Usefulness and limitations of transthoracic echocardiography in heart transplantation recipients

Comparative Analysis of Conventional and Speckle Tracking Echocardiographic Variables between Patients with Unrejected Heart Transplants and Healthy Individuals

BACKGROUND

Echocardiography is essential for the assessment of patients with heart transplants. However, normal values in such individuals are not clearly defined.

OBJECTIVES

To compare conventional echocardiographic and speckle tracking variables between patients with unrejected heart transplants and healthy individuals.

METHODS

:A prospective study was conducted with adult patients having undergone heart transplantation at least one year earlier and submitted to endomyocardial biopsy followed by transthoracic echocardiogram (TTE). Conventional TTE measures and mechanical heart strain assessments using speckle tracking were performed and the results were compared to those of a group of healthy volunteers. Statistical significance was set at 5% (p < 0.05).

RESULTS

Thirty-six transplant patients without rejection were analyzed and compared to 30 healthy individuals. Chagas disease was the main reason for transplantation. Lower left ventricular global longitudinal strain expressed in absolute values was found (11.99% in transplant patients vs. 20.60% in controls; p <0.0001), right ventricular free wall longitudinal strain (16.67% in transplant patients vs. 25.50% in controls; p <0.0001) and myocardial work indices (p < 0.0001) as well as a larger size of the left atrium (38.17 ml/m2 in transplant patients vs. 18.98 ml/m2 in controls; p <0.0001) and greater mass and relative wall thickness (p <0.0001).

CONCLUSION

Stable patients having undergone heart transplants without rejection have differences concerning echocardiographic variables compared to healthy individuals. These findings indicate that conventional echocardiographic measures and heart mechanics are altered in transplant patients even in the absence of rejection. Such findings are relevant to the clinical context and follow-up of the patient.

Speckle-Tracking Echocardiography in Right Ventricular Function of Clinically Well Patients with Heart Transplantation

Heart transplantation (HT) is the mainstream therapy for end-stage heart disease. However, the cardiac graft function can be affected by several factors. It is important to monitor HT patients for signs of graft dysfunction. Transthoracic echocardiography is a simple, first-line, and non-invasive method for the assessment of cardiac function. The emerging speckle-tracking echocardiography (STE) could quickly and easily provide additive information over traditional echocardiography. STE longitudinal deformation parameters are markers of early impairment of ventricular function. Although once called the "forgotten ventricle", right ventricular (RV) assessment has gained attention in recent years. This review highlights the potentially favorable role of STE in assessing RV systolic function in clinically well HT patients.

A Comprehensive Excursus of the Roles of Echocardiography in Heart Transplantation Follow-Up

Current guidelines for the care of heart transplantation recipients recommend routine endomyocardial biopsy and invasive coronary angiography as the cornerstones in the surveillance for acute rejection (AR) and coronary allograft vasculopathy (CAV). Non-invasive tools, including coronary computed tomography angiography and cardiac magnetic resonance, have been introduced into guidelines without roles of their own as gold standards. These techniques also carry the risk of contrast-related kidney injury. There is a need to explore non-invasive approaches providing valuable information while minimizing risks and allowing their application independently of patient comorbidities. Echocardiographic examination can be performed at bedside, serially repeated, and does not carry the burden of contrast-related kidney injury and procedure-related risk. It provides comprehensive assessment of cardiac morphology and function. Advanced echocardiography techniques, including Doppler tissue imaging and strain imaging, may be sensitive tools for the detection of minor myocardial dysfunction, thus providing insight into early detection of AR and CAV. Stress echocardiography may offer a valuable tool in the detection of CAV, while the assessment of coronary flow reserve can unravel coronary microvascular impairment and add prognostic value to conventional stress echocardiography. The review highlights the role of Doppler echocardiography in heart transplantation follow-up, weighting advantages and limitations of the different techniques.

The Clinical Role of Cardiovascular Magnetic Resonance Imaging in the Assessment of Cardiac Diastolic Dysfunction

