Relation of Left Atrial Appendage Morphology Determined by Computed Tomography to Prior Stroke or to Increased Risk of Stroke in Patients With Atrial Fibrillation

Cardiac imaging correlates and predictors of stroke in patients with atrial fibrillation: a meta-analysis

BACKGROUND

New nonclinical parameters are needed to improve the current stroke risk stratification schemes for patients with atrial fibrillation. This study aimed to summarize data on potential cardiac imaging correlates and predictors of stroke or systemic embolism in patients with atrial fibrillation.

METHODS

MEDLINE, EMBASE, and Web of Science were searched to identify all published studies providing relevant data through 16 November 2022. Random effects meta-analysis method was used to pool estimates.

RESULTS

We included 64 studies reporting data from a pooled population of 56 639 patients. Left atrial spontaneous echo-contrast [adjusted odds ratio (aOR) 3.32, 95% confidence interval (CI) 1.98-5.49], nonchicken wing left atrial appendage (LAA) morphology (aOR 2.15, 95% CI 1.11-4.18), left atrial enlargement (aOR 2.12, 95% CI 1.45-3.08), and higher LAA orifice diameter (aOR 1.56, 95% CI 1.18-2.05) were highly associated with stroke. Other parameters associated with stroke included higher left atrial sphericity (aOR 1.14, 95% CI 1.01-1.29), higher left atrial volume (aOR 1.03, 95% CI 1.01-1.04), higher left atrial volume index (aOR 1.014, 95% CI 1.004-1.023), lower left atrial reservoir strain [adjusted hazard ratio (aHR) 0.86, 95% CI 0.76-0.98], higher left ventricular mass index (aOR 1.010, 95% CI 1.005-1.015) and E / e' ratio (aOR 1.12, 95% CI 1.07-1.16). There was no association between LAA volume (aOR 1.37, 95% CI 0.85-2.21) and stroke.

CONCLUSION

These cardiac imaging parameters identified as potential predictors of thromboembolism may improve the accuracy of stroke risk stratification schemes in patients with atrial fibrillation. Further studies should evaluate the performance of holistic risk scores including clinical factors, biomarkers, and cardiac imaging.

Mechanisms and Prediction of Ischemic Stroke in Atrial Fibrillation Patients

Atrial fibrillation (AF) is the most common arrhythmia in adults worldwide and represents an important burden for patients, physicians, and healthcare systems. AF is associated with substantial mortality and morbidity, due to the disease itself and its specific complications, such as the increased risk of stroke and thromboembolic events associated with AF. The temporal relation between AF episodes and stroke is nonetheless incompletely understood. The factors associated with an increased thromboembolic risk remain unclear, as well as the stroke risk stratification. Therefore, in this review, we intend to expose the mechanisms and physiopathology leading to intracardiac thrombus formation and stroke in AF patients, together with the evidence supporting the causal hypothesis. We also expose the risk factors associated with increased risk of stroke, the current different risk stratification tools as well as future prospects for improving this risk stratification.

Accuracy and Reliability of Left Atrial Appendage Morphology Assessment by Three-Dimensional Transesophageal Echocardiographic Glass Rendering Modality: A Comparative Study With Computed Tomography

BACKGROUND

Contrast-enhanced computed tomography is the reference-standard imaging technique to assess left atrial appendage (LAA) morphology. The aim of this study was to evaluate the accuracy and reliability of two-dimensional and new three-dimensional (3D) transesophageal echocardiographic rendering modalities in assessing LAA morphology.

METHODS

Seventy consecutive patients who underwent both computed tomography and transesophageal echocardiography (TEE) were retrospectively enrolled. The traditional LAA morphology classification system (LAAcs; chicken wing, cauliflower, cactus, and windsock) and a new simplified LAAcs based on the LAA bend angle were used for the analysis. LAA morphology was independently assessed by two trained readers using three different modalities: two-dimensional TEE, 3D TEE with multiplanar reconstruction, and a new 3D transesophageal echocardiographic rendering modality with improved transparency (Glass). The new LAAcs and traditional LAAcs were compared in terms of intra- and interrater reliability.

