Cardiac allograft vasculopathy: A review

Comprehensive Non-invasive Versus Invasive Approach to Evaluate Cardiac Allograft Vasculopathy in Heart Transplantation: The CCTA-HTx Study

BACKGROUND

Coronary computed tomography angiography (CCTA) is emerging as a valuable tool for noninvasive surveillance of cardiac allograft vasculopathy (CAV) in patients with heart transplant (HTx). We assessed the diagnostic performance of a comprehensive CCTA-based approach compared with the invasive reference, which includes invasive coronary angiography, intravascular ultrasound, and fractional flow reserve, for detecting CAV.

METHODS

This was a multicenter prospective study including 37 patients with HTx who underwent CCTA, invasive coronary angiography, intravascular ultrasound, and fractional flow reserve. The comprehensive CCTA-based approach included quantitative and qualitative plaque analysis and functional assessment by fractional flow reserve derived from coronary computed tomography. CAV was diagnosed based on invasive coronary angiography (International Society for Heart and Lung Transplantation criteria) and intravascular ultrasound. Univariable logistic regression analysis was performed to test CCTA-derived predictors of CAV. The area under the curve and accuracy indicators were calculated to evaluate the performance and best cutoffs of CCTA predictors of CAV.

RESULTS

The median interval between CCTA and HTx was 5 years. Among the 37 recipients, 23 (62.2%) were diagnosed with CAV. The integration of diameter stenosis and plaque morphology (including plaque burden at minimum lumen area >42% and percent atheroma volume >23%) at CCTA yielded the highest diagnostic performance (accuracy, 84%; sensitivity, 83%; specificity, 86%). The integration of ∆fractional flow reserve derived from coronary computed tomography trans-vessel gradient led to increased sensitivity, albeit with decreased specificity and overall accuracy. The noninvasive approach was associated with a lower contrast and radiation dose, compared with the invasive approach.

CONCLUSIONS

A noninvasive strategy based on CCTA is accurate for managing patients with HTx. CCTA might be considered the preferred imaging modality for annual CAV surveillance after the first year post-HTx.

Regulation of cardiac allograft immune responses by microRNA-155

INTRODUCTION

A better understanding of the immune mechanisms involved in allograft rejection after transplantation is urgently needed to improve patient outcomes. As microRNA-155 (miR155) plays a critical role in inflammation, we postulated that a deficiency of miR155 will improve cardiac allograft survival and enhance tolerance induction after heart transplantation.

METHODS

We developed an acute rejection mouse model through heterotopic BALB/c cardiac transplantation to C57BL/6 (wild-type) and C57BL/6 miR155 knock-out (miR155KO) mice. Further, we induced tolerance in both groups through a costimulatory blockade with CTLA4-Ig (200 μg; post-transplant day 2) and MRI antibodies (250 μg; post-transplant day 0), targeting CD28/B7 and CD40/CD154 signals, respectively. Finally, we examined the effects of injecting 100 μg of small extracellular vesicles (sEVs) isolated from wild-type mice undergoing rejection into tolerant miR155KO mice.

RESULTS

Mean survival time (MST) of the cardiac allografts in wild-type and miR155KO mice was 7 and 15 days, respectively (p < 0.0001). Costimulatory blockade increased MST to 65 days and > 100 days in the wild-type and miR155KO recipients, respectively (p < 0.001). Injection of sEVs isolated from wild-type mice undergoing rejection into tolerant miR155KO mice decreased the allograft survival to 9 days, significantly lower than the tolerant miR155KO mice without injection of sEVs (>100 days; p < 0.0001).

CONCLUSION

miR155KO mice have improved cardiac allograft survival and enhanced induction of tolerance after heterotopic cardiac transplantation. Injection of sEVs from wild-type mice undergoing rejection into the miR155KO mice reversed these benefits.

Coronary Computed Tomography Angiography in Heart Transplant Patients: Current Insights and Future Directions

Cardiac allograft vasculopathy (CAV) remains a significant challenge after heart transplantation, necessitating effective surveillance methods. This review centers around the role of coronary computed tomography angiography (CCTA) in CAV surveillance, given its unique capabilities to visualize and quantify CAV in comparison with other imaging modalities, including invasive coronary angiography and intravascular ultrasound. CCTA has shown good diagnostic performance for detecting and monitoring CAV, exemplified by a higher sensitivity and negative predictive value compared with invasive coronary angiography. Additionally, CCTA can provide valuable functional insights with fractional flow reserve integration. An additional, considerable benefit of CCTA is that it allows for the opportunity to assess other imaging markers of cardiometabolic and general health, including coronary artery calcium score, epicardial fat volume, liver fat, vertebral bone density, and lung density, which allows for a comprehensive assessment of the overall health of the patient.

Leukotriene B4: A potential mediator and biomarker for cardiac allograft vasculopathy

BACKGROUND

Cardiac allograft vasculopathy (CAV) remains the leading cause of long-term graft failure and mortality after heart transplantation. Effective preventive and treatment options are not available to date, largely because underlying mechanisms remain poorly understood. We studied the potential role of leukotriene B4 (LTB4), an inflammatory lipid mediator, in the development of CAV.

METHODS

We used an established preclinical rat CAV model to study the role of LTB4 in CAV. We performed syngeneic and allogeneic orthotopic aortic transplantation, after which neointimal proliferation was quantified. Animals were then treated with Bestatin, an inhibitor of LTB4 synthesis, or vehicle control for 30 days post-transplant, and evidence of graft CAV was determined by histology. We also measured serial LTB4 levels in a cohort of 28 human heart transplant recipients with CAV, 17 matched transplant controls without CAV, and 20 healthy nontransplant controls.

