High-sensitivity cardiac troponin I assay to screen for acute rejection in patients with heart transplant

Association Between High Sensitivity Troponin Levels Following Pediatric Orthotopic Heart Transplantation and Intensive Care Unit Resource Utilization

The utility of troponin levels, including high sensitivity troponin T (hs-TnT), after orthotopic heart transplant (OHT) is controversial. Conflicting data exist regarding its use as a marker of acute rejection. Few studies have examined possible associations of hs-TnT levels immediately after OHT with metrics of intensive care unit (ICU) resource utilization or risk of acute rejection. We performed a retrospective cohort chart review including all OHT recipients < 20 years of age at our center between June 2019 and December 2022. Patients were divided into two groups based on supra- or sub-median initial hs-TnT levels (median 3462.5 ng/L). Primary outcome was days requiring ICU-level care, secondary outcomes included days intubated, days requiring positive pressure ventilation (PPV), days on inotropic medications, actual ICU length of stay, Vasoactive Inotrope Scores (VIS) on postoperative days (POD) 0 through 7, and acute rejection at 30 days and one year after OHT. Patients with higher hs-TnT required ICU level care for longer [13.5 (10-17.5) vs. 9.5 (8-12) days, p = 0.01] and spent more days intubated [6 (4-7) vs. 3 (3-5) days, p < 0.001], on PPV [9 (6-15) vs. 6 (5-8.5) days, p = 0.02], and on inotropes [11 (9-14) vs. 8 (7-11) days, p = 0.025]. VIS was only different between groups on POD7 [5 (3-7) vs. 3 (0-5), p = 0.04]. There was no difference in rejection between the groups. Higher hs-TnT immediately following pediatric OHT may predict higher ICU resource utilization, despite no difference in VIS, although it does not predict acute rejection in the first year after OHT.

Heart transplantation and biomarkers: a review about their usefulness in clinical practice

Advanced heart failure (AdvHF) can only be treated definitively by heart transplantation (HTx), yet problems such right ventricle dysfunction (RVD), rejection, cardiac allograft vasculopathy (CAV), and primary graft dysfunction (PGD) are linked to a poor prognosis. As a result, numerous biomarkers have been investigated in an effort to identify and prevent certain diseases sooner. We looked at both established biomarkers, such as NT-proBNP, hs-troponins, and pro-inflammatory cytokines, and newer ones, such as extracellular vesicles (EVs), donor specific antibodies (DSA), gene expression profile (GEP), donor-derived cell free DNA (dd-cfDNA), microRNA (miRNA), and soluble suppression of tumorigenicity 2 (sST2). These biomarkers are typically linked to complications from HTX. We also highlight the relationships between each biomarker and one or more problems, as well as their applicability in routine clinical practice.

High sensitivity troponin I as a biomarker for cardiac allograft vasculopathy: Evaluation of diagnostic potential and clinical utility

INTRODUCTION

Cardiac allograft vasculopathy (CAV) limits long-term survival in heart transplant (HTx) recipients. The use of biomarkers in CAV surveillance has been studied, but none are used in clinical practice. The predictive value of high-sensitivity troponin I (hsTnI) has not been extensively investigated in HTx recipients.

METHODS

HTx patients undergoing surveillance coronary angiograms and enrolled in the Emory Cardiovascular Biobank had plasma hsTnI measured. CAV grade was assessed using ISHLT nomenclature. Multivariable cumulative link mixed modeling was performed to determine association between hsTnI level and CAV grade. Patients were followed for adverse outcomes over a median 10-year period. Kaplan-Meier survival analysis and Cox proportional hazard modeling were performed.

RESULTS

Three hundred and seventy-two angiograms were analyzed in 156 patients at a median 8.9 years after transplant. hsTnI levels were positively correlated with concurrent CAV grade after adjustment for age, age at transplant, sex, BMI, hypertension, diabetes, hyperlipidemia, estimated glomerular filtration rate, and history of acute cellular rejection (p = .016). In an adjusted Cox proportional hazard model, initial hsTnI level above the median (4.9 pg/mL) remained a predictor of re-transplantation or death (hazard ratio 1.82; 95% confidence interval 1.16-2.90; p = .01).

CONCLUSION

An elevated hsTnI level reflects severity of CAV and is associated with poor long-term outcomes in patients with HTx.

The utilization of molecular microscope in management of heart transplant recipients in the era of noninvasive monitoring

INTRODUCTION

Monitoring for graft rejection is a fundamental tenet of post-transplant follow-up. In heart transplantation (HT) in particular, rejection has been traditionally assessed with endomyocardial biopsy (EMB). EMB has potential complications and noted limitations, including interobserver variability in interpretation. Additional tests, such as basic cardiac biomarkers, cardiac imaging, gene expression profiling (GEP) scores, donor-derived cell-free DNA (dd-cfDNA) and the novel molecular microscope diagnostic system (MMDx) have become critical tools in rejection surveillance beyond standard EMB.

METHODS

This paper describes an illustrative case followed by a review of MMDx within the context of other noninvasive screening modalities for rejection.

CONCLUSIONS

We suggest MMDx be used to assist with early detection of rejection in cases of discordance between EMB and other noninvasive studies.

Alpha-cardiac Actin Serum Expression Levels Detect Acute Cellular Rejection in Heart Transplant Patients

BACKGROUND

Given the central role of sarcomeric dysfunction in cardiomyocyte biology and sarcomere alterations described in endomyocardial biopsies of transplant patients with rejection, we hypothesized that the serum expression levels of genes encoding sarcomeric proteins were altered in acute cellular rejection (ACR). The aim of this study is to identify altered sarcomere-related molecules in serum and to evaluate their diagnostic accuracy for detecting rejection episodes.

METHODS

Serum samples from transplant recipients undergoing routine endomyocardial biopsies were included in an RNA sequencing analysis (n = 40). Protein concentrations of alpha-cardiac actin were determined using a specific enzyme-linked immunoassay (n = 80).

