Right Ventricular Outflow Tract Velocity Time Integral Determination in 570 Healthy Children and in 52 Pediatric Atrial Septal Defect Patients

A guide to echocardiographic assessment in children and adolescents with pulmonary hypertension

While the current definition of pulmonary hypertension (PH) is still based on haemodynamic variables, transthoracic echocardiography is the most important diagnostic clinical tool for the first assessment and evaluation of a patient, in whom PH is suspected. In addition, it is the most important clinical modality in long term follow-up and the utility of echocardiography has widely been demonstrated in patients with PH. Echocardiography not only reveals the underlying cardiac morphology and diagnosis of any associated cardiac defects. In most patients with PH right ventricular (RV) pressure estimation is feasible. In addition, ventricular systolic and diastolic function, as well as ventricular-ventricular interactions of both ventricles can be assessed by using echocardiography. Maximizing the use of echocardiography by reporting several measures to gain information and quantitatively describe the parameters, that are linked to prognosis, seem particularly appealing in these children, in whom other advanced imaging modalities requiring anaesthesia is associated with a considerable risk. Herein we provide a practical approach and a concise and clinically applicable echocardiographic guidance and present basic variables, which should be obtained at any assessment. Moreover, we present additional advanced echocardiographic measures, that can be applied in a research or clinical setting when progressive PH needs a deeper insight to assess heart function, estimation of pulmonary artery pressures among others, by echocardiography. Finally, clinically relevant studies in view of the prognostic properties with a focus on the most important echocardiographic variables in pediatric PH are summarized.

Echocardiography for the Assessment of Pulmonary Hypertension and Congenital Heart Disease in the Young

While invasive assessment of hemodynamics and testing of acute vasoreactivity in the catheterization laboratory is the gold standard for diagnosing pulmonary hypertension (PH) and pulmonary vascular disease (PVD) in children, transthoracic echocardiography (TTE) serves as the initial diagnostic tool. International guidelines suggest several key echocardiographic variables and indices for the screening studies when PH is suspected. However, due to the complex anatomy and special physiological considerations, these may not apply to patients with congenital heart disease (CHD). Misinterpretation of TTE variables can lead to delayed diagnosis and therapy, with fatal consequences, or–on the other hand-unnecessary invasive diagnostic procedures that have relevant risks, especially in the pediatric age group. We herein provide an overview of the echocardiographic workup of children and adolescents with PH with a special focus on children with CHD, such as ventricular/atrial septal defects, tetralogy of Fallot or univentricular physiology. In addition, we address the use of echocardiography as a tool to assess eligibility for exercise and sports, a major determinant of quality of life and outcome in patients with PH associated with CHD.

The right ventricular outflow tract in pediatric pulmonary hypertension-Data from the European Pediatric Pulmonary Vascular Disease Network

OBJECTIVE

The right ventricular outflow tract (RVOT) is pivotal for adequate RV function and known to be adversely affected by elevated pulmonary arterial pressure (PAP) in adults with pulmonary hypertension (PH). Aim of this study was to determine the effects of increased RV pressure afterload in children with PH on RVOT size, function, and flow parameters.

METHODS

We conducted a transthoracic echocardiographic study in 51 children with PH (median age: 5.3 years; range 1.5 months to 18 years) and determined the following RVOT variables: RVOT diameter, RVOT velocity time integral (VTI), ratio of tricuspid regurgitation velocity (TRV)/RVOT VTI, and RVOT systolic excursion (SE).

RESULTS

In our pediatric PH cohort, the age-specific RVOT diameter z-score was higher compared to normal values. Deviation from normal RVOT diameter values increased with age, disease severity, and New York Heart Association functional class. Significant correlations were found between RVOT diameter and the RV end-diastolic area and right atrial area. The age-specific RVOT VTIz-score values were significantly lower in children with PH vs healthy controls. The TRV/RVOT VTI ratio increased with rising systolic RV pressure, while the RVOT SE was similar between PH children and control subjects.

CONCLUSIONS

In pediatric PH cohort, the RVOT VTI is decreased, and the TRV/RVOT VTI ratio and the RVOT diameter increased compared to healthy subjects. Assessment of RVOT variables, together with established RV parameters, allows for a comprehensive assessment of global right heart size and performance in children with PH.

