Atrial Septal Defect (ASD) is a defect or hole in the wall separating the two upper receiving chambers (the right and left atriums) of the heart - see figure 2.1.
ASD is one of more common "hole in the heart" seen, and it can occur in isolation or in combination with other congenital heart defects. Cardiologists subclassify these defects according to their locations on the atrial septum. The secundum ASD is the more common defect to occur as an isolated lesion. It represents about 5 - 10% of all congenital heart defects seen and is more common in females than males.
Figure 2.1 On the left is a diagram of a heart with an atrial septal defect (ASD), compared to a normal heart on the right. Hover the mouse pointer over the diagram to see the description. LA - Left Atrium, RA - Right Atrium, LV - Left Ventricle, RV - Right Ventricle.
The left atrium is normally at a higher pressure than the right atrium. The atrial septal defect allows blood to flow from the left atrium to the right atrium. The blood shunted across the ASD is re-circulated back to the lungs. As seen in figure 2.2, some red blood returning from the lungs into the right upper heart chamber (right atrium) now can flow across the ASD to mix with the blue blood, which is then re-circulated to the lungs. Compare this to the normal heart in figure 2.3, where there is no ASD and no mixing of the red and blue blood.
Blood circulation in a heart with an ASD. Note some red blood now crosses the ASD to mix with the blue blood.
Blood circulation in a normal heart. Note that the red and blue bloods do not mix during circulation through the heart.
The effects of having "extra" blood flowing across the ASD into the right atrium and subsequently into the right ventricle and then re-circulated to the lungs are:
The degree to which these effects occur would depend on the size of the ASD and the amount of blood that is re-circulated back to the lungs. This can range from insignificant to severe.
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