RESULTS

We showed that infiltration of the arterial wall with macrophages leads to neointimal thickening and a rise in serum LTB4 levels in our rat model of CAV. Inhibition of LTB4 production with the drug Bestatin prevents development of neointimal hyperplasia, suggesting that Bestatin may be effective therapy for CAV prevention. In a parallel study of heart transplant recipients, we found nonsignificantly elevated plasma LTB4 levels in patients with CAV, compared to patients without CAV and healthy, nontransplant controls.

CONCLUSIONS

This study provides key evidence supporting the role of the inflammatory cytokine LTB4 as an important mediator of CAV development and provides preliminary data suggesting the clinical benefit of Bestatin for CAV prevention.

Biomarkers from subcutaneous engineered tissues predict acute rejection of organ allografts

Invasive graft biopsies assess the efficacy of immunosuppression through lagging indicators of transplant rejection. We report on a microporous scaffold implant as a minimally invasive immunological niche to assay rejection before graft injury. Adoptive transfer of T cells into Rag2-/- mice with mismatched allografts induced acute cellular allograft rejection (ACAR), with subsequent validation in wild-type animals. Following murine heart or skin transplantation, scaffold implants accumulate predominantly innate immune cells. The scaffold enables frequent biopsy, and gene expression analyses identified biomarkers of ACAR before clinical signs of graft injury. This gene signature distinguishes ACAR and immunodeficient respiratory infection before injury onset, indicating the specificity of the biomarkers to differentiate ACAR from other inflammatory insult. Overall, this implantable scaffold enables remote evaluation of the early risk of rejection, which could potentially be used to reduce the frequency of routine graft biopsy, reduce toxicities by personalizing immunosuppression, and prolong transplant life.

Five-year outcomes of double kissing mini-culotte stenting vs. mini-culotte stenting using drug-eluting stents for the treatment of true coronary bifurcation lesions

Objective

This study aimed to compare the clinical outcomes of double kissing mini-culotte (DKMC) stenting with those of mini-culotte (MC) stenting in treating patients with true coronary bifurcation lesions (CBLs) in the clinical real world.

Methods

This retrospective observational cohort study included 180 consecutive patients with true CBLs (Medina type 1,1,1; 1,0,1; 0,1,1). All eligible patients underwent coronary angiography and percutaneous coronary intervention with two-stent techniques in our hospital; among them, 97 received DKMC treatment and 83 MC treatment. The primary clinical endpoints were the major adverse cardiovascular events (MACE), which included cardiac death, myocardial infarction, and target vessel/lesion revascularization (TVR/TLR). The secondary endpoints were stent thrombosis, in-stent restenosis, and individual components of MACE.

Results

Quantitative coronary angiography analysis (at 5 years) revealed that late lumen loss (0.25 ± 0.41 mm vs. 0.14 ± 0.32 mm, P = 0.032) and segmental diameter restenosis of the side branch (27.84 ± 12.34% vs. 19.23 ± 9.76%, P = 0.016) were lower in the DKMC treatment group than that in the MC treatment group. Notably, compared to that in the MC treatment group, the cumulative event rate of MACE at 5 years (22.8% vs. 8.3%, P = 0.007) and TVR/TLR (17.7% vs. 6.3%, P = 0.018) was higher in the DKMC treatment group, driven mainly by TVR/TLR. Especially, the DKMC group was related to a significant reduction in the primary and secondary endpoints in high-risk patients.

Conclusion

DKMC treatment was associated with less late lumen loss and restenosis in the side branch and a lower rate of cumulative MACE and TVR/TLR. DKMC treatment is more effective for treating true CBLs than MC treatment; however, these findings warrant further confirmation through a randomized clinical trial.

Conversion between sirolimus and everolimus in heart transplant recipients

BACKGROUND

Sirolimus and everolimus are mechanistic target of rapamycin inhibitors (mTORi) that may be included in immunosuppression regimens for orthotopic heart transplant (OHT) recipients. mTORi play a role in slowing progression of cardiac allograft vasculopathy; however, they have poor tolerability, sometimes necessitating a change between agents or therapies. The literature surrounding a conversion between mTORi are incongruent, thus this study was designed to assess the concentration/dose ratio for each medication around the time of conversion to provide guidance for a conversion strategy between mTORi.

METHODS

We conducted a retrospective study of adult OHT recipients who were maintained on both sirolimus- and everolimus-based immunosuppression regimens. The primary outcome was the concentration/dose (C/d) ratio of sirolimus to everolimus. Secondary outcomes included changes in hematologic and lipid labs and patient-reported intolerances.

RESULTS

The C/d ratio of sirolimus was 4.42, whereas the everolimus ratio was 2.23, resulting in a sirolimus: everolimus ratio of 1.98. Secondarily, after converting between mTORi, 93% of patients who reported intolerance(s) to one agent had a resolution of that intolerance. In our patient population, everolimus appeared better tolerated than sirolimus, with significantly more patients having no reported intolerances and significantly fewer patients experiencing edema. Other lab values were similar between patients receiving sirolimus and everolimus, except for an increased hemoglobin level in those receiving everolimus.

CONCLUSIONS

The conversion ratio of 1:2 observed in our population suggests OHT recipients may require an increased dose of EVL compared with SRL to maintain the same goal trough levels. A conversion between mTORi appeared to improve tolerability and did not lead to clinically significant worsening of any measured lab value.

