Septal Thrombus in the Left Atrium: Is the Left Atrial Septal Pouch the Culprit?

Abstract

N S I B L E for more than 20% of all ischemic strokes. The examination of atrial sources of cardioembolic strokes has focused almost exclusively on the left atrial appendage (LAA) and the pathophysiology of thrombus formation at this site is well understood. However, especially in rheumatic heart disease, thrombi can occur in the left atrium (LA) outside the appendage a significant proportion of the time with poor understanding of the underlying mechanism. We present 3 patients in whom a thrombus was seen adherent to the septal LA. The probable underlying pathophysiology and the relationship to a recently described novel atrial structure, the left atrial septal pouch (LASP) (Fig. 1) that has the potential to be a site of stasis with thromboembolic complications, is discussed (1). Figure 1. Examples of LASP(A) Autopsy example of the left atrial septal pouch (LASP). A probing rod is inserted into the blind pouch that opens into the left atrial cavity. In our autopsy study, a LASP was seen in 37 of 94 hearts examined, with an average depth of 8.3 Ϯ 3.5 mm (1). Subsequent studies with transesophageal echocardiograms (B) and computed tomography angiograms (C) revealed the LASP to be present in about 30% to 35% of individuals with a depth similar to the autopsy study. The pouch is felt to represent an incomplete closure of the foramen ovale where fusion between the septum primum and secundum is limited to the caudal portion of the zone of overlap.

Clinical Significance of Left Atrial Anatomic Abnormalities Identified by Cardiac Computed Tomography

“…Krishnan et al theorized that septal pouches, which have access to the systemic circulation, comparable to the left atrial appendage, may serve as a site for thrombus formation and embolization especially during low flow states [5]. In fact, thrombi originating from aberrant spaces within the interatrial septum have been implicated in individual case reports of patients with coronary emboli and TIA [18]- [20]. Thrombi within accessory left atrial appendages and diverticula have been described in previous case reports as well [10] [13] [17].…”

“…Recently, ectopic fibrillatory activity and thrombus has been described in patients with accessory appendages and diverticula [10] [13] [16] [17]. Septal pouches, given their blind end morphology, have been implicated in case reports of thromboembolic disease as well as arrhythmia [5] [18]- [20].…”

Patent foramen ovale with right atrial septal pouch

“…A left atrial septal pouch (LASP), which has its base opening into the left atrium, was described to have a potential to form thrombi and cause embolic events [5,6]. However, Tugcu et al reported a lack of association between the presence of a LASP and ischemic or cryptogenic stroke [7].…”

Thromboembolic stroke with concurrent left atrial appendage and left atrial septal pouch thrombus

“…It is thought to represent an incomplete closure of the foramen ovale where the fusion line between the septum primum and secundum is limited to the caudal area of the overlapping zone, resulting in a blind recess with no communication into the right atrium. Its continuity with the left atrium is thought to make a LASP a potential site for thrombus formation, and a potential cause for thromboembolic events [6].In the case presented, due to severe left atrial dysfunction and stasis, it is likely that the thrombus, wholly contained within the LASP without extension into the right atrium, formed in-situ rather than having transited from another location such as the venous system. (S. Buchholz).…”

“…It is thought to represent an incomplete closure of the foramen ovale where the fusion line between the septum primum and secundum is limited to the caudal area of the overlapping zone, resulting in a blind recess with no communication into the right atrium. Its continuity with the left atrium is thought to make a LASP a potential site for thrombus formation, and a potential cause for thromboembolic events [6].…”