Septal Pouch Research Articles

Abstract WP261: The Left Atrial Septal Pouch: A New Stroke Risk Factor?

Background: The left atrial septal pouch (LASP) is a common anatomic variant produced by the incomplete fusion of septa primum and secondum at the inter-atrial septum, thus creating a potential embolic source from an open flap or blind pouch in the left atrium. Our prior work demonstrated increased prevalence of LASP in cryptogenic strokes (Frontiers Neurology 3-24-15). The aim of the current study was to examine the prevalence of LASP in a separate, more recent group of stroke patients and control subjects who underwent transesophageal echocardiography (TEE). Methods: We examined consecutive TEE studies performed between July, 2011 and December, 2018 at UC Irvine Medical Center. Prevalence of LASP was determined in TEE studies referred for ischemic stroke or TIA (“stroke subjects”), and compared to LASP prevalence in patients undergoing TEE for other reasons (“control subjects”). Stroke subtyping was performed using TOAST (Trial of Org 10172 in Acute Stroke Treatment) criteria. Results: TEE studies were performed on 221 cerebrovascular cases and 164 control subjects. Age and sex were 57±1 years (mean±SE) and 53% male for stroke subjects, and 56±1 years and 62% male for control subjects. Prevalence of LASP was 24% (40/164) in control subjects, 17% (24/138) in non-cryptogenic stroke subjects, and 36% (30/83) in cryptogenic stroke subjects. LASP prevalence was significantly higher for cryptogenics compared to the other groups (p=0.007). There was no significant difference between LASP prevalence in controls vs non-cryptogenic stroke. Elimination from analysis of subjects with other inter-atrial septal abnormalities (ie, patent foramen ovale or atrial septal defect) did not significantly change results. Conclusions: These findings demonstrate an increased prevalence of LASP in cryptogenic stroke, confirming our prior published findings. Given the plausibility of LASP acting as a thromboembolic nidus, additional studies are needed to determine the generalizability of these findings and their therapeutic implications.

Prevalencia de septal pouch en una cohorte derivada para ecocardiograma transesofágico

Introduction: the interatrial septum defects are frequent. A new entity has recently been identified, known as septal pouch. Prevalence data in general population is scarce, and is estimated between 30%-50%. The role as a source of cardioembolism is unclear.Objectives: the primary objective is to determine the prevalence and characterize the septal pouch; secondarily to define the interobserver variability for the diagnosis.Material and methods: observational, descriptive and analytical study. Consecutive patients were recruited for transesophageal echocardiography between 4/20/2018 and 8/30/2018. Werecorded patronymic data, personal history of stroke, heart rate, and the reason for the study. The presence of septal pouch was defined and characterized as left-sided septal pouch or rigth-sided septal pouch; depth was measured, presence of thrombus inside and echocardiographic study measures were completed. The images were evaluated by two blind echocardiographers. The qualitative variables are presented in relative frequency (RF), the quantitative variables in median and interquartile interval. Chi square test was carried out. The reproducibility of the diagnosis of septal pouch was evaluated by Kappa index.Results: 50 subjects were included. The prevalence of septal pouch was 0.5 (RF), 0.46 left-sided septal pouch and 0.04 rigth-sided septal pouch. The interobserver Kappa index for diagnosis is 0.68, standard error 0.14, with 84% agreement. 14 subjects had stroke, in 9 of them septal pouch was diagnosed (chi square p=0.21); 18 patients had atrial fibrillation or flutter, half of them had septal pouch (chi square p=1).Conclusion: the prevalence of septal pouch was half of the population, predominantly the left-sided septal pouch, with good reproducibility in diagnosis. It is an underdiagnosed finding; further investigation is necessary to assess its relation to stroke.

