The left atrial septal pouch as a risk factor for stroke: A systematic review

Left Atrial Septal Pouch (LASP) and Cryptogenic Stroke: A Narrative Review

Over 20% of ischemic strokes are cardioembolic strokes, necessitating research into thrombus formation locations, particularly the left atrial appendage (LAA). The left atrial septal pouch (LASP), which is linked to thrombus development and stasis, has drawn attention recently as a possible thromboembolic location, especially in atrial fibrillation (AF). The primary aim of this review is to explore LASP's role in cryptogenic strokes and to discuss the methods used to assess LAA anatomy. Imaging modalities such as cardiac computed tomography (CT) and transesophageal echocardiography (TEE) are crucial for diagnosing and characterizing LASP. LASP, found in about one-third of individuals, provides an additional site for thrombus development in the left atrium. The potential clinical implications of LASP-related thromboembolic events include the need for targeted therapeutic strategies, such as anticoagulant medication and, in some cases, consideration of LASP closure to prevent recurrent strokes. Further investigation is required to elucidate LASP's involvement in thromboembolic events and to guide stroke prevention in at-risk patients.

Left Atrial Septal Pouch (LASP) and cryptogenic stroke risk: An updated systematic review and meta-analysis of observational studies

BACKGROUND

The left atrial septal pouch (LASP) is a small anatomical septal recess in the heart that has been linked with cardioembolic events. A systematic appraisal of the existing literature is necessary to establish a better understanding of the risk as studies continue to indicate a correlation between LASPs and cryptogenic strokes.

OBJECTIVES

To determine the level of association between the presence of LASP and the risk of developing cryptogenic stroke.

METHODS

We searched PubMed, EMBASE and Scopus for studies comparing the prevalence of LASP in patients with cryptogenic stroke against non-cryptogenic stroke control groups from inception till December, 2023. The Newcastle Ottawa scale was used for quality assessment and Comprehensive Meta-Analysis Version 3.3 was used for data analysis with odds ratio (OR) as the effect measure.

RESULTS

Our review included a total of 10 retrospective, observational studies published between 2010 to 2022. A total of 683 cases of cryptogenic strokes were identified, out of which 33.1 % (n = 271) were associated with a LASP. Among the non-cryptogenic stroke controls (n = 2641), LASP was present in 20.6 % cases (n = 476). The aggregate OR for cryptogenic stroke was 1.618 times greater than non-cryptogenic stroke (p < 0.001) among LASP cases, CONCLUSION: The presence of a septal pouch in the left atrium is significantly linked to a higher risk of developing cryptogenic strokes. As a potential site of thrombus formation and subsequent dislodgement, further large-scale studies are necessary to establish the guidelines for management and prophylaxis to prevent embolic events.

Atrial septal pouches and ridges: Morphological features and potential implications in clinical practice

Incomplete or irregular fusion of the interatrial septum may result in several anatomic variants, including atrial septal pouches and ridges, whose knowledge and recognition are still poorly widespread in clinical practice. An educational review focused on the definition, clinical significance and diagnostic work-up of these anatomic findings was performed using PubMed, MEDLINE, Embase and Cochrane Central databases up to June 2023. Atrial septal pouches and ridges have been associated with an increased difficulty of catheter-based interventions requiring a transseptal approach, due to procedural challenges for transseptal puncture and the restricted motion of guidewires and catheters through the transseptal access. Additionally, left atrial septal pouch may serve as a thrombogenic nidus and a source of systemic embolism, mostly in the presence of factors leading to higher left atrial pressure and/or atrial blood stasis, which increase the risk of thrombus formation and embolic events, rather than for the only presence of left atrial septal pouch itself. Further investigations are needed in order to better elucidate the implications of such anatomic findings in daily clinical practice, and to provide the most appropriate decision-making strategies.

The 2022 FASEB Virtual Catalyst Conference on the Cardiac Interatrial Septum and Stroke Risk, December 7, 2022

There is emerging evidence that the cardiac interatrial septum has an important role as a thromboembolic source for ischemic strokes. There is little consensus on treatment of patients with different cardiac interatrial morphologies or pathologies who have had stroke. In this paper, we summarize the important background, diagnostic, and treatment considerations for this patient population as presented during the Federation of American Societies for Experimental Biology (FASEB) Virtual Catalytic Conference on the Cardiac Interatrial Septum and Stroke Risk, held on December 7, 2022. During this conference, many aspects of the cardiac interatrial septum were discussed. Among these were the embryogenesis of the interatrial septum and development of anatomic variants such as patent foramen ovale and left atrial septal pouch. Also addressed were various mechanisms of injury such as shunting physiologies and the consequences that can result from anatomic variants, as well as imaging considerations in echocardiography, computed tomography, and magnetic resonance imaging. Treatment options including anticoagulation and closure were addressed, as well as an in-depth discussion on whether the left atrial septal pouch is a stroke risk factor. These issues were discussed and debated by multiple experts from neurology, cardiology, and radiology.