Echocardiography is the gold standard clinical tool for the evaluation of left ventricular diastolic dysfunction (LVDD) and is used to validate other cardiac imaging modalities in measuring diastolic dysfunction. We examined Cardiac Magnetic Resonance Imaging (CMR) in detecting diastolic dysfunction using the time-volume curve-derived parameters compared to echocardiographic diastolic parameters. We evaluated patients who underwent both CMR and transthoracic echocardiography (TTE) within 2 ± 1 weeks of each other. On echo, Doppler/Tissue Doppler Imaging (TDI) measurements were obtained. On CMR, peak filling rate (PFR), time to PFR (TPFR), 1/3 filling fraction (1/3FF), and 1/3 filling rate (1/3FR) were calculated from the time-volume curve. Using the commonly employed E/A ratio, 44.4% of patients were found to have LVDD. Using septal E/E′ and lateral E/E′, 29.6% and 48.1% of patients had LVDD, respectively. Correlation was found between left atrial (LA) size and E/A ratio (R = −0.36). Using LVDD criteria for CMR, 63% of patients had diastolic dysfunction. CMR predicted LVDD in 66.7% of the cases. CMR-derived diastolic filling parameters provided a relatively easy and promising method for the assessment of LVDD and can predict the presence of LVDD as assessed by traditional Doppler and TDI methods.

Multimodality Imaging to Detect Rejection, and Cardiac Allograft Vasculopathy in Pediatric Heart Transplant Recipients—An Illustrative Review

The three most common modalities of graft surveillance in pediatric heart transplant (HT) recipients include echocardiography, coronary angiography, and endomyocardial biopsy (EMB). The survival outcomes after HT in children have improved considerably in recent years. However, allograft rejection and cardiac allograft vasculopathy remain the leading cause of death or re-transplantation. The routine surveillance by EMB and coronary angiography are invasive and risky. Newer noninvasive echocardiographic techniques, including tissue Doppler imaging (TDI), 2-D speckle tracking echocardiography, CT coronary angiography (CTCA), cardiovascular magnetic resonance (CMR), single-photon emission computed tomography (SPECT), and positron emission tomography (PET) and invasive techniques such as intravascular ultrasound (IVUS), functional flow reserve (CFR) of coronary arteries, optical coherence tomography (OCT), have emerged as powerful tools which may help early recognition of sub-clinical rejection, response to treatment, early detection, and progression of CAV. The multimodality imaging approach, including noninvasive and invasive tests, is the future for the transplanted heart to detect dysfunction, rejections, and early CAV. This review illustrates noninvasive and invasive imaging techniques currently used or could be considered for clinical use in detecting heart transplant rejection, dysfunction, and CAV in children.

Insight into Noninvasive Radiological Modalities to Detect Heart Transplant Rejection

Purpose Patients with end-stage heart failure who remain symptomatic even with exemplary medical and device therapy are treated with heart transplantation. Multitudes of endeavor have been contrived during the last decennium in the field of noninvasive tests to rule out heart transplant rejection (HTR). In spite of having supportive literature, noninvasive imaging techniques lack acceptable documentation of clinical robustness, and endomyocardial biopsy (EMB) still remains the gold standard. The aim of this review is to shed light on the existing noninvasive radiological modalities to detect rejection among heart transplant recipients.

Methods A comprehensive search was conducted for this review article on the basis of literature available including scientific databases of PubMed, Embase, and Google Scholar, using keywords of “Heart transplantation,” “Acute allograft rejection,” “Arrhythmias,” “Echocardiography,” “Speckle tracking echocardiography,” and “Cardiac magnetic resonance imaging” from inception until September 2020.

Results After preliminary screening of the databases, details regarding existent noninvasive radiological modalities to detect HTR were gathered and compiled in this review article. Currently, deformation imaging using speckle tracking and T2 time using cardiac magnetic resonance imaging can serve as screening tools based on which further invasive investigations can be planned. Standardization of blood-based and imaging modalities as screening and possible diagnostic tools for rejection would have obvious clinical and financial benefits in the care of growing number of post heart transplant recipients in our country.

Conclusion Diagnosis of allograft rejection in heart transplant recipients through noninvasive techniques is demanding. To unravel the potential of noninvasive radiological modalities that can serve as a standard-of-care test, a prospective multicentric study randomizing noninvasive modality as first strategy versus current EMB-based gold standard of care is the need of the hour.

The Role of Echocardiography in the Management of Heart Transplant Recipients

Transthoracic echocardiography is the primary non-invasive modality for the investigation of heart transplant recipients. It is a versatile tool that provides comprehensive information on cardiac structure and function. Echocardiography is also helpful in diagnosing primary graft dysfunction and evaluating the effectiveness of therapeutic approaches for this condition. In acute rejection, echocardiography is useful with suspected cellular or antibody-mediated rejection, with findings confirmed and quantified by endomyocardial biopsy. For identifying chronic rejection, ultrasound has a more significant role and, in some specific patients (e.g., patients with renal failure), it may offer a role comparable to coronary angiography to identify cardiac allograft vasculopathy. This review highlights the usefulness of echocardiography in evaluating normal graft function and its role in the management of heart transplant recipients.

