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Archives of cardiovascular diseases
Volume 103, n° 11-12
pages 603-614 (novembre 2010)
Doi : 10.1016/j.acvd.2010.09.004
Received : 9 August 2010 ;  accepted : 9 September 2010
Developments in echocardiographic techniques for the evaluation of ventricular function in children
L’évaluation de la fonction ventriculaire chez l’enfant – nouvelles techniques échocardiographiques
 

Andreea Dragulescu, Luc L. Mertens
Department of Cardiology, Hospital for Sick Children, 555 University Avenue, Toronto, ON, M5G 1X8 Canada 

Corresponding author. Fax: +416 813 5857.
Summary

Echocardiography is a very important tool for the diagnosis and follow-up of children with congenital and acquired heart disease. One of the challenges that remains in paediatric heart disease is the assessment of systolic and diastolic function in children, as this is influenced by growth, morphology and loading conditions. New echocardiographic techniques, such as tissue Doppler, deformation imaging and three-dimensional echocardiography, have great potential application in this field. They may provide new insights into the influence of growth, morphology and loading on cardiac mechanics, and could become useful clinical tools. In this review, we discuss the potential use and limitations of these new echocardiographic techniques in paediatric and congenital heart disease.

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Résumé

L’échocardiographie est un outil très important dans le diagnostic et le suivi des patients avec cardiopathies congénitales et acquises. L’évaluation de la fonction systolique et diastolique chez l’enfant reste un problème due aux influences liées à la croissance, la morphologie ventriculaire et les conditions de charge. Les nouvelles techniques échographiques comme le Doppler tissulaire, l’imagerie de déformation et l’échographie 3D ont des applications potentielles importantes dans ce cadre. Elles peuvent apporter des nouvelles informations concernant la mécanique cardiaque dans différentes conditions pendant la croissance. Dans cette revue, on présente les indications potentielles et les limitations de ces techniques échographiques chez l’enfant.

The full text of this article is available in PDF format.

Keywords : Echocardiography, Tissue Doppler, Speckle tracking, Ventricular function

Mots clés : Échocardiographie, Doppler tissulaire, Speckle tracking, Fonction ventriculaire

Abbreviations : 2D, 3D, ASD, EF, IVA, LV, MRI, RV, TD


Introduction

Echocardiography has become the most important noninvasive technique for the diagnosis and follow-up of heart disease in children. Cross-sectional Doppler echocardiography allows a detailed description of cardiac anatomy and haemodynamics. Currently, the majority of children are referred for cardiac surgery based on echocardiography only. The diagnostic accuracy for describing cardiac morphology is extremely high, with a reported incidence of diagnostic errors of only 87 errors in more than 50,660 echocardiograms in an established paediatric echocardiography laboratory [1], demonstrating the level of accuracy that can be reached.

Cardiac MRI and cardiac computed tomography are the main imaging techniques used for extracardiac anatomy (pulmonary arteries and aortic arch) if not visualized properly by echocardiography. Diagnostic cardiac catheterization has become more obsolete and is restricted mainly to haemodynamic assessment in more complex lesions and the assessment of pulmonary vascular resistance. One of the challenges remaining for paediatric echocardiography is the availability of good techniques for assessing systolic and diastolic ventricular function. Most functional variables used in echocardiography were developed for the assessment of the morphologically normal LV. The diversity of congenital heart defects complicates the interpretation of functional variables, because of the anatomical variability, the effect of growth on myocardial function and the differences in loading conditions. For the LV, adult techniques are extrapolated to paediatrics often without good validation. For the RV and the single ventricle, qualitative subjective assessment is the technique used routinely in most laboratories.

