11 Ostium secundum defect

Dr. F Moler
Date: 1909
Size (H x W x D cm): 18 x 18 x 8

A 4 x 2 cm defect can be seen in the upper part of the inter-atrial septum (persistent ostium secundum). The aorta is narrowed (2.5 cm) and the atrium (* on back view, A) is dilated (diameter about 6 cm).

A. Click on image to enlarge.

History: 64 year old-woman. Unknown history except for “terminal cyanosis”.

Comment: In early development, the atria are recognizable as separate bulges as part of a common chamber. As they enlarge, a fold develops superiorly and extends inferiorly (the septum primum), eventually fusing with the endocardial cushions at the ventricular junction. This process continually narrows the inter-atrial communication, forming the ostium primum. Normally, the latter closes completely; however, before this occurs, the septum primum develops perforations which coalesce to form the ostium secundum, allowing blood to flow from the right to the left atrium.

As the atria continue to develop, a second fold (the septum secundum) is produced to the right of septum primum. When viewed from the side, this septum is concave in shape, with the anterior limb extending toward the atrioventricualr canal. The flap of tissue thus formed overlaps and partially closes the ostium secundum. The unformed portion of the septum secundum adjacent to the septum primum is the foramen ovale. After birth, with increased pulmonary blood flow and elevation of left atrial pressure, the septum primum is pushed against the septum secundum, effectively closing the ostium secundum. Fusion of the septum primum and the septum secundum completely closes the foramen ovale in most individuals. However, in about 10 - 15% of normal adult hearts, a probe can be passed from the right to the left atrium via the foramen ovale through the persistent ostium secundum (probe patent foramen ovale). Usually, this has no clinical consequence. However, if the pressure in the right atrium becomes greater than that in the left (e.g., secondary to pulmonary hypertension), a right to left shunt can develop.

An ostium secundum defect such as seen in this specimen occurs when there is excessive resorption of the septum primum or incomplete development of the septum secundum. Although compatible with life (as demonstrated by the age of the patient from whom this specimen originated), the communication can be associated with several complications, including pulmonary hypertension and right heart failure (secondary to a left to right shunt), dysrythmia (as a result of right atrial dilatation) and systemic (“paradoxical”) thromboemboli (resulting, for example, in stroke).

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