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Objective: To investigate prenatal changes in cardiac biometric and flow parameters in fetuses with bicuspid aortic valve (BAV) diagnosed neonatally compared with controls with normal cardiac anatomy., Methods: This analysis was conducted as part of the Copenhagen Baby Heart Study, a multicenter cohort study of 25 556 neonates that underwent second-trimester anomaly scan at 18 + 0 to 22 + 6 weeks' gestation and neonatal echocardiography within 4 weeks after birth, in Copenhagen University Hospital Herlev, Hvidovre Hospital and Rigshospitalet in greater Copenhagen, between April 2016 and October 2018. From February 2017 (Rigshospitalet) and September 2017 (Herlev and Hvidovre hospitals), the protocol for second-trimester screening of the heart was extended to include evaluation of the four-chamber view, with assessment of flow across the atrioventricular valves, sagittal view of the aortic arch and midumbilical artery and ductus venosus pulsatility indices. All images were evaluated by two investigators, and cardiac biometric and flow parameters were measured and compared between cases with BAV and controls. All cases with neonatal BAV were assessed by a specialist. Maternal characteristics and first- and second-trimester biomarkers were also compared between the two groups., Results: Fifty-five infants with BAV and 8316 controls with normal cardiac anatomy were identified during the study period and assessed using the extended prenatal cardiac imaging protocol. There were three times as many mothers who smoked before pregnancy in the group with BAV as in the control group (9.1% vs 2.7%; P = 0.003). All other baseline characteristics were similar between the two groups. Fetuses with BAV, compared with controls, had a significantly larger diameter of the aorta at the level of the aortic valve (3.1 mm vs 3.0 mm (mean difference, 0.12 mm (95% CI, 0.03-0.21 mm))) and the pulmonary artery at the level of the pulmonary valve (4.1 mm vs 3.9 mm (mean difference, 0.15 mm (95% CI, 0.03-0.28 mm))). Following conversion of the diameter measurements of the aorta and pulmonary artery to Z-scores and Bonferroni correction, the differences between the two groups were no longer statistically significant. Pregnancy-associated plasma protein-A (PAPP-A) multiples of the median (MoM) was significantly lower in the BAV group than in the control group (0.85 vs 1.03; P = 0.04)., Conclusions: Our findings suggest that fetuses with BAV may have a larger aortic diameter at the level of the aortic valve, measured in the left-ventricular-outflow-tract view, and a larger pulmonary artery diameter at the level of the pulmonary valve, measured in the three-vessel view, at 20 weeks' gestation. Moreover, we found an association of maternal smoking and low PAPP-A MoM with BAV. © 2021 International Society of Ultrasound in Obstetrics and Gynecology., (© 2021 International Society of Ultrasound in Obstetrics and Gynecology.)

Objectives: Prenatal diagnosis of coarctation of the aorta (CoA) is associated with reduced mortality and morbidity, however, accurate prenatal prediction remains challenging. To date, studies have used retrospective measurements of the outflow tracts to evaluate their potential to predict CoA. Our primary objective was to evaluate prospectively acquired measurements of the outflow tracts in fetuses with prenatally suspected CoA. A secondary aim was to report the postnatal prevalence of bicuspid aortic valve in this cohort., Methods: Pregnancies with suspicion of isolated CoA and with a minimum of 6 months' postnatal follow-up available were identified from the cardiac database of a tertiary fetal cardiology center in the UK, between January 2002 and December 2017. Measurement of the aortic valve, pulmonary valve, distal transverse aortic arch (DTAA) and arterial duct (AD) diameters were undertaken routinely in fetuses with suspected CoA during the study period. Z-scores were computed using published reference ranges based on > 7000 fetuses from our own unit., Results: Of 149 pregnancies with prenatally suspected CoA included in the study, CoA was confirmed within 6 months after birth in 77/149 (51.7%) cases. DTAA diameter Z-score and the Z-score of second-trimester DTAA/AD diameter ratio were smaller in fetuses with postnatally confirmed CoA than those in false-positive cases (-2.8 vs -1.9; P = 0.039 and -3.13 vs -2.61; P = 0.005, respectively). Multiple regression analysis demonstrated that the Z-scores of DTAA and AD diameters were the only significant predictors of postnatal CoA (P = 0.001). Bicuspid aortic valve was identified in 30% of the false-positive cases., Conclusions: Measurement of DTAA and AD diameter Z-scores can be used to ascertain risk for postnatal CoA in a selected cohort. The high incidence of bicuspid aortic valve in false-positive cases merits further study with respect to both etiology and longer-term significance. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd., (Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.)

Tetralogy of Fallot with absent pulmonary valve syndrome is a rare form of congenital heart disease. Among the different variations with this rare anomaly is nonconfluent pulmonary artery branches with anomalous origin of the left pulmonary artery from the ductus arteriosus. The authors present one such case which was diagnosed prenatally to have tetralogy of Fallot with absent pulmonary valve and identified postnatally to have nonconfluent pulmonary artery branches in addition. We discuss the conundrum of respiratory management in this patient pre- and postoperatively due to a unique ventilation perfusion mismatch problem, which varies between the two lungs.

Tetralogy of Fallot/Absent Pulmonary Valve (TOF/APV) has been classically associated with the absence of a patent ductus arteriosus (PDA). We present a rare case of APV in TOF with a discontinuous left pulmonary artery (LPA) that was suspected during fetal echocardiogram. Postnatal echocardiogram confirmed the origin of a hypoplastic LPA from the PDA. Despite an aneurysmal (right pulmonary artery) (RPA), axial imaging demonstrated widely patent tracheobronchial system with no evidence of bronchial compression. Clinically, the child required only minimal respiratory support. Genetic testing was positive for 22 q11deletion, commonly associated with this lesion. Surgery consisted of unifocalization of the discontinuous LPA with placement of a valved pulmonary homograft during complete repair of this lesion. Our case highlights the importance of prenatal detection, to aid in the prompt initiation of prostaglandins so as to ensure early rehabilitation of the left lung. Inability to visualize one of the branch pulmonary arteries (PA's) and a PDA on fetal echocardiogram in TOF/APV must raise suspicion for an eccentric branch PA with ductal origin., (© 2019 Wiley Periodicals, Inc.)