Left-Sided Atrial Septal Pouch as a Risk Factor of Cryptogenic Stroke: A Systematic Review and Meta-Analysis

Background: Despite some evidence of left-sided septal pouch (LSSP) involvement in the pathogenesis of cardioembolic stroke, the question of LSSP clinical significance still remains unsolved. In this study, we aimed to determine the association between the LSSP presence and cryptogenic stroke using meta-analytical approach. Methods: We performed a systematic review of electronic databases for studies that compared the presence of LSSP in subjects with cryptogenic stroke and non-stroke control. Data were extracted and pooled into a meta-analysis. Results: Seven studies (400 cryptogenic stroke patients and 1,456 non-stroke controls) were included in the meta-analysis. A total of 138 LSSPs were identified among the cryptogenic stroke patients, with a pooled prevalence of 29.8% (95% CI 17.5–43.7%), and 268 LSSPs were identified in the non-stroke controls, with a pooled prevalence of 21.0% (95% CI 13.7–29.5%). After meta-analysis, the risk of cryptogenic stroke was higher in patients with an LSSP than in patients without LSSP (OR 1.52; 95% CI 1.15–2.00; p < 0.001). No significant heterogeneity was detected across the included studies (p > 0.05). Conclusion: Our meta-analysis demonstrated association between LSSP and cryptogenic stroke. In our univariate analysis, the risk of cryptogenic stroke is higher among patients with LSSP than in cases without the LSSP.

P6349Left-sided atrial septal pouch as a risk factor of cryptogenic stroke: a meta-analysis

P6349Left-sided atrial septal pouch as a risk factor of cryptogenic stroke: a meta-analysis

Cardiac computed tomography compared with two-dimensional transesophageal echocardiography for the detection and assessment of atrial septal pouches

The aim of this study is to compare the two-dimensional transesophageal echocardiography (2D-TEE) with multi-slice computed tomography (MSCT) and with autopsied material to evaluate the ability and precision of the imaging methods for the detection and assessment of septal pouch (SP). One hundred and fifty patients that underwent both 2D-TEE and MSCT and 50 autopsied human hearts were investigated. In MSCT, the interatrial septum was classified as a left SP in 37.3%, right SP in 3.3%, and patent foramen ovale (PFO) channel in 3.3%. In 2D-TEE, the interatrial septum was classified as a left SP in 39.3%, right SP in 11.3%, double SP in 4.7%, and PFO channel in 2.0%. The weighted kappa coefficient between MSCT and 2D-TEE in assessing the septum morphology was 0.59. The prevalence of the left SP is lower when it is evaluated by MSCT or 2D-TEE than by anatomical study, but this difference is insignificant (37.3% vs. 44.0%, p = 0.40, and 39.3% vs. 44.0%, p = 0.56, respectively). The prevalence of left SPs is lower when detected by MSCT or 2D-TEE than during autopsy, but the difference is statistically insignificant (37.3% vs. 44.0%, p = 0.40, and 39.3% vs. 44.0%, p = 0.56, respectively). Both 2D-TEE and MSCT are comparable techniques for detecting left-sided SPs with the insignificant lower prevalence of detecting left-sided SPs compared to autopsied material. However, TEE with the contrast seems to be superior over MSCT due to the possibility of unambiguous PFO channel detection. Therefore, TEE with contrast should be preferred over MSCT in the identification of left-sided SPs.

Left-Sided Atrial Septal Pouch is a Risk Factor for Cryptogenic Stroke

The atrial septal pouch is an anatomic variant of the interatrial septum. The morphology of the left-sided septal pouch (LSSP) may favor blood stasis and predispose to thromboembolic events. The aim of this study was to determine the association between LSSP presence and cryptogenic stroke. A total of 126 consecutive patients with cryptogenic stroke and 137 age-matched control patients without stroke were analyzed retrospectively. The presence and dimensions of LSSPs were assessed using transesophageal echocardiography. LSSP was present in 55.6% of patients with cryptogenic stroke and in 40.9% of those without stroke (P=.02). In univariate analysis, patients with LSSP were more likely to have cryptogenic stroke (odds ratio, 1.81; 95% CI, 1.11-2.95; P=.02). After adjusting for other risk factors using multiple logistic regression, the presence of an LSSP was found to be associated with an increased risk for cryptogenic stroke (odds ratio, 2.02; 95% CI, 1.19-3.41; P=.01). There were no statistically significant differences in size of the LSSP between patients with and those without stroke (P>.05). There is an association between the presence of an LSSP and an increased risk for cryptogenic stroke. More attention should be paid to clinical evaluations of LSSPs.

