS: Between 1953 and 2009, 10 635 patients underwent surgery for congenital heart defects at <15 years of age in Finland. We obtained 4 control subjects per patient, matched by age, sex, birth time, and hospital district, from Statistics Finland, which also provided data on the highest education level, employment status, marital status, and progeny for both patients and control subjects. We included patients who were alive and ≥18 years of age at the end of the follow-up on December 31, 2017. RESULTS: A total of 7308 patients met inclusion criteria. Patients had on average similar high school or vocational education rates as the general population but lower undergraduate or higher education rates (female patients: risk ratio [RR] 0.8 [95% confidence interval (CI) 0.8-0.9]; male patients: RR 0.8 [95% CI 0.7-0.9]). Patients were less likely to be married or have progeny compared with the general population. The rate of employment was significantly lower (female patients: RR 0.8 [95% CI 0.8-0.9]; male patients: RR 0.8 [95% CI 0.8-0.9]) and the rate of retirement (female patients: RR 2.1 [95% CI 2.0-2.3]; male patients RR 3.1 [95% CI 2.9-3.5]) significantly higher among patients. CONCLUSIONS: Patients who undergo CHS at childhood age are, on average, more disadvantaged from both an educational and professional standpoint compared with the general population, regardless of the severity of the defect.

Chronic Disease Burden After Congenital Heart Surgery: A 47-Year Population-Based Study With 99% Follow-Up.

Background Postoperative morbidity is an increasingly important outcome measure of patients who have undergone congenital heart surgery (CHS). We examined late postoperative morbidity after CHS on the basis of patients' government-issued medical special reimbursement rights. Methods and Results Between 1953 and 2009, 10 635 patients underwent CHS at <15 years of age in Finland. We excluded early deaths and mental disabilities. Noncyanotic and cyanotic defects were divided into simple and severe groups, respectively. We obtained 4 age-, sex-, birth time-, and hospital district-matched control subjects per patient. The Social Insurance Institution of Finland provided data on all medical special reimbursement rights granted between 1966 and 2012. Follow-up started at the first operation and ended at death, date of emigration, or December 31, 2012. A total of 8623 patients met inclusion criteria. Follow-up was 99.9%. A total of 3750 patients (43%) required special reimbursements rights for a chronic disease. Cardiovascular disease was the most common late morbidity among patients (28%), followed by obstructive pulmonary disease (9%), neurologic disease (3%), and psychiatric disease (2%). Heart failure (simple hazard ratio [HR], 56.3 [95% CI, 35.4-89.7]; severe HR, 918.0 [95% CI, 228.9-3681.7]) and arrhythmia (simple HR, 11.0 [95% CI, 7.1-17.0]; severe HR, 248.0 [95% CI, 61.3-1002.7]) were the most common cardiovascular morbidities. Hypertension was common among patients with coarctation of the aorta (13%; incidence risk ratio [RR], 8.9; 95% CI, 7.5-10.7). Psychiatric disease was more common among simple defects, particularly ventricular septal defects. Conclusions Chronic cardiac and noncardiac sequelae are common after CHS regardless of the severity of the defect, underscoring the importance of long-term follow-up of all patients after CHS.

Development of Human Leukocyte Antigen (HLA) Antibodies Against Vascular Homograft Donor in Pediatric Heart Transplant Recipients.