Background: Assessment of the outflow tract views is an integral part of routine fetal cardiac scanning. For some congenital heart defects, notably coarctation of the aorta, pulmonary valve stenosis, and aortic valve stenosis, the size of vessels is important both for diagnosis and prognosis. Existing reference ranges of fetal outflow tracts are derived from a small number of cases., Methods and Results: The study population comprised 7945 fetuses at 13 to 36 weeks' gestation with no detectable abnormalities from pregnancies resulting in normal live births. Prospective measurements were taken of (1) the aortic and pulmonary valves in diastole at the largest diameter with the valve closed, (2) the distal transverse aortic arch on the 3 vessel and trachea view beyond the trachea at the distal point at its widest systolic diameter, and (3) the arterial duct on the 3 vessel and trachea view at its widest systolic diameter. Regression analysis, with polynomial terms to assess for linear and nonlinear contributors, was used to establish the relationship between each measurement and gestational age. The measurement for each cardiac diameter was expressed as a z score (difference between observed and expected value divided by the fitted SD corrected for gestational age) and percentile. Analysis included calculation of gestation-specific SDs. Regression equations are provided for the cardiac outflow tracts and for the distal transverse aortic arch:arterial duct ratio., Conclusions: The study established reference ranges for fetal outflow tract measurements at 13 to 36 weeks' gestation that are useful in clinical practice., (© 2018 American Heart Association, Inc.)

Objectives: This study aimed to determine fetal echocardiographic features of tetralogy of Fallot in association with postnatal outcomes., Methods: The Z-scores of the main and bilateral pulmonary arteries and the aorta were measured, and the following variables were calculated in 13 fetuses with tetralogy of Fallot: pulmonary artery-to-aorta ratio and main pulmonary artery cross-section ratio - the main pulmonary artery diameter squared divided by the sum of the diameter squared of the left and right pulmonary arteries. Fetuses were classified as having ductus arteriosus-dependent or ductus arteriosus-independent pulmonary circulation., Results: We included two infants with pulmonary atresia and six infants with ductus-dependent pulmonary circulation, who underwent systemic-to-pulmonary shunt surgeries at ⩽1 month of age. The Z-scores of the main pulmonary artery and the pulmonary artery-to-aorta ratio in fetuses with ductus-dependent pulmonary circulation were lesser than those in fetuses with ductus independence, but not significantly. The main pulmonary artery cross-section ratio in fetuses with ductus dependence was significantly lesser (0.65±0.44 versus 1.56±0.48, p<0.005). Besides, the flow of the ductus arteriosus was directed from the aorta to the pulmonary artery in the ductus arteriosus-dependent group during the fetal period., Conclusions: The main pulmonary artery cross-section ratio was the most significant variable for predicting postnatal outcomes in fetuses with tetralogy of Fallot.

Outflow tract development of the heart is complex. The presence, differential growth and interactions of the various tissues through space and time contribute to the final development of the tract. This paper presents a novel interpretation of observations of outflow tract development, in particular of the aortic and pulmonary semilunar valves in embryos from the Shaner Collection at the University of Alberta. Three-dimensional reconstructions assist in the visualization of the spatial relationships of the developing valve tissues. In some embryos the aortic intercalated valve swelling is displaced proximally, giving rise to a bicuspid aortic semilunar valve more distally. In addition, the developing valve tissue first appears external to the myocardial cuff. The pulmonary semilunar valve regions appear to be more normal. This paper thus proposes a novel mechanism for generating a bicuspid aortic valve and also supports the idea that there is some independence of the aortic and pulmonary regions from each other during development., (Copyright © 2017 The Author(s). Published by Elsevier GmbH.. All rights reserved.)

Background: Absent arterial valve leaflets are rare anomalies. On the basis of our understanding of the normal development of the arterial valves, we draw inferences that might offer clues to their morphogenesis., Methods: We describe the findings from four human fetal autopsies with so-called "absent" arterial valvar leaflets. We then make inferences relative to these finding on the basis of our current understanding of normal development, the latter obtained by analysis of episcopic data sets from a large series of mouse embryos., Results: The fetuses had died between 12 and 15 weeks of gestation. In two cases, we found absence of the leaflets of the pulmonary valve, with patency of the arterial duct, but otherwise normal hearts. In a third case, there was absence of the leaflets of both arterial valves, along with a perimembranous ventricular septal defect and a "window-type" arterial duct. This fetus had a completely muscular subaortic infundibulum. The last fetus had a pulmonary dominant common arterial trunk, with absence of the truncal valvar leaflets, but again with a muscular subtruncal infundibulum. Findings from the analysis of the mouse embryos reveal that the arterial valvar leaflets are formed from the distal outflow cushions, but that the cushions have a separate function in septating the arterial roots and the proximal outflow tracts., Conclusions: When interpreting the fetal findings in the light of development, we conclude that there had been normal fusion of the major outflow cushions, but failure in excavation of their peripheral margins in three of the cases. In the fourth case, however, the cushions had not only failed to excavate but had also failed to separate the arterial roots.

Objectives: The purpose of this study was to determine whether the morphologic characteristics and area of the semilunar valves in healthy fetuses and fetuses with cardiac defects can be visualized by using spatiotemporal image correlation (STIC)., Methods: Spatiotemporal image correlation volumes from 74 healthy fetuses were recorded in 5 examinations between the 15th and 36th weeks of pregnancy. Second, we recorded STIC volumes from 64 fetuses with various cardiac defects. The quality of the volumes was rated. The areas of the aortic and pulmonary valves were measured in systole by rendering the valves on 4-dimensional sonography. The number of leaflets was examined. Longitudinal data analysis using linear mixed models was performed., Results: Two hundred ninety-three volumes from normal hearts were examined. In 82.5%, the quality of the normal volumes was sufficient. Visualization of the valve opening was feasible in 96.1% of the normal hearts and 97.4% of the abnormal hearts. The success rate of visualization of the pulmonary and aortic valve leaflets was dependent on the gestational age, with the highest percentage (72.1% in normal hearts) at 19 to 24 weeks. Longitudinal regression analysis showed a positive relationship of the aortic and pulmonary valve areas with gestational age (P < .0001) and fetal biometric measurements (P < .0001). Fifty-eight abnormal volumes were examined. Cardiac defects with abnormal valve areas due to aortic and pulmonary stenosis could be clearly visualized by using STIC., Conclusions: Examination of the morphologic characteristics of the semilunar valves using STIC is feasible, which is difficult when using 2-dimensional sonography. With increasing implementation of 4-dimensional sonography, the understanding of rendered images might be useful for anyone practicing fetal echocardiography., (© 2016 by the American Institute of Ultrasound in Medicine.)