An agent-based model of cardiac allograft vasculopathy: toward a better understanding of chronic rejection dynamics

Cardiac allograft vasculopathy (CAV) is a coronary artery disease affecting 50% of heart transplant (HTx) recipients, and it is the major cause of graft loss. CAV is driven by the interplay of immunological and non-immunological factors, setting off a cascade of events promoting endothelial damage and vascular dysfunction. The etiology and evolution of tissue pathology are largely unknown, making disease management challenging. So far, in vivo models, mostly mouse-based, have been widely used to study CAV, but they are resource-consuming, pose many ethical issues, and allow limited investigation of time points and important biomechanical measurements. Recently, agent-based models (ABMs) proved to be valid computational tools for deciphering mechanobiological mechanisms driving vascular adaptation processes at the cell/tissue level, augmenting cost-effective in vivo lab-based experiments, at the same time guaranteeing richness in observation time points and low consumption of resources. We hypothesize that integrating ABMs with lab-based experiments can aid in vivo research by overcoming those limitations. Accordingly, this work proposes a bidimensional ABM of CAV in a mouse coronary artery cross-section, simulating the arterial wall response to two distinct stimuli: inflammation and hemodynamic disturbances, the latter considered in terms of low wall shear stress (WSS). These stimuli trigger i) inflammatory cell activation and ii) exacerbated vascular cell activities. Moreover, an extensive analysis was performed to investigate the ABM sensitivity to the driving parameters and inputs and gain insights into the ABM working mechanisms. The ABM was able to effectively replicate a 4-week CAV initiation and progression, characterized by lumen area decrease due to progressive intimal thickening in regions exposed to high inflammation and low WSS. Moreover, the parameter and input sensitivity analysis highlighted that the inflammatory-related events rather than the WSS predominantly drive CAV, corroborating the inflammatory nature of the vasculopathy. The proof-of-concept model proposed herein demonstrated its potential in deepening the pathology knowledge and supporting the in vivo analysis of CAV.

A case report of cardiac allograft vasculopathy complicated with coronary vasospasm: insights from near-infrared spectroscopy, intravascular ultrasound, and optical coherence tomography

Background

Cardiac allograft vasculopathy (CAV) remains a major complication after heart transplantation. Although coronary vasospasm after heart transplantation has occasionally been reported, the association between CAV and coronary vasospasm remains unclear.

Case summary

A 68-year-old male with a history of heart transplantation 21 years ago presented with atypical angina. Coronary angiography demonstrated intermediate stenoses in the proximal and mid left anterior descending artery (LAD) and right posterolateral artery. Intracoronary acetylcholine provocation testing resulted in subtotal occlusion of the coronary arteries bilaterally, which was resolved by nitroglycerine administration, but the intermediate stenoses remained. The stenosis in the proximal LAD was physiologically significant based on fractional flow reserve. The patient was diagnosed with a developed CAV and concomitant coronary vasospasm and treated with percutaneous coronary intervention and nifedipine. Near-infrared spectroscopy and intravascular ultrasound showed a large isoechoic plaque with a low lipidic burden, suggesting a non-atherosclerotic plaque. Optical coherence tomography revealed a layered homogenous plaque, an intravascular imaging finding common in both CAV and coronary vasospasm. A drug-eluting stent dilated the stenosis, and follow-up angiography at 4 months showed no CAV progression.

Discussion

This case highlights the potential association between CAV and coronary vasospasm. Intravascular imaging detected similarities in plaque morphology between CAV and coronary vasospasm, suggesting that coronary vasospasm might contribute to the development of CAV. Although coronary vasospasm may be underdiagnosed in heart transplant recipients due to the lack of symptoms involving the denervated heart, this case showed that appropriate provocation testing may be beneficial for evaluating the cause of CAV.

Diagnostic accuracy of brain natriuretic peptide and N-terminal-pro brain natriuretic peptide to detect complications of cardiac transplantation in adults: A systematic review and meta-analysis

BACKGROUND

We aimed to evaluate the utility of BNP and NT-proBNP in identifying adverse recipient outcomes following cardiac transplantation.

METHODS

We searched MEDLINE (Ovid), Embase (Ovid), and the Cochrane Library from inception to February 2023. We included studies reporting associations between BNP or NT-proBNP and adverse outcomes following cardiac transplantation in adults. We calculated standardised mean differences (SMD) with 95% confidence intervals (CI); or confusion matrices with sensitivities and specificities. Where meta-analysis was inappropriate, studies were analysed descriptively.

RESULTS

Thirty-two studies involving 2,297 cardiac transplantation recipients were included. We report no significant association between BNP or NT-proBNP and significant acute cellular rejection of grade 3A or higher (SMD 0.40, 95% CI -0.06-0.86) as defined by the latest 2004 International Society for Heart and Lung Transplantation Guidelines. We also report no strong associations between BNP or NT-proBNP and cardiac allograft vasculopathy or antibody mediated rejection.

CONCLUSION

In isolation, serum BNP and NT-proBNP lack sufficient sensitivity and specificity to reliably predict adverse outcomes following cardiac transplantation.

PCSK9 Inhibition in Patients After Heart Transplantation: a Retrospective Review and Literature Analysis

PURPOSE OF REVIEW

Following cardiac transplantation, patients have an increased risk of developing cardiac allograft vasculopathy and atherosclerotic cardiovascular disease. Therefore, aggressive lipid management is indicated. Some patients do not achieve optimal lipid profiles with statin monotherapy, however, or discontinue statins due to intolerance. In this review, we investigated the use of PCSK9 inhibitors as an alternative treatment for hyperlipidemia following cardiac transplantation.