RESULTS

We identified 17 sarcomeric genes differentially expressed in patients with clinically relevant rejection (grade ≥2R ACR). A receiver operating characteristic curve was done to assess their accuracy for ACR detection and found that 6 relevant actins, myosins, and other sarcomere-related genes showed great diagnostic capacity with an area under the curve (AUC) > 0.800. Specifically, the gene encoding alpha-cardiac actin ( ACTC1 ) showed the best results (AUC = 1.000, P < 0.0001). We determine ACTC1 protein levels in a larger patient cohort, corroborating its overexpression and obtaining a significant diagnostic capacity for clinically relevant rejection (AUC = 0.702, P < 0.05).

CONCLUSIONS

Sarcomeric alterations are reflected in peripheral blood of patients with allograft rejection. Because of their precision to detect ACR, we propose sarcomere ACTC1 serum expression levels as potential candidate for to be included in the development of molecular panel testing for noninvasive ACR detection.

Liquid Biopsy, a Potential New Detection Method in Heart Allograft Rejection

Allografts rejection remains the most important reason causing allograft dysfunction in heart transplantation recipients. Currently, the golden standard for detecting graft rejection is endomyocardial biopsy (EMB). As a new noninvasive technique, liquid biopsy emerges along with the great developments of droplet-based digital PCR and the various optimizations of next-generation sequencing technologies, which is also cheaper than EMB. This review introduces several types of liquid biopsy and its application in heart transplantation.

Elevated Cardiac Troponin to Detect Acute Cellular Rejection After Cardiac Transplantation: A Systematic Review and Meta-Analysis

Cardiac troponin is well known as a highly specific marker of cardiomyocyte damage, and has significant diagnostic accuracy in many cardiac conditions. However, the value of elevated recipient troponin in diagnosing adverse outcomes in heart transplant recipients is uncertain. We searched MEDLINE (Ovid), Embase (Ovid), and the Cochrane Library from inception until December 2020. We generated summary sensitivity, specificity, and Bayesian areas under the curve (BAUC) using bivariate Bayesian modelling, and standardised mean differences (SMDs) to quantify the diagnostic relationship of recipient troponin and adverse outcomes following cardiac transplant. We included 27 studies with 1,684 cardiac transplant recipients. Patients with acute rejection had a statistically significant late elevation in standardised troponin measurements taken at least 1 month postoperatively (SMD 0.98, 95% CI 0.33–1.64). However, pooled diagnostic accuracy was poor (sensitivity 0.414, 95% CrI 0.174–0.696; specificity 0.785, 95% CrI 0.567–0.912; BAUC 0.607, 95% CrI 0.469–0.723). In summary, late troponin elevation in heart transplant recipients is associated with acute cellular rejection in adults, but its stand-alone diagnostic accuracy is poor. Further research is needed to assess its performance in predictive modelling of adverse outcomes following cardiac transplant.

Systematic Review Registration: identifier CRD42021227861

High-sensitivity Cardiac Troponin Is Not Associated With Acute Cellular Rejection After Heart Transplantation

BACKGROUND

Acute cellular rejection (ACR) is common in the first year after cardiac transplantation, and regular surveillance endomyocardial biopsy (EMB) is required. An inexpensive, simple noninvasive diagnostic test would be useful. Prior studies suggest cardiac troponin (cTn) has potential as a "rule-out" test to minimize the use of EMB. Our aim was to determine whether a new high-sensitivity cardiac troponin I (hs-cTnI) assay would have utility as a "rule-out" test for ACR after heart transplantation.

METHODS

Blood samples at patient follow-up visits were collected and stored over a period of 5 y. Serum cTnI concentrations were measured using the ARCHITECTSTAT hs-cTnI assay and compared with an EMB performed on the same day. Receiver-operator curve analysis based on mixed-effects logistic regression models that account for repeated measurements in individuals was performed to determine a serum troponin level below which ACR could be reliably excluded.

RESULTS

One hundred seventy patients had 883 serum hs-cTnI results paired to a routine surveillance EMB. Fifty-one (6%) EMB showed significant ACR (grade ≥2R). Receiver-operator curve analysis approximated the null hypothesis area under the curve 0.509 (95% CI, 0.428-0.591). Sub-analysis including repeated hs-cTnI levels in a single individual, and early (<3 mo) EMB also showed no diagnostic utility of hs-cTnI measurement (area under the curve 0.512).

CONCLUSIONS

In the largest published study to date, we found no association between hs-cTnI concentration and the presence of significant ACR on surveillance EMB. Measurement of hs-cTnI may not be a useful technique for diagnosis or exclusion of ACR after heart transplantation.

Noninvasive biomarkers in heart transplant: 2020-2021 year in review

PURPOSE OF REVIEW

Endomyocardial biopsy (EMB), the current gold standard for cardiac allograft monitoring is invasive, may have a low sensitivity and is associated with significant variability in histopathologic interpretation. Fortunately, on-going research is identifying noninvasive biomarkers that address some of these limitations. This review provides an update on noninvasive blood-based methods for rejection surveillance and diagnosis in heart transplantation.

RECENT FINDINGS

Recent studies highlight good test performance to detect acute rejection for donor-derived cell-free DNA (dd-cfDNA) and microRNAs (miR). dd-cfDNA is sensitive, nonspecific, and has a high negative predictive value for acute cellular and antibody-mediated rejection. Clinical utility trials are being planned to test its role as a rule-out test for acute rejection as compared to the EMB. miRs may have an added advantage as it may phenotype the subtypes of rejection alleviating the need for an EMB or permitting the initiation of targeted therapy while awaiting the results of the EMB.

SUMMARY

In this review, we discuss recent advances in the field of noninvasive biomarkers to detect allograft rejection after heart transplant. We provide a perspective of additional studies needed to prove their clinical utility and bring these biomarkers to widescale clinical use.

