Feasibility and interpretation of global longitudinal strain imaging in pediatric heart transplant recipients

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.

Rejection surveillance in pediatric heart transplant recipients: Critical reflection on the role of frequent and long-term routine surveillance endomyocardial biopsies and comprehensive review of non-invasive rejection screening tools

BACKGROUND

Despite significant medical advances in the field of pediatric heart transplantation (HT), acute rejection remains an important cause of morbidity and mortality. Endomyocardial biopsy (EMB) remains the gold-standard method for diagnosing rejection but is an invasive, expensive, and stressful process. Given the potential adverse consequences of rejection, routine post-transplant rejection surveillance protocols incorporating EMB are widely employed to detect asymptomatic rejection. Each center employs their own specific routine rejection surveillance protocol, with no consensus on the optimal approach and with high inter-center variability. The utility of high-frequency and long-term routine surveillance biopsies (RSB) in pediatric HT has been called into question.

METHODS

Sources for this comprehensive review were primarily identified through searches in biomedical databases including MEDLINE and Embase.

RESULTS

The available literature suggests that the diagnostic yield of RSB is low beyond the first year post-HT and that a reduction in RSB intensity from high-frequency to low-frequency can be done safely with no impact on early and mid-term survival. Though there are emerging non-invasive methods of detecting asymptomatic rejection, the evidence is not yet strong enough for any test to replace EMB.

CONCLUSION

Overall, pediatric HT centers in North America should likely be doing fewer RSB than are currently performed. Risk factors for rejection should be considered when designing the optimal rejection surveillance strategy. Noninvasive testing including emerging biomarkers may have a complementary role to aid in safely reducing the need for RSB.

Predictive Parameters of Decreased Left Ventricular Global Longitudinal Strain at 1 Month After Pediatric Heart Transplantation

Previous reports indicate that the decreased left ventricular global longitudinal strain (LVGLS) seen in the early postoperative period of pediatric heart transplant patients generally recovers over the course of 1-2 years. In this study, we investigate the predictive capacity of preoperative parameters on the LVGLS decline seen at 1 month post transplant. Forty-six transplant subjects with 2D echocardiographic images sufficient for speckle tracking echocardiography were enrolled. We excluded patients diagnosed with cardiac allograft vasculopathy or with an episode of rejection 1 month before or after their echocardiographic examinations. The mean LVGLS was significantly reduced at 1 month when compared to 1 year following transplant (- 15.5% vs. - 19.4%, respectively, p < 0.001). The predictors of LVGLS that decline at 1 month were the LV mass z-score [odds ratio (OR) 1.452; 95% confidence interval (CI) 1.007-2.095, p = 0.046], recipient age (OR 1.124; 95% CI 1.015-1.245, p = 0.025), and donor age (OR 1.081; 95% CI 1.028-1.136, p = 0.002) in the univariate logistic regression analyses. Although multivariate analysis yielded no significant predictors, higher LV mass z-scores showed a trend associated with the decline of LVGLS (p = 0.087). The donor/recipient weight ratio was associated with the LV mass z-score (R² = 0.412, p < 0.001).

Reproducibility and Intervendor Agreement of Left Ventricular Global Systolic Strain in Children Using a Layer-Specific Analysis

BACKGROUND

Speckle-tracking strain analysis provides additive data to the assessment of pediatric and congenital heart disease; however, the variety of strain analysis software platforms by different vendors and the lack of data on intervendor strain agreement in children have limited its utility. The purpose of this study is to evaluate the intervendor agreement of strain on two commonly used analysis platforms in pediatrics by layer of myocardium and data compression.

METHODS

This prospective study analyzed two-dimensional speckle-tracking strain on two software platforms in 53 children with normal cardiac segmental anatomy and varying function. Three standard apical views and one parasternal short-axis view were exported at their acquired frame rates to workstations with GE EchoPAC and TomTec software and then also to TomTec at compressed frame rates. Both software platforms had been updated with European Association of Cardiovascular Imaging/American Society of Echocardiography Task Force recommendations for left ventricular (LV) global strain. Intravendor and intervendor agreement between layer-specific comparisons were assessed using Bland-Altman analysis (limits of agreement and bias) and intraclass correlation coefficients.

RESULTS

This study included subjects with normal LV function (n = 38) and cardiomyopathy (n = 15) with an age range of 1 month to 18 years. Intertechnique agreement by default vendor myocardial layer (GE mid-TomTec endocardial layer) was robust for both global longitudinal (GLS) and circumferential strain (GCS; higher for GLS than GCS). Intravendor (inter- and interreader) agreement was slightly higher than intervendor. Only small differences in intraclass correlation coefficients were present between various myocardial layers and acquired versus compressed TomTec data with narrow limits of agreement and small bias except in certain subgroup comparisons.

CONCLUSIONS

Comparison of LV GLS and GCS between two commonly used software platforms after European Association of Cardiovascular Imaging/American Society of Echocardiography Industry Task Force recommendations demonstrated good to excellent agreement in pediatrics, regardless of the layer of analysis or the image format, although some degree of variability remains between vendor platforms. Overall, GLS agreement was more robust than GCS, and this difference is exaggerated in specific subanalyses. These data suggest that comparisons of strain values obtained on these two vendors will be reasonable, but caution should be used when the indication is the detection of small differences between serial echocardiograms.

