Atrial situs refers to the relative position of the cardiac atria in relation to abdominal viscera and the midline.
Identification of atrial situs is an important initial step in the antenatal and postnatal diagnosis of cardiac structural and situs anomalies.
Basic determination of situs relies on the ability to discriminate right and left atria, which depends on the morphologic characteristics of the atria and other features including the:
- internal and external anatomy of the atrial appendages
- connections of systemic and pulmonary vascular systems to the heart
- anatomy of the interatrial septum
Out of these features, the most reliable method is the morphologic characteristic differences between the right and left atria.
- connections: superior and inferior vena cavae
- crista terminalis: it is a smooth thickened muscular structure which represents junction between sinus venosus and developing heart
- right atrial appendages: triangular or pyramidal shaped and broad-based; it contains pectinate muscles extending towards the atrioventricular valve
- see: normal anatomy of the left atrium
- 1. Wolla CD, Hlavacek AM, Schoepf UJ et-al. Cardiovascular manifestations of heterotaxy and related situs abnormalities assessed with CT angiography. J Cardiovasc Comput Tomogr. 2013;7 (6): 408-16. doi:10.1016/j.jcct.2013.11.008 - Free text at pubmed - Pubmed citation
- 2. Caruso G, Becker AE. How to determine atrial situs? Considerations initiated by 3 cases of absent spleen with a discordant anatomy between bronchi and atria. Br Heart J. 1979;41 (5): 559-67. doi:10.1136/hrt.41.5.559 - Free text at pubmed - Pubmed citation