There is limited information about age-specific structural and functional properties of human heart valves, while this information is key to the development and evaluation of living valve replacements for pediatric and adolescent patients. Here, we present an extended data set of structure-function properties of cryopreserved human pulmonary and aortic heart valves, providing age-specific information for living valve replacements. Tissue composition, morphology, mechanical properties, and maturation of leaflets from 16 pairs of structurally unaffected aortic and pulmonary valves of human donors (fetal-53 years) were analyzed. Interestingly, no major differences were observed between the aortic and pulmonary valves. Valve annulus and leaflet dimensions increase throughout life. The typical three-layered leaflet structure is present before birth, but becomes more distinct with age. After birth, cell numbers decrease rapidly, while remaining cells obtain a quiescent phenotype and reside in the ventricularis and spongiosa. With age and maturation-but more pronounced in aortic valves-the matrix shows an increasing amount of collagen and collagen cross-links and a reduction in glycosaminoglycans. These matrix changes correlate with increasing leaflet stiffness with age. Our data provide a new and comprehensive overview of the changes of structure-function properties of fetal to adult human semilunar heart valves that can be used to evaluate and optimize future therapies, such as tissue engineering of heart valves. Changing hemodynamic conditions with age can explain initial changes in matrix composition and consequent mechanical properties, but cannot explain the ongoing changes in valve dimensions and matrix composition at older age.

Objective: To describe antenatal sonographic signs that help in the differentiation of truncus arteriosus Types II and III (TA-II/III) from pulmonary atresia with ventricular septal defect (PA-VSD)., Methods: From a database of fetal echocardiographic examinations, we identified fetuses with sonographic features of a single great artery with VSD and relatively normal four-chamber view. Records were reviewed, comparing fetuses with TA-II/III and those with PA-VSD, with particular focus on: 1) characteristics of the overriding vessel, 2) appearance of the semilunar valves, 3) competence of the semilunar valves, 4) presence of major aortopulmonary collateral arteries (MAPCA), 5) main pulmonary artery being without antegrade flow, 6) site of arterial branching from the great artery and 7) other minor features, such as cardiac axis or associated anomalies., Results: Seventeen fetuses were identified, eight with TA-II/III and nine with PA-VSD. Among the eight fetuses with TA-II/III, seven had abnormal valves and six had valve regurgitation, compared with none of the nine PA-VSD fetuses. Five TA-II/III fetuses had early branching to supply the lungs, whereas most fetuses with PA-VSD had more distal branching. Notably, in six of the TA-II/III fetuses, the root of the single great artery originated predominantly from the right ventricle, while all but one of the PA-VSD fetuses had typical equal overriding of the VSD. The main pulmonary artery was without antegrade flow in two cases with PA-VSD. Finally, four cases with PA-VSD had MAPCA, in two of which this was identified prenatally., Conclusion: Identification of abnormal arterial valves or valve regurgitation, site of origin of branching, presence of overriding of the great artery, a main pulmonary artery without antegrade flow and MAPCA are helpful in differentiating between TA-II/III and PA-VSD., (Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.)

Objectives: We aimed to construct reference ranges for time intervals of each component of cardiac flow velocity waveforms in normal fetuses, comparing those variables between right and left ventricles., Methods: In 359 fetuses at the gestational age of 17-38 weeks, the durations of atrioventricular (AV) valve opening (AVVO), AV valve closure (AVVC), total E- (total-E) and A- (total-A) waves, total ejection time (total-ET), acceleration time (acc-E for E-wave, acc-A for A-wave, and acc-ET for ejection time), and deceleration time (dec-E for E-wave, dec-A for A-wave, and dec-ET for ejection time) were studied cross sectionally., Results: Both right and left acc-E showed the strongest correlations with gestational age (r = 0.478 and r = 0.519, respectively). Left AVVO showed a stronger correlation (r = 0.474) than right AVVO (r = 0.282) and, conversely, right AVVC showed a stronger correlation (r = 0.399) than left AVVC (r = 0.195) with gestational age. Significant differences (all P values <0.001) were observed for all right and left parameters other than total-A and acc-E., Conclusions: Characteristic differences between right and left ventricles were found in the reference ranges, suggesting the developmental properties of the fetal heart. © 2014 John Wiley & Sons, Ltd., (© 2014 John Wiley & Sons, Ltd.)

Background: Surgical management of tetralogy of Fallot (TOF) is increasingly moving toward valve-sparing approaches rather than transannular patch (TAP). We evaluate whether fetal pulmonary valve (PV) size is predictive of postnatal course and surgical approach in TOF., Methods: In this retrospective study, fetal and postnatal demographic, clinical, and echocardiographic data on 66 patients diagnosed prenatally with TOF were collected. We compared those with midgestation PV z-score > -3.5 to those with z-score ≤-3.5. We analyzed fetal and postnatal PV size and growth and outcomes between groups, Results: Gestational age at first fetal echo was 23 weeks (range 18-28). PV diameter and z-score on midgestation echo were 3.5 mm (1.3-6.0) and -2.8 (-0.5 to -6.0) respectively. Patients with PV z-score ≤ -3.5 on first fetal echo had smaller PV diameter (4.5 vs. 5.0 mm, P = .047) and PV z-score (-3.8 vs. -2.8, P < .001) in late gestation and at time of surgery (6.0 mm vs. 7.0 mm, P = .01; z-score = -2.9 vs. -1.7, P = .007). Similarly, those with smaller fetal PV z-score had smaller main and branch pulmonary arteries at time of surgery. PV growth rate over gestation was similar between groups, while after-birth PV growth rate was lower in those with smaller PV (0 mm/month vs. 0.6 mm/month, P = .002). Those with smaller pulmonary valve were more likely to be cyanotic (P = .05), to undergo surgery at <1 month (P < .01), and to have a TAP repair (P = .01). Among patients undergoing valve-sparing repair, those with smaller PV underwent more reinterventions for residual valvar PS (P < .01)., Conclusion: Midgestation fetal PV size is predictive of postnatal PV and PA size in TOF. Midgestation PV size has implications for timing and type of surgical management as well as for need for reintervention in valve-sparing repair patients and is therefore important to consider in prenatal counseling for TOF fetuses., (© 2013 Wiley Periodicals, Inc.)