Nox2-deficient Tregs improve heart transplant outcomes via their increased graft recruitment and enhanced potency

Nox2 is a ROS-generating enzyme, deficiency of which increases suppression by Tregs in vitro and in an in vivo model of cardiac remodeling. As Tregs have emerged as a candidate therapy in autoimmunity and transplantation, we hypothesized that Nox2 deficiency in Tregs in recipient mice may improve outcomes in a heart transplant model. We generated a potentially novel B6129 mouse model with Treg-targeted Nox2 deletion (Nox2fl/flFoxP3Cre+ mice) and transplanted with hearts from CB6F1 donors. As compared with those of littermate controls, Nox2fl/flFoxP3Cre+ mice had lower plasma levels of alloantibodies and troponin-I, reduced levels of IFN-γ in heart allograft homogenates, and diminished cardiomyocyte necrosis and allograft fibrosis. Single-cell analyses of allografts revealed higher absolute numbers of Tregs and lower CD8+ T cell infiltration in Nox2-deficient recipients compared with Nox2-replete mice. Mechanistically, in addition to a greater suppression of CD8+CD25- T effector cell proliferation and IFN-γ production, Nox2-deficient Tregs expressed higher levels of CCR4 and CCR8, driving cell migration to allografts; this was associated with increased expression of miR-214-3p. These data indicate that Nox2 deletion in Tregs enhances their suppressive ability and migration to heart allografts. Therefore, Nox2 inhibition in Tregs may be a useful approach to improve their therapeutic efficacy.

Serum biomarkers of acute rejection: Towards precision medicine in heart transplant

Despite the important changes in the management of heart transplantation in the recent decades, the use of endomyocardial biopsy is still necessary for the follow-up of these patients. However, this technique has several limitations, the most important being the substantial interobserver variability. In the last years multiple attempts have been made to find non-invasive assays for cardiac allograft surveillance, such as imaging modalities and serum biomarkers. This state-of-the-art review focuses on describing the different serum biomarkers that have been proposed for non-invasive diagnosis of acute rejection and that are paving the way towards precision medicine in the field of heart transplantation.

Circulating growth differentiation factor-15 as a novel biomarker in heart transplant

Aims

This study aimed to examine (i) whether circulating growth differentiation factor‐15 (GDF‐15) is associated with acute cellular cardiac allograft rejection (ACR); (ii) a longitudinal trend of GDF‐15 after heart transplantation; and (iii) the prognostic value of GDF‐15 in predicting a composite outcome of severe primary graft dysfunction (PGD) and 30 day mortality post‐transplant.

Methods and results

Serum samples were collected before heart transplantation and at every endomyocardial biopsy (EMB) post‐heart transplantation in de novo transplant patients. A total of 60 post‐transplant serum samples were matched to the corresponding EMBs. Seven (12%) were considered International Society for Heart Lung Transplantation Grade 1R ACR, and one (2%) was identified as Grade 2R ACR. GDF‐15 levels in patients with ACR were not different from those in the non‐rejection group (6230 vs. 6125 pg/mL, P = 0.27). GDF‐15 concentration gradually decreased from 8757 pg/mL pre‐transplant to 5203 pg/mL at 4 weeks post‐transplant. The composite adverse outcome of PGD and 30 day mortality was significantly associated with increased post‐operative GDF‐15 (odds ratio: 40; 95% confidence interval: 2.01–794.27; P = 0.005) and high inotrope score post‐transplant (odds ratio: 18; 95% confidence interval: 1.22–250.35; P = 0.01).

Conclusions

Circulating GDF‐15 concentration was markedly elevated in patients with end‐stage heart failure and decreased after heart transplantation. GDF‐15 was significantly associated with post‐transplant PGD and mortality. A lack of association between ACR and GDF‐15 did not support routine use of GDF‐15 as a biomarker to detect ACR. However, GDF‐15 may be potentially useful to determine heart transplant recipients at high risk for adverse post‐transplant outcomes. We suggest that GDF‐15 levels in recipient serum can provide risk stratification for severe PGD including death during post‐operative period. This novel biomarker may serve to inform and guide timely interventions against severe PGD and adverse outcomes during the first 4 weeks after transplantation. Further studies to support the utility of GDF‐15 in heart transplantation are required.

Longitudinal profiling of circulating miRNA during cardiac allograft rejection: a proof-of-concept study

AIMS

Allograft rejection following heart transplantation (HTx) is a serious complication even in the era of modern immunosuppressive regimens and causes up to a third of early deaths after HTx. Allograft rejection is mediated by a cascade of immune mechanisms leading to acute cellular rejection (ACR) and/or antibody-mediated rejection (AMR). The gold standard for monitoring allograft rejection is invasive endomyocardial biopsy that exposes patients to complications. Little is known about the potential of circulating miRNAs as biomarkers to detect cardiac allograft rejection. We here present a systematic analysis of circulating miRNAs as biomarkers and predictors for allograft rejection after HTx using next-generation small RNA sequencing.

METHODS AND RESULTS

We used next-generation small RNA sequencing to investigate circulating miRNAs among HTx recipients (10 healthy controls, 10 heart failure patients, 13 ACR, and 10 AMR). MiRNA profiling was performed at different time points before, during, and after resolution of the rejection episode. We found three miRNAs with significantly increased serum levels in patients with biopsy-proven cardiac rejection when compared with patients without rejection: hsa-miR-139-5p, hsa-miR-151a-5p, and hsa-miR-186-5p. We identified miRNAs that may serve as potential predictors for the subsequent development of ACR: hsa-miR-29c-3p (ACR) and hsa-miR-486-5p (AMR). Overall, hsa-miR-486-5p was most strongly associated with acute rejection episodes.

CONCLUSIONS

Monitoring cardiac allograft rejection using circulating miRNAs might represent an alternative strategy to invasive endomyocardial biopsy.

Cell-free DNA in the surveillance of heart transplant rejection

BACKGROUND

Circulating cell-free deoxyribonucleic acid (cfDNA) is promptly materializing as a highly useful tool for the surveillance of solid-organ transplant rejection. Donor-specific fraction (DF) cfDNA is a potential marker of selective donor organ injury. It is emerging as a promising analytical target in the near future. The aim of this systematic review is to throw light on the importance of cfDNA and future perspective in detecting acute rejection in heart transplantation.

METHODS

An exhaustive search was carried out for this review article on the basis of literature available including scientific databases of PubMed, Embase, and ClinicalTrials.gov. The search engines were systematically explored using the search terms "cell free DNA," "Heart transplant," and "Rejection" from inception until August 2020, and narrative analysis was accomplished. Majority of the studies described endomyocardial biopsy-proven acute rejection as reference standard.

