Excursion index of the septum primum as a parameter for diastolic function assessment of Thai fetuses: at 32 to 35 weeks' gestation

OBJECTIVE

To establish the normal value of fetal diastolic function by the measurement of the excursion index of the septum primum (EISP) from 32 to 35 weeks' gestation in Thai fetuses.

MATERIAL AND METHOD

Fetuses of normal Thai pregnant women were recruited for 2-dimensional echocardiographic measurements of the EISP (the ratio between the linear displacement of the flap valve and the left atrial diameter) from 32 to 35 weeks' gestation. All had a confirmed gestational age, normal structural scanning, and negative diabetic screening at 24 to 28 weeks' gestation. The 5th, 50th and 95th percentile of the EISP were demonstrated The relationship between the EISP and gestational age were determined

RESULTS

Three hundred twenty-seven measurements were obtained The normal values of the EISP according to gestational age were presented as 5th, 50th, and 95th percentile ranks. The correlation coefficients (r) between the EISP and gestational age were 0.03. The EISP were not statistically different with advancing gestation. The 5th, 50th, and 95th of the EISP were 0.32, 0.45, and 0.59 respectively. The intra-observer variability was 5.5%.

CONCLUSION

The normal values of fetal EISP in the Thai population from 32 to 35 weeks' gestation were established This could serve as a baseline data in detection of the alteration of left ventricular diastolic function during fetal life.

Atrioventricular valve development during late embryonic and postnatal stages involves condensation and extracellular matrix remodeling

Although the signaling molecules regulating the early stages of valvular development have been well described, little is known on the late steps leading to mature fibrous leaflets. We hypothesized that atrioventricular (AV) valve development continues after birth to adjust to the postnatal maturation of the heart. By doing a systematic analysis of the AV valves of mice from embryonic day (E) 15.5 to 8 weeks old, we identified key developmental steps that map the maturation process of embryonic cushion-like leaflets into adult stress-resistant valves. Condensation of the mesenchymal cells occurred between E15.5 and E18.5 and was accompanied by increased cellular proliferation and adhesion. Cellular proliferation also contributed transiently to the concomitant elongation of the leaflets. Patterning of the extracellular matrix (ECM) proteins along the AV axis was achieved 1 week after birth, with the differentiation of two reciprocal structural regions, glycosaminoglycans and versican at the atrial side, and densely packed collagen fibers at the ventricular side. Formation and remodeling of the nodular thickenings at the closure points of the leaflets occurred between N4.5 and N11.5. In conclusion, AV valve development during late embryonic and postnatal stages includes condensation, elongation, formation of nodular thickenings, and remodeling of tension-resistant ECM proteins.

Interventricular septal thickness of Thai fetuses: at 32 to 35 weeks' gestation

OBJECTIVE

To establish the normal value of fetal InterVentricular Septal Thickness (IVST) from 32 to 35 weeks' gestation in Thai fetuses.

MATERIAL AND METHOD

Thai pregnant women with normal fetuses were recruited for prenatal 2-dimensional M-mode echocardiographic measurements of fetal IVST at 32 to 35 weeks' gestation. All had a confirmed gestational age, normal structural scanning and negative diabetic screening at 24 to 28 weeks 'gestation. The IVST was measured from the 4-chamber view during diastole and systole. The 5th, 50th and 95th percentile of the IVST during Diastole (IVSD) and the IVST during Systole (IVSS) were demonstrated The relationship between the IVSD and IVSS and gestational age were determined

RESULTS

A total of 410 measurements were obtained. The normal values of the IVSD and IVSS according to gestational age were presented as 5th, 50th and 95th percentile ranks. The correlation coefficients (r) between the IVSD and IVSS and gestational age were 0.11 and 0.12, respectively. The IVSD and IVSS were not statistically different with advancing gestation. The 95th, percentile of the IVSD was 4.51 millimeters (mm) (range = 4.26 to 4.74 mm) and IVSS was 6.23 mm (range = 5.96 to 6.68 mm). The intraobserver variability was 7.6%.

CONCLUSION

The normal values of fetal IVSD and IVSS in a Thai population from 32 to 35 weeks' gestation were established. This could be used as a baseline data in detecting the asymmetrical septal hypertrophy during fetal life.