Three-Dimensional Speckle-Tracking Echocardiographic Monitoring of Acute Rejection in Heart Transplant Recipients

OBJECTIVES

This study assessed the use of 3-dimensional (3D) speckle-tracking echocardiography for noninvasive monitoring and diagnosis of acute rejection in heart transplant recipients.

METHODS

Fifteen heart transplant recipients underwent 32 endomyocardial biopsies; echocardiography was performed within 3 hours before biopsy. Twenty-four biopsies (acute rejection-negative group) showed grade 0 or 1A rejection, and 8 biopsies (acute rejection-positive group) showed grade 1B or higher rejection (based on the International Society for Heart and Lung Transplantation criteria). Two-dimensional, M-mode, pulsed Doppler, and tissue Doppler echocardiography were performed to assess conventional heart structure and function, and 3D full-volume echocardiography was recorded and analyzed.

RESULTS

Global peak longitudinal strain was significantly lower in the acute rejection-negative group compared to the positive group (mean ± SD, -7.38% ± 1.34% versus -10.88% ± 3.81%; P = .017). Differences in left ventricular global peak radial strain (28.79% ± 10.79% versus 24.32% ± 5.24%; P= .272), global peak circumferential strain (-12.16% ± 4.87% versus -12.61% ± 2.38%; P = .806), and ejection fraction (49.42% ± 12.17% versus 50.68% ± 7.26%; P = .824) between the negative and positive groups were not significant. Significant correlations were observed between the left ventricular ejection fraction and global peak longitudinal, global peak radial, and global peak circumferential (r = -0.72; P < .001; r = 0.60; P < 0.001; and r = -0.69; P < 0.001, respectively). Receiver operating characteristic curve analysis showed that a global peak longitudinal strain cutoff value of less than -9.55% could predict grade 1B or higher rejection with sensitivity of 87.50% and specificity of 54.17%.

CONCLUSIONS

Three-dimensional speckle-tracking echocardiography-derived global peak longitudinal strain is a useful parameter for detecting acute rejection; thus, 3D speckle-tracking echocardiography can monitor dynamic and acute rejection (≥1B) in heart transplant recipients.

Two-dimensional speckle tracking echocardiography of acute cardiac transplant rejection following pregnancy

A 44-year-old woman, who had undergone orthotopic cardiac transplantation in 1999, presented acute allograft rejection 4 months after childbirth. Analysis of myocardial deformation by speckle tracking echocardiography showed, in contrast with traditional markers of systolic function, a strong reduction of left ventricular strain, which recovered, together with rejection, under pharmacological treatment. This case documents the potential advantages of speckle tracking echocardiography in the noninvasive management of transplant recipients.

Brain natriuretic peptide induces CD8+ T cell death via a caspase 3 associated pathway--implications following heart transplantation

BACKGROUND

Brain natriuretic peptide (BNP) remains elevated after cardiac transplantation despite replacement of the failing ventricle. Serum peaks are also seen during acute rejection episodes independent of intracardiac hemodynamic disturbance. High BNP levels are also reported during bacterial sepsis, burns, stroke and myocardial infarction. Given all of these conditions are linked by immune activation processes, we hypothesised that BNP is an immunoactive agent.

METHODS

Peripheral blood mononuclear cells (PBMCs) were isolated from whole blood of 40 cardiac transplant recipients. Cells were co-cultured for 72h in the presence or absence of BNP. Cells were then immunophenotyped using flow cytometry. Cell death pathways were determined using caspase 3 quantification and mitochondrial membrane assessment. Supernatants were analysed for cytokine, chemokine and growth factor production using luminex.

RESULTS

Co-culture of CD8+ T cells with BNP reduced cell number, and increased intracellular caspase 3. Supernatant analysis revealed that BNP reduced the expression of inflammatory cytokines including TNF-α, IL-1α and IL-6. However it preserved the production of anti-inflammatory and regulatory cytokines such as IL-4, 5 and 13.

CONCLUSION

Our findings provide evidence that BNP directly induces CD8+ T cell apoptosis via a caspase 3 associated mechanism from cardiac transplant patients. This may impart significant consequences on immune mediated disease processes, such as allograft rejection.

Cellular and Functional Imaging of Cardiac Transplant Rejection

Heart transplantation is now an established treatment for patients suffering from end-stage heart diseases. With the advances in immunosuppressive treatment, the survival rate for transplant patients has improved greatly. However, allograft rejection, both acute and chronic, after heart transplantation is still a limitation leading to morbidity and mortality. The current clinical gold standard for screening rejection is endomyocardial biopsy (EMB), which is not only invasive, but also error-prone, due to the limited sample size and the site location of sampling. It would be highly desirable to have reliable and noninvasive alternatives for EMB in monitoring cardiac allograft rejection. The objective of this review is to highlight how cardiovascular imaging can contribute to noninvasively detecting and to evaluating both acute and chronic allograft rejection after heart transplantation, in particular, cardiovascular MRI (CMRI); and how CMRI can assess both immune cell infiltration at the rejecting organ, and the cardiac dysfunctions resulting from allograft rejection.