RESULTS

After initial screening of 331 articles, 11 studies were included and discussed in detail in the present review article. Majority of the studies showed prospective designs. A firm correlation was noted between acute rejection (identified on endomyocardial biopsy) and cfDNA levels by most of the studies.

CONCLUSIONS

cfDNA is a promising tool to replace repeated biopsies to detect rejection. The development in the area of digital droplet polymerase chain reaction and massive parallel sequencing, along with the overall reduction in cost of sequencing with its automation, has helped establish its role in the transplant population.

The State of the Heart Biopsy: A Clinical Review

Endomyocardial biopsy (EMB) is an invaluable and underused diagnostic tool for myocardial disease. The primary indications are surveillance of cardiac allograft rejection and the diagnosis of inflammatory and infiltrative cardiomyopathies. EMB is typically performed by sampling the right ventricular septum via the right internal jugular vein using fluoroscopic guidance. The diagnostic yield of EMB is improved by sampling both ventricles and with the use of guidance from imaging or electroanatomic mapping. The risk of major cardiac complications is operator dependent and < 1% in experienced centres. EMB is the gold standard and most common form of cardiac allograft rejection surveillance, whereas advanced cardiac imaging and donor-specific antibody quantification provide complementary information. Gene expression profiling is an alternative surveillance strategy to EMB for low-risk patients. EMB is recommended for myocarditis and can guide therapy for giant-cell myocarditis, necrotizing eosinophilic myocarditis, sarcoidosis, and immune checkpoint inhibitor myocarditis. There is growing interest in using EMB to guide therapy for viral myocarditis, although the uptake of this approach is limited to specialized centres. EMB has been replaced as a first-line test for infiltrative cardiomyopathy by nonbiopsy diagnostic techniques, but is still useful to clarify the diagnosis or disease subtype. The miniaturization of bioptomes and advances in laboratory techniques such as microarrays promises to improve the safety and yield of EMB. We review the contemporary use of EMB for cardiac allograft rejection, inflammatory cardiomyopathy, and infiltrative cardiomyopathy.

A Changing Paradigm in Heart Transplantation: An Integrative Approach for Invasive and Non-Invasive Allograft Rejection Monitoring

Cardiac allograft rejection following heart transplantation is challenging to diagnose. Tissue biopsies are the gold standard in monitoring the different types of rejection. The last decade has seen an increased emphasis on identifying non-invasive methods to improve rejection diagnosis and overcome tissue biopsy invasiveness. Liquid biopsy, as an efficient non-invasive diagnostic and prognostic oncological monitoring tool, seems to be applicable in heart transplant follow-ups. Moreover, molecular techniques applied on blood can be translated to tissue samples to provide novel perspectives on tissue and reveal new diagnostic and prognostic biomarkers. This review aims to provide a comprehensive overview of the state-of-the-art of the new methodologies in cardiac allograft rejection monitoring and investigate the future perspectives on invasive and non-invasive rejection biomarkers identification. We reviewed literature from the most used scientific databases, such as PubMed, Google Scholar, and Scopus. We extracted 192 papers and, after a selection and exclusion process, we included in the review 81 papers. The described limitations notwithstanding, this review show how molecular biology techniques and omics science could be deployed complementarily to the histopathological rejection diagnosis on tissue biopsies, thus representing an integrated approach for heart transplant patients monitoring.

C-Reactive protein level and left ventricular mass are associated with acute cellular rejection after heart transplant

OBJECTIVES

Acute cellular rejection (ACR) remains a major complication of heart transplant (HT). The gold standard for its diagnosis is endomyocardial biopsy (EMB), whereas the role of non-invasive biomarkers for detecting ACR is unclear. This study aimed to identify non-invasive biomarkers for the diagnosis of ACR in patients undergoing HT and presenting with normal left ventricular function.

METHODS

We evaluated patients who underwent HT at a single center between January 2010 and June 2019. Patients were enrolled after HT, and those with left ventricular (LV) systolic dysfunction before EMB were excluded. We included only the results of the first EMB performed at least 30 days after HT (median, 90 days). Troponin, B-type natriuretic peptide (BNP), and C-reactive protein (CRP) levels were measured and echocardiography was performed up to 7 days before EMB. ACR was defined as International Society for Heart and Lung Transplantation grade 2R or 3R on EMB. We performed logistic regression analysis to identify the non-invasive predictors of ACR (2R or 3R) and evaluated the accuracy of each using area under the receiver operator characteristic curve analysis.

RESULTS

We analyzed 72 patients after HT (51.31±13.63 years; 25 [34.7%] women); of them, 9 (12.5%) developed ACR. Based on multivariate logistic regression analysis, we performed forward stepwise selection (entry criteria, p<0.05). The only independent predictors that remained in the model were CRP level and LV mass index. The optimal cut-off point for CRP level was ≥15.9 mg/L (odds ratio [OR], 11.7; p=0.007) and that for LV mass index was ≥111 g/m2 (OR, 13.6; p=0.003). The area under the receiver operating characteristic curve derived from this model was 0.87 (95% confidence interval [CI], 0.75-0.99), with sensitivity of 85.7% (95% CI, 42.1%-99.6%), specificity of 78.4% (95% CI, 64.7%-88.7%), positive predictive value of 35.3% (95% CI, 14.3%-61.7%), and negative predictive value of 97.6% (95% CI, 87.1%-99.9%).

CONCLUSIONS

Among patients undergoing HT, CRP level and LV mass were directly associated with ACR, but troponin and BNP levels were not.

Canadian Cardiovascular Society/Canadian Cardiac Transplant Network Position Statement on Heart Transplantation: Patient Eligibility, Selection, and Post-Transplantation Care

Significant practice-changing developments have occurred in the care of heart transplantation candidates and recipients over the past decade. This Canadian Cardiovascular Society/Canadian Cardiac Transplant Network Position Statement provides evidence-based, expert panel recommendations with values and preferences, and practical tips on: (1) patient selection criteria; (2) selected patient populations; and (3) post transplantation surveillance. The recommendations were developed through systematic review of the literature and using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system. The evolving areas of importance addressed include transplant recipient age, frailty assessment, pulmonary hypertension evaluation, cannabis use, combined heart and other solid organ transplantation, adult congenital heart disease, cardiac amyloidosis, high sensitization, and post-transplantation management of antibodies to human leukocyte antigen, rejection, cardiac allograft vasculopathy, and long-term noncardiac care. Attention is also given to Canadian-specific management strategies including the prioritization of highly sensitized transplant candidates (status 4S) and heart organ allocation algorithms. The focus topics in this position statement highlight the increased complexity of patients who undergo evaluation for heart transplantation as well as improved patient selection, and advances in post-transplantation management and surveillance that have led to better long-term outcomes for heart transplant recipients.