Hemodynamic forces play an important role in sculpting the embryonic heart and its valves. Alteration of blood flow patterns through the hearts of embryonic animal models lead to malformations that resemble some clinical congenital heart defects, but the precise mechanisms are poorly understood. Quantitative understanding of the local fluid forces acting in the heart has been elusive because of the extremely small and rapidly changing anatomy. In this study, we combine multiple imaging modalities with computational simulation to rigorously quantify the hemodynamic environment within the developing outflow tract (OFT) and its eventual aortic and pulmonary valves. In vivo Doppler ultrasound generated velocity profiles were applied to Micro-Computed Tomography generated 3D OFT lumen geometries from Hamburger-Hamilton (HH) stage 16-30 chick embryos. Computational fluid dynamics simulation initial conditions were iterated until local flow profiles converged with in vivo Doppler flow measurements. Results suggested that flow in the early tubular OFT (HH16 and HH23) was best approximated by Poiseuille flow, while later embryonic OFT septation (HH27, HH30) was mimicked by plug flow conditions. Peak wall shear stress (WSS) values increased from 18.16 dynes/cm(2) at HH16 to 671.24 dynes/cm(2) at HH30. Spatiotemporally averaged WSS values also showed a monotonic increase from 3.03 dynes/cm(2) at HH16 to 136.50 dynes/cm(2) at HH30. Simulated velocity streamlines in the early heart suggest a lack of mixing, which differed from classical ink injections. Changes in local flow patterns preceded and correlated with key morphogenetic events such as OFT septation and valve formation. This novel method to quantify local dynamic hemodynamics parameters affords insight into sculpting role of blood flow in the embryonic heart and provides a quantitative baseline dataset for future research.

Semilunar valve malformations are common human congenital heart defects. Bicuspid aortic valves occur in 2-3% of the population, and pulmonic valve stenosis constitutes 10% of all congenital heart disease in adults (Brickner et al., 2000) [1]. Semilunar valve defects cause valve regurgitation, stenosis, or calcification, leading to endocarditis or congestive heart failure. These complications often require prolonged medical treatment or surgical intervention. Despite the medical importance of valve disease, the regulatory pathways governing semilunar valve development are not entirely clear. In this report we investigated the spatiotemporal role of calcineurin/Nfatc1 signaling in semilunar valve development. We generated conditional knockout mice with calcineurin gene disrupted in various tissues during semilunar valve development. Our studies showed that calcineurin/Nfatc1 pathway signals in the secondary heart field (SHF) but not in the outflow tract myocardium or neural crest cells to regulate semilunar valve morphogenesis. Without SHF calcineurin/Nfatc1 signaling, the conal endocardial cushions-the site of prospective semilunar valve formation--first develop and then regress due to apoptosis, resulting in a striking phenotype with complete absence of the aortic and pulmonic valves, severe valve regurgitation, and perinatal lethality. This role of calcineurin/Nfatc1 signaling in the SHF is different from the requirement of calcineurin/Nfatc1 in the endocardium for semilunar valve formation (Chang et al., 2004) [2], indicating that calcineurin/Nfatc1 signals in multiple tissues to organize semilunar valve development. Also, our studies suggest distinct mechanisms of calcineurin/Nfat signaling for semilunar and atrioventricular valve morphogenesis. Therefore, we demonstrate a novel developmental mechanism in which calcineurin signals through Nfatc1 in the secondary heart field to promote semilunar valve morphogenesis, revealing a new supportive role of the secondary heart field for semilunar valve formation., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Objective: To develop reference ranges of fetal aortic and pulmonary valve diameter derived from volume datasets of spatio-temporal image correlation (STIC)., Methods: A cross-sectional study was undertaken on low-risk pregnancies with well-established data from 14 to 40 weeks. Volume datasets of STIC were acquired for subsequent off-line analysis. Aortic and pulmonary valve diameters were measured in STIC multiplanar view using 4D-View version 9. Normal Z scores and centile reference ranges were constructed from these measurements against gestational age (GA) and biparietal diameter (BPD) as independent variables, using regression models for both mean and SD., Results: A total of 606 volume datasets were successfully measured. Normal reference ranges for predicting mean values and SD of aortic and pulmonary valve diameter were constructed based on best-fit equations (linear function) as follows: mean aortic diameter (mm) was modeled as a function of GA (weeks) and BPD (mm) as - 2.4838 + 0.2702 × GA, (SD = 0.1482 + 0.0156 × GA) and - 1.5952 + 0.0989 × BPD (SD = 0.1672 + 0.00572 × BPD). Mean pulmonary diameter was modeled as - 2.5924 + 0.2935 × GA (SD = 0.2317 + 0.01524 × GA) and - 1.6830 + 0.1083 × BPD (SD = 0.1971 + 0.0059 × BPD)., Conclusion: We have provided nomograms and Z scores of fetal aortic and pulmonary valve diameters. These reference ranges may be a useful tool in the assessment of fetal cardiac abnormalities., (Copyright © 2011 John Wiley & Sons, Ltd.)

Objective: To investigate the impact of selective fetoscopic laser photocoagulation (SFLP) on pre-existing pulmonary valve pathology in the recipient twin in twin-twin transfusion syndrome (TTTS)., Methods: We evaluated preoperative echocardiograms of all pregnancies with TTTS treated with SFLP at our institution from 2001 to 2009 (n = 76). Sixteen (21%) recipients had an abnormal pulmonary valve (stenosis/dysplasia, insufficiency or functional atresia) before SFLP. Postoperative echocardiograms and medical records from these 16 recipients were reviewed. Changes in pulmonary valve structure and function, and overall cardiac function, were noted after SFLP., Results: The mean gestational age at SFLP was 21 (range, 18.7-24.3) weeks. Seven of sixteen (44%) recipients with abnormal pulmonary valve prior to SFLP survived. Six of the 16 (37.5%) recipient twins had documented absence of persistent pulmonary valve abnormalities at birth or at autopsy. Two (12.5%) of the 16 recipients (2.6% of the original cohort) had persistent pulmonary valve abnormalities at birth, requiring intervention. Systolic and diastolic function improved or normalized after SFLP in all patients undergoing longitudinal follow-up. There was a tendency for a better cardiovascular profile score (best = 10 points) at initial evaluation in pregnancies with survivors compared with those with no survivors (mean (SD): 5.6 (2.2) vs. 6.75 (1.28)), but this was not statistically significant. Severity of cardiac involvement did not predict persistence of valve pathology or survival., Conclusions: SFLP can improve flow through the pulmonary valve of the recipient twin in TTTS, probably as a consequence of improvements in right ventricular systolic and diastolic function. However, pulmonary valve pathology may persist and require postnatal intervention.