RESULTS

With the new LAAcs, two-dimensional TEE was fairly accurate in identifying LAA morphology (κ = 0.43, P < .05), with moderate interrater (κ = 0.50, P < .05) and substantial intrarater (κ = 0.65, P < .005) agreement. Three-dimensional TEE showed higher accuracy and reliability: 3D TEE with multiplanar reconstruction had almost perfect accuracy (κ = 0.85, P < .001) and substantial (κ = 0.79, P < .001) interrater reliability, while 3D TEE with Glass had substantial accuracy (κ = 0.70, P < .001) and almost perfect (κ = 0.84, P < .001) interrater reliability. Intrarater agreement was almost perfect for both 3D transesophageal echocardiographic modalities (κ = 0.85, P < .001). Accuracy was considerably lower when the traditional LAAcs was used, with 3D TEE with Glass being the most reliable technique (κ = 0.75, P < .05). The new LAAcs showed higher inter- and intrarater reliability compared with the traditional LAAcs (interrater, κ = 0.85 vs κ = 0.49; intrarater, κ = 0.94 vs κ = 0.68; P < .05).

CONCLUSIONS

Three-dimensional TEE is an accurate, reliable, and feasible alternative to computed tomography in assessing LAA morphology with the new LAAcs. The new LAAcs shows higher reliability rates than the traditional one.

Left atrial appendage structural characteristics predict thrombus formation

INTRODUCTION

Nonvalvular atrial fibrillation (NVAF) is a highly prevalent arrhythmia where loss of synchronized atrial contraction increases the risk of intracardiac thrombus particularly within the left atrial appendage (LAA). Anticoagulation is the mainstay of stroke prevention based on the CHA2 DS2 -VASc score; however, it does not account for LAA structural characteristics.

METHODS

The research comprises a retrospective matched case-control study of 196 subjects with NVAF who underwent transesophageal echo (TEE). The control group, without thrombus (n = 117), was selected from two different groups, both pools had: NVAF and CHA2 DS2 -VASc score ≥ 3. One group underwent screening TEE before Watchman closure device placement from January 2015 to December 2019 (n = 74) the second underwent TEE before cardioversion from February to October 2014 (n = 43). The study group, with thrombus (n = 79), included patients with NVAF, TEE study performed between February 2014 and December 2020, and LAA thrombus. The propensity score method was utilized to determine the matched controls while accounting for confounding from prognostic variables resulting in 61 matched pairs included in the analysis data set. LAA ostial area (OA) (calculated from orthogonal measurements 0°, 90° or 45°, 135°), LAA maximal depth, and peak LAA outflow velocity were measured.

RESULTS

Patient characteristics and TEE data were collected and compared using the t test or χ2 analysis. We observed a lower LAA peak exit velocity in the thrombus group as compared to the control group. Additionally, we found that patients in the thrombus group had smaller LAA OA at 0° and 90°, at 45° and 135°, using largest diameter, as well as using aggregate OA, and smaller maximum LAA depth compared to patients in the control group. Candidate conditional logistic regression models for the outcome of the presence of thrombus were evaluated. Statistical results from the best-fitting conditional regression model were calculated showing a significant association between aggregate OA and LAA exit velocity with presence of thrombus.

CONCLUSION

Utilizing LAA structural characteristics to predict thrombus formation may help refine current cardioembolic stroke (CES) risk estimation.

Left Atrial Thrombus-Are All Atria and Appendages Equal?

Although the left atrial appendage (LAA) seems useless, it has several critical functions that are not fully known yet, such as the causes for being the main origin of cardioembolic stroke. Difficulties arise due to the extreme range of LAA morphologic variability, making the definition of normality challenging and hampering the stratification of thrombotic risk. Furthermore, obtaining quantitative metrics of its anatomy and function from patient data is not straightforward. A multimodality imaging approach, using advanced computational tools for their analysis, allows a complete characterization of the LAA to individualize medical decisions related to left atrial thrombosis patients.

Gross anatomic relationship between the human left atrial appendage and the left ventricular summit region: implications for catheter ablation of ventricular arrhythmias originating from the left ventricular summit

PURPOSE

The left ventricular summit (LVS) is a source of difficult-to-treat arrhythmias because of anatomical limitations. The aim of this study was to perform detailed research of the left atrial appendage (LAA) anatomy of cadaveric hearts to analyze their complex anatomy and coverage of the LVS.

METHODS AND RESULTS

Eighty human formalin fixed hearts (mean age 44.4 ± 15.5, 27.5% females) were investigated. Each LAA size, type, and its relationship to the LVS were analyzed, as well as possible access sites for mapping/ablating electrode. Four types of LAA were observed over two LVS sites that are either accessible or not. The highest coverage over an inaccessible LVS area was observed in the Broccoli type, followed by the Windsock then the Chicken Wing and finally the Cactus types; over the accessible area of the LVS was observed in the Windsock, then in the Chicken Wing, then in the Cactus, and finally in the Broccoli types. The attainable coverage for electrode access is diminished from 25 to 65% because of the complex pectinate muscles and sharp angles. The highest density of the LAA floor made by pectinate muscles can be found in the Broccoli type (p < 0.005), while the Chicken Wing had the highest number of paper-thin-like pouches.