BACKGROUND The appearance of human leukocyte antigen (HLA) antibodies after solid organ transplantation predisposes recipients to graft dysfunction. In theory, vascular homografts, which are widely used in children with congenital heart defects, may cause allosensitization. MATERIAL AND METHODS In this single-center retrospective study, the presence of pre-existing HLA antibodies in pediatric heart transplant (HTx) recipients with a vascular homograft was evaluated in a cohort of 12 patients. HLA antibodies were screened before and after HTx and positive screening results were confirmed and identified using the Luminex® single antigen bead method. Endomyocardial biopsies (EMB) and coronary angiography studies were re-evaluated to assess the prevalence of acute rejections and coronary artery change in these patients. RESULTS At the time of HTx, 8 patients (67%) had HLA antibodies detected by the Luminex assay, none of which were heart donor specific (DSA). All patients had negative leukocyte crossmatch. One patient developed DSAs against homograft donor prior to HTx. After the HTx, 5 patients (42%) developed DSAs against the heart donor and 4 patients (40%) against the homograft donor. In 2 patients (17%), the antibodies were against both heart and homograft donors. The rejection rate or prevalence of coronary artery vasculopathy did not differ significantly between the homograft cohort and our historical controls. CONCLUSIONS Our results suggest that the prevalence of DSAs against homograft donor prior to HTx is relatively rare. However, almost half of the patients developed DSAs against homograft post-HTx. The clinical importance of these antibodies warrants further studies.

The effect of sildenafil on pleural and peritoneal effusions after the TCPC operation.

BACKGROUND: We evaluated whether the administration of sildenafil in children undergoing the TCPC operation shortened the interval from the operation to the removal of the pleural and peritoneal drains. METHODS: We retrospectively reviewed the data of 122 patients who had undergone the TCPC operation between 2004 and 2014. Patients were divided into two groups on the basis of their treatments. Sildenafil was orally administered pre-operatively in the morning of the procedure or within 24 hours after the TCPC operation to the sildenafil group (n = 48), which was compared to a control group (n = 60). Fourteen patients were excluded from the study. RESULTS: The primary outcome measure was the time from the operation to the removal of the drains. The study groups had similar demographics. The median [interquartile range] time for the removal of drains (sildenafil group 11 [8-19] vs control group 11 [7-16] d, P = .532) was comparable between the groups. The median [interquartile range] fluid balance on the first post-operative day was significantly higher (P = .001) in the sildenafil group compared with controls (47 [12-103] vs 7 [-6-67] mL kg-1 ). The first post-operative day fluid balance was a significant predictor for a prolonged need for drains in the multivariate analysis. CONCLUSIONS: Sildenafil administration, pre-operatively or within 24 hours after the TCPC operation, did not reduce the required time for pleural and peritoneal drains but was associated with a significantly higher positive fluid balance.

Hypoxia-inducible factor controls immunoregulatory properties of myeloid cells in mouse cardiac allografts - an experimental study.

Hypoxia-inducible factors (HIFs) play a critical role in inflammatory properties of myeloid-derived cells. The effect of HIFs on myeloid-derived cell functions in organ transplantation remains unknown, however. We transplanted hearts into transgenic mice with myeloid cell-targeted deletions of HIF-1α or its negative regulator von Hippel-Lindau (VHL) to investigate the effects of HIF-1α inactivation or HIF pathway activation, respectively, on ischemia-reperfusion injury (IRI) and acute rejection. Deletion of VHL in myeloid cells enhanced mRNA expression of anti-inflammatory genes IDO, Arg-1, and HO-1 in vitro. In vivo, VHL-/- myeloid-derived cells of allograft recipients alleviated IRI and acute rejection, evidenced by reduced cardiomyocyte damage, decreased proinflammatory cytokine mRNA levels, and absence of inflammatory infiltrate at 5 days after transplantation. Ultimately, allograft survival was significantly prolonged. In vitro, VHL-/- myeloid-derived cells dose-dependently inhibited T-cell proliferation. Myeloid cells with HIF-1α-deletion retained proinflammatory qualities in vitro and in vivo. Deletion of VHL in myeloid cells of nonimmunosuppressed cardiac allograft recipients reduced myocardial injury and acute rejection. We suggest that HIF transcription factors induce a regulatory phenotype in myeloid-derived cells, which may be harnessed as a novel therapeutic strategy to regulate immune responses after heart transplantation.

Outcomes after the Mustard, Senning and arterial switch operation for treatment of transposition of the great arteries in Finland: a nationwide 4-decade perspective.