During the past decade, different echocardiographic techniques have been developed that allow a more detailed analysis of cardiac function. These techniques have potential application in and substantial benefit for the assessment of ventricular dysfunction in paediatric patients. TD echocardiography and speckle-tracking-based strain imaging provide direct quantitative information about myocardial motion and deformation, which is more geometry independent than measurement of EF; they give more insight into myocardial mechanics and could provide guidance in treatment and response to therapies. Current 3D echocardiographic techniques enable the acquisition of full volumetric datasets, which can be analysed offline for the calculation of ventricular volumes, mass and EF. The impact of these technologies on paediatric functional echocardiography will be discussed in the current review.

Tissue Doppler velocities

The analysis of pulsed TD signals to interpret cardiac motion has been used since the early 1960s [2]. It took until the 1990s for it to be recognized as a potentially useful clinical technique for the assessment of global and regional myocardial function [3]. In a pig ischaemic model, tissue velocities were shown to change very quickly and consistently after the induction of ischaemia [4]. Several subsequent clinical studies investigated the use of regional myocardial velocities in various adult diseases, such as ischaemic heart disease, aortic insufficiency and hypertrophic cardiomyopathy [4, 5]. The advantage for paediatric and congenital heart disease is that these techniques are geometry independent and can be applied to any chamber morphology.

Colour TD imaging was introduced in the early 1990s as an alternative technique for measuring tissue velocities. In contrast to pulsed Doppler, which measures peak velocities, it uses autocorrelation techniques to measure regional mean velocities. This technical difference explains why colour TD-derived myocardial velocities are on average 15–20% lower than pulsed wave-derived myocardial velocities [6] (Figure 1A and B). Very high frame rates can be obtained by image optimization (>250 frames/second), which is very useful for the analysis of short-lived myocardial movements, such as during the isovolumetric periods, and is important for adequate temporal resolution at higher heart rates. An advantage of colour TD is that tissue velocities can be recorded simultaneously in different myocardial segments during the same cardiac cycle. This allows the comparison of regional wall motion and timing of cardiac events between different myocardial segments during the same cardiac cycle, which is important for dyssynchrony evaluation.



Figure 1


Figure 1. 

Tissue Doppler imaging in a patient after Fontan completion for hypoplastic left heart syndrome. (A) Pulse Doppler in the basal segment of the lateral wall with reduced systolic and diastolic velocities. (B) Simultaneous tissue Doppler velocities in six segments of the systemic ventricle. The absolute value for each segment is lower than the corresponding pulse Doppler velocity. (C and D) Tissue Doppler-derived strain and strain rate for the same ventricle with abnormal curves for the septal segments (not involved in ejection).

Zoom

The limitations of TD velocity imaging are related to its angle dependency (Doppler technique) and the unidimensional assessment of myocardial motion (longitudinal, circumferential or radial). Global cardiac translation of the entire heart during the cardiac cycle will also affect the measurement and tethering effects between myocardial segments; if a dysfunctional segment is moved by a healthy segment, this can also contribute to regional motion masking regional dysfunction.

Clinical application of tissue velocities in children

One of the challenges when introducing new techniques into paediatric echocardiography is that the methodology must be validated first for paediatric use, especially the establishment of normal values for different paediatric age groups. Normal paediatric TD data have been published by different groups [7, 8, 9]. In these studies, it was shown that tissue velocities vary with age and heart rate. Eidem et al. included 325 children and showed that pulsed-wave TD velocities also correlate with cardiac growth variables, especially the LV end-diastolic dimension and LV mass [7], indicating that tissue velocities are not entirely geometry independent. This has important implications when applying this methodology to children with congenital heart disease, where there is a large variability in ventricular geometry. Apart from the influence of geometry, changes in loading conditions also affect TD velocity measurements. Acute preload changes clearly affect tissue velocities [10], while this is less clear for the effect of chronic volume loading, where the ventricle has adjusted to the chronic load [11]. Studies in children with chronic LV volume loading related to a ventricular septal defect or patent ductus arteriosus have documented only minimal changes in TD velocities compared with normal paediatric controls [11]. Acute increase in afterload results in decreased TD velocities [12], while chronic adaptation by the concentric hypertrophic response results in decreased longitudinal velocities during the remodelling process. In children with aortic valve stenosis, systolic longitudinal velocities were shown to be reduced in the basal segments of the interventricular septum and the LV lateral wall. This could be an effect of hypertrophy and associated subendocardial dysfunction. In an adult population with aortic stenosis, the degree of reduction in longitudinal function was shown to be related to the degree of fibrosis in the LV and was also predictive of outcome after aortic valve replacement [13]. Kiraly et al. [14] showed that in children with aortic valve stenosis, longitudinal TD velocities were reduced more significantly compared with radial velocities. More research is warranted in children, as the mechanisms for adaptation to increased pressure loading could be different in the paediatric population.