CONCLUSIONS

The LAA appears to be a promising entry for ablation-qualified patients with the LV summit originate arrhythmias. The complex internal structure of the LAA may complicate ablation procedures. More prominent appendages are promising in more extensive mapping areas over the LVS.

Left atrial appendage filling defects restricted to the early phase of cardiac computed tomography is significantly associated with ischemic stroke

PURPOSE

To investigate the relationship between filling defects in the left atrial appendage restricted to the early phase of cardiac computed tomography (CCT), and ischemic stroke in patients with atrial fibrillation (AF).

MATERIALS AND METHODS

A total of 152 patients with non-valvular AF were retrospectively enrolled and divided into two groups according to the stroke history, as confirmed by brain computed tomography (CT) or magnetic resonance imaging (MRI), as the non-stroke group (n = 89) and stroke group (n = 63), respectively. The numbers of patients with filling defects in the early phase of CCT images without thrombi were recorded. Morphological parameters of the LAA were measured for all participants. All patients with early-phase filling defects (n = 44) were assigned to two groups according to ischemic stroke history: the filling defects with stroke group (n = 28) and the filling defects without stroke group (n = 16). The clinical characteristics and LAA morphological parameters were compared.

RESULTS

Univariate analysis showed that compared with the non-stroke group，LAA volume index and age were higher in the stroke group, and the ratio of early phase filling defect in LAA, hypertension and diabetes were also higher, in the meanwhile the LVEF and BMI were lower (P < 0.05).After adjusting confounding factors by the multivariate logistic regression analysis, filling defect was significantly related with stroke [odds ratio (OR): 4.339, 95% confidence interval (CI): 1.951-9.653, P = 0.000]. LAA morphological parameters were not significantly different between the filling defects with stroke group and the group without stroke.

CONCLUSION

AF patients with LAA non-thrombotic filling defects in the early-phase of CCT had an increased risk of ischemic stroke compared to those without filling defects. This finding may help to optimize stroke risk stratification in patients with AF.

Atrial fibrillation ablation: the position of computed tomography in pre-procedural imaging

Atrial fibrillation (AF) is the most common supraventricular arrhythmia. Despite significant advances in its treatment, it still remains one of the leading causes of cardiovascular morbidity and mortality. In the last two decades, pulmonary vein isolation (PVI) was developed as the most effective treatment option. The reported effectiveness of a single ablation procedure ranges from 40% to 69% with single, and up to 88% with repeated procedures, with acceptable safety profile. The PubMed database was searched, using terms including ‘atrial fibrillation ablation’, ‘pulmonary vein isolation’, ‘computed tomography’, ‘pulmonary vein anatomy’ and ‘ovality index’. Papers were reviewed for relevance and scientific merit. Different imaging techniques are used for pre-procedural assessment of left atrial (LA) anatomy, of which computed tomography (CT) is the most common. It allows assessing pulmonary vein (PV) anatomy, the LA wall thickness in different regions and the left atrial appendage (LAA) anatomy, together with excluding the presence of intracardiac thrombi. Pre-procedural PVs imaging is important regardless of the selected ablation technique, however, cryoballoon (CB) ablation seems to be particularly anatomy-dependent. Additionally, CT also permits assessment of several PVs characteristics (geometry, dimensions, angulations, the ostium area, orientation and ovality index (OI), which are essential for the patients’ qualification and designing the strategy of AF ablation. In this paper, we have reviewed the role of CT imaging in patients undergoing ablation procedure due to recurrent/symptomatic atrial fibrillation. Moreover, we discussed the relevant literature.

Stroke risk evaluation for patients with atrial fibrillation: Insights from left atrial appendage

Left atrial appendage (LAA) is believed to be a common site of thrombus formation in patients with atrial fibrillation (AF). However, the commonly-applied stroke risk stratification model (such as. CHA2DS2-VASc score) does not include any structural or hemodynamic features of LAA. Recent studies have suggested that it is important to incorporate LAA geometrical and hemodynamic features to evaluate the risk of thrombus formation in LAA, which may better delineate the AF patients for anticoagulant administration and prevent strokes. This review focuses on the LAA-related factors that may be associated with thrombus formation and cardioembolic events.