RECENT FINDINGS

Nine published articles were identified that included 110 patients treated with alirocumab or evolocumab after cardiac transplantation. PCSK9 inhibitors were tolerated by all patients, and each study demonstrated an effective reduction of low-density lipoprotein ranging from 40 to 87% decrease from baseline. In our study, the 110 patients from literature review were added to a cohort of 7 similar patients from our institution for combined analysis. This report supports that PCSK9 inhibitors should be considered following cardiac transplantation when conventional medial therapy is not tolerated or ineffective.

Animal Models for Heart Transplantation Focusing on the Pathological Conditions

Cardiac transplant recipients face many complications due to transplant rejection. Scientists must conduct animal experiments to study disease onset mechanisms and develop countermeasures. Therefore, many animal models have been developed for research topics including immunopathology of graft rejection, immunosuppressive therapies, anastomotic techniques, and graft preservation techniques. Small experimental animals include rodents, rabbits, and guinea pigs. They have a high metabolic rate, high reproductive rate, small size for easy handling, and low cost. Additionally, they have genetically modified strains for pathological mechanisms research; however, there is a lacuna, as these research results rarely translate directly to clinical applications. Large animals, including canines, pigs, and non-human primates, have anatomical structures and physiological states that are similar to those of humans; therefore, they are often used to validate the results obtained from small animal studies and directly speculate on the feasibility of applying these results in clinical practice. Before 2023, PubMed Central^® at the United States National Institute of Health's National Library of Medicine was used for literature searches on the animal models for heart transplantation focusing on the pathological conditions. Unpublished reports and abstracts from conferences were excluded from this review article. We discussed the applications of small- and large-animal models in heart transplantation-related studies. This review article aimed to provide researchers with a complete understanding of animal models for heart transplantation by focusing on the pathological conditions created by each model.

The cathepsin-S/protease-activated receptor-(PAR)-2 axis drives chronic allograft vasculopathy and is a molecular target for therapeutic intervention

BACKGROUND

Cathepsin S (CatS) and proteinase-activated receptor (PAR)-2 are involved in the remodelling of vascular walls and neointima formation as well as in alloantigen presentation and T-cell priming. Therefore, we hypothesized that CatS/PAR-2 inhibition/deficiency would attenuate chronic allograft vasculopathy.

METHODS

Heterotopic aortic murine transplantation was performed from C57BL/6J donors to C57BL/6J recipients (syngeneic control group), Balb/c to C57BL/6J without treatment (allogenic control group), Balb/c to C57BL/6J with twice daily oral CatS inhibitor (allogenic treatment group) and Balb/c to Par2-/- C57BL/6J (allogenic knockout group). The recipients were sacrificed on day 28 and the grafts were harvested for histological analysis and RT-qPCR.

RESULTS

After 28 days, mice of the allogenic control group exhibited significant neointima formation and massive CD8 T-cell infiltration into the neointima while the syngeneic control group showed negligible allograft vasculopathy. The mRNA expression level of CatS in allografts was 5-fold of those in syngeneic grafts. Neointima formation and therefore intima/media-ratio were significantly decreased in the treatment and knockout group in comparison to the allogenic control group. Mice in treatment group also displayed significantly fewer CD8 T cells in the neointima compared with allogeneic controls. Additionally, treatment with the CatS inhibitor and PAR2-deficiency decreased mRNA-levels of interleukins and cytokines.

CONCLUSION

In conclusion, our data indicate that inhibiting CatS and PAR-2 deficiency led to a marked reduction of neointima formation and associated inflammation in a murine heterotopic model for allograft vasculopathy.

First- Versus New-Generation Drug-Eluting Stents in Patients With Heart Transplant With Cardiac Allograft Vasculopathy

Although several studies have previously reported on the efficacy of percutaneous coronary intervention (PCI) with first-generation drug-eluting stents (DES) in heart transplant patients with cardiac allograft vasculopathy, few data regarding new-generation DES are currently available. We sought to compare the efficacy of new-generation versus first-generation DES in 90 consecutive patients with heart transplant (113 de novo coronary lesions) who underwent urgent or elective PCI with first-generation (28 patients) or new-generation (62 patients) DES. For each patient, the severity of cardiac allograft vasculopathy and postprocedural extent of revascularization were quantified calculating baseline and residual SYNTAX score, respectively. The primary end point was a composite of major adverse cardiac events-myocardial infarction, cardiovascular death, or target vessel revascularization-at 3 years. Overall, the median baseline SYNTAX score was 8 (5 to 15), and a total number of stents per patient of 1.6 ± 0.9 was implanted. Post-PCI residual SYNTAX score was 1.5 (0 to 4), with 13 patients having a score >8. At 3 years, the Kaplan-Meier estimate of freedom from major adverse cardiac events was 64%, with no differences between first-generation and new-generation DES groups (log-rank test p = 0.269). Nevertheless, patients treated with new-generation DES experienced a lower rate of target vessel revascularization (15% vs 31%, log-rank test p = 0.058). In the multivariate Cox regression analysis, a post-PCI residual SYNTAX score >8 (hazard ratio 2.37, confidence interval 0.98 to 5.73, p = 0.054) was identified as an independent predictor of the primary end point.