As congenital heart disease frequently affects the RV, data on right ventricular TD velocities have been published in different conditions that affect the RV. With the predominantly longitudinal orientation of the RV myofibres, the quantification of longitudinal function is especially important when assessing RV function. Good correlations between systolic velocities and RV EF were found in an adult population that included patients with congenital heart disease [15]. Several studies have shown elevated RV systolic velocities in patients with ASDs before closure of the defect, which normalized within 24hours after closure [16, 17]. Quantitative assessment of right ventricular performance after repair of tetralogy of Fallot has also been the subject of considerable investigation. TD velocities are decreased in tetralogy patients after repair, with some RV regional wall motion abnormalities [18]. However, in these patients, regional functional variables obtained at the base of the RV free wall correlate less well with RV EF assessed by MRI, as this includes the patched and often dilated right ventricular outflow tract, influencing the assessment of global RV function. Hence, the use of regional variables in this condition is still unproven and requires further study.

The use of TD velocities in functionally univentricular hearts has also been studied. Frommelt et al. [19] used serial measurements for the evaluation of patients with hypoplastic left heart syndrome from the neonatal period until after the second stage palliation, and showed a trend towards a decrease in systolic and diastolic tissue velocities, with no difference regarding the type of initial palliation. However, the interpretation of these data is difficult, as there were significant changes in loading conditions and also changes in ventricular growth that could have influenced the observed changes. Vitarelli et al. [20] evaluated ventricular function at midterm (7.4±2.8 years) after Fontan completion, using myocardial velocities derived from the computed tomography dose index. They compared morphologically LVs (tricuspid atresia, double inlet LV) with normal controls and analysed the anterior and inferior wall (groups more comparable). There were significantly lower systolic and early diastolic tissue velocities in the Fontan group, which correlated well with the EF and the mass/volume ratio, respectively.

Tissue velocities are used in the evaluation of mechanical dyssynchrony. Mechanical dyssynchrony, as assessed by TD imaging and speckle tracking, is often present in patients with cardiomyopathy unrelated to electrical dyssynchrony, and correlates with the severity of LV dysfunction [21, 22]. This probably reflects regional differences in myocardial dysfunction. Mechanical dyssynchrony by TD imaging was analysed in only 64% of patients in a multicentre European study evaluating the current practice and results of cardiac resynchronization therapy in paediatric and congenital heart disease [23].

Overall, the effect of growth and variability in loading conditions on myocardial velocities limits their use in paediatric heart disease, except for serial follow-up in the same patient. However, only limited data are available. For example, after heart transplantation in children, a significant decrease in systolic and diastolic RV tissue velocities has been noted 3–6 months before terminal graft failure [24].

Tissue velocity tracings have also been used to calculate myocardial performance index, with good correlations with standard pulse Doppler measurements [25]. The use of TD imaging tracings is especially useful for the RV, allowing simultaneous measurement of systolic and diastolic events. It has been described as being useful in the assessment of patients after repair of tetralogy of Fallot and other congenital heart diseases [26]. An animal study by Cheung et al., using invasive measurements, demonstrated that the myocardial performance index was affected significantly by acute changes in loading conditions and was unable to detect acute changes in contractile function consistently [27], making its interpretation difficult in clinical settings. Additionally, we believe that if you combine systolic and diastolic time intervals in a single index, you do not know how to interpret the index when it is abnormal or when it changes; when it is abnormal, you can only conclude that something is wrong with either the systolic or diastolic function or that the loading of the heart changed. We do not use it routinely in our laboratory because of these considerations.