Biomarkers in Advanced Heart Failure: Implications for Managing Patients With Mechanical Circulatory Support and Cardiac Transplantation

Biomarkers have a well-defined role in the diagnosis and management of chronic heart failure, but their role in patients with left ventricular assist devices and cardiac transplant is uncertain. In this review, we summarize the available literature in this patient population, with a focus on clinical application. Some ubiquitous biomarkers, for example, natriuretic peptides and cardiac troponin, may assist in the diagnosis of left ventricular assist device complications and transplant rejection. Novel biomarkers focused on specific pathological processes, such as left ventricular assist device thrombosis and profiling of leukocyte activation, continue to be developed and show promise in altering the management of the advanced heart failure patient. Few biomarkers at this time have been assessed with sufficient scrutiny to warrant broad, universal application, but encouraging limited data and large potential for impact should prompt ongoing investigation.

Circulating miR-181a-5p as a new biomarker for acute cellular rejection in heart transplantation

BACKGROUND

Acute cellular rejection (ACR) is a major complication in heart transplantation (HTx). Endomyocardial biopsy is the reference method for early detection of ACR, but a new non-invasive approach is needed. Tentative candidates could be circulating microRNAs. This study aimed to discover and validate microRNAs in serum for ACR detection after HTx.

METHODS

This prospective, observational, single-center study included 121 HTx patients. ACR was graded according to International Society of Heart and Lung Transplantation classification (0R-3R). First, in the discovery phase, microRNA expression profile was carried out in serum samples from patients at pre-rejection, during, and post-rejection time (0R_S1 → 2R_S2` → 0R_S3). Relative expression (2^-∆Cq) of 179 microRNAs per sample was analyzed by reverse transcription quantitative polymerase chain reaction. Second, a microRNA with a significant rise and fall pattern during ACR was selected for the next validation phase, where it was analyzed (reverse transcription quantitative polymerase chain reaction) in serum samples from 2 groups of patients: the no-ACR group (0R grade) and the ACR group (≥2R grade). Finally, a sensitivity analysis (receiver operating characteristic curve) was done to assess microRNA accuracy for ACR detection in HTx.

RESULTS

A total of 21 ACR episodes (0R_S1 → 2R_S2 → 0R_S3) with their respective serum samples (n = 63) were included in the discovery phase. Among the 179 microRNAs analyzed, only miR-181a-5p met the rise and fall criteria. In the validation phase, miR-181a-5p relative expression (2^-∆Cq) in the ACR group (n = 45) was significantly overexpressed (p < 0.0001) vs the no-ACR group (n = 45). miR-181a-5p showed an area under the curve of 0.804 (95% confidence interval: 0.707-0.880); sensitivity and specificity of 78% and 76%, respectively; and a negative predicted value of 98%.

CONCLUSIONS

miR-185a-5p in serum is a candidate as a non-invasive ACR biomarker (area under the curve = 0.80 and negative predicted value = 98%). Thus, this biomarker could reduce the need for endomyocardial biopsies and the associated risks and costs of this invasive procedure.

Cell-free DNA donor fraction analysis in pediatric and adult heart transplant patients by multiplexed allele-specific quantitative PCR: Validation of a rapid and highly sensitive clinical test for stratification of rejection probability

Lifelong noninvasive rejection monitoring in heart transplant patients is a critical clinical need historically poorly met in adults and unavailable for children and infants. Cell-free DNA (cfDNA) donor-specific fraction (DF), a direct marker of selective donor organ injury, is a promising analytical target. Methodological differences in sample processing and DF determination profoundly affect quality and sensitivity of cfDNA analyses, requiring specialized optimization for low cfDNA levels typical of transplant patients. Using next-generation sequencing, we previously correlated elevated DF with acute cellular and antibody-mediated rejection (ACR and AMR) in pediatric and adult heart transplant patients. However, next-generation sequencing is limited by cost, TAT, and sensitivity, leading us to clinically validate a rapid, highly sensitive, quantitative genotyping test, myTAI_HEART^®, addressing these limitations. To assure pre-analytical quality and consider interrelated cfDNA measures, plasma preparation was optimized and total cfDNA (TCF) concentration, DNA fragmentation, and DF quantification were validated in parallel for integration into myTAI_HEART reporting. Analytical validations employed individual and reconstructed mixtures of human blood-derived genomic DNA (gDNA), cfDNA, and gDNA sheared to apoptotic length. Precision, linearity, and limits of blank/detection/quantification were established for TCF concentration, DNA fragmentation ratio, and DF determinations. For DF, multiplexed high-fidelity amplification followed by quantitative genotyping of 94 SNP targets was applied to 1168 samples to evaluate donor options in staged simulations, demonstrating DF call equivalency with/without donor genotype. Clinical validation studies using 158 matched endomyocardial biopsy-plasma pairs from 76 pediatric and adult heart transplant recipients selected a DF cutoff (0.32%) producing 100% NPV for ≥2R ACR. This supports the assay’s conservative intended use of stratifying low versus increased probability of ≥2R ACR. myTAI_HEART is clinically validated for heart transplant recipients ≥2 months old and ≥8 days post-transplant, expanding opportunity for noninvasive transplant rejection assessment to infants and children and to all recipients >1 week post-transplant.

High-Sensitivity Troponin T and Soluble Form of AXL as Long-Term Prognostic Biomarkers after Heart Transplantation

Antecedents

Cardiac allograft vasculopathy (CAV) is a frequent complication limiting the long-term (>1 year) survival after heart transplantation (HTx). CAV is initiated by endothelial dysfunction and can lead to severe cardiovascular (CV) complications. Since CAV is often clinically silent, biomarkers could help identifying HTx patients at risk of CAV and their severe complications.