Immunoengineered MXene nanosystem for mitigation of alloantigen presentation and prevention of transplant vasculopathy

MXenes are an emerging class of nanomaterials with significant potential for applications in nanomedicine. Amongst MXene technologies, titanium carbide (Ti₃C₂T_x) nanomaterials are the most mature and have received significant attention to tackle longstanding clinical challenges due to its tailored physical and material properties. Cardiac allograft vasculopathy is an aggressive form of atherosclerosis and a major cause of mortality among patients with heart transplants. Blood vessel endothelial cells (ECs) stimulate alloreactive T-lymphocytes to result in sustained inflammation. Herein, we report the first application of Ti₃C₂T_x MXene nanosheets for prevention of allograft vasculopathy. MXene nanosheets interacted with human ECs and downregulated the expression of genes involved in alloantigen presentation, and consequently reduced the activation of allogeneic lymphocytes. RNA-Seq analysis of lymphocytes showed that treatment with MXene downregulated genes responsible for transplant-induced T-cell activation, cell-mediated rejection, and development of allograft vasculopathy. In an in vivo rat model of allograft vasculopathy, treatment with MXene reduced lymphocyte infiltration and preserved medial smooth muscle cell integrity within transplanted aortic allografts. These findings highlight the potential of Ti₃C₂T_x MXene in treatment of allograft vasculopathy and inflammatory diseases.

Atherosclerotic Cardiovascular Risk as an Emerging Priority in Pediatrics

Over the last decades, childhood and adolescence have emerged as an important window of opportunity to prevent atherosclerotic cardiovascular disease (ASCVD) later in life. Here, we discuss the underlying advances in the field. First, atherosclerosis development starts as early as childhood. Atherogenesis initiates in the iliac arteries and abdominal aorta and subsequently develops in higher regions of the arterial tree, as has been demonstrated in nonhuman primate studies and human autopsy studies. Obesity, hypertension, hyperlipidemia, and hyperglycemia at a young age can accelerate atherogenesis. Children and adolescents with obesity have a relative risk of ∼ 2.5 for ASCVD mortality later in life, compared to peers with a normal weight. Conversely, early prevention improves long-term cardiovascular outcomes. Second, we review disease-associated factors that add to the traditional risk factors. Various pediatric disorders carry similar or even higher risks of ASCVD than obesity, including chronic inflammatory disorders, organ transplant recipients, familial hypercholesterolemia, endocrine disorders, childhood cancer survivors, chronic kidney diseases, congenital heart diseases, and premature birth, especially after fetal growth restriction. The involved disease-associated factors that fuel atherogenesis are diverse and include inflammation, vascular, and endothelial factors. The diverse and growing list of pediatric groups at risk underscores that cardiovascular risk management has solidly entered the realm of general pediatrics. In a second review in this series, we will, therefore, focus on recent advances in cardiovascular risk assessment and management and their implications for pediatric practice.

Multiparametric Cardiac Magnetic Resonance Imaging Detects Altered Myocardial Tissue and Function in Heart Transplantation Recipients Monitored for Cardiac Allograft Vasculopathy

BACKGROUND

Cardiac allograft vasculopathy (CAV) is a complication beyond the first-year post-heart transplantation (HTx). We aimed to test the utility of cardiac magnetic resonance (CMR) to detect functional/structural changes in HTx recipients with CAV.

METHODS

Seventy-seven prospectively recruited HTx recipients beyond the first-year post-HTx and 18 healthy controls underwent CMR, including cine imaging of ventricular function and T1- and T2-mapping to assess myocardial tissue changes. Data analysis included quantification of global cardiac function and regional T2, T1 and extracellular volume based on the 16-segment model. International Society for Heart and Lung Transplantation criteria was used to adjudicate CAV grade (0–3) based on coronary angiography.

RESULTS

The majority of HTx recipients (73%) presented with CAV (1: n = 42, 2/3: n = 14, 0: n = 21). Global and segmental T2 (49.5 ± 3.4 ms vs 50.6 ± 3.4 ms, p < 0.001;16/16 segments) were significantly elevated in CAV-0 compared to controls. When comparing CAV-2/3 to CAV-1, global and segmental T2 were significantly increased (53.6 ± 3.2 ms vs. 50.6 ± 2.9 ms, p < 0.001; 16/16 segments) and left ventricular ejection fraction was significantly decreased (54 ± 9% vs. 59 ± 9%, p < 0.05). No global, structural, or functional differences were seen between CAV-0 and CAV-1.

CONCLUSIONS

Transplanted hearts display functional and structural alteration compared to native hearts, even in those without evidence of macrovasculopathy (CAV-0). In addition, CMR tissue parameters were sensitive to changes in CAV-1 vs. 2/3 (mild vs. moderate/severe). Further studies are warranted to evaluate the diagnostic value of CMR for the detection and classification of CAV.

Evaluation of cardiac allograft vasculopathy by positron emission tomography

Cardiac allograft vasculopathy (CAV) remains one of the most important late occurring complications in heart transplant (HT) recipients significantly effecting graft survival. Recently, there has been tremendous focus on the development of effective and safe non-invasive diagnostic strategies for the diagnosis of CAV employing a wide range of imaging technologies. During the past decade multiple studies have been published using positron emission tomography (PET) myocardial perfusion imaging, establishing the value of PET myocardial blood flow quantification for the evaluation of CAV. These independent investigations demonstrate that PET can be successfully used to establish the diagnosis of CAV, can be utilized for prognostication and may be used for serial monitoring of HT recipients. In addition, molecular imaging techniques have started to emerge as new tools to enhance our knowledge to better understand the pathophysiology of CAV.