Centile Curves for Velocity-Time Integral Times Heart Rate as a Function of Ventricular Length: The Use of Minute Distance Is Advantageous to Enhance Clinical Reliability in Children

BACKGROUND

The generation of velocity-time integrals (VTIs) from Doppler signals is an essential component of standard echocardiographic investigations. The most effective algorithm to compensate for growth in children has, however, not yet been identified. This study was initiated to establish pediatric reference values for VTI and to enhance the interpretability of those values, considering technical and physiological factors.

METHODS

The echocardiographic data sets of healthy children and adolescents (N = 349; age range, 0-20 years) were recorded in a prospective approach and subsequently analyzed. In a pilot study, aortic and pulmonary VTIs were set in relation to the physiologic parameters of heart size as possible influencing parameters in a subgroup of children with comparable physical characteristics. The ratio with the smallest SD was taken as the base to generate centile curves using the LMS method. The clinical utility of the model was tested by examining patients (n = 80) with shunt lesions such as patent ductus arteriosus and atrial septal defect.

RESULTS

Feasibility was 94.6% for aortic VTI and 92.8% for pulmonary VTI. The pilot study identified ventricular length and heart rate as suitable parameters with the lowest relative SDs and high correlations with VTI. Gender differences were not relevant for children <7 years of age, and with increasing age, SD increased because of higher stroke volume variations. The detection of increased aortic VTI was possible with sensitivity of 73% for patients with patent ductus arteriosus with moderate or large hemodynamically significant ductus arteriosus. Patients with atrial septal defects with enlarged right ventricles could be identified as having increased pulmonary VTI with sensitivity of 84%.

CONCLUSIONS

These new reference values for VTI times heart rate as a function of ventricular length may be of specific clinical value to improve the assessment of cardiac function, therapeutic decision making, and follow-up in pediatric patients with heart disease.

Diagnostics in Children and Adolescents with Suspected or Confirmed Pulmonary Hypertension

We provide a practical approach on the initial assessment and diagnostic work-up of children and adolescents with pulmonary hypertension (PH). Transthoracic echocardiography (TTE) often serves as initial study tool before invasive cardiac catheterization. Misinterpretation of TTE variables may lead to missed or delayed diagnosis with devastating consequences, or unnecessary invasive diagnostics that have inherited risks. In addition to clinical and biochemical markers, serial examination of patients with PH using a standardized TTE approach, determining conventional and novel echocardiographic variables, may allow early diagnosis and treatment in paediatric PH. Cardiac magnetic resonance imaging and computed tomography represent important non-invasive imaging modalities, that together with TTE may enable comprehensive assessment of ventricular function and pulmonary hemodynamics. Invasive assessment of haemodynamics (ventricular, pulmonary) and testing of acute vasoreactivity in the catheterization laboratory is still the gold standard for the diagnosis of PH and pulmonary hypertensive vascular disease (PHVD) in children and for the initiation of specific PH therapy. We suggest the regular assessment of prognostic TTE variables as part of a standardized approach for initial diagnosis of children with PH. Overreliance on any single TTE variable should be avoided as it detracts from the overall diagnostic potential of a standardized TTE examination for PH.

Right Ventricular Outflow Tract (RVOT) Changes in Children with an Atrial Septal Defect: Focus on RVOT Velocity Time Integral, RVOT Diameter, and RVOT Systolic Excursion

OBJECTIVE

Aim of the study was to determine the influence of right heart volume overload in children with atrial septal defect (ASD) on right ventricular outflow tract (RVOT) variables.

METHODS

A prospective study was conducted in 115 children (age range: 2 days-18.1 years) with a moderate to large ASD. We determined effects of age, body length (BL), body weight (BW), and body surface area (BSA) on the variables RVOT diameter, RVOT velocity time integral (VTI), and RVOT systolic excursion (SE), and tested the predictive value of published normal values for age, BW, BL, and BSA in our ASD patients.