To overcome the effect of loading conditions on the measurements, myocardial acceleration during IVA was proposed as an index of myocardial contractility. IVA calculates the average rate of myocardial acceleration during the IVA period, which makes it insensitive to afterload changes and also, to some extent, to preload changes. In experimental studies, IVA has been validated as a sensitive noninvasive index of RV and LV contractility, which is unaffected by preload and afterload within a physiological range [28]. It requires imaging at very high frame rates, as IVA is a short-lived event (30–40ms). The disadvantage of IVA is that it is extremely sensitive to heart rate due to the force–frequency relationship. The heart rate sensitivity has been used to its advantage, to assess contractile reserve by studying the force–frequency relationship during pacing, dobutamine stress echocardiography or exercise [29, 30, 31]. However, intra- and interobserver variabilities have been shown to be problematic. The reproducibility of LV IVA was demonstrated to be relatively poor, especially in patients with impaired LV function [32]. Moreover, Lyseggen et al. showed that LV IVA is not a good variable for assessing regional myocardial function and, with non-physiological preload changes, is also preload sensitive. In paediatric patients, LV IVA was used after heart transplantation, where it was shown to be a useful noninvasive marker of allograft rejection [33].

The clinical use of RV IVA seems more promising. In patients with repaired tetralogy of Fallot, RV IVA was shown to be reduced and was related to the degree of pulmonary insufficiency, suggesting reduced contractile RV function in patients with pulmonary regurgitation or, alternatively, that the increased loading also affects the RV IVA measurement. For patients with a systemic RV, systolic functional reserve was assessed by dobutamine stress echocardiography, and the change in IVA during dobutamine exposure was shown to correlate well with the change in the end-systolic pressure–volume relationship assessed by conductance catheter measurements [34]. The force–frequency relationship was studied noninvasively using IVA in the perioperative period in patients after congenital heart surgery [30]. There was a large variability in the postoperative response, with a preserved force–frequency relationship after ASD closure and significant reduction after the arterial switch operation. The same principle could be used during stress echocardiography, as demonstrated by Pauliks et al. [31]. In single ventricles, the technique can be used to assess contractile reserve, and initial data suggest a preserved systolic reserve in children after the Fontan operation [29].

Deformation imaging: strain, strain rate

Myocardial velocities are influenced by global cardiac translational motion and myocardial tethering, which limits their use in the assessment of regional myocardial function. This limitation can be overcome by using regional myocardial deformation or strain imaging. Two different technologies are currently available for studying regional myocardial deformation. The first technique is based on TD imaging and is based on calculating myocardial velocity gradients. The second is based on tracking speckles on the grey-scale images in different frames throughout the cardiac cycle, and calculates the displacement of the speckles throughout the cardiac cycle. Two variables for cardiac deformation can be calculated (Figure 1C and D). Regional strain rate is the rate of deformation (per second) and is calculated as the velocity difference between two segments of myocardium divided by the distance between them. In younger children, we use computational distances of 4–5mm in the radial direction and 8–9mm in the longitudinal direction. Regional strain represents the amount of deformation (%) or the fractional change in length, caused by an applied force, and is calculated by integrating the strain rate curve over time during the cardiac cycle.

Experimental studies suggest that deformation variables can be used as noninvasive indices of ventricular function. End-systolic strain measurements correlate well with EF measurements, while peak systolic strain rate correlates relatively well with dP/dt and end-systolic elastance [35].

