The foramen ovale of the foetal and neonatal foal

Echocardiographic Features of the Ductus Arteriosus and the Foramen Ovale in a Hospital-Based Population of Neonatal Foals

Simple Summary

In fetal circulation, the distribution of oxygenated blood from the maternal placenta is facilitated by two intracardiac shunts. Oxygenated blood flows from the right atrium to the left heart through the foramen ovale, which is formed by the septum primum and septum secundum. Less oxygenated blood is directed to the placenta through the ductus arteriosus, which connects the pulmonary artery and the aorta. The ductus arteriosus and foramen ovale should close after birth. However, knowledge about the exact time of closure of those structures in foals is limited. The current study investigates the ultrasonographical closure of both the ductus arteriosus and the foramen ovale in healthy and diseased neonatal foals. Cardiac auscultation and ultrasound were performed on fifty foals. Cardiac murmurs were common, and in some foals, the ductus arteriosus was still open at ten days of age. The foramen ovale was not open; however, a fluttering motion of the septum primum into the left atrium was a common finding in healthy and diseased foals. The exact clinical importance of those findings needs to be further elucidated.

Abstract

The ductus arteriosus (DA) and foramen ovale (FO), including the septum primum (SP) and septum secundum (SS), are important structures in fetal circulation and are unexplored in neonatal equids. The objective of this study is to describe echocardiographic characteristics in a hospital-based population of neonatal foals. On days 2, 5 and 10 after parturition, cardiac ultrasound was performed, and clinical data were collected in healthy and diseased Warmblood foals. Fifty healthy (n = 15) and diseased (n = 35) Warmblood foals were examined. A left-sided and right-sided holosystolic murmur was audible in 98% (n = 42) and 51% (n = 22), respectively, on day 2; in 81% (n = 25) and 19% (n = 6) on day 5; and in 44% (n = 4) and 11% (n = 1) on day 10. The median grade of the systolic murmurs was higher when the DA was open. Flow through the DA could be visualized with color flow and continuous wave (CW) Doppler from the left parasternal long-axis view of the pulmonary artery in 40/43 foals on day 2, 9/31 foals on day 5 and 2/9 foals on day 10. The DA diameter was 2 ± 1 mm on day 2, 2 ± 1 mm on day 5 and 1 mm on day 10. The thickness of both septa of the FO was similar. The SP fluttered into the left atrium at all ages, but the maximal distance between the SP and SS decreased over time. In conclusion, cardiac murmurs, a patent DA and fluttering FO are frequent findings in neonatal foals. While these findings are probably physiological, the clinical importance needs to be further elucidated.

Three‐dimensional and catheter‐based intracardiac echocardiographic characterization of the interatrial septum in 2 horses with suspicion of a patent foramen ovale

This case report describes the 2‐dimensional transthoracic (2D‐TTE), 3‐dimensional transthoracic (3D‐TTE) and intracardiac echocardiographic (ICE) characterization of the fossa ovalis region in 2 horses. The first case was presented for poor performance and showed an anechoic zone in the interatrial septum on 2D‐TTE. Based on 3D‐TTE a deepened fossa ovalis could be identified and using ICE the presence of an interatrial shunt could be excluded. The second case was referred for a cardiac murmur and the presence of turbulent flow in and around the interatrial septum on 2D‐TTE color flow Doppler. The complementary use of 2D‐TTE, 3D‐TTE, and ICE allowed detailed characterization of a patent foramen ovale, with evidence of a left‐to‐right shunt in a dorsocranial to ventrocaudal direction with limited hemodynamic implications. These 2 cases underline the feasibility of 3D‐TTE and ICE in horses and especially show the added value of ICE in a clinical setting.