Morphogenetic differences of secundum atrial septal defects

It is generally considered that the development of secundum atrial septal defect (ASDII) or oval fossa defect is the result of excessive resorption of the embryological atrial septum primum, but this does not seem to explain all defects. We investigated 58 postmortem hearts with an ASDII and 22 normal hearts from patients ranging in age from 1 day to 49 years. The different structures of the oval fossa were examined. In 86% of the specimens, the defects were the result of a malformation of the valvula foraminis ovalis or embryological atrial septum primum, and in 14% an absent superior limbus (septum secundum) was the cause of the interatrial communication. The "septum primum" ASDs were divided into four subgroups based on the degree of deficiency of the septum primum and position of the ostium secundum within the septum primum. We conclude that the morphogenesis of ASDII is variable and both septum primum and septum secundum defects occur, which may be relevant in view of genetic studies that may lead to further differentiation of patients with and without genetically determined ASDIIs.

Development of the human pulmonary vein and its incorporation in the morphologically left atrium

OBJECTIVE

Using a newly acquired archive of previously prepared material, we sought to re-examine the origin of the pulmonary vein in the human heart, aiming to determine whether it originates from the systemic venous sinus ("sinus venosus"), or appears as a new structure draining to the left atrium. In addition, we examined the temporal sequence of incorporation of the initially solitary pulmonary vein to the stage at which four venous orifices opened to the left atrium.

METHODS

We studied 26 normal human embryos, ranging from 3.8 mm to 112 mm crown-rump length, and representing the period from the 12th Carnegie stage to 15 weeks of gestation.

RESULTS

The pulmonary vein canalised as a solitary vessel within the mediastinal tissues so as to connect the intraparenchymal pulmonary venous networks to the heart, using the regressing dorsal mesocardium as its portal of cardiac entry. The vein was always distinct from the tributaries of the embryonic systemic venous sinus. The orifice of the solitary vein became committed to the left atrium by growth of the vestibular spine. During development, a marked disparity was seen between the temporal and morphological patterns of incorporation of the left-sided and right-sided veins into the left atrium. The pattern of the primary bifurcation was asymmetrical, a much longer tributary being formed on the left than on the right. Contact between the atrial wall and the venous tributary on the left initially produced a shelf, which became effaced with incorporation of the two left-sided veins into the atrium.

CONCLUSIONS

The initial process of formation of the human pulmonary vein is very similar to that seen in animal models. The walls of the initially solitary vein in humans become incorporated by a morphologically asymmetric process so that four pulmonary veins eventually drain independently into the left atrium. Failure of incorporation on the left side may provide the substrate for congenital division of the left atrium.

Clinical anatomy of the atrial septum with reference to its developmental components

Knowledge of development is of crucial importance and can help clarify mechanisms of maldevelopment, but it must be properly validated. Concepts of development must be consistent with the anatomy seen in postnatal life. Such consistency is not always achieved. We have reviewed new and old accounts of cardiac embryology with regard to the definitive structure of the atrial septum. The key to understanding is to distinguish between folds of the atrial wall and true interatrial partitions. The flap valve of the oval foramen, and its inferior rim, are true septal structures, whereas the other rims, particularly the antero-superior rim, are infoldings enclosing extracardiac fat. During embryonic life, the systemic venous tributaries must achieve entrance only to the right side of the primary atrium. Development of the pulmonary venous component is a late event, with the canalizing vein using the dorsal mesocardium to gain access to the left side of the atrium. Once the systemic venous tributaries have achieved their rightward shift, the primary septum, together with the mesenchymal cap, grows between the systemic and pulmonary venous orifices. Closure of the primary foramen is achieved by fusion of the mesenchymal cap of the primary septum with the atrioventricular endocardial cushions and the vestibular spine (an additional mesenchymal structure carried on the right side of the pulmonary venous orifice). The superior margin of the newly formed secondary foramen is produced by an infolding of the atrial walls. Historically these mechanisms received appropriate recognition, but not all receive their proper due in current writings.

Atrial septal defect in cyanotic CL/Fr mice

OBJECTIVE

It is widely known that some newborn CL/Fr mice with cleft lip and palate (CLP) also have cyanotic symptoms, which have been thought to depend on an atrial septal defect (ASD). In a previous study, we found that cyanotic mice tended to have more severe types of CLP. We hypothesize that the mechanical airway obstruction due to a poorly developed palatal shelf and unmoved tongue in CLP(+) mice might be related to the occurrence of cyanosis. The purpose of this study was to examine the relationships between ASD and cyanosis in CLP(+) newborns.

METHOD

The newborn hearts from CLP(-), noncyanotic CLP(+), cyanotic CLP(+), CL/Fr mice and ICR mice were examined histologically, and the incidence and size of ASD was determined on neonatal day (ND) 0. In CLP(-) newborns, similar procedures were performed from ND 1 to ND 4. Furthermore, in CLP(+) newborns, development of the palatal shelf was examined.

