Utility of biochemical markers in the follow-up of heart transplant recipients

European Society for Organ Transplantation (ESOT) Consensus Statement on the Use of Non-invasive Biomarkers for Cardiothoracic Transplant Rejection Surveillance

While allograft rejection (AR) continues to threaten the success of cardiothoracic transplantation, lack of accurate and repeatable surveillance tools to diagnose AR is a major unmet need in the clinical management of cardiothoracic transplant recipients. Endomyocardial biopsy (EMB) and transbronchial biopsy (TBBx) have been the cornerstone of rejection monitoring since the field's incipience, but both suffer from significant limitations, including poor concordance of biopsy interpretation among pathologists. In recent years, novel molecular tools for AR monitoring have emerged and their performance characteristics have been evaluated in multiple studies. An international working group convened by ESOT has reviewed the existing literature and provides a series of recommendations to guide the use of these biomarkers in clinical practice. While acknowledging some caveats, the group recognized that Gene-expression profiling and donor-derived cell-free DNA (dd-cfDNA) may be used to rule out rejection in heart transplant recipients, but they are not recommended for cardiac allograft vasculopathy screening. Other traditional biomarkers (NT-proBNP, BNP or troponin) do not have sufficient evidence to support their use to diagnose AR. Regarding lung transplant, dd-cfDNA could be used to rule out clinical rejection and infection, but its use to monitor treatment response is not recommended.

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

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.

Study of young patients with myocardial infarction: Design and rationale of the YOUNG-MI Registry

The YOUNG-MI registry is a retrospective study examining a cohort of young adults age ≤ 50 years with a first-time myocardial infarction. The study will use the robust electronic health records of 2 large academic medical centers, as well as detailed chart review of all patients, to generate high-quality longitudinal data regarding the clinical characteristics, management, and outcomes of patients who experience a myocardial infarction at a young age. Our findings will provide important insights regarding prevention, risk stratification, treatment, and outcomes of cardiovascular disease in this understudied population, as well as identify disparities which, if addressed, can lead to further improvement in patient outcomes.

Thoracic organ transplantation: laboratory methods

Although great progress has been achieved in thoracic organ transplantation through the development of effective immunosuppression, there is still significant risk of rejection during the early post-transplant period, creating a need for routine monitoring for both acute antibody and cellular mediated rejection. The currently available multiplexed, microbead assays utilizing solubilized HLA antigens afford the capability of sensitive detection and identification of HLA and non-HLA specific antibodies. These assays are being used to assess the relative strength of donor specific antibodies; to permit performance of virtual crossmatches which can reduce the waiting time to transplantation; to monitor antibody levels during desensitization; and for heart transplants to monitor antibodies post-transplant. For cell mediated immune responses, the recent development of gene expression profiling has allowed noninvasive monitoring of heart transplant recipients yielding predictive values for acute cellular rejection. T cell immune monitoring in heart and lung transplant recipients has allowed individual tailoring of immunosuppression, particularly to minimize risk of infection. While the current antibody and cellular laboratory techniques have enhanced the ability to manage thoracic organ transplant recipients, future developments from improved understanding of microchimerism and graft tolerance may allow more refined allograft monitoring techniques.

Use of a highly sensitive assay for cardiac troponin T and N-terminal pro-brain natriuretic peptide to diagnose acute rejection in pediatric cardiac transplant recipients

BACKGROUND

Biomarkers have been proposed to augment or replace endomyocardial biopsy (EMB) to diagnose acute transplant rejection (AR). A new, highly sensitive assay for troponin T detects levels of cardiac troponin T (cTnT) 10- to 100-fold lower than standard assays but has not been investigated in transplant patients. N-terminal pro-brain natriuretic peptide (NT-proBNP) has not been evaluated in pediatric transplant patients. The purpose of this pilot study was to evaluate the association of cTnT and NT-proBNP with AR in pediatric cardiac transplant patients.

METHODS

Plasma was obtained at the time of EMB from pediatric patients ≥ 1 year old. N-terminal pro-brain natriuretic peptide was measured in fresh plasma at the time of biopsy, and cTnT was measured from frozen, stored samples using the highly sensitive assay for troponin T. Biomarker data were correlated with EMB results. Cellular AR was defined as an International Society for Heart and Lung Transplantation biopsy score of grade ≥ 2R.

RESULTS

Fifty-three blood samples were obtained from 42 patients (mean age 11 years). Seven episodes of AR occurred in 5 patients. Biopsies with vs without AR were associated with higher cTnT (median [interquartile range {IQR}] 66 [45-139] vs 7 [2-13] pg/mL, P = .001) and NT-proBNP (median [IQR] 11,169 [280-23,317] vs 334 [160-650] pg/mL, P < .01). After successful treatment of AR in 5 patients, cTnT fell markedly (median [IQR] 53.5 [44.8-66.5] to 10.7 [1.5-16.4], P = .05).