Tissue Doppler-derived deformation imaging

The underlying principle of TD-derived strain imaging is that instantaneous differences in tissue velocity between two adjacent segments reflect either expansion or compression of the tissue in between. The disadvantage of tissue velocity-based strain imaging is that it is angle dependent and is a unidimensional technique; it also requires extensive postprocessing, influencing intra- and interobserver variabilities [36]. Despite this limitation, if well standardized, radial strain evaluation in the LV posterior wall remains one of the more reproducible techniques and performs better than speckle-tracking techniques [36]. The high frame rates (>200 frames/second) that can be obtained provide a major advantage, especially in younger children with fast heart rates. This was the first technique available for measuring strain and strain rate and the first clinical data in children were obtained using this method. In particular, longitudinal strain measurements in the interventricular septum and LV and RV lateral walls were used to quantify regional and global myocardial function. The first paper on normal strain rate and strain data in children was published by Weidemann et al. [37]. Recently, Pena et al. published normal values in neonates (Table 1) [38].

Quantification of regional myocardial function can be useful for different indications in children. Firstly, quantification of regional myocardial function can be used in children where coronary perfusion can be an issue and regional myocardial ischaemia and dysfunction can be present. This includes patients after coronary reimplantation, i.e. arterial switch operation, repair of abnormal left coronary artery from the pulmonary artery, the Ross operation and other similar interventions. Long-term follow-up after coronary reimplantation for abnormal origin of the left coronary artery from the pulmonary artery showed that, despite normalization of the EF, longitudinal deformation remained abnormal in the septal and lateral wall [39]. This is probably related to residual subendocardial dysfunction resulting in decreased longitudinal function. Although coronary-related myocardial ischaemia is rare in children, the analysis of regional function by deformation imaging can provide additional information in children with congenital or acquired heart disease.

Secondly, strain imaging is also useful for the early detection of regional myocardial function. While in most patients with hypertrophic cardiomyopathy, global LV systolic function is generally considered to be preserved, deformation imaging has demonstrated significant regional differences in systolic deformation variables. Peak systolic strain was shown to be reduced significantly in the more hypertrophic regions, and was independent of the underlying aetiology [40, 41]. In young patients with Duchenne muscular dystrophy, deformation analysis showed a significant decrease in radial and longitudinal peak systolic strain and strain rate in the LV inferolateral and anterolateral walls in patients with normal EF. This corresponds to the regions in the myocardium where early fibrotic changes can be observed using gadolinium late-enhancement cardiac MRI techniques [42]. In Duchenne patients, these changes progressed with time, suggesting that early deformation changes could be an early marker for cardiac dysfunction. Also, in patients after anthracycline exposure, acute changes were observed after low-to-moderate doses of anthracycline, with alteration of systolic and diastolic TD-derived variables. These changes worsened after subsequent infusions. Moreover, in patients studied during long-term follow-up after anthracycline exposure, a decrease in deformation variables was observed, despite normal EF and fractional shortening [43, 44]. The significance of these early changes for long-term outcomes needs to be further defined.

Thirdly, deformation imaging is particularly useful for the quantitative assessment of RV function (Figure 1C and D). In postoperative tetralogy of Fallot patients, Weidemann et al. demonstrated that in the basal, mid and apical segments of the right ventricular free wall and interventricular septum, peak systolic strain and strain rate values were reduced [45]. Eyskens et al. demonstrated that these changes were related to the degree of pulmonary regurgitation [46]. Reduced regional peak systolic strain and strain rate values in the basal, mid and apical segments of the RV free wall were also found in patients with a systemic RV, such as after a Senning or Mustard operation [47]. Similarly to these data, reduced longitudinal RV deformation was measured in patients with congenitally corrected transposition of the great arteries [48]. Another study compared RV ventricular function after the Sano operation vs the classical Norwood initial palliation for hypoplastic left heart syndrome, and showed that RV free wall TD-derived strain and strain rate after RV to pulmonary artery conduit palliation was significantly better than after the classical Norwood intervention [49].

Finally, TD and deformation techniques can also be used for the detection of myocardial dyssynchrony and the identification of patients who might benefit from resynchronization therapy [21].

