Endocardial Cushions

Endocardial Cushion Component of the Septum

The Common Vein  Copyright 2008


The endocardial cushions are embryological precursors of the lower portion of the interatrial septum, the upper portion of the superior end of the interventricular septum, and portions of the mitral and tricuspid valves.

Structurally the epicentre of the endocardial cushions is at the crux of the heart, so that many structures can be affected when there is a disorder of the embryological tissue.

In the extreme of disease, known as a complete A-V canal defect, all the chambers of the heart are potentially connected and blood from any one of the chambers can flow to any one of the others.  In addition the conduction system is close by and so it is often affected by endocardial cushion defects.  The atrial septum can be affected in both the complete and the partial defects.  An isolated primum ASD affects the lowest portion of the atrial septum and usually affects the conduction system and left axis deviation ofn the EKG is characteristic.  Sometimes a cleft mitral valve is associated with the primum ASD.

The diagnosis is made clinically with ejection flow murmur, loud fixed P2, and occasionally a murmur of mitral regurgitation.  Echocardiography is the study of choice.

Treatment is surgical.

Atrial Septum

The drawing shows to better effect the 3 different tissues from which the interatrial septum arises.  Purple = sinus venosus, green = mesoderm (septum primum), and pink the endocardial cushhions.  Note that the endocardial cushions also contribute to the formation of the mitral and tricuspid valves as well as the interventricular septum.

01669b04  Davidoff drawing

Upper Middle and Lower Septal Regions of the Atrial Septum

The endocardial cushions (light pink) is a small but critical part of the atrial septum since it is at the crux of the heart and it contributes to many parts of the heart.

01653c11b05a04 Courtesy Ashley Davidoff MD copyright 2008 all rights reserved

Types of ASD’s

The drawing shows the interatrial septum and the defects associated with each of the components. Image a shows a single defect in the septum primum and this is called an ASD secundum, or a secundum ASD. This is the most common ASD. The second image (b) shows an A-V canal defect in green and it is in the lower portion of the septum and is commonly associated with a cleft mitral valve. The third and least common defect is the sinus venosus defect. (purple)

heart inteatrial septum ASD atrial septal defect secundum ASD primum ASD ASD of the sinus venosus type congenital Davidoff art copyright 2008 all rights reserved 01685c02.8