Fabrication of Smart Tantalum Carbide MXene Quantum Dots with Intrinsic Immunomodulatory Properties for Treatment of Allograft Vasculopathy

MXene nanomaterials have sparked significant interest among interdisciplinary researchers to tackle today's medical challenges. In particular, colloidal MXene quantum dots (MQDs) offer the high specific surface area and compositional flexibility of MXene while providing improvements to aqueous stability and material-cell interactions. The current study for the first time reports the development and application of immunoengineered tantalum-carbide (Ta4C3T x ) MQDs for in vivo treatment of transplant vasculopathy. This report comes at a critical juncture in the field as poor long-term safety of other MXene compositions challenge the eventual clinical translatability of these materials. Using rational design and synthesis strategies, the Ta4C3T x MQDs leverage the intrinsic anti-inflammatory and antiapoptotic properties of tantalum to provide a novel nanoplatform for biomedical engineering. In particular, these MQDs are synthesized with high efficiency and purity using a facile hydrofluoric acid-free protocol and are enriched with different bioactive functional groups and stable surface TaO2 and Ta2O5. Furthermore, MQDs are spontaneously uptaken into antigen-presenting endothelial cells and alter surface receptor expression to reduce their activation of allogeneic T-lymphocytes. Finally, when applied in vivo, Ta4C3T x MQDs ameliorate the cellular and structural changes of early allograft vasculopathy. These findings highlight the robust potential of tailored Ta4C3T x MQDs for future applications in medicine.

Steroid withdrawal after heart transplantation in adults

Corticosteroids (CSs) are a key component of immunosuppressive treatment after heart transplantation (HTx). While effectively preventing acute rejection, several adverse effects including diabetes, hypertension, osteoporosis, and hyperlipidemia are associated with long-term use. As these complications may impair long-term outcome in HTx recipients, withdrawal of CSs is highly desirable, however, no uniform approach exists. Previous experience suggests that CS withdrawal can be accomplished without an increase in the incidence of acute rejection and even carrying a survival benefit. Also, common complications related to long-term CS use appear to be less frequent following CS discontinuation. Recipients who successfully discontinue CSs, however, likely belong to an immune-privileged subset of patients with low risk of post-transplant complications. Available studies evaluating CS withdrawal are highly heterogeneous and consensus on optimal timing and eligibility for withdrawal is lacking. Efforts to improve the understanding of optimal CS withdrawal strategy are of great importance in order to safely promote CS weaning in eligible patients and thereby alleviate the adverse effects of long-term CS use on post-transplant outcomes. The purpose of this review was to evaluate different protocols of CS withdrawal after HTx in terms of clinical outcomes and to explore criteria for successful CS withdrawal.

PLX3397, a CSF1 receptor inhibitor, limits allotransplantation-induced vascular remodelling

AIMS

Graft vascular disease (GVD), a clinically important and highly complex vascular occlusive disease, arises from the interplay of multiple cellular and molecular pathways. While occlusive intimal lesions are composed predominantly of smooth-muscle-like cells (SMLCs), the origin of these cells and the stimuli leading to their accumulation in GVD are uncertain. Macrophages have recently been identified as both potential drivers of intimal hyperplasia and precursors that undergo transdifferentiation to become SMLCs in non-transplant settings. Colony-stimulating factor-1 (CSF1) is a well-known regulator of macrophage development and differentiation, and prior preclinical studies have shown that lack of CSF1 limits GVD. We sought to identify the origins of SMLCs and of cells expressing the CSF1 receptor (CSF1R) in GVD, and to test the hypothesis that pharmacologic inhibition of CSF1 signalling would curtail both macrophage and SMLC activities and decrease vascular occlusion.

METHODS AND RESULTS

We used genetically modified mice and a vascular transplant model with minor antigen mismatch to assess cell origins. We found that neointimal SMLCs derive from both donor and recipient, and that transdifferentiation of macrophages to SMLC phenotype is minimal in this model. Cells expressing CSF1R in grafts were identified as recipient-derived myeloid cells of Cx3cr1 lineage, and these cells rarely expressed smooth muscle marker proteins. Blockade of CSF1R activity using the tyrosine kinase inhibitor PLX3397 limited the expression of genes associated with innate immunity and decreased levels of circulating monocytes and intimal macrophages. Importantly, PLX3397 attenuated the development of GVD in arterial allografts.

CONCLUSION

These studies provide proof of concept for pharmacologic inhibition of the CSF1/CSF1R signalling pathway as a therapeutic strategy in GVD. Further preclinical testing of this pathway in GVD is warranted.

Feasibility and safety of quantitative adenosine stress perfusion cardiac magnetic resonance imaging in pediatric heart transplant patients with and without coronary allograft vasculopathy

BACKGROUND

Pediatric heart transplant patients require cardiac catheterization to monitor for coronary allograft vasculopathy. Cardiac catheterization has no safe and consistent method for measuring microvascular disease. Stress perfusion cardiac magnetic resonance imaging (MRI) assessing microvascular disease has been performed in adults.

OBJECTIVE

To investigate the feasibility and safety of performing cardiac MRI with quantitative adenosine stress perfusion testing in pediatric heart transplant patients with and without coronary allograft vasculopathy.

MATERIALS AND METHODS

All pediatric heart transplant patients with coronary vasculopathy at our institution were asked to participate. Age- and gender-matched pediatric heart transplant patients without vasculopathy were recruited for comparison. Patients underwent cardiac MRI with adenosine stress perfusion testing.

RESULTS

Sixteen pediatric heart transplant patients, ages 6-22 years, underwent testing. Nine patients had vasculopathy by angiography. No heart block or other complications occurred during the study. The myocardial perfusion reserve for patients with vasculopathy showed no significant difference with comparison patients (median: 1.43 vs. 1.48; P=0.49). Values for both groups were lower than expected values based on previous adult studies. The patients were also analyzed for time after transplant and the number of rejection episodes. Patients within 6 years of transplantation had a nonsignificant trend toward a higher myocardial perfusion reserve (median: 1.57) versus patients with older transplants (median: 1.47; P=0.46). Intra- and interobserver reproducibility were 97% and 92%, respectively.

