Summary
Background
Accurate evaluation of the pulmonary valve (PV) is crucial before surgical repair of Tetralogy of Fallot (TOF).
Aims
To assess PV and pulmonary annulus (PA) morphology using three-dimensional (3D) transthoracic echocardiography (TTE) in infants referred for surgical repair of TOF. Also, to compare PA measurements obtained by 3D TTE with those from other imaging modalities, including two-dimensional (2D) TTE and computed tomography (CT), with reference to surgical measurements.
Methods
3D zoom mode was used to assess PV morphology. 2D TTE and CT PA diameters were compared to both vertical and horizontal diameters obtained from 3D datasets. Surgical PA diameters were measured using Hegar’s dilators.
Results
A total of 29 patients with TOF (median [range] age 6 [3–24] months) were included and all successfully underwent 2D and 3D TTE; 22 also underwent CT. The number of pulmonary leaflets could be visualized in 24 patients (82.8%), with complete concordance with surgical findings. Vertical diameter was significantly longer than horizontal diameter ( P < 0.001)–underlying PA eccentricity–and was more important in bicuspid than tricuspid valves. Correlations between 2D and 3D TTE diameters were good. Surgical diameter was better correlated with 2D and 3D diameters than with CT diameter. 3D minimum, 2D and CT diameters were significantly lower than surgical diameters, but 3D mean and maximum diameters were not.
Conclusion
3D TTE is accurate to assess PV morphology and PA size in patients with TOF. 2D TTE and CT underestimate PA diameter with reference to surgical diameter, however 3D mean and maximum diameters did not differ significantly.
Résumé
Contexte
L’évaluation de la valve pulmonaire est cruciale avant la correction chirurgicale de la tétralogie de Fallot.
Objectifs
Évaluer la morphologie de la valve et de l’anneau pulmonaire par l’échocardiographie tridimensionnelle (3D) chez les patients avec Fallot. Comparer les mesures de l’anneau pulmonaire obtenues par 3D avec d’autres modalités d’imagerie (échocardiographie bidimensionnelle [2D] et scanner cardiaque), en référence aux mesures chirurgicales.
Méthodes
Le 3D zoom a été utilisé pour décrire la morphologie de la valve pulmonaire. Les diamètres en 2D et en scanner ont été comparés aux diamètres vertical et horizontal de l’anneau obtenus à partir des volumes 3D. Le diamètre chirurgical a été mesuré par la bougie de Hegar.
Résultats
Un total de 29 patients avec Fallot ont été inclus (l’âge médian [intervalle] était de 6 [3–24] mois). Des échocardiographies 2D et 3D ont été effectuées sur tous les patients ; parmi ces derniers, 22 ont eu un scanner cardiaque. Un nombre des feuillets pulmonaires a été visualisé chez 24 patients (82,8 %) avec une complète concordance peropératoire. Le diamètre vertical était plus grand que l’horizontal soulignant l’excentricité de l’anneau pulmonaire, celle-ci était plus importante pour la bicuspidie que pour la valve tricuspide. La corrélation entre le diamètre 2D et 3D était excellente. Le diamètre chirurgical était mieux corrélé avec les diamètres 2D et 3D qu’avec le diamètre scanner. Les diamètres 2D et scanner étaient significativement inférieurs au diamètre chirurgical. Celui-ci n’avait pas de différence significative avec les diamètres moyen et maximal 3D.
Conclusion
L’échocardiographie 3D est fiable pour évaluer la valve et l’anneau pulmonaire chez les patients avec Fallot. L’échocardiographie des diamètres 2D et le CT sous-estiment le diamètre chirurgical, cependant les diamètres 3D ne diffèrent pas significativement.
Background
Tetralogy of Fallot (TOF) is one of the most common forms of cyanotic congenital heart disease . The objective of the surgical repair is to close the shunt and relieve the right ventricular outflow tract obstruction. The aim is to preserve the pulmonary valve (PV) when possible, to prevent late complications . However, transannular patch is sometimes necessary when the PV is severely dysplastic or the size of the pulmonary annulus (PA) is not adequate . Morphological assessment of PV is crucial before surgical repair of TOF. Assessment of PV using conventional two-dimensional (2D) transthoracic echocardiography (TTE) is hard to achieve, as the short-axis view of the valve cannot be obtained. Previous studies have highlighted the interest of three-dimensional (3D) TTE to describe PV and PA in adult populations with or without congenital heart diseases , but little is known about its use in children. We describe the PV and PA morphology using 3D TTE in children with TOF referred for surgical repair, and compare PA measurements obtained by 3D TTE with other imaging modalities, including 2D TTE and cardiac computed tomography (CT), with reference to surgical measurements as the gold standard.
