title: Development of the atrial septum in relation to postnatal anatomy and interatrial communications.
abstract: The atrial septum is probe patent in some 30% of the population, and is prone to have overt defects. Atrial septation is the coming together of several myocardial structures and mesenchymal tissues of intracardiac and extracardiac origin that must change identity to myocardium. We propose that the propensity for malformation of the atrial septum reflects this complicated morphogenesis. The morphogenesis of the atrial septum initiates from a ridge of mesenchyme, only a few hundred micrometres long, in the roof of the undivided atrial cavity. By growth of the myocardial primary septum, the mesenchymal ridge will be approximated to, and ultimately fuse, with the mesenchyme of the atrioventricular cushions. This fusion also takes in the so-called vestibular spine, and serves to close the primary atrial foramen. Interatrial communication is maintained by the development of perforations in the myocardial septum that will coalesce to produce the secondary foramen. Late in gestation, an infolding of the right atrial roof, previously identified as the secondary septum, will come to form the roof of the secondary foramen. Muscularisation of the mesenchymal ridge and vestibular spine serves to reinforce the attachment of the primary muscular septum to the atrioventricular insulating plane, with the muscularised components, and the cranial infolding, then producing the rims of the oval fossa as seen in the postnatal heart. We show that other lesions that produce the potential for interatrial shunting are outside the confines of the atrial septum, and hence are best considered as interatrial communications, rather than 'atrial septal defects'.
authors.affiliation: Department of Anatomy, Embryology & Physiology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Bjarke
authors.initials: B
authors.lastname: Jensen
authors.affiliation: Division of Pediatric Cardiology, Department of Pediatrics, University of Florida, Gainesville, Florida, USA.
authors.forename: Diane E
authors.initials: DE
authors.lastname: Spicer
authors.affiliation: Department of Cardiovascular Pathology, St George's Medical School, London, UK.
authors.forename: Mary N
authors.initials: MN
authors.lastname: Sheppard
authors.affiliation: Department of Cardiovascular Pathology, St George's Medical School, London, UK.|Institute of Genetic Medicine, Newcastle University, Newcastle-upon-Tyne, UK.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Anderson
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D054087:Atrial Septum / Q000196:embryology* / Q000503:physiopathology; D006344:Heart Septal Defects, Atrial / Q000196:embryology* / Q000503:physiopathology; D006439:Hemodynamics; D006801:Humans; D009024:Morphogenesis; D013045:Species Specificity; D013314:Stress, Mechanical