During the fetal-to-neonatal transition, transvalvular pressures (TVPs) on the aortic and pulmonary valves change dramatically-but differently for each valve. We have examined changes in the molecular stability and crosslinking of collagen during this transition. Aortic and pulmonary valves were harvested from fetal and neonatal cattle. Using differential scanning calorimetry (DSC), denaturation of valvular collagen was examined and, using HPLC, the types and quantities of enzymatic crosslinks were examined. No difference in hydrothermal stability was found between the collagens in the fetal aortic and pulmonary valves; this was expected since the TVP is approximately the same across both valves before birth. Only in the neonatal samples was the collagen from aortic valves (higher TVP) less stable than that from pulmonary valves (lower TVP). Surprisingly, the enthalpy of denaturation did not differ either between valve type or with age, suggesting an entropic mechanism of altered molecular stability. A significant difference in immature-to-mature crosslink ratio was found between neonatal aortic and pulmonary valves: a difference absent in fetal valves. This ratio-indicative of remodeling rate-parallels (and may be a function of) the changing in vivo load. This study highlights the relationship between in vivo load and both (i) molecular stability and (ii) collagen remodeling in heart valves.

The extremely rare syndrome including absent pulmonary valve associated with membranous tricuspid atresia or severe tricuspid stenosis, intact ventricular septum and patent ductus arteriosus has been reported sporadically in the postnatal literature. This cardiac defect is characterized by right ventricular dysplasia with asymmetrical ventricular septal hypertrophy, ventricular septum bulging into the left ventricle, small right ventricular cavity, membranous tricuspid atresia or severe stenosis with abnormal papillary muscles and leaflets and absence of the pulmonary valve leaflets. The only prenatal case reported so far was diagnosed at 33 weeks of gestation and terminated shortly thereafter; the natural history of prenatally diagnosed cases is therefore unknown. We report on the intrauterine course of a case diagnosed at 17 weeks of gestation that had a favorable postnatal outcome after palliation.

The great arteries of embryos are small channels of a complex three-dimensional arrangement. Measurements of their diameters, as required for understanding cardiovascular morphogenesis and the genesis of malformations, cannot be performed in two-dimensional histological sections. We present and evaluate a quick and simple method for performing highly significant and objective measurements of the diameters of blood vessels in vertebrate embryos and used this method for providing statistics of the diameter of the semi-lunar valves and the lumina of the great arteries of early chick and mouse foetus. We employed the high-resolution episcopic microscopy technique for generating volume data and three-dimensional computer models of the arterial trees of 30 chick embryos (Hamburger Hamilton stage 34), 30 mouse embryos of the OF1 strain harvested on 14.5 dpc, 30 embryos of the OF1 strain harvested on 15.5 dpc and 28 mouse embryos of the PARKES strain harvested on 14.5 dpc. The three-dimensional models (voxel size 2 mum x 2 mum x 2 mum and 3 mum x 3 mum x 3 mum) were used for defining virtual resection planes perpendicular to the longitudinal axis of the blood vessels at comparable positions. In these planes, we measured the lumen areas and the lumen perimeters. We also calculated the lumen diameter and the true lumen area from the perimeter and present statistical analysis. Finally, we evaluate and discuss the reliability and reproducibility of our method and present all measurements in a form that minimizes the influence of specimen size variation, specimen processing and data generation methods.

Objective: To determine the relationship between visualization of key fetal anatomic structures during mid-trimester ultrasound examination with gestational age and duration of examination., Methods: One hundred ultrasound examinations at 16-22 weeks' gestation were reviewed to determine the times at which key fetal anatomic features were seen. Scans were terminated at 30 min or when a comprehensive anatomic survey was complete. Exclusion criteria included multiple gestation, maternal weight>77 kg, abdominal wall scarring, and suspected fetal anomalies., Results: Visualization of cranial anatomy including lips, face, midline, ventricles, choroid plexus, and cerebellum was achieved in 98% of patients within 30 min. The corresponding figures for spine, cardiac screening (four-chamber, aortic, and pulmonary outflow views) and for abdominal anatomy (stomach, kidneys, bladder, ventral wall, and three-vessel cord) were 91%, 91%, and 99%, respectively. A complete anatomic survey including each of the above elements was obtained by 10, 15, 20, 25, and 30 min in 8%, 31%, 53%, 72% and 81% of the subjects. Rates of complete anatomic surveys within 30 min improved by gestational age interval, from 20/30 (67%) at 16-18 weeks, to 36/44 (82%) at 18-20 weeks, and 25/26 (96%) at 20-22 weeks; this rise was primarily due to improvements in visualization of the spine and heart., Conclusions: A comprehensive anatomical survey can be completed in 10 min or less in a minority of patients. For each 5-min time increment up to 30 min, the rate of complete surveys improves. Rates of completed anatomic surveys rise with gestational age., (Copyright (c) 2005 ISUOG.)

Phospholipase Cepsilon is a novel class of phosphoinositide-specific phospholipase C, identified as a downstream effector of Ras and Rap small GTPases. We report here the first genetic analysis of its physiological function with mice whose phospholipase Cepsilon is catalytically inactivated by gene targeting. The hearts of mice homozygous for the targeted allele develop congenital malformations of both the aortic and pulmonary valves, which cause a moderate to severe degree of regurgitation with mild stenosis and result in ventricular dilation. The malformation involves marked thickening of the valve leaflets, which seems to be caused by a defect in valve remodeling at the late stages of semilunar valvulogenesis. This phenotype has a remarkable resemblance to that of mice carrying an attenuated epidermal growth factor receptor or deficient in heparin-binding epidermal growth factor-like growth factor. Smad1/5/8, which is implicated in proliferation of the valve cells downstream of bone morphogenetic protein, shows aberrant activation at the margin of the developing semilunar valve tissues in embryos deficient in phospholipase Cepsilon. These results suggest a crucial role of phospholipase Cepsilon downstream of the epidermal growth factor receptor in controlling semilunar valvulogenesis through inhibition of bone morphogenetic protein signaling.