CONCLUSION

In this pilot study, we found marked elevation of cTnT and NT-proBNP among children with AR. Moreover, reduction in cTnT levels after treatment paralleled improvement in EMB results. If these findings are confirmed in larger prospective studies, monitoring with these biomarkers may obviate surveillance EMB.

[Usefulness of high sensitivity troponin T assay in detecting acute allograft rejection after heart transplantation]

INTRODUCTION AND OBJECTIVES

Detection of acute allograft rejection in heart transplant recipients by noninvasive methods is a challenge in the management of these patients. In this study, the usefulness of a new highly sensitive method for the measurement of troponin T is evaluated.

METHODS

We designed a case-crossover study, in which each patient served as his or her own control, by selecting samples from treated acute rejection episodes (29 cases) and samples obtained immediately before and/or after rejection (38 controls). The highly sensitive troponin T was measured by a new pre-commercial test (Elecsys Troponin T HS).

RESULTS

In all samples, highly sensitive troponin T was detectable, with a median of 0.068 ng/L (IQR, 0.030-0.300 ng/L). The levels correlated with right atrial pressure (r=0.37; P=.002), N-terminal pro-brain natriuretic peptide concentration (r=0.67; P<.001), and time since transplantation (r=-0.81; P<.001). The highly sensitive troponin T concentrations were higher in patients with rejection (0.155 ng/mL vs 0.047 ng/mL; P=.006). In the receiver operating characteristic analysis, the area under the curve was 0.67 (95% confidence interval, 0.53-0.77) and the best cutoff was 0.035 ng/mL, which was associated with rejection (odds ratio=3.7; 95% confidence interval, 1.2-11.9; P=.02). By restricting the analysis to the first 2 months, the area under the curve increased to 0.86 (95% confidence interval 0.66-0.97), with an optimal cutoff of 1.10 ng/mL (S=58% [28%-85%]; E=100% [74%-100%]).

CONCLUSIONS

Troponin T was detectable in all samples when a new highly sensitive assay was used, and at higher concentrations in the presence of acute rejection; however, the usefulness of this test in patient management is limited to support for clinical or histological suspicion of rejection, especially in the early post-transplant period.

Increases of cardiac troponin in conditions other than acute coronary syndrome and heart failure

BACKGROUND

Although cardiac troponin (cTn) is a cornerstone marker in the assessment and management of patients with acute coronary syndrome (ACS) and heart failure (HF), cTn is not diagnostically specific for any single myocardial disease process. This narrative review discusses increases in cTn that result from acute and chronic diseases, iatrogenic causes, and myocardial injury other than ACS and HF.

CONTENT

Increased cTn concentrations have been reported in cardiac, vascular, and respiratory disease and in association with infectious processes. In cases involving acute aortic dissection, cerebrovascular accident, treatment in an intensive care unit, and upper gastrointestinal bleeding, increased cTn predicts a longer time to diagnosis and treatment, increased length of hospital stay, and increased mortality. cTn increases are diagnostically and prognostically useful in patients with cardiac inflammatory diseases and in patients with respiratory disease; in respiratory disease cTn can help identify patients who would benefit from aggressive management. In chronic renal failure patients the diagnostic sensitivity of cTn for ACS is decreased, but cTn is prognostic for the development of cardiovascular disease. cTn also provides useful information when increases are attributable to various iatrogenic causes and blunt chest trauma.

SUMMARY

Information on the diagnostic and prognostic uses of cTn in conditions other than ACS and heart failure is accumulating. Although increased cTn in settings other than ACS or heart failure is frequently considered a clinical confounder, the astute physician must be able to interpret cTn as a dynamic marker of myocardial damage, using clinical acumen to determine the source and significance of any reported cTn increase.

Increased serum creatine kinase is a reliable marker for acute transplanted heart rejection diagnosis in rats

Different molecules have been studied as biochemical markers in heart transplantation. However, their utility is under discussion as results in human and animal models are controversial. In this work, lactate dehydrogenase (LDH), creatine kinase (CK) and cardiac troponin I (TnI) were studied as serologic markers of acute rejection after heterotopical heart transplantation in rats. In predictable rejection experiments, animals were divided into three groups: nonoperated (Lewis rats), control group (Lewis-Lewis isografts) and rejection group (Brown Norway-Lewis allografts). Nonpredictable rejection experiments were performed using nonconsanguineous Sprague-Dawley allografts. In predictable rejection experiments, LDH activity was similar between control and rejection groups. TnI values were heterogeneous in control and rejection groups. In contrast, the rejection group showed CK activity increased 4.5-fold compared with the control group. In addition to these predictable studies, we also presented novel nonpredictable experiments in which rats were divided into groups based on low and high CK activity. Histologic studies in these rats showed that none of those with low CK activity presented rejection signs, while all animals with high CK levels showed grade 2R rejection. These results suggest that CK might be an excellent marker for prediction of rejection in heart transplantation.