A new dynamic 3D virtual methodology for teaching the mechanics of atrial septation as seen in the human heart

Abstract

Learning embryology remains difficult, since it requires understanding of many complex phenomena. The temporal evolution of developmental events has classically been illustrated using cartoons, which create difficulty in linking spatial and temporal aspects, such correlation being the keystone of descriptive embryology. We synthesized the bibliographic data from recent studies of atrial septal development. On the basis of this synthesis, consensus on the stages of atrial septation as seen in the human heart has been reached by a group of experts in cardiac embryology and pediatric cardiology. This has permitted the preparation of three-dimensional (3D) computer graphic objects for the anatomical components involved in the different stages of normal human atrial septation. We have provided a virtual guide to the process of normal atrial septation, the animation providing an appreciation of the temporal and morphologic events necessary to separate the systemic and pulmonary venous returns. We have shown that our animations of normal human atrial septation increase significantly the teaching of the complex developmental processes involved, and provide a new dynamic for the process of learning.

Figure 1

This sagittal section is from a human embryo of Carnegie stage 14, taken in a plane paralleling the so-called parasternal long axis section. It shows the initial location of the solitary pulmonary vein adjacent to the atrioventricular junction. Note the unfused cushions in the atrioventricular canal.

Figure 2

This frontal section, again from a human embryo, but at the early part of Carnegie stage 16, shows the primary atrial septum, with its mesenchymal cap, growing towards the superior endocardial cushion.

Figure 3

This section, again in the frontal plane, is from a human embryo in the later part of the 16^th Carnegie stage. The mesenchymal structures have fused, but the superior roof of the atrial component is flat (black line), with no evidence of formation of a “septum secundum”.

Figure 4

The cartoon shows a representation of the reconstruction made by His in the 19^th century to show the development of the “spina vestibule”, or vestibular spine.

Figure 5

This section comes from a human embryo after the completion of cardiac septation. It shows that formation of the superior interatrial fold is not possible until the pulmonary veins have migrated to the atrial roof. Note the muscularisation of the mesenchymal mass to form the antero-inferior buttress of the atrial septum.

Figure 6

This section is from an adult human heart, and shows that the so-called “septum secundum” is, in reality, a deep interatrial fold. It also shows the muscularised antero-inferior buttress.

Figure 7

Drawing of the storyboard in colour: The origins, forms, dimensions, spatial extension and the relationship in space and temporal changes between the different elements involved in the atrial septation are defined. In red: the primary atrial septum; in yellow: the vestibular spine; in blue: the atrioventricular endocardial cushions and the mesenchymal cap of the primary atrial septum and the mesenchymal tissue of the vestibular spine. A: anterior, P: posterior, S: superior, I: inferior.

Figure 8

Successive pictures showing the deformations of the shapes over time. A: anterior, P: posterior, S: superior, I: inferior.

Figure 9

The hypothesis used to explain atrial septation is designed as follows: the primary septum (in yellow) grows from the cranial part of the primary atrium, leaving a foramen distal to its leading edge called the primary foramen. The vestibular spine (in purple) enters the heart and grows towards the inferior atrioventricular cushion on the right side of the primary septum. A second partition, in brown, is produced by folding of the atrial roof. The primary foramen is closed by an expansion of tissue coming from the endocardial cushions, in white. The successive pictures are particularly relevant, permitting students to visualize the chronological and spatial changes that occur within the atrial chambers. A: anterior, P: posterior, S: superior, I: inferior.