We used lacZ-retrovirus labeling combined with neural crest ablation in chick embryos to determine whether the cardiac neural crest cells constitute one group of multipotent cells, or they emigrate from the neural tube in time-dependent groups with different fates in the developing cardiovascular system. We demonstrated that early-migrating cardiac neural crest cells (HH9-10) massively target the aorticopulmonary septum and pharyngeal arch arteries, while the late-migrating cardiac neural crest cells (HH12) are restricted to the proximal part of the pharyngeal arch arteries. These results suggest a prominent role for early-migrating cells in outflow tract septation, and a function for late-migrating cells in pharyngeal arch artery remodeling. We demonstrated in cultures of neural tube explants an intrinsic difference between the early and late populations. However, by performing heterochronic transplantations we showed that the late-migrating cardiac neural crest cells were not developmentally restricted, and could contribute to the condensed mesenchyme of the aorticopulmonary septum when transplanted to a younger environment. Our findings on the exact timing and migratory behavior of cardiac neural crest cells will help narrow the range of factors and genes that are involved in neural crest-related congenital heart diseases., (Copyright 2003 Wiley-Liss, Inc.)

The cardiac outflow tract is the site of anomalies that affect a substantial proportion of individuals with congenital heart defects. The morphogenesis of this site is complex, and requires coordinated development of many cell types and tissues. It is therefore not surprising that developmental mistakes arise here, and that the steps and mechanisms of morphogenesis are still controversial and poorly understood, despite advances in molecular techniques. Recent findings have provided new insight into mechanisms of outflow tract morphogenesis, including clarification of its origins and the fate of cardiomyocytes, as well as invading cell populations. Application of new and old techniques and a wide range of approaches to tackle the unanswered questions about the outflow tract calls for collaboration among investigators from different disciplines including anatomists, physiologists, and molecular biologists.

Objective: To test the hypothesis that identical twins show no inter-twin differences in cardiovascular structure or physiology in fetal life unless there has been twin-twin transfusion syndrome., Design: Unselected prospective case-control observational study of fetoplacental haemodynamics including echocardiography at a median of 24 (16.7 to 32.3) weeks, with postnatal confirmation of congenital heart disease or normality., Setting: Fetal medicine unit., Patients: 136 women with monochorionic diamniotic twin pregnancies, of which 47 fetal twin pairs (35%) had twin-twin transfusion syndrome., Results: There were no haemodynamic differences between the bigger fetus (twin 1) and the smaller co-twin (twin 2) in uncomplicated monochorionic diamniotic pairs. In twin-twin transfusion syndrome, recipient fetuses had increased aortic and pulmonary velocities compared with their donor co-twins (mean (SD): 0.73 (0.23) m/s and 0.63 (0.14) m/s), respectively, v 0.53 (0.16) m/s and 0.48 (0.10) m/s in donor twins; p = 0.003 (aortic) and < 0.0001 (pulmonary)), and also in comparison with twin 1 and twin 2. The overall prevalence of congenital heart disease was increased above that in singletons (3.8% v 0.56%; 6.9% in twin-twin transfusion v 2.3% in uncomplicated monochorionic diamniotic twins), with inter-twin discordance for defects. The prevalence in recipient twins was 11.9% (p = 0.014 v uncomplicated control twins)., Conclusions: Fetuses with an identical genome but no circulatory imbalance have similar cardiovascular physiology but discordant phenotypic expression of congenital heart disease. The high prevalence of congenital heart disease in monochorionic diamniotic twins merits detailed fetal echocardiography.

The development of cartilage in the aortic and pulmonary valves of chick and quail was studied using histological, histochemical and immunohistochemical techniques. In both species, the earliest evidence of chondrogenesis is the formation of smooth muscle alpha-actin-negative prechondrogenic (type II collagen-negative) cellular condensations in the tunica media of the proximal aorta and pulmonary trunk, in front of or slightly distal to the valvular commissures. Such condensations are present as early as stage 37 of Hamburger-Hamilton in the aortic and pulmonary valves of the chick. In quail embryos, they form somewhat later, namely, at stage 38 in the aortic valves and stage 39 in the pulmonary valves. In the chick, synthesis of type II collagen starts in the central core of the aortic cellular condensations at stage 38. In the pulmonary valves of chick and aortic and pulmonary valves of quail, production of type II collagen does not begin until stage 40. This production then gradually increases toward the periphery of the condensations, which remain devoid of perichondrium prior to hatching. After birth, the condensations become transformed into hyaline cartilaginous foci. In the aortic valves of some chickens and quails, more or less extensive deposits of hyaline cartilage or fibrocartilage form along the attachments of the leaflets to their supporting sinuses. They develop later than the commissural cartilages. The present findings, together with previous data from the literature, suggest that the aortic and pulmonary valve cartilages differentiate from neural crest-derived nonmuscular cells.

Atrioventricular and semilunar valve abnormalities are common birth defects, but how cardiac valvulogenesis is directed remains largely unknown. During studies of genetic interaction between Egfr, encoding the epidermal growth factor receptor, and Ptpn11, encoding the protein-tyrosine-phosphatase Shp2, we discovered that Egfr is required for semilunar, but not atrioventricular, valve development. Although unnoticed in earlier studies, mice homozygous for the hypomorphic Egfr allele waved-2 (Egfrwa2/wa2) exhibit semilunar valve enlargement resulting from over-abundant mesenchymal cells. Egfr-/- mice (CD1 background) have similar defects. The penetrance and severity of the defects in Egfrwa2/wa2 mice are enhanced by heterozygosity for a targeted mutation of exon 2 of Ptpn11 (ref. 3). Compound (Egfrwa2/wa2:Ptpn11+/-) mutant mice also show premature lethality. Electrocardiography, echocardiography and haemodynamic analyses showed that affected mice develop aortic stenosis and regurgitation. Our results identify the Egfr and Shp2 as components of a growth-factor signalling pathway required specifically for semilunar valvulogenesis, support the hypothesis that Shp2 is required for Egfr signalling in vivo, and provide an animal model for aortic valve disease.

Embryonic mice lacking functional Sox4 transcription factor die from cardiac failure at embryonic day (ED) 14. Heart morphogenesis in these embryos was analyzed in hematoxylin-azophlochsin or immunohistochemically stained, 3-dimensionally reconstructed serial sections between ED12 and ED14. Although Sox4 is expressed in the endocardially derived tissue of both the outflow tract and atrioventricular canal, Sox4-deficient hearts only suffer from defective transformation of the endocardial ridges into semilunar valves and from lack of fusion of these ridges, usually resulting in common trunk, although the least affected hearts should be classified as having a large infundibular septal defect. The more serious cases are, in addition, characterized by an abnormal number and position of the semilunar valve-leaflet anlagen, a configuration of the ridges typical for transposition of the great arteries (with linear rather than spiral course of both ridges and posterior position of the pulmonary trunk at the level of the valve), and variable size of the aorta relative to the pulmonary trunk. The coronary arteries always originated from the aorta, irrespective of its position relative to the pulmonary trunk. The restriction of the malformations to the arterial pole implies that the interaction between the endocardially derived tissue of the outflow tract and the neural crest-derived myofibroblasts determines proper development of the arterial pole.