Cardiac myocyte-specific overexpression of human GTP cyclohydrolase I protects against acute cardiac allograft rejection

GTP cyclohydrolase I (GTPCH) is the rate-limiting enzyme for tetrahydrobiopterin (BH(4)) synthesis. Decreases in GTPCH activity and expression have been shown in late stages of acute cardiac rejection, suggesting a deficit in BH(4). We hypothesized that increasing intracellular levels of BH(4) by cardiac myocyte-targeted overexpression of GTPCH would diminish acute cardiac allograft rejection. Transgenic mice overexpressing GTPCH in the heart were generated and crossed on C57BL6 background. Wild-type and transgenic mouse donor hearts were transplanted into BALB/c recipient mice. Left ventricular (LV) function, histological rejection, BH(4) levels, and inflammatory cytokine gene expression (mRNA) were examined. Expression of human GTPCH was documented by PCR, Western analysis, and function by a significant (P < 0.001) increase in cardiac BH(4) levels. GTPCH transgene decreased histological rejection (46%; P < 0.003) and cardiac myocyte injury (eosin autofluorescence; 56%; P < 0.0001) independent of changes in inflammatory cytokine expression or nitric oxide content. GTPCH transgene decreased IL-2 (88%; P < 0.002), IL-1R2 (42%; P < 0.0001), and programmed cell death-1 (67%; P < 0.0001) expression, whereas it increased fms-like tyrosine kinase 3 (156%; P < 0.0001) and stromal-derived factor-1 (2; 190%; P < 0.0001) expression. There was no difference in ejection fraction or fractional shortening; however, LV mass was significantly increased (P < 0.05) only in wild-type grafts. The decreases in LV mass, cardiac injury, and histological rejection support a protective role of cardiac GTPCH overexpression and increased BH(4) synthesis in cardiac allografts. The mechanism of the decreased rejection appears related to decreased T cell proliferation and modulation of immune function by higher expression of genes involved in hematopoietic/stromal cell development and recruitment.

Speckle-tracking 2-dimensional strain echocardiography: a new noninvasive imaging tool to evaluate acute rejection in cardiac transplantation

BACKGROUND

There remains no reliable non-invasive method to detect cardiac transplant rejection. Recently, speckle-tracking 2-dimensional strain echocardiography (2DSE) was shown to be sensitive in the early detection of myocardial dysfunction in various models of cardiomyopathy. We aim to determine if 2DSE-derived functional indices can detect cardiac transplant rejection.

METHODS

Heterotopic rat cardiac transplantation was performed in histocompatible isografts or histoincompatible allografts. Histologic rejection scores were determined. Short-axis, mid-left ventricular (LV) echocardiography was performed on Day 6 after transplantation. Conventional measures of function were measured, (including LV fractional shortening and ejection fraction) as well as 2DSE parameters.

RESULTS

Despite class IIIB rejection in allografts and no rejection in isografts, there was no difference between isografts vs allografts in fractional shortening (15% +/- 3% vs 12% +/- 3%) or ejection fraction (36% +/- 5% vs 26% +/- 6%; both not significant). In contrast, 2DSE revealed decreases between isografts and allografts in global radial strain (12.6% +/- 5.6% vs 1.1% +/- 0.2%, p < 0.05), peak radial systolic strain rate (3.10 +/- 0.74/s vs 0.54 +/- 0.13/s, p < 0.001), and peak circumferential systolic strain rate (-1.99 +/- 0.55 vs -0.43 +/- 0.11/s; p < 0.01).

CONCLUSIONS

Systolic strain imaging using 2DSE differentiates myocardial function between experimental cardiac transplant rejection in allografts and non-rejection in isografts. Therefore, 2DSE may be useful in early non-invasive detection of transplant rejection.

Assessment of left atrial volumes and function in orthotopic heart transplant recipients by dual-source CT: comparison with MRI

INTRODUCTION

To compare left atrial performance with dual-source CT (DSCT) with respect to magnetic resonance imaging (MRI) in orthotopic heart transplant recipients.