Two-dimensional-based deformation imaging–speckle tracking

Given the various limitations of Doppler-derived deformation imaging, new echocardiographic techniques were developed to analyse cardiac deformation, based on grey-scale imaging. Speckle tracking is based on 2D images and is relatively easy to perform with a short analysis time. Our recent work in children has shown that speckle-tracking techniques can be used in children to reliably quantify longitudinal and circumferential strain with reasonable inter- and intraobserver variabilities. Radial strain measurements are highly variable and strain rate measurements are less reliable [36]. An example of LV longitudinal strain by speckle tracking is shown in Figure 2. Further optimization of the techniques is required in children. One of the problems is the lower temporal resolution of the technique compared with Doppler-based technology, which might be an issue in smaller children with higher heart rates.



Figure 2


Figure 2. 

Longitudinal strain in a patient with dilated cardiomyopathy and severely impaired systolic function. It is easy to appreciate the presence of dyskinetic motion and postsystolic shortening of some segments. The global longitudinal strain is severely reduced.

Zoom

The major advantage of speckle-tracking technology is that it allows the study of radial, longitudinal and circumferential deformation as well as the assessment of ventricular rotation and torsion [50]. It also is angle independent. As with any strain technique, it is, however, load dependent, and the influence of geometry on the measurements has not been well defined.

Normal data on LV longitudinal strain and strain rate, as well as rotation and twist, have been published recently [51, 52] (Table 1). Longitudinal strain does not change significantly with maturation and decreasing heart rate, and LV torsion and rotation remain relatively constant when normalized by LV length and cardiac cycle, with a tendency towards faster deformation at a younger age. More data are required in smaller children and infants.

Clinical applications

The major clinical applications of speckle-tracking techniques should be the same as for TD-derived deformation imaging. Despite the fact that it is relatively easy to use, only a few studies have been published so far in children. Our group validated the methodology on different ultrasound systems [36]. An example of abnormal rotation in a patient with hypertrophic cardiomyopathy is shown in Figure 3. Other groups have looked at different applications. One group looked at regional deformation properties after successful repair of aortic coarctation and showed decreased deformation in the LV anterior wall [53]. A recent paper also showed that in patients with aortic stenosis and aortic coarctation, LV torsion was increased before and decreased after interventional treatment [54]. This is related to subendocardial dysfunction with an effect on epicardial force development. Most of the studies in the paediatric age group have been performed in patients with RV disease. However, as the technology was developed for the LV, most of the research work has focused on the effect of RV disease on LV function. Left ventricular torsion seems to be impaired in conditions associated with RV volume load, mostly due to reduced basal rotation. In young adults with secundum ASD, acute unloading of the RV improves LV twist by increasing basal rotation [55]. Further studies are needed to assess this mechanism in children with other conditions with RV volume load, such as patients after tetralogy of Fallot repair. It has been shown that RV dilatation has a negative impact on LV circumferential deformation but not longitudinal or radial deformation [56].



Figure 3


Figure 3. 

Hypertrophic cardiomyopathy with preserved longitudinal function but abnormal rotation pattern with counterclockwise rotation of both apex and base.

Zoom

Speckle-tracking analysis has been applied to the RV in patients after tetralogy of Fallot repair to evaluate the changes in RV function after surgical pulmonary valve replacement [57]. There was a significant increase in peak systolic and diastolic velocities, but not in global longitudinal strain, and all indices remained significantly lower compared with normal values. This could be related to persistent RV dysfunction but also to the acute effect of volume unloading. A similar study evaluated the acute effect of transcatheter pulmonary valve implantation, showing an acute improvement in RV free wall and septal longitudinal function [58]. More studies are needed to evaluate whether deformation analysis can predict RV functional recovery after pulmonary valve replacement.