Aim

Evaluate the clinical yield of high-sensitivity cardiac troponin T (hs-cTnT), marker of cardiomyocyte damage, and the soluble form of AXL (sAXL), biomarker of endothelial dysfunction, to assess the prognosis of long-term cardiovascular (CV) events occurring after HTx.

Methods

96 patients were evaluated at least > 1 year after HTx. CAV was evaluated by coronary angiography or multisliced tomography, and hs-cTnT and sAXL measured 6 months before or after CAV evaluation. Patients were followed during 42 ± 15 months for a combined end point including cardiac death, angina or acute myocardial infarction, left ventricular ejection fraction < 50%, or heart failure not due to an acute rejection.

Results

51 patients (53%) presented CAV at evaluation; 21 of them had CV events. Hs-cTnT (56 ± 45 versus 20 ± 18 ng/L; p = 0.04) and sAXL concentrations (98 ± 51 versus 26 ± 26 ng/L; p = 0.01) were significantly higher in patients with CV events. Hs-cTnT (HR 1.03; 95% CI 1.015–1.042, p = 0.0001) and sAXL (HR 1.01; 95% CI 1.001–1.019, p = 0.02) were independent predictors of CV events. A hs-cTnT concentration < 21 ng/L, detected by AUC ROC, predicted the absence of CV events with a predictive value of 91%; sAXL did not add more predictive value to hs-cTnT. Survival free of CV events was 92% in patients with hs-cTnT < 21 ng/L and 57% in those with hs-cTnT > 21 ng/L (p < 0.001).

Conclusion

Hs-cTnT, but not sAXL, measured during the long-term follow-up of HTx patients appears as a helpful biomarker to identify patients at low risk of adverse CV outcomes.

Biomarkers to Assess Right Heart Pressures in Recipients of a Heart Transplant: A Proof-of-Concept Study

Background

This proof-of-concept study investigated the feasibility of using biomarkers to monitor right heart pressures (RHP) in heart transplanted (HTx) patients.

Methods

In 298 patients, we measured 7.6 years post-HTx mean pressures in the right atrium (mRAP) and pulmonary artery (mPAP) and capillaries (mPCWP) along with plasma high-sensitivity troponin T (hsTnT), a marker of cardiomyocyte injury, and the multidimensional urinary classifiers HF1 and HF2, mainly consisting of dysregulated collagen fragments.

Results

In multivariable models, mRAP and mPAP increased with hsTnT (per 1-SD, +0.91 and +1.26 mm Hg; P < 0.0001) and with HF2 (+0.42 and +0.62 mm Hg; P ≤ 0.035), but not with HF1. mPCWP increased with hsTnT (+1.16 mm Hg; P < 0.0001), but not with HF1 or HF2. The adjusted odds ratios for having elevated RHP (mRAP, mPAP or mPCWP ≥10, ≥24, ≥17 mm Hg, respectively) were 1.99 for hsTnT and 1.56 for HF2 (P ≤ 0.005). In detecting elevated RHPs, areas under the curve were similar for hsTnT and HF2 (0.63 vs 0.65; P = 0.66). Adding hsTnT continuous or per threshold or HF2 continuous to a basic model including all covariables did not increase diagnostic accuracy (P ≥ 0.11), whereas adding HF2 per optimized threshold increased both the integrated discrimination (+1.92%; P = 0.023) and net reclassification (+30.3%; P = 0.010) improvement.

Conclusions

Correlating RHPs with noninvasive biomarkers in HTx patients is feasible. However, further refinement and validation of such biomarkers is required before their clinical application can be considered.

Sensitivity to perioperative ischemia/reperfusion injury in male and female donor myocardium

Many functions of the cardiovascular apparatus are affected by gender. The aim of our study was find out whether markers of cell death present in the donor myocardium differ in male and female hearts. The study involved 81 patients undergoing heart transplantation from September 2010 to January 2013. Patients were divided into two groups: male allograft (n=49), and female allograft (n=32). Two types of myocardial cell death were analyzed. High-sensitive cardiac troponin T as a necrosis marker and protein bcl-2, caspase 3 and TUNEL as apoptosis markers were measured. We observed a significantly higher level of high-sensitive cardiac troponin T after correcting for predicted ventricular mass in female donors before transplantation as well as in the female allograft group after transplantation throughout the monitored period (P=0.011). There were no differences in apoptosis markers (bcl-2, caspase 3, TUNEL) between male and female hearts before transplantation. Both genders showed a significant increase of TUNEL-positive myocytes one week after transplantation without differences between the groups. Moreover, there were no differences in caspase 3 and bcl-2 expression between the two groups. Our results demonstrated the presence of necrotic and apoptotic cell death in human heart allografts. High-sensitive cardiac troponin T adjusted for predicted ventricular mass as a marker of myocardial necrosis was higher in female donors, and this gender difference was even more pronounced after transplantation.

Utility of troponin assays for exclusion of acute cellular rejection after heart transplantation: A systematic review

BACKGROUND

Acute cellular rejection (ACR) is a common complication in the first year after heart transplantation (HT). Routine surveillance for ACR is undertaken by endomyocardial biopsy (EMB). Measurement of cardiac troponins (cTn) in serum is an established diagnostic test of cardiac myocyte injury. This systematic review aimed to determine whether cTn measurement could be used to diagnose or exclude ACR.

METHODS

PubMed, Google Scholar and the JHLT archive were searched for studies reporting the result of a cTn assay and a paired surveillance EMB. Significant ACR was defined as International Society for Heart and Lung Transplantataion (ISHLT) Grade ≥3a/≥2R. Considerable heterogeneity between studies precluded quantitative meta-analysis. Individual study sensitivity and specificity data were examined and used to construct a pooled hierarchical summary receiver-operator characteristic (ROC) curve.

RESULTS

Twelve studies including 993 patients and 3,803 EMBs, of which 3,729 were paired with cTn levels, had adequate data available for inclusion. The overall rate of significant ACR was 12%. There was wide variation in diagnostic performance. cTn assays demonstrated sensitivity of 8% to 100% and specificity of 13% to 88% for detection of ACR. The positive predictive value (PPV) was low but the negative predictive value (NPV) was relatively high (79% to 100%). High-sensitivity cTn assays had greater sensitivity and NPV than conventional cTn assays for detection of ACR (sensitivity: 82% to 100% vs 8% to 77%; NPV: 97% to 100% vs 81% to 95%, respectively).