OBJECTIVES: We analysed nationwide early and late results after the Mustard, Senning and arterial switch operation. METHODS: We included all paediatric patients (<18 years) who underwent a Senning, a Mustard or an arterial switch operation for transposition of the great arteries from 1968 to 2009 in Finland. Data were obtained retrospectively from a paediatric cardiac surgical database and population data from the Finnish national registry. RESULTS: Early mortality (<30 days) was 11% after Mustard and 5% after Senning operation, while the rate decreased from 19% during 1976-1999 to 2% during 2000-2009 for arterial switch patients (P < 0.0001). The 43-year survival rate was 75% [95% confidence interval (CI) 70-80%] for all patients and 97% (95% CI 94-98%) for the general population. Late survival improved during later eras, with a 10-year survival of 96% (95% CI 92-99%) for those operated during 2000-2009 vs 81% (95% CI 74-88%) in the 1990s (hazard ratio 3.7, 95% CI 1.4-9.6, P = 0.008). Twenty-year survival rates (without 30-day mortality) after arterial switch operation, Mustard and Senning were 97% (95% CI 95-100%), 78% (95% CI 68-87%) and 84% (95% CI 77-90%), respectively. No late sudden deaths or fatal heart failures occurred after the arterial switch operation. CONCLUSIONS: Outcome after surgery for transposition of the great arteries has improved, mostly due to the arterial switch operation but also due to improvements in perioperative care and follow-up. Operative deaths after the arterial switch operation have diminished, and no late sudden deaths or fatal heart failures occurred during the first 25-30 years after the procedure.

Vascular Endothelial Growth Factor-B Overexpressing Hearts Are Not Protected From Transplant-Associated Ischemia-Reperfusion Injury.

OBJECTIVES: Cardiac vascular endothelial growth factor-B transgene limits myocardial damage in rat infarction models. We investigated whether heart transplant vascular endothelial growth factor-B overexpression protected against ischemia-reperfusion injury. MATERIALS AND METHODS: We transplanted hearts heterotopically from Dark Agouti to Wistar Furth rats. To characterize the role of vascular endothelial growth factor-B in ischemia-reperfusion injury, we transplanted either long-term human vascular endothelial growth factor-B transgene overexpressing hearts from Wistar Furth rats or short-term adeno-associated virus 9-human vascular endothelial growth factor-B-transduced hearts from Dark Agouti rats into Wistar Furth rats. Heart transplants were subjected to 2 hours of cold and 1 hour of warm ex vivo ischemia. Samples were collected 6 hours after reperfusion. RESULTS: Two hours of cold and 1 hour of warm ischemia increased vascular endothelial growth factor-B mRNA levels 2-fold before transplant and 6 hours after reperfusion. Transgenic vascular endothelial growth factor-B overexpression caused mild cardiac hypertrophy and elevated cardiac troponin T levels 6 hours after reperfusion. Laser Doppler measurements indicated impaired epicardial tissue perfusion in these transgenic transplants. Recombinant human vascular endothelial growth factor-B increased mRNA levels of cytochrome c oxidase and extracellular ATPase CD39, suggesting active oxidative phosphorylation and high ATP production. Adeno-associated virus 9-mediated vascular endothelial growth factor-B overexpression in transplanted hearts increased intragraft macrophages 1.5-fold and proinflammatory cytokine interleukin 12 p35 mRNA 1.6-fold, without affecting recipient serum cardiac troponin T concentration. CONCLUSIONS: Vascular endothelial growth factor-B expression in transplanted hearts is linked to ischemia and ischemia-reperfusion injury. Cardiac transgenic vascular endothelial growth factor-B overexpression failed to protect heart transplants from ischemia-reperfusion injury.

Late Causes of Death After Pediatric Cardiac Surgery: A 60-Year Population-Based Study.