Multi-modal imaging of the pediatric heart transplant recipient

The assessment of pediatric patients after orthotropic heart transplantation (OHT) relies heavily on non-invasive imaging. Because of the potential risks associated with cardiac catheterization, expanding the role of non-invasive imaging is appealing. Echocardiography is fast, widely available, and can provide an accurate assessment of chamber sizes and function. Advanced echocardiographic methods, such as myocardial deformation, have potential to assess for acute rejection or cardiac allograft vasculopathy (CAV). While not currently part of routine care, cardiac magnetic resonance imaging (CMR) and computed tomography may potentially aid in the detection of graft complications following OHT. In particular, CMR tissue characterization holds promise for diagnosing rejection, while quantitative perfusion and myocardial late gadolinium enhancement may have a role in the detection of CAV. This review will evaluate standard and novel methods for non-invasive assessment of pediatric patients after OHT.

Left ventricular adaptation following orthotopic heart transplantation in children: A speckle tracking echocardiographic imaging study

BACKGROUND

Evolution of left ventricle (LV) function in the pediatric OHT population has not been well described. Our hypothesis was that, in children following OHT without any rejection, there would be progressive normalization of LV size and function over 2 years.

METHODS

LV function was evaluated using STE and conventional echo parameters at five time points in pediatric OHT patients without any rejection in the first 2 years following OHT and normal controls. LV global peak systolic longitudinal strain (LVPLS) and strain rate, LV peak systolic radial and circumferential strain (LVRS and LVCS), and strain rate were analyzed.

RESULTS

We had twenty two patients with median age at OHT of 1.27 years ( IQR 0.19, 5.6 years). The LVPLS (mean ± SD) was abnormal in the post-OHT echocardiograms at 1 week (-12.4 ± 3.7) and 1 month (-13.9 ± 3.7) and significantly improved at 6 months (-15.8 ± 3.2), 1 year (-15.7 ± 3.1), and 2 years (-17.8 ± 2.8). However, LVPLS remained below the normal group even at 2 years following OHT (-21.3 ± 1.76).

CONCLUSION

In children following OHT, despite the absence of rejection, strain values are significantly impaired in the initial months, improve progressively over the first 2 years but remain abnormal compared with healthy controls.

Temporal changes in left ventricular strain with the development of rejection in paediatric heart transplant recipients

INTRODUCTION

Myocardial strain measurements are increasingly used to detect complications following heart transplantation. However, the temporal association of these changes with allograft rejection is not well defined. The aim of this study was to describe the evolution of strain measurements prior to the diagnosis of rejection in paediatric heart transplant recipients.

METHODS

All paediatric heart transplant recipients (2004-2015) with at least one episode of acute rejection were identified. Longitudinal and circumferential strain measurements were assessed at the time of rejection and retrospectively on all echocardiograms until the most recent negative biopsy. Smoothing technique (LOESS) was used to visualise the changes of each variable over time and estimate the time preceding rejection at which alterations are first detectable.

RESULTS

A total of 58 rejection episodes were included from 37 unique patients. In the presence of rejection, there were decrements from baseline in global longitudinal strain (-18.2 versus -14.1), global circumferential strain (-24.1 versus -19.6), longitudinal strain rate (-1 versus -0.8), circumferential strain rate (-1.3 versus -1.1), peak longitudinal early diastolic strain rate (1.3 versus 1), and peak circumferential early diastolic strain rate (1.5 versus 1.3) (p<0.01 for all). The earliest detectable changes occurred 45 days prior to rejection with simultaneous alterations in myocardial strain and ejection fraction.

CONCLUSIONS

Changes in graft function can be detected non-invasively prior to the diagnosis of rejection. However, changes in strain occur concurrently with a decline in ejection fraction. Strain measurements aid in the non-invasive detection of rejection, but may not facilitate earlier diagnosis compared to more traditional measures of ventricular function.

Speckle tracking stress echocardiography in children: interobserver and intraobserver reproducibility and the impact of echocardiographic image quality

Speckle tracking echocardiography (STE) is increasingly used during functional assessments. However, reproducibility and dependence on echocardiographic image quality for speckle tracking stress echocardiography in pediatric patients have not been studied to date. 127 consecutive normotensive children without structural heart disease (mean age 13.4 ± 3.0 years, 50.4% female) underwent a stepwise semisupine cycle ergometric protocol. Left ventricular (LV) myocardial peak strain and strain rate were assessed at rest and during exercise. Interobserver and intraobserver assessments were performed and analyzed regarding echocardiographic image quality. LV peak global strain and strain rate were well reproducible with narrow limits of agreement without any significant bias both at rest and during all stages of exercise testing. Moreover, strain rate reproducibility slightly deteriorated in values between -1.5 and -3 s^-1. Surprisingly, there was no significant difference in reproducibility between optimal, intermediate and poor quality of echocardiographic images. STE derived strain and strain rate measurements in children are feasible and highly reproducible during semisupine cycle ergometric stress echocardiography. Echocardiographic image quality does not seem to influence strain (rate) reproducibility. Myocardial deformation measurements in images with suboptimal visualization quality must be interpreted with caution.