Physiological development of the equine fetus during late gestation

In many species, the pattern of growth and physiological development in utero has an important role in determining not only neonatal viability but also adult phenotype and disease susceptibility. Changes in fetal development induced by a range of environmental factors including maternal nutrition, disease, placental insufficiency and social stresses have all been shown to induce adult cardiovascular and metabolic dysfunction that often lead to ill health in later life. Compared to other precocious animals, much less is known about the physiological development of the fetal horse or the longer-term impacts on its phenotype of altered development in early life because of its inaccessibility in utero, large size and long lifespan. This review summaries the available data on the normal metabolic, cardiovascular and endocrine development of the fetal horse during the second half of gestation. It also examines the responsiveness of these physiological systems to stresses such as hypoglycaemia and hypotension during late gestation. Particular emphasis is placed on the role of the equine placenta and fetal endocrine glands in mediating the changes in fetal development seen towards term and in response to nutritional and other environmental cues. The final part of the review presents the evidence that the early life environment of the horse can alter its subsequent metabolic, cardiovascular and endocrine phenotype as well as its postnatal growth and bone development. It also highlights the immediate neonatal environment as a key window of susceptibility for programming of equine phenotype. Although further studies are needed to identify the cellular and molecular mechanisms involved, developmental programming of physiological phenotype is likely to have important implications for the health and potential athletic performance of horses, particularly if born with abnormal bodyweight, premature or dysmature characteristics or produced by assisted reproductive technologies, indicative of an altered early life environment.

Evolution and Development of the Atrial Septum

The complete division of the atrial cavity by a septum, resulting in a left and right atrium, is found in many amphibians and all amniotes (reptiles, birds, and mammals). Surprisingly, it is only in eutherian, or placental, mammals that full atrial septation necessitates addition from a second septum. The high incidence of incomplete closure of the atrial septum in human, so-called probe patency, suggests this manner of closure is inefficient. We review the evolution and development of the atrial septum to understand the peculiar means of forming the atrial septum in eutherian mammals. The most primitive atrial septum is found in lungfishes and comprises a myocardial component with a mesenchymal cap on its leading edge, reminiscent to the primary atrial septum of embryonic mammals before closure of the primary foramen. In reptiles, birds, and mammals, the primary foramen is closed by the mesenchymal tissues of the atrioventricular cushions, the dorsal mesenchymal protrusion, and the mesenchymal cap. These tissues are also found in lungfishes. The closure of the primary foramen is preceded by the development of secondary perforations in the septal myocardium. In all amniotes, with the exception of eutherian mammals, the secondary perforations do not coalesce to a secondary foramen. Instead, the secondary perforations persist and are sealed by myocardial and endocardial growth after birth or hatching. We suggest that the error-prone secondary foramen allows large volumes of oxygen-rich blood to reach the cardiac left side, needed to sustain the growth of the extraordinary large offspring that characterizes eutherian mammals. Anat Rec, 302:32-48, 2019. © 2018 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

The Equine Neonatal Cardiovascular System in Health and Disease

The neonatal foal is in a transitional state from prenatal to postnatal circulation. Healthy newborn foals often have cardiac murmurs and dysrhythmias, which are usually transient and of little clinical significance. The neonatal foal is prone to infection and cardiac trauma. Echocardiography is the main tool used for valuation of the cardiovascular system. With prompt identification and appropriate action, dysrhythmias and other sequel to cardiac trauma can be corrected. With infection, the management and prognosis are driven by concurrent sepsis. Congenital disease represents an interesting diagnostic challenge for the neonatologist, but surgical correction is not appropriate for most equids.