BACKGROUND: Comprehensive information regarding causes of late post-operative death following pediatric congenital cardiac surgery is lacking. OBJECTIVES: The study sought to analyze late causes of death after congenital cardiac surgery by era and defect severity. METHODS: We obtained data from a nationwide pediatric cardiac surgery database and Finnish population registry regarding patients who underwent cardiac surgery at <15 years of age at 1 of 5 universities or 1 district hospital in Finland from 1953 to 2009. Noncyanotic and cyanotic defects were classified as simple and severe, respectively. Causes of death were determined using International Classification of Diseases diagnostic codes. Deaths among the study population were compared to a matched control population. RESULTS: Overall, 10,964 patients underwent 14,079 operations, with 98% follow-up. Early mortality (<30 days) was 5.6% (n = 613). Late mortality was 10.4% (n = 1,129). Congenital heart defect (CHD)-related death rates correlated with defect severity. Heart failure was the most common mode of CHD-related death, but decreased after surgeries performed between 1990 and 2009. Sudden death after surgery for atrial septal defect, ventricular septal defect, tetralogy of Fallot, and transposition of the great arteries decreased to zero following operations from 1990 to 2009. Deaths from neoplasms, respiratory, neurological, and infectious disease were significantly more common among study patients than controls. Pneumonia caused the majority of non-CHD-related deaths among the study population. CONCLUSIONS: CHD-related deaths have decreased markedly but remain a challenge after surgery for severe cardiac defects. Premature deaths are generally more common among patients than the control population, warranting long-term follow-up after congenital cardiac surgery.

Simvastatin pretreatment reduces caspase-9 and RIPK1 protein activity in rat cardiac allograft ischemia-reperfusion.

BACKGROUND: In transplantation-associated ischemia/reperfusion injury (Tx-IRI), tumor necrosis factor alpha and damage-associated molecular patterns promote caspase-8 and -9 apoptotic and receptor-interacting protein kinase-1 and -3 (RIPK1/3) necroptotic pathway activation. The extent of cell death and the counterbalance between apoptosis and regulated necrosis eventually determine the immune response of the allograft. Although simvastatin prevents Tx-IRI, its role in apoptotic and necroptotic activity remains unsolved. METHODS: Rat allograft donors and recipients were treated with a single-dose of simvastatin 2h prior to allograft procurement and reperfusion, respectively. Intragraft caspase-3, -8, and -9 and RIPK1 and -3 mRNA expression was analysed by quantitative RT-PCR and protein activity measured by immunohistochemistry and luminescent assays 6h after reperfusion. Lactate and lactate dehydrogenase (LDH) levels were analysed from allograft recipient and from hypoxic endothelial cell cultures having treated with activated simvastatin. RESULTS: When compared to without cold ischemia, prolonged 4-hour cold ischemia significantly enhanced intragraft mRNA expression of caspase-3 and -9, and RIPK1 and -3, and elevated protein activity of caspase-9 and RIPK1 in the allografts. Simvastatin pretreatment decreased mRNA expression of caspase-3 and -9, and RIPK1 and -3 and protein activity of caspase-9 and RIPK1 in the allografts. Intragraft caspase-8 mRNA expression remained constant regardless of cold ischemia or simvastatin pretreatment. Simvastatin pretreatment attenuated lactate and LDH levels, both in the allograft recipients and in hypoxic endothelial cell cultures. CONCLUSIONS: The beneficial effects of simvastatin pretreatment in cardiac allograft IRI may involve prevention of apoptosis and necroptosis.

Late outcome after paediatric heart transplantation in Finland.