CONCLUSIONS

cTn assays do not have sufficient specificity to diagnose ACR in place of EMB. However, hs-cTn assays may have sufficient sensitivity and negative predictive value to exclude ACR and limit the need for surveillance EMB. Further research is required to assess this strategy.

Molecular Diagnostic Testing in Cardiac Transplantation

PURPOSE OF REVIEW

Acute rejection is one of the most feared complications of cardiac transplantation. Developing non-invasive methods for detection and surveillance of acute rejection have long been a goal for post-transplant care.

RECENT FINDINGS

Here, we will review molecular diagnostic tests that are currently in use or under development to diagnose acute cellular rejection after cardiac transplantation. Gene expression, microRNA, molecular microscope, and cell-free DNA assays offer non-invasive alternatives to the endomyocardial biopsy for acute rejection surveillance.

Role of miR-29 as marker of risk of acute rejection after heart transplant

BACKGROUND

Circulating miRNAs are potential biomarkers of the pathogenesis of certain diseases and in monitoring therapeutic responses. We hypothesized that serum miR-29 can determine risk of acute cardiac allograft rejection.

METHODS

Peripheral vein blood was collected from 50 healthy volunteers and 506 patients during post-transplant surveillance. Serum cardiac troponin I (cTnI) and miR-29 was detected by ELISA and qRT-PCR assay respectively. Rejection risk was defined as International Society of Heart and Lung Transplant score from leukocyte infiltration of an endomyocardial biopsy. No evidence of rejection was defined as grade R0, mild as R1, moderate as 2R and severe as 3R. Specificity and sensitivity of miR-29 to discriminate rejection was determined by the area under the curve (AUC) of receiver operating characteristic curve analysis. Correlations between miR29 and rejection grade were compared.

RESULTS

Serum miR-29 was 100.8 ± 42.4 copies/μl in R0 groups (P = 0.164 versus controls), 537.5 ± 84.3 copies/μl in R1 groups (P = 0.024) and 1478.4 ± 198.7 copies/μl in the joint R2/R3 groups (P = 0.001). MiR-29 was 1963.5 ± 214.7 six months after transplantation, 1242.5 ± 103.8 after a year, 825.6 ± 58.2 after 2 years, 413.8 ± 61.9 after 3 years and 270.6 ± 34.6 ng/mL after 4 years (P < 0.001). The level of miR-29 correlated positively with cTnI, NT-proBNP, white blood cell counts, and negatively with lymphocyte counts (all P < 0.001). The AUC values (95% CI) for discriminating R0 and R1 was 0.81 (0.75-0.89), and was 0.79 (0.72-0.86) for R0 and R2/R3 (both P < 0.01).

CONCLUSION

miR-29 is a promising predictor of the risk of heart transplant rejection.

Role of Soluble ST2 as a Marker for Rejection after Heart Transplant

Background and Objectives

Endomyocardial biopsy is obligatory during the first year after heart transplant (HTx) for the surveillance of acute rejection. Previous attempts using cardiac biomarkers for the detection of rejection failed to show enough evidence to substitute endomyocardial biopsy. Therefore, this study sought the possibility of using soluble ST2 (sST2), a novel cardiovascular marker, as a surrogate marker for acute allograft rejection after HTx.

Subjects and Methods

A total of 494 blood samples acquired at the time of endomyocardial biopsy were analyzed in 67 HTx cases from September 2006 to August 2014. Significant rejection was defined as International Society of Heart and Lung Transplant (ISHLT) score ≥2R and humoral rejection accompanied by hemodynamic instability.

Results

Twenty cases of HTx with 22 blood samples showed significant rejection in endomyocardial biopsy at 4.0 (2.0-9.0) months after HTx. The level of sST2 showed positive correlation with cardiac troponin I, and N-terminal pro-B-type natriuretic peptide (all p<0.001), and negative correlation with post-HTx months (p<0.001). The levels of sST2 according to the ISHLT scores were 36 (19-98), 28 (18-62), 15 (16-37), and 191 (85-343) ng/mL, consecutively 0R, 1R, 2R, and 3R+ (3R plus hemodynamically-unstable humoral rejection) (p=0.003). However, when we studied within-subject effects of sST2 using a mixed model, the sST2 level according to the predefined time point was not different according to the presence of significant rejection (p for interaction=0.94).

Conclusion

Although sST2 is known as a promising predictor for cardiovascular events, its role in HTx patients to predict acute allograft rejection seems to be limited.

Advances in diagnostics for transplant rejection

INTRODUCTION

Identification of allograft injury, including acute clinical and subclinical injury, is vital in increasing the longevity of the transplanted organ. Acute rejection, which occurs as a result of a variety of immune and non-immune factors including the infiltration of immune cells and antibodies to the donor specific epitopes, poses a significant risk to the organ. Recent years have marked an increase in the discovery of new genomic, transcriptomic, and proteomic biomarkers in molecular diagnostics, which offer better potential for personalized management of the transplanted organ by providing earlier detection of rejection episodes. Areas covered: This review was compiled from key word searches of full-text publications relevant to the field. Expert commentary: Many of the recent advancements in the molecular diagnostics of allograft injury show much promise, but before they can be fully realized further validation in larger sample sets must be conducted. Additionally, for better informed therapeutic decisions, more work must be completed to differentiate between different causes of injury. Moreover, the diagnostics field is looking at methodologies that allow for multiplexing, the ability to identify multiple targets simultaneously, in order to provide more robust biomarkers and better understanding.

Novel Biomarker Approaches for Managing Patients With Cardiac Transplantation

Despite major advances in the medical care of patients following heart transplantation (HTx) and a steady increase in long-term survival, allograft surveillance is still based on endomyocardial biopsy, the gold standard since the 1970s. This invasive procedure calls for less burdening and more cost-effective approaches. In recent years, impressive progress has been made in utilizing blood-based biomarkers for the diagnosis and management of diseases in a variety of fields. Hence, a number of trials have been performed testing the usefulness of circulating molecules or other technical methods to overcome the need for surveillance myocardial biopsy in HTx patients. Here, we review current approaches and the state of research on novel biomarkers for the management of patients following heart transplantation.

