Right atrial function in pediatric heart transplant patients by echocardiographic strain measurements

Echocardiographic Assessment of Right Ventricular Diastolic Function in Children and Adults: Present State and Future Directions

Diastolic function plays an important but often overlooked role in overall ventricular performance and is comprised of a sequence of events, which together result in adequate filling at low filling pressures. From a physiologic point of view there are 2 distinct, yet related periods that drive diastole: active relaxation and late filling. Much of the literature on diastolic function focuses on the left ventricle, however, there are significant differences in morphology, physiology, and adaptation between ventricles. Echocardiographic assessment of right ventricular diastolic function is challenging because of our imperfect understanding of right ventricular physiology, suboptimal imaging tools, and the use of models that have been built using the left ventricle. Conventional assessment includes inferior vena cava size, right atrial volume, and the use of Doppler to quantify tissue and blood velocity. In adults, the tricuspid valve E wave to A wave ratio (TV E/A) used in combination with early diastolic tricuspid valve annular velocity (e') and inferior vena cava size can be used to classify diastolic impairment, however, in children these are dependent to a greater degree on age and pathology. Right atrial and ventricular strain suffers from fewer limitations and might show incremental benefit, however, remains understudied, particularly in children. Novel methods made possible with ultrafast ultrasound provide a means to noninvasively assess intraventricular pressure differences as a measure of active relaxation, and shear wave velocity to directly assess myocardial stiffness, however, these remain in preclinical stages. In this review we discuss right ventricular diastolic physiology, the current state, and limitations of echocardiographic evaluation, and explore promising new methods for its assessment.

Size and Function of the Right Atrium in Healthy Children by Three-Dimensional Echocardiography

PURPOSE

Right atrial volume (RAV) and function have proven prognostic value in the assessment of cardiac disease and may be more accurately assessed using three-dimensional echocardiography (3DE). Normal 3DE reference values for the right atrial (RA) volume and function in healthy children have not yet been published. Furthermore, current methods of indexing cardiac measurements to body surface area (BSA) alone may be insufficient. We aimed to develop reference values for 3DE-derived RAV and function in the pediatric population, to provide a comparison of regression methods using BSA, height, weight, and sex, and to compare 3DE values to two-dimensional echocardiography (2DE) derived volumes.

METHODS

We retrospectively analyzed 187 3DE datasets acquired for a multi-center study on healthy children at two international centers. 3DE volumes were measured with vendor-agnostic software (Tomtec), and 2DE endo-diastolic volume (EDV) using the area-length single-plane approach. Regression curve-fitting of height (Ht), weight (Wt), BSA, and sex were explored to optimize Pearson coefficient and homoscedasticity.

RESULTS

The relationship of 3DE RAVs to BSA alone was heteroscedastic, with a residual positive relationship on indexing (R2 = 0.2506). Optimal regression of Ln (Volume) = b0 + x*Ln (Ht) + y*Ln (Wt) + z*Sex was homoscedastic. Total RA emptying fraction (EF) did not vary across age or sex, however active and passive emptying was best fit by a spline curve with a knot at approximately BSA = 1 m2. Strong agreement with 2DE-derived EDV was present (r2 = 0.83).

CONCLUSION

We provide reference values for RA size and function in the pediatric population and provide a comparison of methods for indexing these values.

Non-invasive myocardial tissue deformation and discoordination indices predict cardiac allograft vasculopathy in pediatric heart transplantation patients

There is an urgent need for non-invasive imaging-based biomarkers suitable for diagnostic surveillance of cardiac allograft vasculopathy (CAV) in pediatric heart transplant (PHT) patients. The purpose of this study was to comprehensively investigate left ventricular (LV) myocardial deformation in conjunction with electromechanical discoordination in PHT. PHT patients with and without CAV were evaluated for echocardiography derived global longitudinal strain (GLS) and electromechanical discoordination indices including systolic stretch fraction (SSF) and diastolic relaxation fraction (DRF). SSF was increased in CAV(+) patients at the time of CAV diagnosis (median CAV(+) 5.0 vs. median CAV(-) 0.0, P = 0.008) and in the echocardiogram preceding the CAV diagnosis (median CAV(+) 29.0 vs. median CAV(-) 0.0, P < 0.001). DRF was also increased in the echocardiogram that preceded CAV diagnosis in CAV(+) patients (0.31 ± 0.08 vs. 0.25 ± 0.05, P = 0.008). The final model using indices 6-12 months prior to CAV diagnosis included GLS, SSF, and DRF providing AUC of 0.94 with sensitivity 98.5%, specificity 80.0%, positive predictive value 85.0%, and negative predictive value 94.1%. Systolic and diastolic electro-mechanical discoordination indices are significantly worse in PHT patients experiencing CAV. Non-invasive imaging guided surveillance using echocardiographic myocardial deformation indices can be improved by adding SSF and DRF to standard GLS measurements.