OBJECTIVES: We studied the long-term survival and rejection episodes of paediatric heart transplant recipients. METHODS: We included all paediatric patients (≤18 years) who underwent heart transplantation during 1991-2014 in Finland. Data were obtained retrospectively from a paediatric cardiac surgery database. Patient status was received from the Finnish population registry. All patients underwent yearly routine postoperative endomyocardial biopsies and coronary angiographies. RESULTS: Between 1991 and 2014, 68 heart transplantations were performed. The early mortality (<30 days after surgery) rate was 10% and follow-up coverage was 100%. The 10- and 15-year survival rates for all patients were 68% (95% confidence internal, CI, 56-80%) and 65% (95% CI 53-78%), respectively, including early mortality. The 1-year survival rate was 100% when excluding early operative mortality. Indications for heart transplantation were cardiomyopathy in 57% and cardiac malformations in 43% of patients, with similar long-term survival between the groups. During 23 years of follow-up, 43 patients (70%) had at least one rejection episode and 17 patients (29%) at least a grade 1 coronary artery vasculopathy finding. Patients with early rejection episodes (<3 months) had a higher incidence of late rejection episodes (P = 0.025). Older age at operation was a significant risk factor for the development of coronary artery vasculopathy (hazard ratio 1.1, 95% CI 1.0-1.3, P = 0.012). CONCLUSIONS: First-year survival was excellent. Asymptomatic rejection episodes were common among patients. Early rejection episodes are a risk factor for late rejection episodes and show a trend towards an increased risk of late death. Coronary artery vasculopathy remains a major challenge for late graft survival.

Increased myeloid cell hypoxia-inducible factor-1 delays obliterative airway disease in the mouse.

BACKGROUND: Obliterative bronchiolitis after lung transplantation is characterized by chronic airway inflammation leading to the obliteration of small airways. Hypoxia-inducible factor-1 (HIF-1) is a master regulator of cellular responses to hypoxia and inflammation. The Von Hippel-Lindau protein (pVHL) drives the degradation of oxygen-sensitive subunit HIF-1α that controls the activity of HIF-1. We investigated the effect of myeloid cell-targeted gene deletion of HIF-1α or its negative regulator pVHL on the development of obliterative airway disease (OAD) in the recipients of tracheal allografts, a mouse model for obliterative bronchiolitis after lung transplantation. METHODS: Tracheal allografts were heterotopically transplanted from BALB/c donor mice to fully major histocompatibility complex-mismatched recipient mice with HIF-1α or VHL gene deletion in myeloid cells. The recipients were left non-immunosuppressed or received tacrolimus daily. Histologic, immunohistochemical, and real-time reverse transcription polymerase chain reaction analyses were performed at 3, 10, and 30 days. RESULTS: In the absence of immunosuppression, myeloid cell-specific VHL deficiency of the recipient mice improved epithelial recovery, decreased inflammatory cell infiltration and expression of pro-inflammatory cytokines, increased regulatory forkhead box P3 messenger RNA expression, and reduced OAD development in tracheal allografts. In the presence of tacrolimus immunosuppression, loss of HIF-1α activity in myeloid cells of the recipient by HIF-1α gene deletion accelerated OAD development in mouse tracheal allografts. CONCLUSIONS: Activity of the HIF-pathway affects the development of allograft rejection, and our results suggest that myeloid cell-specific VHL-deficiency that potentially increases HIF-activity decreases allograft inflammation and the subsequent development of OAD in mouse tracheal allografts.

Platelet-derived Growth Factor-B Protects Rat Cardiac Allografts From Ischemia-reperfusion Injury.

BACKGROUND: Microvascular dysfunction and cardiomyocyte injury are hallmarks of ischemia-reperfusion injury (IRI) after heart transplantation. Platelet-derived growth factors (PDGF) have an ambiguous role in this deleterious cascade. On one hand, PDGF may exert vascular stabilizing and antiapoptotic actions through endothelial-pericyte and endothelial-cardiomyocyte crosstalk in the heart; and on the other hand, PDGF signaling mediates neointimal formation and exacerbates chronic rejection in cardiac allografts. The balance between these potentially harmful and beneficial actions determines the final outcome of cardiac allografts. METHODS AND RESULTS: We transplanted cardiac allografts from Dark Agouti rat and Balb mouse donors to fully major histocompatibility complex-mismatched Wistar Furth rat or C57 mouse recipients with a clinically relevant 2-hour cold ischemia and 1-hour warm ischemia. Ex vivo intracoronary delivery of adenovirus-mediated gene transfer of recombinant human PDGF-BB upregulated messenger RNA expression of anti-mesenchymal transition and survival factors BMP-7 and Bcl-2 and preserved capillary density in rat cardiac allografts at day 10. In mouse cardiac allografts PDGF receptor-ß, but not -α intragraft messenger RNA levels were reduced and capillary protein localization was lost during IRI. The PDGF receptor tyrosine kinase inhibitor imatinib mesylate and a monoclonal antibody against PDGF receptor-α enhanced myocardial damage evidenced by serum cardiac troponin T release in the rat and mouse cardiac allografts 6 hours after reperfusion, respectively. Moreover, imatinib mesylate enhanced rat cardiac allograft vasculopathy, cardiac fibrosis, and late allograft loss at day 56. CONCLUSIONS: Our results suggest that PDGF-B signaling may play a role in endothelial and cardiomyocyte recovery from IRI after heart transplantation.