Effect of treatment with rosiglitazone on high-sensitivity cardiac troponin levels among patients with type 2 diabetes mellitus

OBJECTIVE

To assess the impact of intermediate-term treatment with rosiglitazone on high-sensitivity cardiac troponin T levels among patients with type 2 diabetes mellitus with or at high risk of coronary artery disease.

METHODS

High-sensitivity cardiac troponin T level was measured at baseline and after 6 months of study treatment in a randomized trial comparing rosiglitazone versus placebo in patients with type 2 diabetes and prevalent cardiovascular disease or multiple cardiovascular disease risk factors. Univariable and multivariable linear regression analyses were performed to assess the effect of rosiglitazone versus placebo on high-sensitivity cardiac troponin T levels.

RESULTS

The study included 150 randomized participants, of whom 106 had paired baseline and end-of-study blood samples for analysis (mean age: 56 ± 8 years, 42% women; 8.8 years average type 2 diabetes duration; mean haemoglobin A1c of 7.5). Almost all study participants (93%) had detectable high-sensitivity cardiac troponin T (⩾ 3 ng/L) at baseline, including 23% with high-sensitivity cardiac troponin T levels exceeding the threshold commonly used to diagnose myocardial infarction (⩾ 14 ng/L). Change in high-sensitivity cardiac troponin T levels from baseline to follow-up was not significantly different between rosiglitazone and placebo groups (p = 0.316).

CONCLUSION

Rosiglitazone did not impact high-sensitivity cardiac troponin T levels, adding to the growing body of literature suggesting that the incremental heart failure risk associated with rosiglitazone is not mediated by direct myocardial injury.

Fully automated ultrasensitive digital immunoassay for cardiac troponin I based on single molecule array technology

BACKGROUND

The association between increases in cardiac troponin and adverse cardiac outcomes is well established. There is a growing interest in exploring routine cardiac troponin monitoring as a potential early indicator of adverse heart health trends. Prognostic use of cardiac troponin measurements requires an assay with very high sensitivity and outstanding analytical performance. We report development and preliminary validation of an investigational assay meeting these requirements and demonstrate its applicability to cohorts of healthy individuals and patients with heart failure.

METHODS

On the basis of single molecule array technology, we developed a 45-min immunoassay for cardiac troponin I (cTnI) for use on a novel, fully automated digital analyzer. We characterized its analytical performance and measured cTnI in healthy individuals and heart failure patients in a preliminary study of assay analytical efficacy.

RESULTS

The assay exhibited a limit of detection of 0.01 ng/L, a limit of quantification of 0.08 ng/L, and a total CV of 10% at 2.0 ng/L. cTnI concentrations were well above the assay limit of detection for all samples tested, including samples from healthy individuals. cTnI was significantly higher in heart failure patients, and exhibited increasing median and interquartile concentrations with increasing New York Heart Association classification of heart failure severity.

CONCLUSIONS

The robust 2-log increase in sensitivity relative to contemporary high-sensitivity cardiac troponin immunoassays, combined with full automation, make this assay suitable for exploring cTnI concentrations in cohorts of healthy individuals and for the potential prognostic application of serial cardiac troponin measurements in both apparently healthy and diseased individuals.

Emerging science in paediatric heart transplantation: donor allocation, biomarkers, and the quest for evidence-based medicine

Heart transplantation offers excellent survival benefit to children with end-stage heart failure. With its success, the number of potential recipients continues to exceed the number of available donors. Developing strategies to safely increase donor utilisation is crucial to decreasing wait-list mortality. A new paediatric heart allocation policy is set to be implemented with the goal of prioritising the most urgent listed candidates. Owing to excellent outcomes of ABO-incompatible heart transplantation, the sickest infants will soon receive priority for heart offers irrespective of blood group. Allosensitisation poses unique challenges within the paediatric population; ongoing multi-centre studies are poised to refine our understanding of key risk factors and optimal treatment strategies. Biomarkers for acute cellular rejection, such as donor-specific cell-free DNA, and cardiac allograft vasculopathy, such as VEGF-A, may lead to a decreased need for invasive screening. Ultimately, well-designed and executed randomised control trials of post-transplant immunosuppression are required to improve long-term outcomes after paediatric heart transplantation.

Perioperative myocardial injury after adult heart transplant: determinants and prognostic value

Background and Aim of the Study

Implications of Cardiac troponin (cTnI) release after cardiac transplantation are still unclear. This study disclosed risk factors and prognostic implication of cTnI early levels in a single centre cohort operated on between January 1999 and December 2010.

Methods

Data on 362 consecutive recipients (mean age: 47.8±13.7, 20.2% female, 18.2% diabetics, 22.1% with previous cardiac operations, 27.6% hospitalized, 84.9±29.4 ml/min preoperative glomerular filtration rate) were analyzed using multivariable logistic regression modeling. Target outcomes were determinants of troponin release, early graft failure (EGF), acute kidney injury (AKI) and operative death.

Results

Mean cTnI release measured 24 hours after transplant was 10.9±11.6 μg/L. Overall hospital mortality was 10.8%, EGF 10.5%, and AKI was 12.2%. cTnI release>10 μg/L proved an independent predictor of EGF (OR 2.2; 95% CI, 1.06–4.6) and AKI (OR 1.031; 95% CI, 1.001-1.064). EGF, in turn, proved a determinant of hospital mortality. Risk factors for cTnI>10 μg/L release were: status 2B (OR 0.35; 95% CI, 0.18-0.69, protective), duration of the ischemic period (OR 1.006; 95% CI, 1.001-1.011), previous cardiac operation (OR 2.9; 95% CI, 1.67-5.0), and left ventricular hypertrophy (OR 3.3; 95% CI, 1.9-5.6).

Conclusions

Myocardial enzyme leakage clearly emerged as an epiphenomenon of more complicated clinical course. The complex interplay between surgical procedure features, graft characteristics and recipient end-organ function highlights cTnI release as a risk marker of graft failure and acute kidney injury. The search for optimal myocardial preservation is still an issue.