RESULTS

While all the ICR mice had a well-developed atrial septum, and the incidence of ASD was 0%, about 80% of CL/Fr mice had ASD, irrespective of the presence or absence of CLP and cyanosis. On ND 0, the septum primum was significantly shorter in cyanotic CLP(+) mice than in CLP(-) mice. It also tended to be shorter in CLP(+) mice than in CLP(-) mice. Between the cyanotics and noncyanotics, there were no significant differences in the incidences of ASD and the rate of septal development. In CLP(-) mice, the septum primum developed well later and no ASD was observed on ND 4. Cyanotic newborns had significantly less developed palatal shelves than did noncyanotics.

CONCLUSIONS

Cyanosis may not be related to ASD and the rate of septal development, but may be related to the occurrence of CLP in this strain. Furthermore, we confirmed that some relationship exists between the development of the palatal shelf and cyanosis. The present study supports our hypothesis concerning the cause of cyanosis in CL/Fr mice.

Mobility of the flap valve of the primary atrial septum in the developing human fetus

It has already been suggested that redundancy of the primary atrial septum could be associated with primary fetal arrhythmias. There are few reports, however, concerning the mobility of the primary septum and its behavior during fetal life. In this study, fifteen fetuses without anatomic heart disease were serially evaluated by fetal echocardiography. The time interval between three separate examinations was at least two weeks. A redundancy index was calculated as the ratio between the maximum excursion of the flap valve of the septum and the maximal left atrium as seen in a four chamber view. The indexes observed in the three examinations were: 0.55 +/- 0.15, 0.48 +/- 0.13 and 0.41 +/- 0.13, respectively. Analysis of variance for normal distribution and Tukey's test were performed. A significant decrease (p < 0.05) in the redundancy index was observed with increasing gestational age. We postulate that this finding may be related to the decrease in frequency of premature atrial beats throughout fetal life.

Changes in left ventricular diastolic filling patterns before and after the closure of the ductus arteriosus in very-low-birth weight infants

To evaluate serial changes in left ventricular diastolic filling patterns in preterm infants, we performed echocardiographic examinations in 18 very-low-birth weight infants and 20 fullterm infants before and after the closure of the ductus arteriosus. In the fullterm infants, the ductal closure induced significant decreases in the peak velocity and flow velocity integral of early diastole, first third filling fraction, and mitral stroke volume. In the preterm infants, by contrast, there were significant increases in the flow velocity integral of early diastole, first third filling fraction, and mitral stroke volume after the ductal closure. No differences following the ductal closure were found in the atrial phase of filling and peak filling rate normalized to stroke volume in either group. When the ductus arteriosus was open, essentially the same left-to-right shunting of the ductus arteriosus was detected in both preterm and fullterm infants, but the Doppler flow patterns of the patent foramen ovale were different: the fullterm infants had a single flow peak mainly during ventricular late systole and early diastole, but the preterm infants had two or three flow peaks with nearly equal amplitudes lasting from ventricular systole to diastole, which resembled the Doppler flow pattern of atrial septal defect. Only a faint Doppler flow signal of the foramen ovale was observed after the ductus arteriosus closed. Our results obtained from the preterms suggest that the left-to-right shunt through the foramen ovale may be one important factor to alter the Doppler transmitral filling patterns during the fetal to neonatal cardiovascular changes.

The anatomy of the heart revisited

BACKGROUND

There is a marked conservative tendency to be found in anatomic descriptions, with a seeming reluctance on the part of acknowledged experts to test new theories by returning to direct studies of gross anatomy. This tendency has become manifest to us during recent attempts to review the structure and function of the heart.

METHODS

We have reviewed our recent experience in trying to describe the structure and development of the atrial septum and arterial roots, attempting at the same time to establish the place of semantic as opposed to morphologic factors in disagreements on these topics.

RESULTS

Dissection of the structures separating the right atrium from the left atrium shows a fundamental difference between the infolded superior rim of the oval foramen, made up of the atrial walls, versus the make up of the sinus and atrioventricular septums, which are true septal structures. Analysis of the arterial roots shows that the major feature is the semilunar attachment of the valvar leaflets, an arrangement not ideally described in terms of an annulus.

CONCLUSIONS

Understanding of details of cardiac anatomy, as set out in standard textbooks, is hindered by a reluctance on the part of some to accept material presented on the basis of straightforward gross dissection. Instead, there is a seeming desire to depend on conventional wisdom, often unsupported by anatomic fact. Such controversies can be ameliorated by appropriate recognition to contributions of gross morphology and by using simple words to describe the observed anatomic features.