Association between pouch morphology, cardiovascular risk factors and ischemic brain lesions in patients with left-sided septal pouches

BACKGROUND

Left atrial outpouching structures such as left atrial diverticula (LADs) and left-sided septal pouches (LSSPs) might be a source of cryptogenic stroke. This imaging study evaluates the association between pouch morphology, patient comorbidities and ischemic brain lesions (IBLs).

METHODS

This is a retrospective single-center analysis of 195 patients who received both a cardiac CT and a cerebral MRI. LADs, LSSPs, and IBLs were retrospectively identified. Size measurements included pouch width, length and volume for LADs and circumference, area and volume for LSSPs. The association between LADs/LSSPs, IBLs and cardiovascular comorbidities was determined by univariate and bivariate regression analyses.

RESULTS

The prevalence and mean volume were 36.4% and 372 ± 569 mm³ for LSSPs, and 40.5% and 415 ± 541 mm³ for LADs. The IBL prevalence was 67.6% in the LSSP group and 48.1% in the LAD group. LSSPs had 2.9-fold increased hazards of IBLs (95%CI: 1.2-7.4, p = 0.024), and LADs showed no significant correlation with IBLs. Size measurements had no impact on IBLs. A co-existing LSSP was associated with an increased prevalence of IBLs in patients with coronary artery disease (HR: 1.5, 95%CI: 1.1-1.9, p = 0.048), heart failure (HR: 3.7, 95%CI: 1.1-14.6, p = 0.032), arterial hypertension (HR: 1.9, 95%CI: 1.1-3.3, p = 0.017), and hyperlipidemia (HR: 2.2, 95%CI: 1.1-4.4, p = 0.018).

CONCLUSION

Co-existing LSSPs were associated with IBLs in patients with cardiovascular risk factors, however, pouch morphology did not correlate with the IBL rate. Upon confirmation by further studies, these findings might be considered in the treatment, risk stratification, and stroke prophylaxis of these patients.

Left Atrial Septal Pouch-Is it Really a New Risk Factor for Ischemic Stroke?: Subanalysis of the ASSAM Study

PURPOSE

The atrial septal pouch is an anatomic variant of the interatrial septum caused by incomplete fusion of the septum primum and secundum. It is debatable whether coexistence of septal pouch and atrial fibrillation (AF) increases the risk of stroke. Thus, the aim of the study was to evaluate the coexistence of left atrial septal pouch (LASP) and AF in patients with a history of stroke in comparison with those without an earlier history of stroke.

MATERIALS AND METHODS

We analyzed 145 patients with AF (68 in the study group, 77 in the control group). The study group consisted of patients with previous stroke and AF; control group consisted of patients scheduled for AF ablation. All patients underwent computed tomography with the assessment of atrial septum morphology and presence of LASP. The study was a subanalysis of the ASSAM (AssesSment of the left atrial appendage morphoLogy in patients aAfter ischaeMic Stroke) study.

RESULTS

The prevalence of LASP in the entire group was 38.6%. There were no significant differences in the prevalence of LASP between the study and control groups (33.8% vs. 42.9%, P=0.265). Mean longitudinal and transverse dimensions of LASP were 9.34±3.27 and 2.4±0.6 mm, respectively, and there was no significant difference between the study and controls. Patients from the stroke group were older (P<0.0001), had a higher CHA2DS2-VASc score (5.41±1.93 vs. 1.62±1.46, P<0.0001) compared with controls.

CONCLUSIONS

Presence of LASP is not more prevalent in patients with a history of stroke. Additional information on the presence of LASP do not improve accuracy of risk stratification for stroke in patients with AF.

Recurrent Cryptogenic Stroke in a Patient With Left Atrial Septal Pouch

The incomplete fusion of the septum primum and septum secundum results in the formation of the left atrial septal pouch (LASP). The clinical significance of this entity is a matter of controversy; however, it may act as a nidus for thrombus formation. We report a case of a 57-year-old male who was brought to the hospital by his girlfriend due to his bizarre behavior and confusion for one day. The initial workup for his altered mental status did not yield a diagnosis. The patient was admitted for further workup, which included an MRI of the brain that showed numerous very small-sized foci of restricted diffusion involving bilateral cerebral and cerebellar hemispheres consistent with thromboembolic infarct. The patient did not receive a tissue plasminogen activator (TPA) as he was out of the window for TPA. Transthoracic echocardiogram (TTE) with bubble study did not show patent foramen ovale (PFO) or atrial septal defect (ASD). ECG and telemetry showed normal sinus rhythm and no atrial fibrillation. A transesophageal echocardiogram (TEE) was obtained to find the source of the thromboembolic stroke. TEE discovered a 22 x 8-mm cystic structure in the interatrial septum consistent with a LASP. We hypothesize that the LASP may be a risk factor for cryptogenic stroke. Further research is needed to determine the prevalence of atrial septal pouch (ASP) in the general population, its clinical significance, and guidelines for treatment implications.