RESULTS

In our pediatric ASD patients, the age-specific RVOT diameter (z-score: +2.2, 95% CI: 2.0-2.4, P < 0.001) was significantly increased compared to normal values with 54% of our ASD patients having a z-score >2.0. The age-specific RVOT VTI z-score (z-score: +3.6, 95% CI: 3.2-3.9, P < 0.001) was significantly increased compared to normal values with 81% of our ASD patients having a z-score >2.0. The age-specific RVOT SE z-score was not increased but slightly lower compared to normal values (z-score: -0.5, 95% CI: -0.7 to -0.3, P < 0.001) with 3% of our ASD patients having a z-score >2.0 while 12% of the patients had a z-score <-2.

CONCLUSION

In our study population, we show the RVOT VTI and diameter to be relevant predictors in identifying an enlarged RVOT size and flow in children with moderate to large ASD.

Echocardiographic Evaluation of Pulmonary Pressures and Right Ventricular Function after Pediatric Cardiac Surgery: A Simple Approach for the Intensivist

Pulmonary hypertension (PH) is diagnosed using cardiac catheterization and is defined as an elevation of mean pulmonary artery pressure (PAP) greater than 25 mmHg. Although invasive hemodynamics remains the gold standard and is mandatory for disease confirmation, transthoracic echocardiography (TTE) is an extremely useful non-invasive and widely available tool that allows for screening and follow-up, in particular, in the acute setting. TTE may be a valuable alternative, allowing for direct measurement and/or indirect assessment of PAP. Because of the complex geometric shape and pattern of contraction of the right ventricle (RV), as well as the inherent complexity of cardiac repair, no single view or measurement can provide definite information on RV function and PAP and/or pulmonary vascular resistance. In addition, specific training and expertise may be necessary to obtain the views and measurements required. Some simple measurements may be of help when rapid evaluation is mandatory and potentially life saving: the assessment of tricuspid and/or pulmonary valve regurgitant jet and the use of the Bernoulli equation allow for measurement of PAP. Measurements such as the analysis of the pulmonary Doppler wave flow, the septal curvature, or the eccentricity index, assessing ventricular interdependence, are useful for indirect assessment. A four-chamber view of the RV gives information on its size, hypertrophy, function (fractional area change), and tricuspid annular plane systolic excursion as an evaluation of the longitudinal function. Based on these simple measurements, TTE can provide detection of PH, measurement or estimation of PAP, and assessment of cardiac function. TTE is also of importance in follow up of PH as well as providing an assessment of therapeutic strategies in the postoperative setting of cardiac surgery. However, PAP may be misleading as it is dependent on cardiac output and requires accurate measurements. In the presence of residual lesions, analyses of some Doppler measurements may be misleading and not reflect real PAP. Should the TTE evaluation reveal non-conclusive, invasive hemodynamics remains the gold standard.

Transthoracic echocardiography in the evaluation of pediatric pulmonary hypertension and ventricular dysfunction

Transthoracic echocardiography (TTE) is the most accessible noninvasive diagnostic procedure for the initial assessment of pediatric pulmonary hypertension (PH). This review focuses on principles and use of TTE to determine morphologic and functional parameters that are also useful for follow-up investigations in pediatric PH patients. A basic echocardiographic study of a patient with PH commonly includes the hemodynamic calculation of the systolic pulmonary artery pressure (PAP), the mean and diastolic PAP, the pulmonary artery acceleration time, and the presence of a pericardial effusion. A more detailed TTE investigation of the right ventricle (RV) includes assessment of its size and function. RV function can be evaluated by RV longitudinal systolic performance (e.g., tricuspid annular plane systolic excursion), the tricuspid regurgitation velocity/right ventricular outflow tract velocity time integral ratio, the fractional area change, tissue Doppler imaging-derived parameters, strain measurements, the systolic-to-diastolic duration ratio, the myocardial performance (Tei) index, the RV/left ventricle (LV) diameter ratio, the LV eccentricity index, determination of an enlarged right atrium and RV size, and RV volume determination by 3-dimensional echocardiography. Here, we discuss the potential use and limitations of TTE techniques in children with PH and/or ventricular dysfunction. We suggest a protocol for TTE assessment of PH and myocardial function that helps to identify PH patients and their response to pharmacotherapy. The outlined protocol focuses on the detailed assessment of the hypertensive RV; RV-LV crosstalk must be analyzed separately in the evaluation of different pathologies that account for pediatric PH.