Systemic overexpression of matricellular protein CCN1 exacerbates obliterative bronchiolitis in mouse tracheal allografts.

Obliterative bronchiolitis (OB) involves airway epithelial detachment, fibroproliferation, and inflammation, resulting in chronic rejection and transplant failure. Cysteine-rich 61 (CCN1) is an integrin receptor antagonist with a context-dependent role in inflammatory and fibroproliferative processes. We used a mouse tracheal OB model to investigate the role of CCN1 in the development of lung allograft OB. C57Bl/6 mice received a systemic injection of CCN1-expressing adenoviral vectors 2 days prior to subcutaneous implantation of tracheal allografts from major MHC-mismatched BALB/c mice. We treated another group of tracheal allograft recipients with cyclic arginine-glycine-aspartic acid peptide to dissect the role of αvß3-integrin signaling in mediating CCN1 effects in tracheal allografts. Allografts were removed 4 weeks after transplantation and analyzed for luminal occlusion, inflammation, and vasculogenesis. CCN1 overexpression induced luminal occlusion (P < 0.05), fibroproliferation, and smooth muscle cell proliferation (P < 0.05). Selective activation of αvß3-integrin receptor failed to mimic the actions of CCN1, and blocking failed to inhibit the effects of CCN1 in tracheal allografts. In conclusion, CCN1 exacerbates tracheal OB by enhancing fibroproliferation via an αvß3-integrin-independent pathway. Further experiments are required to uncover its potentially harmful role in the development of OB after lung transplantation.

Progress in late results among pediatric cardiac surgery patients: a population-based 6-decade study with 98% follow-up.

BACKGROUND: Surgical treatment of congenital cardiac defects in Finland started >60 years ago. We analyzed the survival of all the pediatric cardiac surgery patients operated on before 2010. METHODS AND RESULTS: Data were obtained retrospectively from a pediatric cardiac surgery database. Patient status was received from the Finnish Population Registry. Survival was determined with the Kaplan-Meier method, and the survival rate was compared with a sex- and age-matched general population. Between 1953 and 2009, 13 876 cardiac operations were performed on 10 964 pediatric patients in Finland. Follow-up coverage was 98%. The 60-year survival for the entire study was 70% versus 86% for the general population. The number and proportion of severe cardiac defects increased in the 2000s. The long-term survival of patients with severe defects improved significantly across decades. For instance, the 22-year survival rate of patients with transposition of the great arteries operated on in 1953 to 1989 and in 1990 to 2009 improved from 71% to 93% (hazard ratio for death, 0.29; 95% confidence interval, 0.17-0.49; P<0.0001), respectively. The mean patient age at operation decreased from 8.9 to 2.2 years (95% confidence interval, 6.2-7.1; P<0.0001). The early mortality of patients decreased from a maximum of 7% in the 1970s to 3% in the 2000s (95% confidence interval, 0.05-0.08; P<0.0001). CONCLUSIONS: Patients are diagnosed and treated at an increasingly younger age. Advanced diagnostics, surgical methods, and postoperative intensive care have led to substantial improvements in both early and late results among pediatric cardiac surgery patients.