METHODS

Twenty-nine consecutive heart transplant recipients (27 male; mean age 64.1 +/- 13 years; mean time from transplantation 122.8 +/- 69.7 months) referred for exclusion of cardiac allograft vasculopathy underwent cardiac DSCT and MRI. Standard biatrial technique was employed in 13 subjects whereas 16 were transplanted after the bicaval technique. Axial 5-mm slice-thickness DSCT datasets reconstructed in 5% steps of the cardiac cycle and axial 5-mm SSFP-MRI images were analyzed. Two blinded readers manually traced left atrial contours in random order to estimate end-diastolic volume (EDV), end-systolic volume (ESV), and ejection fraction (EF). Parameters were compared with a paired sample Student t test. Concordance correlation coefficient (CCC) was calculated to determine measurement agreement between techniques and observers.

RESULTS

Left atrial volumes were significantly higher with cardiac DSCT (EDV: 170.9 +/- 78.1 mL; ESV: 139.5 +/- 76.6 mL) than with MRI (EDV: 158.2 +/- 72.5 mL; ESV: 124.2 +/- 68.2 mL), whereas left atrial EF was lower with DSCT (EF: 20.8% +/- 7.5% vs. 23.6% +/- 7.7%) (P < 0.05). Measurement agreement between DSCT and MRI was excellent for all parameters (CCC > or =0.82). Individuals operated with the biatrial anastomosis technique presented significantly higher left atrial volumes and lower EF compared with subjects with bicaval anastomosis. Interobserver agreement was excellent for all parameters (CCC > or =0.80).

CONCLUSION

Even if DSCT slightly overestimates left atrial volumes with respect to MRI, results remain clinically valid. Bicaval surgical technique offers improved left atrial performance compared with standard biatrial anastomosis. DSCT may be used as a reliable tool to estimate left atrial parameters in orthotopic heart transplant recipients.

Sepiapterin decreases acute rejection and apoptosis in cardiac transplants independently of changes in nitric oxide and inducible nitric-oxide synthase dimerization

Tetrahydrobiopterin (BH(4)), a cofactor of inducible nitric-oxide synthase (iNOS), is an important post-translational regulator of NO bioactivity. We examined whether treatment of cardiac allograft recipients with sepiapterin [S-(-)-2-amino-7,8-dihydro-6-(2-hydroxy-1-oxopropyl)-4-(1H)-pteridinone], a precursor of BH(4), inhibited acute rejection and apoptosis in cardiac transplants. Heterotopic cardiac transplantation was performed in Wistar-Furth donor to Lewis recipient strain rats. Recipients were treated daily after transplantation with 10 mg/kg sepiapterin. Grafts were harvested on post-transplant day 6 for analysis of BH(4) (high-performance liquid chromatography), expression of inflammatory cytokines (reverse transcription- and real-time polymerase chain reaction), iNOS (Western blots), and NO (Griess reaction and NO analyzer). Histological rejection grade was scored, and graft function was determined by echocardiography. Apoptosis, protein nitration, and oxidative stress were determined by immunohistochemistry. Treatment of allografts with sepiapterin increased cardiac BH(4) levels by 3-fold without changing protein levels of GTP cyclohydrolase, the enzyme that regulates de novo BH(4) synthesis. Sepiapterin decreased inflammatory cell infiltrate and significantly inhibited histological rejection scores and apoptosis similar in magnitude to cyclosporine. Sepiapterin also decreased nitrative and oxidative stress. Sepiapterin caused a smaller increase in left ventricular mass versus untreated allografts but without improving fractional shortening. Sepiapterin did not alter tumor necrosis factor-alpha and interferon-gamma expression, whereas it decreased interleukin (IL)-2 expression. Sepiapterin did not change total iNOS protein or monomer levels, or plasma and tissue NO metabolites levels. It is concluded that the mechanism(s) of antirejection are due in part to decreased apoptosis, protein nitration, and oxidation of cardiomyocytes, which seems to be mediated at the immune level by limiting inflammatory cell infiltration via decreased IL-2-mediated T-lymphocyte expansion.

Where, when and how much: regulation of myelin proteolipid protein gene expression

The myelin proteolipid protein (PLP) gene ( Plp) encodes the most abundant protein found in myelin from the central nervous system (CNS). Expression of the gene is regulated in a spatiotemporal manner with maximal levels of expression occurring in oligodendrocytes during the active myelination period of CNS development, although other cell types in the CNS as well as in the periphery can express the gene to a much lower degree. In oligodendrocytes, Plp gene expression is tightly regulated. Underexpression or overexpression of the gene has been shown to have adverse effects in humans and other vertebrates. In light of this strict control, this review provides an overview of the current knowledge of Plp gene regulation.