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Septal Pouch in the Left Atrium

A New Anatomical Entity With Potential for Embolic Complications

University of California at Irvine Medical Center, Orange, California

^_* Reprint requests and correspondence: Dr. Subramaniam C. Krishnan, Arrhythmia Services, University of California at Irvine Medical Center, 101 The City Drive, Room 100, Building 53, Orange, California 92868 (Email: krishnan{at}uci.edu).

Objectives: The purpose of this study was to develop a better understanding of the pathophysiology of the condition, we studied the patterns by which the septum primum (SP) and septum secundum (SS) fuse.

Background: A patent foramen ovale (PFO) is a communication across the interatrial septum between a nonadherent SP and SS and is considered to be a risk factor for serious clinical syndromes.

Methods: We examined the interatrial septum in 94 randomly selected autopsied hearts, with a focus on the SP and SS and the patterns by which the 2 structures fuse.

Results: Of the 94 specimens that were suitable for analysis, 26 (27.66%) had a PFO. Of the remaining 68 hearts, complete fusion of the SP and SS along the entire zone of overlap was seen in 27 (28.7%) hearts. In the remaining 41 hearts (60.29%), a PFO was absent, but incomplete fusion of the SP and SS was seen. Of 41 hearts, 37 (90%) had a septal pouch that opened into the left atrial (LA) cavity. Four hearts (10%) had a pouch accessible from the right atrium. Hearts with left-sided pouches tended to be younger (50 ± 18 years of age) than hearts where there was complete fusion (age 63 ± 23 years) (p = 0.06).

Conclusions: Our data suggest that when a foramen ovale closes spontaneously, the SP and SS fuse initially at the caudal limit of the zone of overlap of the 2 structures. This incomplete fusion results in a pouch that, in the majority of instances, communicates with the LA cavity.

Key Words: adhesions • autopsy • closure • patent foramen ovale • stroke

Abbreviations and Acronyms   IVC = inferior vena cava   LA = left atrium/atrial   LSP = left-sided pouch   PFO = patent foramen ovale   RA = right atrium/atrial   RSP = right-sided pouch   SP = septum primum   SS = septum secundum   TEE = transesophageal echocardiogram

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