CONCLUSION

Myocardial perfusion reserve is a safe and feasible method for estimating myocardial perfusion in pediatric heart transplant patients. There is no reliable way to monitor microvascular disease in pediatric patients. This method shows potential and deserves investigation in a larger cohort.

Symptomatic Presentation of Acute Myocardial Infarction in Heart Transplantation Patients

Patients with acute myocardial infarction with a history of an orthotopic heart transplantation rarely present with classic anginal symptoms, secondary to cardiac denervation. We present 2 cases, the first of a patient with a ST-segment elevation myocardial infarction and the second who presented with a non-ST-segment elevation myocardial infarction. Both patients presented with typical symptoms and were treated with percutaneous coronary intervention. (Level of Difficulty: Intermediate.).

Cardiac allograft vasculopathy: Differences of absolute and relative intimal hyperplasia in children versus adults in optical coherence tomography

BACKGROUND

Intracoronary imaging enables an early detection of intimal changes. To what extend the development of absolute and relative intimal hyperplasia in intracoronary imaging differs depending on age and post-transplant time is not known.

METHODS

Aim of our retrospective study was to compare findings between 24 pediatric (cohort P) and 21 adult HTx patients (cohort A) using optical coherence tomography (OCT) at corresponding post-transplant intervals (≤5 years: P1 (n = 11) and A1 (n = 10); >5 and ≤ 10 years: P2 (n = 13) and A2 (n = 11),. Coronary intima thickness (IT), media thickness (MT) and intima to media ratio (I/M) were assessed per quadrant. Maximal IT >0.3 mm was considered absolute, I/M > 1 relative intimal hyperplasia.

RESULTS

Compared to A1, I/M was significantly higher in P1 (maximal I/M: P1: 5.41 [2.81-13.39] vs. A1: 2.30 [1.55-3.62], p = 0.005), whereas absolute IT values were comparable. In contrast, I/M was comparable between P2 and A2, but absolute IT were significantly higher in A2 (maximal IT: P2: 0.16 mm [0.11-0.25] vs. A2: 0.40 mm [0.30-0.71], p < 0.001). A2 presented with higher absolute IT (maximal: A1: 0.16 mm [0.12-0.44] vs. A2: 0.40 mm [0.30-0.71], p = 0.02) and I/M (maximal I/M A1: 2.30 [1.55-3.62] vs. A2: 3.79 [3.01-5.62], p = 0.04).

CONCLUSION

Our results suggest an age- and time-dependent difference in the prevalence of absolute and relative intimal hyperplasia in OCT, with an early peak in children and a progressive increase in adults.

Clinical characteristics and in hospital outcomes of heart transplant recipients undergoing percutaneous coronary intervention: Insights from the National Inpatient Sample

OBJECTIVES

Cardiac transplant patients are at increased risk of Coronary Allograft Vasculopathy which requires percutaneous coronary intervention (PCI).

BACKGROUND

We aim to determine national epidemiology describing trends, mortality, and morbidity risks in patients with heart transplant undergoing PCI.

METHODS

We used Nationwide Inpatient Sample (NIS) data from 2002 to 2014 to identify adult hospitalizations with PCI using ICD 9 codes. Acute myocardial infarction (AMI), cardiac transplant status and complications were identified using validated ICD-9-CM diagnosis codes. Endpoints were in-hospital mortality and peri-procedural complications. Propensity match analysis was performed to compare the end-points between DES and BMS.

RESULTS

Total 8,613,900 patients underwent PCI, of which 1,531(0.002%) patients had prior heart transplant status. Among these 1,531 PCIs, 311(20%) were due to AMI including 125(8%) due to STEMI. 74% of PCIs were done in males and 78% of the PCIs were performed in the 60-79 age group. Out of 1,380 stents placed, 1,090 were DES (79%) and 290 (21%) were BMS. Mortality was higher in the BMS versus DES (8.34% vs. 3.45%, p = .012), CONCLUSION: We concluded that majority of the population who underwent PCI were older males. DES was used more than BMS. The use of BMS is associated with increased mortality, cardiac complications and Acute Kidney Injury requiring dialysis compared with DES which likely is representative of preferential use of DES in these patient population.

Vessel Fractional Flow Reserve and Graft Vasculopathy in Heart Transplant Recipients

Background

Cardiac allograft vasculopathy (CAV) remains the Achilles' heel of long-term survival after heart transplantation (HTx). The severity and extent of CAV is graded with conventional coronary angiography (COR) which has several limitations. Recently, vessel fractional flow reserve (vFFR) derived from COR has emerged as a diagnostic computational tool to quantify the functional severity of coronary artery disease.

Purpose

The present study assessed the usefulness of vFFR to detect CAV in HTx recipients.

Methods

In HTx patients referred for annual check-up, undergoing surveillance COR, the extent of CAV was graded according to the criteria proposed by the international society of heart and lung transplantation (ISHLT). In addition, three-dimensional coronary geometries were constructed from COR to calculate pressure losses using vFFR.