Mid-esophageal bicaval versus short-axis view of interatrial septum in two-dimensional transesophageal echocardiography for diagnosis and measurement of atrial septal pouches.

Recent studies suggest that the left-sided septal pouch (SP) may increase the risk of cryptogenic stroke and act as an arrhythmogenic substrate. The aim of this study was to compare two transesophageal echocardiography (TEE) projections of the interventricular septum: mid-esophageal bicaval and short-axis views toward evaluating their ability to detect SPs. A total of 146 patients with both bicaval and short-axis TEE views were included in this study. The presence of SPs was determined, and they were evaluated for morphology. Irrespective of TEE projection view, the left SP was detected in 74 cases (50.7%), right SP in 16 cases (11.0%), and double in one case (0.7%). Agreement between both projections occurred in 119 cases (81.5%) with a weighted kappa coefficient of 0.68 (good agreement). We detected more left SPs from the bicaval view compared to the short-axis view; however, the observed difference was statistically insignificant (72 vs 59, P=.13). The detection of right SPs was higher in the short-axis view, but also statistically insignificant (9 vs 13, P=.38). Bland-Altman analysis revealed a significant difference in the left SP depth with higher values in the bicaval than short-axis view (systematic difference=1.17mm, LoA: -4.88-7.22mm, P=.02, ICC=0.58). The mid-esophageal bicaval view should be preferable over mid-esophageal short-axis view of interatrial septum for the diagnosis and measurement of the left SP.

Porcine heart interatrial septum anatomy

BackgroundThe left-sided atrial septal pouch (SP), a recently re-discovered anatomical structure within the human interatrial septum, has emerged as a possible source of thrombi formation and a trigger for atrial fibrillation, thereby potentially increasing the risk for ischemic stroke. In many studies, the swine interatrial septum has been used as model of the human heart. Also, possible new strategies and devices for management of the SPs may first be tested in this pig model. Therefore, in this study, we aimed to evaluate swine interatrial septum morphology and to compare it with the human analog, especially in the light of SP occurrence. MethodsA total of 75 swine (Sus scrofa f. domestica) hearts were examined. The interatrial septum morphology was assessed, and SPs were measured. ResultsThe most common variant of the interatrial septum was smooth septum (26.6%) followed by the patent foramen ovale channel and right SP (both 22.7%). No left or double SPs were observed. In 28.0% of all cases the fold of tissue (left septal ridge) was observed on the left side of the interatrial septum in the location where the left-sided SP should be expected. The mean length of the patent foramen ovale channel was 7.1±1.5mm. The mean right SP depth was 6.3±2.2mm, and its ostium width and height were 5.8±1.2 and 5.3±1.6mm, respectively. ConclusionsThere are significant differences between human and porcine interatrial septum morphology that should be taken into account during experimental studies. The absence of the left SP in swine results in the inability to use porcine heart as an experimental model for left-sided SP management.