Comparative anatomy of the foramen ovale in the hearts of cetaceans

The structure of the cardiac foramen ovale from 17 species representing six cetacean families, the Monodontidae, Phocoenidae, Delphinidae, Ziphiidae, Balaenidae and the Balaenopteridae, was studied using the scanning electron microscope. Eight white whale fetuses (Delphinapterus leucas) and a narwhal fetus (Monodon monoceros) represented the Monodontidae; one fetal and nine neonatal harbour porpoises (Phocoena phocoena) and a finless porpoise fetus (Neophocoena phocoenoides) represented the Phocoenidae; two white-beaked dolphin fetuses (Lagenorhynchus albirostris), four fetal and one neonatal Atlantic white-sided dolphins (Lagenorhynchus acutus), a Risso's dolphin fetus (Grampus griseus), two common bottle-nosed dolphin neonates (Tursiops truncatus), a female short-beaked common dolphin fetus (Delphinus delphis), four killer whale fetuses (Orcinus orca) and two long-finned pilot whale fetuses (Globicephala melas) represented the Delphinidae; two northern bottlenose whale fetuses (Hyperoodon ampullatus) represented the Ziphiidae; one bowhead whale fetus (Balaena mysticetus) represented the Balaenidae and five Common minke whale fetuses (Balaenoptera acutorostrata), one blue whale fetus (Balaenoptera musculus), nine fin whale fetuses (Balaenoptera physalus) and four humpback whale fetuses (Megaptera novaeangliae) represented the Balaenopteridae. The hearts of an additional two incompletely identified toothed and four baleen whale fetuses were also studied. In each species the fold of tissue derived from the cardiac septum primum and subtended by the foramen ovale had the appearance of a short tunnel or sleeve which was fenestrated at its distal end. In the toothed whales the tissue fold was tunnel-shaped with the interatrial septum as the floor whereas in baleen whales it was more sleeve-like. In toothed whales thin threads extended from the fold to insert into the interatrial septum whereas a network of threads covered the distal end of the sleeve in the baleen whales. Similar structures were present in the corresponding cardiac tissues of neonatal Hippopotamidae.

Comparative anatomy of the cardiac foramen ovale in the Pinnipedia

The structure of the cardiac foramen ovale from eight genera of pinnipeds was studied using the scanning electron microscope. Specimens were obtained from fetuses or neonates of the Californian sea lion (Zalophus californianus), Antarctic fur seal (Arctocephalus gazella), walrus (Obenus rosmarus), grey seal (Halichoerus gryphus), ringed seal (Phoca hispida), bearded seal (Erignathus barbatus), Weddell seal (Leptonychotes weddelli), and crabeater seal (Lobodon carcinophagus). In each species, the structure that permits oxygenated blood from the placenta flowing in the caudal vena cava to pass directly into the left side of the heart, the foramen ovale, when viewed from the terminal part of the caudal vena cava had the appearance of the entrance to a short tunnel. A thin fold of tissue, the developed remains of the septum primum, projected from the caudal edge of the foramen ovale into the lumen of the left atrium. It constituted about 75% of the inner surface of the tunnel, and was generally unfenestrated. The wall of the interatrial septum contributed the "floor." The distal end of the tunnel was straight-edged. In most cases the septum primum was long enough to cover the foramen ovale. The siting of pulmonary veins in the roof of the left atrium appeared to be such that drainage from them after birth would press the septum primum over the foramen opening, thereby functionally closing it. Collapses of the tunnel was seen in all the neonatal seals, and in the 1-month-old neonate the fold of tissue was anchored to the interatrial septum along the surface of the crista dividens, which lay in the left atrium. Cellular protrusions and thread formation may play a role in the closure of the foramen ovale.

Comparative anatomy of the foramen ovale in the Suina

The structure of the foramen ovale from six species of Suina was studied using the scanning electron microscope. In each species, the foramen ovale, when viewed from the terminal part of the caudal vena cava had the appearance of a short tunnel. In the domestic pig (Sus scrofa), the wart hog (Phacochoerus aethiopicus) and the bush pig (Potamochoerus porcus) a fold of tissue projected from the caudal edge of the foramen ovale into the lumen of the left atrium. It constituted a large proportion of the tube, and its distal end was generally straight-edged. In some domestic pig hearts small holes were found in the fold, and single threads of tissue arose from its trailing edge. These were not found in specimens from the other pigs or from the collared peccary (Tayassu tajacu), which had a thin unfenestrated tissue fold ending in a straight edge. In both species of hippopotamidae, the hippopotamus (Hippopotamus amphibius) and the pigmy hippopotamus (Choeropsis liberiensis) the fold of tissue was tubular, with strands of tissue extending from the atrial wall to insert on the outer surface of its proximal half. This tube was orientated at an angle of approximately 90 degrees to the caudal vena cava. Its walls were unfenestrated proximally and fenestrated distally, the latter forming a network over the end of the tube. The knotted appearance of the fold after birth suggested that the strands of the network had shortened and coalesced.