In situ morphology of the foramen ovale in the fetal and neonatal rat

In situ cross-sectional morphology of the foramen ovale was studied after rapid whole-body freezing of the fetal and neonatal rat. In the fetus, the foramen ovale was open widely toward the left atrium with a thin, short primum septum. The opening area of the foramen ovale was 40% of the cross-section of the thoracic inferior vena cava, and the ratio of the long diameter to the short diameter was 2 to 1. After birth, the primum septum became longer, thicker, and straighter, with less leftward bowing. The opening of the foramen ovale diminished in the first 2 d and closed completely 3 d after birth. Postnatal thickening of the primum septum was very remarkable, increasing by 400% in the first 2d, while only minimal change was noticed in the right and the left atrial walls. The length of the primum septum was short and was only 90% of the diameter of the fossa ovalis in the fetus. It increased and reached 97% and 111% of the diameter of the fossa ovalis 1 and 2 d after birth, respectively. The septum secundum also grew rapidly after birth, and its length and width increased by 40% and 29% after 1 and 2 d, respectively. These observations indicate a sudden, explosive growth of the atrial septum in the early neonatal period in the rat.

Perinatal adaptation of the cardiovascular system

The perinatal changes in the cardiovascular system were studied in fetal rats. The changes in the cardiovascular system occurred earlier than in humans. The ductus arteriosus closes in the rat in one and a half hours.

Bulboventricular foramen size in infants with double-inlet left ventricle or tricuspid atresia with transposed great arteries: Influence on initial palliative operation and rate of growth

Bulboventricular foramen obstruction may complicate the management of patients with single left ventricle. Bulboventricular foramen size was measured in 28 neonates and infants greater than 5 months old and followed up for 2 to 5 years in those patients whose only systemic outflow was through the foramen. The bulboventricular foramen was measured in two planes by two-dimensional echocardiography, its area calculated and indexed to body surface area. One patient died before surgical treatment. The mean initial bulboventricular foramen area index was 0.94 cm2/m2 in 12 patients (Group A) in whom the foramen was bypassed as the first procedure in early infancy. The remaining 15 patients underwent other palliative operations but the bulboventricular foramen continued to serve as the systemic outflow tract. There was one surgical death. Six (Group B) of the 14 survivors developed bulboventricular foramen obstruction during follow-up (mean initial bulboventricular foramen area index 1.75 cm2/m2). The remaining eight patients (Group C) did not develop obstruction during follow-up and had an initial bulboventricular foramen larger than that in the other two groups (mean initial bulboventricular foramen area index 3.95 cm2/m2). All patients with an initial bulboventricular foramen area index less than 2 cm2/m2 who did not undergo early bulboventricular foramen bypass developed late obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)

[Single ventricle and malposition of the dorsal part of the interampullary septum. Experimental study on the chick embryo heart]

After the blood has passed through the atrioventricular orifice or orifices or the atrioventricular canal when present, it is distributed to the ventricular ampullae. This distribution depends on the position of the dorsal component or dorsal horn of the interampullary septum with respect to the atrioventricular canal. The position of dorsal horn seems itself to depend on unequal or differential growth of the basal part of the ventricular ampullae. This has been demonstrated by the results, selectively destroying myocardial tissues by cauterisation: "high" cauterisation of the dorsal side of the right ampulla leads to the formation of a single ventricle of the left type; "high" cauterisation of the left side of the left ampulla leads to the formation of a single ventricle right type. In the first case, the dorsal component remains too far to the right, and, in the second, too far to the left. This differential growth which is exaggerated in these cases, also occurs in normal development. The right ampulla seems to be dominant with respect to the left and is responsible for the normal position of the dorsal horn to the left of the right atrioventricular orifice.

Great vessel, cardiac chamber, and wall growth patterns in normal children

The purpose of this study was to establish normal echocardiographic measurements of valvular motion, cavity dimensions, great vessel diameters, and right, left and septal wall thicknesses of children ranging in size from infants to full growth. The study group was composed of 205 normal, healthy children for whom echocardiograms and subsequent measurements were performed in a standardized manner. The following measurements were performed: left ventricular end-diastolic and end-systolic dimension, right ventricular end-diastolic cavity dimension, right ventricular end-diastolic anterior wall thickness, left ventricular end-diastolic posterior wall thickness, ventricular septal end-diastolic thickness, maximal left atrail dimension, end-diastolic aortic and pulmonary artery diameter, end-diastolic cardiac and septal depth, maximal aortic leaflet separation, and maximal anterior mitral and anterior tricupsid amplitude. Data are grouped into the fifth, fiftieth, and ninety-fifty percentiles according to body surface area. These graphs allow measurements of a single patient to be compared to normal measurements of individuals with similar body surface area.