The left atrial septal pouch as a possible location for thrombus formation

The left atrial septal pouch as a possible location for thrombus formation

Left atrial accessory appendages, diverticula, and left-sided septal pouch in multi-slice computed tomography. Association with atrial fibrillation and cerebrovascular accidents

BackgroundThe aim of this study is to provide a morphometric description of the left-sided septal pouch (LSSP), left atrial accessory appendages, and diverticula using cardiac multi-slice computed tomography (MSCT) and to compare results between patient subgroups. MethodsTwo hundred and ninety four patients (42.9% females) with a mean of 69.4±13.1years of age were investigated using MSCT. The presence of the LSSP, left atrial accessory appendages, and diverticula was evaluated. Multiple logistic regression analysis was performed to check whether the presence of additional left atrial structures is associated with increased risk of atrial fibrillation and cerebrovascular accidents. ResultsAt least one additional left atrial structure was present in 51.7% of patients. A single LSSP, left atrial diverticulum, and accessory appendage were present in 35.7%, 16.0%, and 4.1% of patients, respectively. After adjusting for other risk factors via multiple logistic regression, patients with LSSP are more likely to have atrial fibrillation (OR=2.00, 95% CI=1.14–3.48, p=0.01). The presence of a LSSP was found to be associated with an increased risk of transient ischemic attack using multiple logistic regression analysis after adjustment for other risk factors (OR=3.88, 95% CI=1.10–13.69, p=0.03). ConclusionsIn conclusion LSSPs, accessory appendages, and diverticula are highly prevalent anatomic structures within the left atrium, which could be easily identified by MSCT. The presence of LSSP is associated with increased risk for atrial fibrillation and transient ischemic attack.

Double Interatrial Septum appearing as an Atrial Myxoma: A Case Report and Review of the Literature

ABSTRACT A double interatrial septum (DIS) is a rare finding during echocardiographic evaluation and can often be mistaken for other more common atrial anomalies. The interatrial cavity created by the septum creates a low-flow state that increases risk of thrombus formation and thromboembolic events. Transesophageal echocardiography (TEE) plays a vital role in accurate diagnosis as a DIS is often not seen during transthoracic echocardiography (TTE). In this case, we report a patient who presented for surgery with a preoperative diagnosis of an atrial myxoma, was instead discovered to have a DIS, and then subsequently underwent DIS resection without complication. We discuss the differential of a DIS, including an atrial septal pouch, cor triatriatum, atrial myxoma, and aneurysmal interatrial septum and the classic features of each anomaly for appropriate diagnosis and management. How to cite this article Wyrobek J, Brown CH IV, Kostibas MP, Mayer SA, Cameron DE, Hayanga HK. Double Interatrial Septum appearing as an Atrial Myxoma: A Case Report and Review of the Literature. J Perioper Echocardiogr 2017;5(1):16-20.

Atrial septal pouch — Morphological features and clinical considerations

BackgroundThe atrial septal pouch (SP) is a new anatomical entity within the interatrial septum. The left-sided SP may be the source of thrombus and contribute to ischemic stroke. The aim of this study was to provide a detailed morphometric description of the SP. MethodsTwo hundred autopsied hearts (23% deriving from females) with a mean age of 46.7±19.1years were investigated. We assessed the morphology of the interatrial septum. We obtained measurements and casts of the SPs, and we conducted histological staining of the left-sided SPs. ResultsPatent foramen ovale was observed in 25% of hearts. We found a left SP in 41.5%, right in 5.5% and a double SP in 5.5% of hearts. We found the patent foramen ovale (PFO) more often in younger hearts, and the SP and smooth septum were more prevalently found in older hearts (p=.0023). The mean volume of the left-sided SP was 0.31±0.11ml, which represented 13.6±9.4% (range: 3.1–44.9%) of the left atrial appendage volume. The SP shape resembled a cone or a cylinder with some smaller diverticula originating from the main body. The SP free wall was composed of two layers of endocardium, transverse muscle fibers and connective tissue. ConclusionsA left-sided SP was present in 47% of individuals. The SP arises as a result of PFO channel closure. The anatomy of left-sided SP may promote blood stasis and thrombus formation. The universal formula for SP volume was calculated.

The Left Atrial Septal Pouch as a Possible Risk Factor for Stroke.