Results

In 65 HTx patients with a mean age of 53.7 ± 10.1 years, 8.5 years (IQR 1.90, 15.2) years after HTx, a total number of 173 vessels (59 LAD, 61 LCX, and 53 RCA) were analyzed. The mean vFFR was 0.84 ± 0.15 and median was 0.88 (IQR 0.79, 0.94). A vFFR ≤ 0.80 was present in 24 patients (48 vessels). HTx patients with a history of ischemic cardiomyopathy (ICMP) had numerically lower vFFR as compared to those with non-ICMP (0.70 ± 0.22 vs. 0.79 ± 0.13, p = 0.06). The use of vFFR reclassified 31.9% of patients compared to the anatomical ISHLT criteria. Despite a CAV score of 0, a pathological vFFR ≤ 0.80 was detected in 8 patients (34.8%).

Conclusion

The impairment in epicardial conductance assessed by vFFR in a subgroup of patients without CAV according to standard ISHLT criteria suggests the presence of a diffuse vasculopathy undetectable by conventional angiography. Therefore, we speculate that vFFR may be useful in risk stratification after HTx.

Prognostic Value of Myocardial Extracellular Volume Fraction and T2-mapping in Heart Transplant Patients

OBJECTIVES

The purpose of this study was to examine prognostic value of T1- and T2-mapping techniques in heart transplant patients.

BACKGROUND

Myocardial characterization using T2 mapping (evaluation of edema/inflammation) and pre- and post-gadolinium contrast T1 mapping (calculation of extracellular volume fraction [ECV] for assessment of interstitial expansion/fibrosis) are emerging modalities that have been investigated in various cardiomyopathies.

METHODS

A total of 99 heart transplant patients underwent the magnetic resonance imaging (MRI) scans including T1- (n = 90) and T2-mapping (n = 79) techniques. Relevant clinical characteristics, MRI parameters including late gadolinium enhancement (LGE), and invasive hemodynamics were collected. Median clinical follow-up duration after the baseline scan was 2.4 to 3.5 years. Clinical outcomes include cardiac events (cardiac death, myocardial infarction, coronary revascularization, and heart failure hospitalization), noncardiac death and noncardiac hospitalization.

RESULTS

Overall, the global native T1, postcontrast T1, ECV, and T2 were 1,030 ± 56 ms, 458 ± 84 ms, 27 ± 4% and 50 ± 4 ms, respectively. Top-tercile-range ECV (ECV >29%) independently predicted adverse clinical outcomes compared with bottom-tercile-range ECV (ECV <25%) (hazard ratio [HR]: 2.87; 95% confidence interval [CI]: 1.07 to 7.68; p = 0.04) in a multivariable model with left ventricular end-systolic volume and LGE. Higher T2 (T2 ≥50.2 ms) independently predicted adverse clinical outcomes (HR: 3.01; 95% CI: 1.39 to 6.54; p = 0.005) after adjustment for left ventricular ejection fraction, left ventricular end-systolic volume, and LGE. Additionally, higher T2 (T2 ≥50.2 ms) also independently predicted cardiac events (HR: 4.92; CI: 1.60 to 15.14; p = 0.005) in a multivariable model with left ventricular ejection fraction.

CONCLUSIONS

MRI-derived myocardial ECV and T2 mapping in heart transplant patients were independently associated with cardiac and noncardiac outcomes. Our findings highlight the need for larger prospective studies.

Combined abdominal heterotopic heart and aorta transplant model in mice

Background

Allograft vasculopathy (AV) remains a major obstacle to long-term allograft survival. While the mouse aortic transplantation model has been proven as a useful tool for study of the pathogenesis of AV, simultaneous transplantation of the aorta alongside the transplantation of another organ may reveal more clinically relevant mechanisms that contribute to the pathogenesis of chronic allograft rejection. Therefore, we developed a combined abdominal heart and aorta transplantation model in mice which benefits from reducing animal and drug utilization, while providing an improved model to study the progressive nature of AV.

Methods

The middle of the infrarenal aorta of the recipient mouse was ligatured between the renal artery and its bifurcation. Proximal and distal aortotomies were performed at this site above and below the ligature, respectively, for the subsequent anastomoses of the donor aorta and heart grafts to the recipient infrarenal aorta in an end-to-side fashion. The distal anastomotic site of the recipient infrarenal aorta was connected with the outlet of the donor aorta. Uniquely, the proximal anastomotic site on the recipient infrarenal aorta was shared to connect with both the inlet of the donor aorta and the inflow tract to the donor heart. The outflow tract from the donor heart was connected to the recipient inferior vena cava (IVC).

Results

The median times for harvesting the heart graft, aorta graft, recipient preparation and anastomosis were 11.5, 8.0, 9.0 and 40.5 min, respectively, resulting in a total median ischemic time of 70 min. The surgery survival rate was more than 96% (29/30). Both the syngeneic C57Bl/6 aorta and heart grafts survived more than 90 days in 29 C57Bl/6 recipients. Further, Balb/c to C57Bl/6 allografts treated with anti-CD40L and CTLA4.Ig survived more than 90 days with a 100% (3/3) survival rate. (3/3).

Conclusions

This model is presented as a new tool for researchers to investigate transplant immunology and assess immunosuppressive strategies. It is possible to share a common anastomotic stoma on the recipient abdominal aorta to reconstruct both the aorta graft entrance and heart graft inflow tract. This allows for the study of allogeneic effects on both the aorta and heart from the same animal in a single survival surgery.

Transcatheter Aortic Valve Replacement of a Bicuspid Aortic Valve in a Heart Transplant Recipient

Patients with heart transplants who present with severe aortic stenosis may be deemed high-risk surgical candidates due to immunosuppression and multiple comorbid conditions. Appropriately selected patients may be successfully treated with transcatheter aortic valve replacement. (Level of Difficulty: Advanced.)