Atrial Septum – Development

The atrial septum is responsible for the initial division of the primitive atrium into the left and right atria. The steps of development are as follows:
1. The septum primum begins to grow toward the atrioventricular (AV) cushions. The orifice (ie, ostium) between the leading edge of the septum primum and the AV cushions is termed the ostium primum (aka foramen primum). The ostium primum is obliterated when the septum primum reaches the AV septum.
2. The ostium secundum (aka foramen secundum) is formed as tissue degenerates in the superior septum primum.
3. The septum secundum forms alongside the right edge of the septum primum.
4. The septum secundum contains the foramen ovale, which allows blood to be shunted from the right atrium (RA) to the left atrium (LA) during fetal life. The septum primum to the left of the septum secundum helps act as a one-way valve for right-to-left flow. After birth, the increase in pressure in the LA causes the septum primum to close and fuse against the septum secundum, forming the mature interatrial septum.
An atrial septal defect (ASD) is an opening in the atrial septum, allowing blood to flow between the atria. The most common form is the ostium secundum type located in the region of the foramen ovale, which is due to excessive resorption of the septum primum or inadequate formation of the septum secundum. Patients are typically
asymptomatic until adulthood, but the clinical course depends on the size of the defect.
Classic signs of ASD include the following:
■ Wide, fixed splitting of S2: Normal splitting occurs because of increased right ventricle preload during inspiration that delays closure of pulmonary valve. In ASD, the right ventricle is always preload overloaded from the left-to-right shunt, and thus there is no increase in splitting during inspiration.
■ Pulmonic flow murmur due to increased flow across the pulmonary valve heard best in the second intercostal space along the left sternal border.

dr.Dukagjin Zeqiraj Author

Hello! I am Dukagjin Zeqiraj from Kosovo. I have finished Medical Faculty in Prishtina ( capital city of Kosovo). Now I live in Pristina and I work in QKMF Podujeve (family medicine center). Tel: +38344311154