The left atrial septal pouch (LASP) is formed by the caudal fusion of the area of overlap of the septum primum and the septum secundum, leaving an opening toward the left atrium. The association between LASP and stroke has not been validated by the previous studies. The prevalence of the LASP was determined in 223 ischemic stroke patients and 223 control subjects with other cardiac pathologies, in a monocentric retrospective case-control study design. Stroke subtypes were defined according to the modified TOAST criteria. The mean age was 66 ± 15, 54% males, with a high prevalence of cardiovascular risk factors. The prevalence of the LASP was 81 (18%), irrespective of age or pathology. The number of LASP was similar in the stroke and control groups (18% vs. 19%, P = 0.7), as well as in the cryptogenic stroke subgroup (16%, P = 0.6). LASP was not associated with ischemic stroke on univariate (OR = 1.095; 95% CI = 0.676-1.772; P = 0.7) and multivariate logistic regression analysis (OR = 1.004; 95%CI = 0.574-1.758, P = 0.98). There was no statistical association between LASP and cryptogenic stroke on univariate (OR = 1.26; 95%CI = 0.526-3.016; P = 0.6) or multivariate analysis (OR = 0.705; 95%CI = 0.193-2.577, P = 0.6). The association of LASP to AF, left ventricular dysfunction, and thrombophilia did not lead to a higher incidence of stroke (OR = 0.99; 95%CI = 0.37-2.66; P = 0.99). Our study did not show any association between LASP and ischemic stroke. A septal pouch was present in 18% of the population. Other associated risk factors need to be considered to incriminate the septal pouch as the etiology of a stroke.

Prevalence of atrial septal pouch and risk of ischemic stroke.

It has been postulated that atrial septal pouch (ASP) may favor the stasis of blood and predispose to thromboembolic complications. We sought to evaluate the prevalence of ASP, and its association with ischemic stroke. We retrospectively studied 500 patients, who underwent transesophageal echocardiography (TEE) due to clinical indications. Seventy two patients due to image quality, and 104 patients with atrial septal defect or PFO were excluded. The remaining 324 patients were included in the analysis. The depth of ASP was measured. ASP was detected in 98 patients [left side ASP (LASP) in 58 (59.2%), and right side ASP (RASP) in 40 (40.8%) patients]. LASPs were significant deeper than RASPs (10.1±5.2 vs 4.4±1.4mm, p<0.0001). Patient characteristics were categorized by the presence or absence of LASP. The age (61±12 vs 61±12), gender and stroke risk factors were no significant difference between patients with or without LAPS. Ischemic stroke occurred in 21 patients without LASP, 10 patients with LASP. The presence of a LASP was found to be associated with an increased risk of ischemic stroke, in either univariable analysis (17.2 vs. 7.9%, p=0.03; OR=2.43, 95% CI=1.1-5.5, p=0.033) or after adjustment for other stroke risk factors using multiple logistic regression analysis (OR=2.45, 95% CI 1.1-5.8, p=0.036). This study demonstrated evidence of association between LASP and ischemic stroke. Among 324 patients, the risk of ischemic stroke was twice more among patients with LASP than cases without LASP.

