Anatomic And Echocardiographic Overview

During embryological development, the right and left cardiac atria are formed with the growth of the atrial septum. This dividing wall between the atria originates with the growth of two separate septa: septum primum and septum secundum. The first to be formed is the septum primum, which grows from the superior aspect of the atria wall inferiorly, toward the enodcar-dial cushions between the atria and ventricles (Fig. 1A). In its normal development, the septum primum attaches to the endocardial cushions, with eventual resorption of the superior attachment. Concurrently, a second septum develops slightly to the right of the septum primum, with progressive growth from the superior aspect of the atrium toward the endocardial cushions, but does not reach or attach to this area. Therefore, when developed, the septum primum attaches inferiorly to the floor of the atrial cavity and the septum secundum superiorly to the roof the atria. Together, these two septa overlap to form the basis of the interatrial septum, between which the foramen ovale is formed (Fig. 1B). The foramen ovale is patent during development but normally closes

From: Contemporary Cardiology: Essential Echocardiography: A Practical Handbook With DVD Edited by: S. D. Solomon © Humana Press, Totowa, NJ

Ostium Secundum Interatriale

Fig. 1. (A) The first step in the formation of the interatrial septum is the growth of the primum septum. (B) Partial resorption of the primum septum leaves fenestrations that coalesce in the formation of a second interatrial connection—the ostium secundum. This occurs concurrently with the descent of a second septum—the septum secundum—to the right of the septum primum. Both septae fuse except in the region called the foramen ovale which permits oxygenated blood to bypass the fetal lungs and hence to the fetal systemic circulation.

Fig. 1. (A) The first step in the formation of the interatrial septum is the growth of the primum septum. (B) Partial resorption of the primum septum leaves fenestrations that coalesce in the formation of a second interatrial connection—the ostium secundum. This occurs concurrently with the descent of a second septum—the septum secundum—to the right of the septum primum. Both septae fuse except in the region called the foramen ovale which permits oxygenated blood to bypass the fetal lungs and hence to the fetal systemic circulation.

Fetal Atrial Septum Thickened

Fig. 2. The anatomic distribution of atrial septal defects. Four major types are described as shown.

Atrial Septal Defects

Fig. 2. The anatomic distribution of atrial septal defects. Four major types are described as shown.

shortly after birth when left-sided pressures exceed right and seal the two septa together.

ASDs form when the interplay of septal formation is deranged. Several forms of interatrial communication can therefore result. Four major ASDs can be classified and correspond to the anatomic region where the defect arises: secundum defect, primum defect, sinus venosus defect, and coronary sinus defect (Fig. 2). Occasionally, when the septum primum and secundum do not fuse after birth, a persistent orifice may be present, the so-called patent foramen ovale (PFO). This foramen can be physiologically patent with interatrial shunting in the direction of higher to lower pressure. Each of these congenital lesions of the atrial septum can be easily characterized by echocardiographic measures.

Transthoracic echocardiography is useful in the diagnosis and assessment of ASDs. Three main transthoracic views can be used to assess for ASDs in the majority of cases: (1) parasternal short axis at the level of the aortic valve, (2) apical four-chamber view, and (3) subcostal four-chamber view. In the apical four-chamber view, the atrial septum is a relatively deep structure and susceptible to echo signal dropout. Echolucency of this region should therefore be interpreted with caution without confirmation in other views or with color Doppler. Of these views, the subcostal four-chamber view may be most suited for the two-dimensional assessment of ASDs, as the ultrasound beam is most perpendicular to the septa in these views.

Table 1

ASD Types and Associated Cardiac Anomalies

Table 1

ASD Types and Associated Cardiac Anomalies

Type

Associated anomalies

Septum secundum

Atrial septal aneurysm

Septum primum

Cleft mitral valve

Sinus venosus

Anomalous pulmonary venous

Mole Removal

Mole Removal

Moles, warts, and other unsightly irregularities of the skin can be bothersome and even embarrassing. They can be removed naturally... Removing Warts and Moles Naturally! If you have moles, warts, and other skin irregularities that you cannot cover up affecting the way you look, you can have them removed. Doctors can be extremely expensive. Learn the natural ways you can remove these irregularities in the comfort of your own home.

Get My Free Ebook


Post a comment