Prevalence of left atrial septal pouch among patients with embolic stroke of undetermined source or stroke of known etiology: A retrospective study

Background and objectives

Cryptogenic strokes can be defined by the criteria established for an embolic stroke of undetermined source (ESUS). Some embolic events might be caused by a left atrial septal pouch (LASP), due to the potential of thrombus formation. In this study we aimed to determine if LASP is a risk factor for ESUS when compared to a population of strokes of known origin, the LASP screening rate in our institution and if LASP dimensions influences the risk of ESUS.

Methods

We retrospectively analyzed transesophageal echocardiograms (TEEs) in a large cohort of patients that had experienced ischemic strokes. Two authors performed blinded, independent searches for LASPs by reviewing 1152 TEEs from patients that had experienced a stroke or transient ischemic attack. We excluded 26 TEEs, due to incorrect imaging. Next, we reviewed patient medical files.

Results

Among the 1126 included patients, 148 had an ESUS (ESUS+ group) and 978 had strokes of known origin (ESUS– group). A LASP was present in 176 patients, including 32 patients (21.6% of LASPs) in the ESUS+ group and 144 patients (14.7% of LASPs) in the ESUS– group. In multivariate analysis, LASP was independently associated with ESUS (P = 0,019). 61.9% of LASPs that we found were not mentioned in reports from the original TEE operators.

Conclusion

This study demonstrated that LASPs were more prevalent in patients with ESUS than in patients with strokes of known origin. Our results gave rise to the question of whether anticoagulation would be appropriate for some patients with ESUS. New large-scale, prospective studies should be conducted to address this issue. Additionally, considering the low rate of LASP descriptions, we concluded that the awareness of operators should be raised to improve their success in identifying LASPs.

Prevalence of left atrial septal pouch among patients with embolic stroke of undetermined source or stroke of known etiology: A retrospective study

Background and objectives

Cryptogenic strokes can be defined by the criteria established for an embolic stroke of undetermined source (ESUS). Some embolic events might be caused by a left atrial septal pouch (LASP), due to the potential of thrombus formation. In this study we aimed to determine if LASP is a risk factor for ESUS when compared to a population of strokes of known origin, the LASP screening rate in our institution and if LASP dimensions influences the risk of ESUS.

Methods

We retrospectively analyzed transesophageal echocardiograms (TEEs) in a large cohort of patients that had experienced ischemic strokes. Two authors performed blinded, independent searches for LASPs by reviewing 1152 TEEs from patients that had experienced a stroke or transient ischemic attack. We excluded 26 TEEs, due to incorrect imaging. Next, we reviewed patient medical files.

Results

Among the 1126 included patients, 148 had an ESUS (ESUS+ group) and 978 had strokes of known origin (ESUS– group). A LASP was present in 176 patients, including 32 patients (21.6% of LASPs) in the ESUS+ group and 144 patients (14.7% of LASPs) in the ESUS– group. In multivariate analysis, LASP was independently associated with ESUS (P = 0,019). 61.9% of LASPs that we found were not mentioned in reports from the original TEE operators.

Conclusion

This study demonstrated that LASPs were more prevalent in patients with ESUS than in patients with strokes of known origin. Our results gave rise to the question of whether anticoagulation would be appropriate for some patients with ESUS. New large-scale, prospective studies should be conducted to address this issue. Additionally, considering the low rate of LASP descriptions, we concluded that the awareness of operators should be raised to improve their success in identifying LASPs.