Left atrial septal pouch thrombus: A common pathology in an uncommon location

Left atrial septal pouch thrombus: A common pathology in an uncommon location

Anatomy of the true interatrial septum for transseptal access to the left atrium

Clinical anatomy of the interatrial septum is treacherous, difficult and its unfamiliarity can cause many serious complications. This work aims to create an anatomical map of the true interatrial septum. An appreciation of the anatomical situation is essential for safe and efficacious transseptal access from the right atrium to the left heart chambers. Examination of 135 autopsied human hearts (Caucasian) of both sexes (28% females) aged from 19 to 94 years old (47.0±18.2) with BMI=27.1±6.0kg/m2 was conducted. Focus was specifically targeted on the assessment of the fossa ovalis, patent foramen ovale (PFO), and right-sided septal pouch (RSP) morphology. Mean values of cranio-caudal and antero-posterior fossa ovalis diameters were 12.1±3.6 and 14.1±3.6mm, respectively. The fossa ovalis was situated an average of 10.1±4.4mm above the inferior vena cava ostium, 20.7±5.2mm from the right atrioventricular ring, and 12.6±5.2mm under the right atrium roof. Four types of fossa ovalis anatomy have been observed (smooth-56.3%, PFO-24.4%, RSP-11.9%, net-like formation-7.4%). The PFO mean channel length was 10.5±5.2mm. The tunnel-like PFO (channel length ≥12mm) was observed in 8.9% of specimens. The RSP was observed in 11.9% of specimens (with mean depth=6.3±3.8mm) and was directed apex upward in all observed specimens (may imitate the PFO channel). The fossa ovalis/interatrial septum surface area ratio was 18.3±9.0%. In conclusion: (1) An anatomical map of the interatrial septum from the right atrial side was presented. (2) The RSP may imitate the PFO channel. (3) The “true” interatrial septum represents only about 20% of the whole interatrial septum area. (4) There is wide variation in the location and geometry of the fossa ovalis. (5) We could distinguish four different types of the fossa ovalis area.

Incremental Value of Live/Real Time Three‐Dimensional over Two‐Dimensional Transesophageal Echocardiography in the Assessment of Atrial Septal Pouch

An atrial septal pouch (ASP) results from partial fusion of the septum primum and the septum secundum, and depending on the site of fusion, the pouch can be left-sided (LASP) or right-sided (RASP). LASPs have been described in association with thrombi found in patients admitted with acute strokes, raising awareness of its potential cardioembolic role, especially in those with no other clearly identifiable embolic source. We retrospectively studied 39 patients in whom the presence of an ASP had been identified by three-dimensional transesophageal echocardiography (3DTEE) and who had a two-dimensional transesophageal echocardiogram (2DTEE) performed during the same clinical encounter. The incremental value provided by 3DTEE over 2DTEE included the detection of six ASPs not found by 2DTEE; the detection of two ASPs in the same subject (in four patients) not identified by 2DTEE; larger ASP measurements of length and height in over 80% of the cases; and measurement of the ASP width (elevational axis) for the calculation of the area of the ASP opening, because of its unique capability to view the pouch en face. In addition, the volume of ASP and of the echogenic masses contained in the ASP (four of 39 patients) could be calculated by 3DTEE, which is a superior parameter of size characterization when compared to individual dimensions. One of these patients who presented with ischemic stroke diagnosed by magnetic resonance imaging had a large (>2 cm) mass in a LASP, with echolucencies similar to those seen in thrombi and associated with clot lysis and resolution. This mass completely disappeared on anticoagulant therapy lending credence that it was most likely a thrombus. There was no history of stroke or any other type of embolic event in the other three patients with masses in ASP. In conclusion, this retrospective study highlights the incremental value of 3DTEE over 2DTEE in the comprehensive assessment and characterization of ASPs, which can aid in the clarification of their role in cryptogenic stroke patients.

Left atrial septal pouch in cryptogenic stroke.

Background: The left atrial septal pouch (LASP), an anatomic variant of the interatrial septum, has uncertain clinical significance. We examined the association between LASP and ischemic stroke subtypes in patients undergoing transesophageal echocardiography (TEE).Methods: We determined the prevalence of LASP among consecutive patients who underwent TEE at our institution. Patients identified with ischemic strokes were further evaluated for stroke subtype using standard and modified criteria from the Trial of Org 10172 in Acute Stroke Treatment (TOAST). We compared the prevalence of LASP in ischemic stroke, cryptogenic stroke, and non-stroke patients using prevalence ratios (PR).Results: The mean age of all 212 patients (including stroke and non-stroke patients) was 57 years. The overall prevalence of LASP was 17% (n = 35). Of the 75 patients who were worked-up for stroke at our institution during study period, we classified 31 as cryptogenic using standard TOAST criteria. The prevalence of LASP among cryptogenic stroke patients (using standard and modified TOAST criteria) was increased compared to the prevalence among other ischemic stroke patients (26 vs. 9%, p = 0.06; PR = 1.8, 95% CI = 1.1–3.1, and 30 vs. 10%, p = 0.04; PR = 2.2, 95% CI = 1.2–4.1, respectively).Conclusion: In this population of relatively young patients, prevalence of LASP was increased in cryptogenic stroke compared to stroke patients of other subtypes. These findings suggest LASP is associated with cryptogenic stroke, which should be verified by future large-scale studies.