The fibrous skeleton of the heart has featured prominently in anatomical and surgical descriptions, although all its purported components are difficult to demonstrate. In descriptions of the skeleton, there have been repeated references to the presence of a tendon (or ligament) between the aortic and pulmonary roots. Such a tendon is rarely, if ever, discussed in the context of surgical procedures being carried out on the ventricular outflow tracts. Our study was undertaken, therefore, to investigate the existence and nature of such a tendon or ligament. Serial transverse sections were made through roots of aorta and pulmonary trunk in an intact fetal heart. In addition, ten normal adult hearts were dissected to display the components of the fibrous skeleton of the heart. No discrete fibrous or elastic structure could be detected in the tissue plane between the aortic sinuses and the subpulmonary muscular infundibulum, although a fascial strand was observed in one heart. Apart from this specimen, the space between the free-standing muscular subpulmonary infundibulum and the sinuses of aorta hearing the coronary arteries was occupied only by loose fibroareolar tissue. The initial presence of the ligament was described following studies of animal and macerated human hearts. Subsequently, it would seem its existence has been passed down through generations of morphologists and surgeons without its presence being reconfirmed. We have been unable to demonstrate any structure approximating to the initial illustrations.

Pathological examination of the heart and great vessels was performed in 61 specimens obtained after surgical termination of pregnancy for psychosocial indications at 9-18 weeks of gestation. The aorta and pulmonary trunk were identified and external diameters were measured at the level of, and distal to the aortic valve and pulmonary valve, the level of the aortic isthmus and thoracic aorta, and the proximal and distal ductus arteriosus. All eight vessel diameters increased linearly with gestational age and the ratio of the diameter of the aortic isthmus to that of the aortic valve or the distal ductus arteriosus also increased with gestation. Early pregnancy is characterized by rapid growth of the fetal head and this may well be the consequence of a preferential distribution of left ventricular output in favour of the head due to relative narrowing of the aortic isthmus at this gestation.

Pulsed Doppler velocimetry of the fetal aortic and pulmonary valves derived in the five-chamber-view and short-axis view were performed in 88 uncomplicated pregnancies between the 20th and 40th week of gestation. The maximal and mean velocities were assessed for both semilunar valves. Considering the valve diameters and heart rate the stroke volume and cardiac output for both ventricles were calculated. Furthermore, the common stroke volume, common cardiac output and the ratio of right to left cardiac output were calculated. Normal ranges for all these parameters were constructed and correlated with gestational age. The maximal velocities were higher in the aorta than in the pulmonary trunk, but no differences were found in the mean velocities. The stroke volume and cardiac output of the right ventricle were in higher ratio 1.3:1 than that of the left ventricle as an expression of the right ventricular dominance in the fetus. Intracardiac Doppler flow velocimetry gives an insight into the physiology of fetal circulation and is a basis for the analysis of blood flow under pathological conditions.

Two fetuses of approximately 11 weeks development with aplasia of the pulmonary as well as the aortic valve leaflets are reported. Both cases showed additional cardiac malformations. Case 1, with all leaflets missing, also had double-outlet right ventricle, hypoplastic left ventricle, large ventricular septal defect, straddling tricuspid valve, and atretic mitral valve. Case 2, with only one hypoplastic aortic valve leaflet, showed hypoplasia of the mitral valve and the left ventricle, and a subaortic ventricular septal defect. The observations made and data in the literature suggest that aplasia of semilunar valve leaflets reflects an underdevelopment of the endocardial cushion swellings at the ventriculoarterial junction, rather than resulting primarily from a malseptation of the cardiac outflow tract.

The present study analyzes the composition and organization of the extracellular matrix (ECM) and its changes in the course of development of the chick embryo semilunar heart valves. In the present work we have employed chick embryos from stage 29 until hatching, using silver and picrosirius red staining, lectin probes and light and transmission electron microscopy. Our results show that during semilunar valve development a series of elements arise and are organized in the ECM which seem to be more closely related to the maintenance of the structural and biomechanical properties of the valvular leaflets than with morphogenetic processes per se.

Fetal in situ cardiovascular and bronchial morphologies were studied in rats with tetralogy of Fallot and absent pulmonary valve to clarify the prenatal pathology of this complex. There were 42 fetal rats with this complex among 300 fetuses treated with N,N'-bis-(dichloroacetyl)-1,8-octamethylenediamine (bis-diamine) (200 mg) on the 10th day of pregnancy. After undergoing rapid whole-body freezing on the 21st day, they were studied by means of serial cross-sectional photographs of the frozen thorax. Fetuses with normal heart treated with bis-diamine served as control. Tetralogy of Fallot and absent pulmonary valve in the fetus was associated with absence of the ductus arteriosus, enlargement and hypertrophy of both ventricles, and enlargement of the pulmonary arteries that compressed the bronchial trees. These abnormalities were inversely correlated with the degree of pulmonary stenosis. Milder stenosis (pulmonary valve ring greater than 50% of control, n = 28) was associated with larger pulmonary arteries (250 +/- 12% of control) (mean +/- SEM) and larger ventricles (volume, 200 +/- 15%; mass, 130 +/- 4%). Severe stenosis (pulmonary valve ring less than 50% of control, n = 14) was associated with mildly enlarged pulmonary arteries and mild bronchial compression. We concluded that enlargement of the pulmonary arteries and bronchial compression develop in fetal life and are associated with mild pulmonary stenosis in tetralogy of Fallot and absent pulmonary valve.

The quail-chick chimera method was used to examine whether neural crest cells were associated with the formation of semilunar valves. From the metencephalon to somite 5, or from the otocyst to somite 3, left, right, or bilateral neural folds, including the neural crest, were transplanted. Among embryos used for the experiment, three into which left neural crest cells were transplanted, two into which right neural crest cells were transplanted, and two into which bilateral neural crest cells were transplanted had a morphologically normal heart. In these embryos, neural crest cells were found in all cusps of the aortic and pulmonary semilunar valves. Although neural crest cells have been thought to have no association with the formation of the semilunar valves, our experiment indicates that such association indeed occurs.