Morphological Study of Fossa Ovalis in Formalin-Fixed Human Hearts and Its Clinical Importance

Background and Objectives: Our study aimed to investigate the gross anatomy aspects of the fossa ovalis (FO) and the presence of some anatomical variation resulting from the incomplete fusion of septum primum and septum secundum, such as an atrial septal pouch (SP) and left atrial septal ridge. Materials and Methods: Thirty-one adult human hearts removed from formalin-fixed specimens were examined to provide information about the morphology of the FO. The organs were free of any gross anatomically visible pathological conditions. Results: The most common variants were the FO located in the inferior part of the interatrial septum (64.51%), circular (61.3%), with a net-like structure (51.62%), prominent limbus (93.55%), and patent foramen ovale (PFO) (25.8%). The right SP was observed in 9.67% of specimens, the left SP was observed in 29.03% of cases, and in 51.61% of cases, a double SP was observed. One sample presented a right SP and a double left SP, and one case showed a triple left SP, which was not reported previously to our knowledge. Conclusions: Knowledge of the interatrial septal anatomy becomes important for interventional cardiologists and should be documented before transeptal puncture.

EACVI recommendations on cardiovascular imaging for the detection of embolic sources: endorsed by the Canadian Society of Echocardiography

Cardioaortic embolism to the brain accounts for approximately 15-30% of ischaemic strokes and is often referred to as 'cardioembolic stroke'. One-quarter of patients have more than one cardiac source of embolism and 15% have significant cerebrovascular atherosclerosis. After a careful work-up, up to 30% of ischaemic strokes remain 'cryptogenic', recently redefined as 'embolic strokes of undetermined source'. The diagnosis of cardioembolic stroke remains difficult because a potential cardiac source of embolism does not establish the stroke mechanism. The role of cardiac imaging-transthoracic echocardiography (TTE), transoesophageal echocardiography (TOE), cardiac computed tomography (CT), and magnetic resonance imaging (MRI)-in the diagnosis of potential cardiac sources of embolism, and for therapeutic guidance, is reviewed in these recommendations. Contrast TTE/TOE is highly accurate for detecting left atrial appendage thrombosis in patients with atrial fibrillation, valvular and prosthesis vegetations and thrombosis, aortic arch atheroma, patent foramen ovale, atrial septal defect, and intracardiac tumours. Both CT and MRI are highly accurate for detecting cavity thrombosis, intracardiac tumours, and valvular prosthesis thrombosis. Thus, CT and cardiac magnetic resonance should be considered in addition to TTE and TOE in the detection of a cardiac source of embolism. We propose a diagnostic algorithm where vascular imaging and contrast TTE/TOE are considered the first-line tool in the search for a cardiac source of embolism. CT and MRI are considered as alternative and complementary tools, and their indications are described on a case-by-case approach.

Newly-found channels in the interatrial septum of the heart by dissection, histologic evaluation, and three-dimensional microcomputed tomography

A minute thrombus can pass through a small type of interatrial communication, which can result in a stroke or transient ischemic attack and several associated symptoms. This study sought to investigate a new type of interatrial communication. Thirty-one hearts from embalmed adult cadavers were investigated. Each interatrial channels (IACs) was classified as either an open or obstructed channel according to the connection of each hole on the right and left surfaces of the interatrial septum. Open channels were found in two specimens (6.5%). Both open and obstructed IACs followed tortuous courses through the interatrial septum. On the right surface of the interatrial septum, the hole was usually found adjacent to the left border of the interatrial septum between the opening of the superior vena cava into the right atrium and the superior margin of the fossa ovalis. Conversely, holes on the left surface of the interatrial septum were usually found in the upper and middle parts adjacent to the left border of the interatrial septum. This novel finding is expected to support our understanding of the onset of possible symptoms such as stroke in the absence of classical atrial septal defects.

Interatrial Thrombus in Left-Atrial Septal Pouch Prohibiting Transseptal Puncture for Percutaneous Mitral Valve Therapy

An 82-year-old female patient with severe mitral regurgitation was referred for evaluation of percutaneous mitral valve repair. Transoesophageal echocardiography revealed a left-atrial septal pouch (LASP) with an echogenic structure. Following the heart-team decision, interventional therapy was therefore discarded. During surgery, a thrombus in the LASP was found and carefully resected. Afterward, conventional valve replacement with a biological 31-mm SJM-EPIC prosthesis (Abbott Structural Heart Devices, Santa Clara, CA) was performed. In the fast-evolving field of interventional mitral valve therapy, a trans-septal approach is the common strategy. Therefore, careful evaluation of the interatrial septum—which may contain thrombi with transoesophageal echocardiography before intervention—is of crucial importance.

Atrium Septal Pouch: An Anatomic Variant of the Interatrial Septum

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SP originates by partial fusion of the septum primum and septum secundum.

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SP may be a site of thrombus formation.

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SP may predispose to thromboembolic events.

Porcine heart interatrial septum anatomy

BACKGROUND

The 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.

METHODS

A total of 75 swine (Sus scrofa f. domestica) hearts were examined. The interatrial septum morphology was assessed, and SPs were measured.

RESULTS

The 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.

CONCLUSIONS

There 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.