Correlation of Left Atrial Septal Pouch with the Prevalence of Patent Foramen Ovale: A Retrospective Review

Purpose: To determine the prevalence of Left Atrial Septal Pouch (LASP) and assess the association with Patent Foramen Ovale (PFO). Materials and Methods: We retrospectively reviewed 275 cardiac-gated CT examinations at Indiana University from January 2010 to June 2012, 160 cardiac CTs performed prior to pulmonary vein ablation, 115 for evaluation of coronary artery evaluation. Consensus readings were performed by two readers on a PACS workstation using the Multiplanar Reformat software to identify the presence or absence of LASP and PFO. PFO was diagnosed by the presence of a contrast jet extending from the left atrium to the right atrium. Results: Overall prevalence of LASP was 24.7% (68 LASPs out of 275 patients). There was no Original Research Article Terpenning et al.; CA, 3(2): 122-129, 2015; Article no.CA.2015.010 123 significant difference regarding the gender and age between patients with and without LASP, pvalues 0.054 and 0.63 respectively. The overall prevalence of PFO in both groups is low 2.2% (6 PFOs out of 275 patients). The prevalence of PFO in patients with LASP was 5.9% (4 out of 68 patients) and was 1.0% (2 PFOs out of 207 patients) in patients without LASP. There was a significant difference in prevalence of PFO between patients with and without LASP, p-value 0.035. Conclusions: LASP is a common finding on cardiac CT, its prevalence not affected by age or gender. Patients with LASP have statistically greater prevalence of PFO than patients without LASP, but the prevalence remains low.

Potential sites of thrombosis in the left atrium

Introduction: Blood clots have a tendency to form within the left atrium and may cause episodes of systemic embolisms. The left atrial appendage (LAA) is widely recognized as a site of blood stasis, but in a substantial proportion of patients with systemic embolisms there is no visible source of thrombi. It raises the question whether there are other sites of blood stasis in the left atrium. Objectives: To evaluate potential sites of thrombi within left atrium, and to present its morphological evaluation. Materials and methods: 130 randomly selected autopsied hearts were dissected from humans aged 7– 94 years (26.2% females). The diameters of the ostium and external circuit of the LAA were measured. The morphology of the interatrial septum and the patterns by which the septum primum and septum secundum fused were assessed. The depth of the left septal pouch was measured. Presence of other cavities, recesses and muscular bridges within the left atrium were evaluated. Results: Patent foramen ovale was noted in 23.3% of the specimens. A septal pouch that opened into the left atrial cavity was found in 66 (50.8%) cases with a mean depth of 9.2±5.5mm. Muscle bridges were found in 21.5% of cases. Mean diameter of the LAA ostium was 14.2±2.3mm and mean LAA circuit was 5.8±1.1cm. The LAA circuit increased with age (r =0.26, P =0.00) and was significantly larger in males (P =0.016). Conclusions: Septal pouches that open into the left atrium (left and double septal pouch) and muscle bridges may act as sites of thrombosis. In 74.1% of patients interatrial septum can be a source of systemic embolisms. In addition to the left atrial appendage occlusion and the patent foramen ovale closure, we propose simultaneous closure of the septal pouch. We present morphological evaluation of the LAA which will be useful to cardiologists during LAA closure. Acknowledgements: Dr WieslawaKlimek-Piotrowska MD, PhD, for supervising this project.