Right atrial function early after tetralogy of Fallot repair

Diastolic dysfunction after repair for Tetralogy of Fallot (TOF) is associated with adverse long-term outcomes. Right atrial (RA) mechanics as a proxy of right ventricular (RV) diastolic function in the early post-operative period after surgical repair for TOF has not been reported. We sought to evaluate RA and RV strain prior to hospital discharge after TOF repair and to identify important patient factors associated with strain using a machine learning method. Single center retrospective cohort study of TOF patients undergoing surgical repair, with analysis of RA and RV strain from pre-and post-operative echocardiograms. RA function was assessed by the peak RA strain, systolic RA strain rate, early diastolic RA strain rate and RA emptying fraction. RV systolic function was measured by global longitudinal strain. Pre- and post-operative values were compared using Wilcoxon rank sum test. Gradient boosted machine (GBM) models were used to identify the most important predictors of post-operative strain. In total, 153 patients were enrolled, median age at TOF repair 3.5 months (25th-75th percentile: 2.2- 5.2), mostly male (67%), and White (64.1%). From pre-to post-operative period, there was significant worsening in all RA parameters and in RV strain. GBM models identified patient, anatomic, and surgical factors that were strong predictors of post-operative RA and RV strain. These factors included pulmonary valve and branch pulmonary artery Z scores, birth weight, gestational age and age at surgery, pre-operative RV fractional area change and oxygen saturation, type of outflow tract repair, duration of cardiopulmonary bypass, and early post-operative partial arterial pressure of oxygen. There is significant worsening in RA and RV strain early after TOF repair, indicating early alteration in diastolic and systolic function after surgery. Several patient and operative factors influence post-operative RV function. Most of the factors described are not readily modifiable, however they may inform pre-operative risk-stratification. The clinical application of RA strain and the prognostic implication of these early changes merit further study.

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.

Assessment of biatrial function in clinically well pediatric bicaval heart transplantation patients by three-dimensional echocardiography

Atrial size and function are closely correlated with atrial contributions to cardiovascular performance. Therefore, in this study, we aimed to assess atrial size and function in pediatric heart transplantation (HTx) patients using three-dimensional echocardiography (3DE). We enrolled 33 clinically well pediatric HTx patients and 33 healthy controls with a similar distribution of sex and age to the HTx patients. All patients underwent two-dimensional echocardiography (2DE) and 3DE. 2DE- and 3DE-derived biatrial maximal volume (Vmax), minimal volume (Vmin), ejection volume (EV), ejection fraction (EF), volume before atrial contraciton (VpreA), passive EV, passive EF, active EV and active EF were obtained in all patients. The 3D left atrail (LA) Vmax, Vmin and VpreA increased significantly in HTx patients after being indexed by BSA, while 3D LAEV and passive EV decreased significantly (P < 0.05). Moreover, the 3D LAEF, LA passive EF, and LA active EF all decreased significantly in HTx patients (P < 0.05). The 3D right atrial (RA) Vmax, Vmin, and VpreA increased significantly in HTx patients (P < 0.05), while the 3D RAEF and RA passive EF decreased significantly in HTx patients (P < 0.05). 3DE-derived LAVmax, LAVpreA, LA passive EV, LAEF, and LA passive EF were all lower than the corresponding 2D parameters. 3DE-derived RAVpreA, RA passive EV and RAEF were all lower than the corresponding 2D parameters. Atrial sizes and function assessed by 3DE- and 2DE-derived parameters, yield significantly discordant results in pediatric HTx patients. 3DE confirms significantly enlarged atrial sizes and decreased atrial functions in pediatric HTx patients.

Altered Biatrial Phasic Function after Heart Transplantation in Children

PURPOSE

We used two-dimensional echocardiographic speckle-tracking to investigate whether left and right atrial (LA and RA) phasic function in pediatric heart transplantation (HT) patients is altered and explored the relationship to HT-related clinical variables.

METHODS

Eighty-six subjects (36 HT and 50 normal children) were prospectively enrolled in two centers. Clinical data included age at HT, bypass time, ischemia time, donor age, and incidence of rejection. Atrial deformation indices including strain and strain rates (SRs) were measured using two-dimensional echocardiographic speckle-tracking. Components of phasic atrial function-reservoir (ε_r, SR_r), conduit (ε_cd, SR_cd), and booster (ε_ct, SR_ct) were calculated. Comparisons with controls were made using t test or Kruskal-Wallis test, and correlations to clinical variables were explored.

RESULTS

The mean age and body surface area of HT subjects were 10.2 ± 6.2 years and 1.2 ± 0.6 m², respectively. The mean heart rates were higher in HT (96 ± 18 vs 88 ± 21 in controls). There were reductions in RA and LA reservoir (ε_r, SR_r), conduit (ε_cd, SR_cd), and booster (ε_ct, SR_ct) function in HT compared with controls. There was no relationship of LA and RA deformation indices with mean age at HT, bypass time, or ischemia time. The LA ε_cd correlated weakly with donor age (r = -0.49, P = .04) and RA SR_r, and SR_cd showed association with duration of HT (P < .05). Nineteen HT recipients had follow-up studies 0.24 ± 0.18 years after the first examination, and deformational indices were not significantly changed.

CONCLUSIONS

Atrial strain determination is feasible in pediatric HT recipients and demonstrates disruption of reservoir, conduit, and booster function of both atria in this population; we speculate this may be a consequence of ventricular diastolic dysfunction.

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.