Methods
Patient characteristics
Consecutive patients referred for surgical repair of TOF were included prospectively. All patients underwent a complete 2D TTE assessment followed by 3D TTE assessment of PV. Some patients also underwent multidetector-row CT within 1 day of echocardiographic assessment. Indications for CT in these patients were to further investigate the pulmonary tree and/or the coronary arteries. Informed consent was obtained from each patient’s legal representative. The study protocol was approved by our institutional review board.
Echocardiographic examination
2D TTE was performed using the IE33 ultrasound system (Philips Medical Systems, Andover, MA, USA). After a full echocardiographic evaluation, PA diameter was obtained by 2D TTE from the parasternal short-axis view at the level of the aortic valve. PA diameter was measured at mid-systole between the insertions of the two cusps hinge point using 2D zoom mode as recommended in guidelines ( Fig. 1 ).
3D TTE of the PV was performed at the end of the 2D TTE study for all patients–from the parasternal view–using X7-2 and X5-1 matrix probes (Philips Medical Systems). Live 3D zoom mode was used to allow a more focused visualization of PV. Attention was paid to optimize gain and brightness. Vision H was chosen to ameliorate visualization of valve leaflets, as this vision can provide depth perception (by coding orange for nearer structures and blue for further structures). After acquisition of 3D volume, the image was rotated 90° down to provide an en face view of the PV from the perspective of the right ventricular outflow tract ( Fig. 2 ). 3D datasets were stored digitally and transferred to a dedicated workstation (QLab 9, Philips Medical Systems) for offline analysis.
CT examination
Multidetector-row CT was performed using a 64-slice Somatom Definition CT-scanner (Siemens, Forchheim, Germany) without sedation in all patients. Non-electrocardiogram (ECG)-gated CT was obtained using the following protocol: rotation time 330 ms, slice thicknesses 1 mm, tube current 50 mAs and tube voltage 80 kVp. ECG-gated CT was performed in patients with suspected coronary artery anomalies. An iodinated contrast (Xenetix 300; Guerbet, France) was injected into all patients with a power injector. The volume injected was adjusted to the child’s weight (2 mL/kg). PA diameter was obtained from axial reconstructed images (maximum-intensity projection) at the level of the pulmonary artery, by measuring the distance between the hinge points of the pulmonary cusps following the edge-to-leading edge rule ( Fig. 3 ).
Perioperative PA sizing
After infundibular resection was performed, the PV was inspected by the surgeon and described as bicuspid or tricuspid. Surgical commissurotomy was performed when there was a commissural fusion; the surgical PA diameter was then measured using Higar’s dilators (Medline Industries Inc., Mundelein, IL, USA). The surgical PA diameter was considered to be the largest dilator that fitted the pulmonary annulus without forcing. PA diameters are expressed as a Z score calculated from the nomogram of Pettersen et al. .
3D TTE dataset analysis
3D TTE image quality was graded according to a simplified four-point scale: poor (PV leaflets not visualized); fair (PV leaflets visualized); good (good visualization of PV leaflets, their coaptation and mobility); and excellent (excellent visualization of PV leaflets, their coaptation, mobility and thickness).
PA sizing from 3D datasets was obtained using Multiplanar reformatting (MPR) mode, with three independent orthogonal cutting planes. Two orthogonal planes were placed in the long axis of the right ventricular outflow tract. The third plane was placed perpendicular to the other two, and moved to the insertion of pulmonary cusps to obtain a short-axis view of the PA ( Fig. 4 ). Both vertical and horizontal diameters of the PA were measured. When the two diameters were different, the largest was called the maximum diameter (3D max) and the smallest was called the minimum diameter (3D min). The 3D mean diameter (3D mean) was calculated as the mean of 3D max and 3D min. PA geometry was expressed by the eccentricity index, which was calculated as 100 × (3D max–3D min)/3D max. An eccentricity index value of zero represents a perfect circle, while a progressively higher eccentricity index represents a more oval geometry.
Statistical analysis
Results are expressed as median (range) for continuous variables or as a number (percentage) for categorical variables. Spearman’s correlation coefficients with their 95% confidence intervals (CIs) were used to assess the correlation between PA measurements. The Bland-Altman method was used to further investigate the differences between measurements. Statistical differences were considered significant when the P value was < 0.05. Statistical analyses were performed using Stata ® 11.2 software (StataCorp LP, College Station, TX, USA).
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