Recent ultrastructural studies have revealed that differences exist in endothelial cell shape and cytoskeletal architecture between the arterial and ventricular faces of developing semilunar valves. In the present work we analyzed the morphologic response of the valvular endothelial cells of chick embryos to colchicine by light microscopy, scanning electron microscopy and transmission electron microscopy. The results show that colchicine administration during the stages of valve morphogenesis causes a very conspicuous disruption of the endothelial layer of the arterial face of the valves. The cells appear rounded and show massive surface blebbing. These alterations were not present in the endothelial cells on the ventricular face of the valves at the same stages. On the basis of these results we suggest that a difference in the degree of cell differentiation exists between the endothelial cells of the arterial and ventricular faces of the cusps and that this difference may have morphogenetic significance.

The developmental anatomy of human cardiac outflow was studied in a series of 16 normal embryos (gestational days 29-39, crown-rump length 6-20 mm, stages 14-19). Structural features and kinetics during truncal septation (TS) were described from external photographs, serial histological sections, and computer graphic reconstructions of selected tissues. Early in the period studied, the tubular myocardium ensheathed the single cardiac lumen and spiralling conotruncal ridges, which were filled with mesenchymal cells during days 31-33. As TS began (late stage 16), the aorticopulmonary (AP) septum appeared across the dorsal wall of the aortic sac between arches IV and VI. Mesenchymal condensations formed within the AP septum, crossing the lumen bifurcation to extend along the truncal ridges to the myocardium. During days 35-37, the cephalic margin of the myocardium grew or folded in toward these mesenchymal condensations between the developing valves and within the nearby conal ridges, which appeared to fuse to separate the subvalvular outflow channels by day 39. These observations are consistent with studies in chicks and rats which suggest that mesenchymal condensations or cell death foci interact with the distal myocardial rim during TS to form a structural septation complex dividing the two arterial streams.

A comparative study was made of the relative position of the outflow tracts of chicken and rat hearts with respect to the ventricles during septation. For this purpose the position of the left and right ventricular outlet including the aortic and pulmonary valve primordia and the left and right ventricle were established with respect to the midsagittal plane of the embryo, using reconstructions of serial sections of chicken (stage 28-30) and rat (stage 28-30) embryos. In the chicken embryo no rotation of the outflow tract occurs, i.e. the position of the aortic and pulmonary valve primordia with respect to the left and right ventricle remains the same. In the rat embryo a clockwise rotation of the aortic and pulmonary valve primordia with respect to the ventricles does occur. This is in fact a detorsion. The left and right ventricle and the left ventricular outlet do not show change in position with regard to the midsagittal plane. The left ventricular outlet always straddles the interventricular septum, both lying in the midsagittal plane. These interspecies differences in the degree of detorsion of the outflow channels before septation may explain the differences in the extent of the region of contact between the endocardial outflow tract ridges.

Pulsed wave Doppler estimates of blood flow velocity were made across the mitral, tricuspid, aortic, and pulmonary valves in a series of 120 normal fetuses (gestational age 16-36 weeks). In 36 of these the data were obtained in all four sites. The maximum and mean velocities were calculated for each valve and these values were plotted against gestational age. There was little change in these values throughout pregnancy. The orifice dimensions of the valves were measured by cross sectional echocardiography. At all ages the tricuspid orifice was larger than the mitral and the pulmonary orifice was larger than the aortic. The blood flow values for each valve were derived from the product of the mean velocity and the valve orifice dimensions. The output of the right ventricle was usually, but not always, greater than that of the left ventricle. Combined ventricular output increased from approximately 50 ml/min at 18 weeks to 1200 ml/min at term. Despite limitations in the accuracy of the technique these results form a useful basis for the analysis of blood flow in the normal fetus and for the interpretation of abnormal Doppler findings in prenatal life.

The combination of absent pulmonary valve with ventricular septal defect, subvalvular pulmonic stenosis and aneurysm of the pulmonary artery presents a characteristic heamodynamic and clinical profile. It should be differentiated from other morphologically related cardiovascular malformations. According to the degree of right ventricular outflow tract obstruction, the circulatory pattern and the clinical picture is varying widely. We are differentiating an obstructive and a congestive form of the disease. An own case is demonstrated. After a short review of the literature the clinical and haemodynamic findings are discussed. The important role of the ductus arteriosus in fetal circulation is emphasized. The development of a huge pulmonary aneurysm and the premature closing of the ductus arteriosus are considered to be secondary to the serious disturbance of fetal haemodynamics.

In order to trace tissue movements during septation of the embryonic truncus arteriosus into aortic and pulmonary cardiac outlets, the cephalic margin of the developing tubular heart of chick embryos was tattooed at Hamilton-Hamburger Stages 20-22 using diffusion micropipettes filled with 0.5% agarose and radioactive macromolecular precursors (tritiated thymidine, uridine, and leucine). Following further incubation for 2, 48, or 96 hours, the locations of such tattoos were determined by autoradiography of sectioned tissue and computer reconstruction of the developing outflow tract. Two hours after tattooing, radiolabeled cells were clustered at the right distal margin of the myocardial tube, as intended. Two days later, during septation of the outflow tract into the two arterial streams, label was concentrated along the posterior margin of the myocardium, between the developing aortic and pulmonary valve anlagen to the embryo's right and left, respectively. Four days following tattooing, as truncal septation neared completion, remaining label was found primarily to the left of the aortic valve ring posterior to the pulmonary outlet. The movements of thymidine tattoos during septation were demonstrated in a series of 31 embryos, 14 fixed at 2 hours, 12 at 2 days, and 5 at 4 days following tattooing; similar results were seen in uridine and leucine labeled hearts. The motion of such tattoos in the developing chick heart suggests that the left side of the definitive semilunar valve ring derives from the right distal margin of the primitive tubular heart and that normal morphogenesis of the great arterial streams involves both retraction and rotation of the embryonic truncus arteriosus.

The developmental changes of collagen and mucopolysaccharides in the semilunar values of the mouse were studied during the embryonic, fetal and postnatal period. The valvular collagen was investigated using Van Gieson and Sirius red-polarization microscopy methods. These procedures showed that the establishment of the fibrosa layer of the cusps does not occur until the second week of the postnatal period. The nature and distribution of the valvular mucopolysaccharides were investigated by staining with Alcian blue at specific pH values and at various critical electrolyte concentrations, with the appropriate enzymatic controls using Streptomyces and testicular hyaluronidase. The results show that hyaluronate and chondroitin 4- and 6-sulphate are the major components during the embryonic and fetal period. In the older fetal stages and during the postnatal period the relative amount of hyaluronate decreases, while chondroitin sulphate increases. It is concluded from this study that the maturation of the valves occurs over a long period of the postnatal life.