Three-dimensional anatomy/volumetry

3D rendering of cardiac structures gained more importance with the development of high-frequency paediatric probes with improved image quality, allowing multiplanar reviews and structural reconstructions [59]. The benefit of this technique has been described in several groups of patients with congenital heart disease, mostly related to valvar and septal structures [60, 61, 62, 63], where good correlations with surgical findings were reported and/or additional information was obtained compared with 2D echocardiography. Volume calculation from 3D echocardiographic datasets has become widely available with the newer generation of echocardiography machines, with good correlations with MRI [64, 65]. It has recently been demonstrated that the different methods used to quantify EF by 2D techniques in children using the area-length or biplane Simpson’s methods, have important intra- and interobserver variabilities that affect the reliability of the measurements. This is especially important in patients with ventricular dysfunction, where the availability of accurate echocardiographic measurements might be helpful for clinical management. 3D echocardiography with semi-automated border detection methods seems to be useful potentially for improving the reproducibility and reliability of the measurements.

Clinical applications of three-dimensional echocardiography

Detailed analysis of LV regional myocardial function can be performed with segmentation of 3D volumes [66]. An example of volumetric assessment of the LV and left atrium is presented in Figure 4.



Figure 4


Figure 4. 

Three-dimensional volumetric assessment of the left heart using one of the commercially available pieces of software. (A) Segmental analysis of left ventricular volumetric change during systole. (B) Left atrial volume.

Zoom

Most of the validation work for RV volumes has been done in adolescents and young adults with congenital heart disease. Obtaining full echocardiographic 3D datasets of the RV remains challenging, and a study in patients with congenital heart disease and dilated RVs showed that, using different quantification techniques, 3D measurements were only feasible in about 50% of all patients [67]. This was due mainly to inadequate image quality and incomplete datasets. The same study showed that while RV EF was reliable in patients in whom measurements could be obtained, RV volumes were underestimated by 20% compared with MRI. Accurate measurement of RV volumes is important for certain diseases such as postoperative tetralogy of Fallot patients, where RV end-diastolic volume index is an important variable in clinical decision-making.

An alternative to 3D echocardiography is 2D echocardiography with knowledge-based 3D reconstruction–a method that has been developed, validated and introduced recently on a commercial basis, specifically to quantify RV volumes in patients after tetralogy of Fallot repair [68]. This method allows the 3D reconstruction of the RV without requiring border tracing or image processing, by using a database of RVs in both healthy and diseased states. A 3D space-localizing magnetic device allows placement of 2D images/planes in a 3D volume. The user identifies anatomical landmarks by point placement on 2D images, on the valves, apex, septum and free wall. These points are used to create a 3D surface with the aid of the database [68, 69]. Currently, datasets are available for postoperative tetralogy of Fallot patients with and without conduit insertion. Figure 5 shows an example of RV volume reconstruction in a patient after repair of tetralogy of Fallot.



Figure 5


Figure 5. 

Knowledge-based three-dimensional reconstruction of right ventricular systolic and diastolic volumes in a patient after repair of tetralogy of Fallot; septal and anterior view of the right ventricle.

Zoom

The anatomical variety of single ventricle anatomy makes the standard assessment of ventricular function difficult in these cases. The method of discs has been used in patients with single ventricles for the estimation of systolic and diastolic volumes, ventricular mass and EJ, with good correlations with MRI [70]. This method requires extensive manual offline tracing and postprocessing. The current semi-automated border detection programmes are not designed to perform the semi-automated segmentation on the 3D volumes of the single ventricles. The software is based on models of normal RVs or LVs. More research is required to make 3D volumetrics easier for single ventricles.

The future

The future of TD and deformation imaging techniques depends on further validation and demonstration of clinical utility. Currently, 3D strain techniques are becoming available but they are limited by lower frame rates and lower spatial resolution. It seems that the continuous technical evolutions are a challenge for paediatric cardiology, as each time a new technique becomes available there is the need for validation and establishment of normal values. Industry should come up with standards for TD and strain measurements, which make the techniques vendor independent, as with the other echocardiographic techniques. There is still a long way to go before the first clinical decision is made based on these new echocardiographic tools. In the meantime, they offer great new insights into the effect of congenital heart disease on cardiac function and mechanics.

Conflict of interest statement

No conflicts of interest to declare.

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