Left Atrial Thrombus-Are All Atria and Appendages Equal?

Although the left atrial appendage (LAA) seems useless, it has several critical functions that are not fully known yet, such as the causes for being the main origin of cardioembolic stroke. Difficulties arise due to the extreme range of LAA morphologic variability, making the definition of normality challenging and hampering the stratification of thrombotic risk. Furthermore, obtaining quantitative metrics of its anatomy and function from patient data is not straightforward. A multimodality imaging approach, using advanced computational tools for their analysis, allows a complete characterization of the LAA to individualize medical decisions related to left atrial thrombosis patients.

Joint Analysis of Morphological Parameters and In Silico Haemodynamics of the Left Atrial Appendage for Thrombogenic Risk Assessment

Background. Atrial fibrillation (AF) is considered the most common human arrhythmia. In nonvalvular AF, around 99% of thrombi are formed in the left atrial appendage (LAA). Nevertheless, there is not a consensus in the community about the relevant factors to stratify the AF population according to thrombogenic risk. Objective. To demonstrate the need for combining left atrial morphological and haemodynamics indices to improve the thrombogenic risk assessment in nonvalvular AF patients. Methods. A cohort of 71 nonvalvular AF patients was analysed. Statistical analysis, regression models, and random forests were used to analyse the differences between morphological and haemodynamics parameters, extracted from computational simulations built on 3D rotational angiography images, between patients with and without transient ischemic attack (TIA) or cerebrovascular accident (CVA). Results. The analysis showed that models composed of both morphological and haemodynamic factors were better predictors of TIA/CVA compared with models based on either morphological or haemodynamic factors separately. Maximum ostium diameter, length of the centreline, blood flow velocity within the LAA, oscillatory shear index, and time average wall shear stress parameters were found to be key risk factors for TIA/CVA prediction. In addition, TIA/CVA patients presented more flow stagnation within the LAA. Conclusion. Thrombus formation in the LAA is the result of multiple factors. Analyses based only on morphological or haemodynamic parameters are not precise enough to predict such a phenomenon, as demonstrated in our results; a better patient stratification can be obtained by jointly analysing morphological and haemodynamic features.

Anatomical Characteristics of the Left Atrium and Left Atrial Appendage in Relation to the Risk of Stroke in Patients With Versus Without Atrial Fibrillation

[Figure: see text].

A Review of Biomarkers for Ischemic Stroke Evaluation in Patients With Non-valvular Atrial Fibrillation

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia worldwide and results in a significantly increased ischemic stroke (IS) risk. IS risk stratification tools are widely being applied to guide anticoagulation treatment decisions and duration in patients with non-valvular AF (NVAF). The CHA₂DS₂-VASc score is largely validated and currently recommended by renowned guidelines. However, this score is heavily dependent on age, sex, and comorbidities, and exhibits only moderate predictive power. Finding effective and validated clinical biomarkers to assist in personalized IS risk evaluation has become one of the promising directions in the prevention and treatment of NVAF. A number of studies in recent years have explored differentially expressed biomarkers in NVAF patients with and without IS, and the potential role of various biomarkers for prediction or early diagnosis of IS in patients with NVAF. In this review, we describe the clinical application and utility of AF characteristics, cardiac imaging and electrocardiogram markers, arterial stiffness and atherosclerosis-related markers, circulating biomarkers, and novel genetic markers in IS diagnosis and management of patients with NVAF. We conclude that at present, there is no consensus understanding of a desirable biomarker for IS risk stratification in NVAF, and enrolling these biomarkers into extant models also remains challenging. Further prospective cohorts and trials are needed to integrate various clinical risk factors and biomarkers to optimize IS prediction in patients with NVAF. However, we believe that the growing insight into molecular mechanisms and in-depth understanding of existing and emerging biomarkers may further improve the IS risk identification and guide anticoagulation therapy in patients with NVAF.

Left Atrial Appendage Morphology and Local Thrombogenesis-Related Blood Parameters in Patients With Atrial Fibrillation

Background

Left atrial appendage (LAA) morphology predicts stroke risk in patients with atrial fibrillation. However, it is not precisely understood how LAA morphology influences stroke risk. The present study aimed to investigate the relationship between LAA morphology and local thrombogenesis‐related blood parameters in LAA.

Methods and Results

We enrolled 205 patients undergoing catheter ablation of atrial fibrillation. The prevalence of chicken wing–, cactus‐, windsock‐, and cauliflower‐type LAAs were 23.9%, 32.7%, 29.3%, and 14.1%, respectively. Blood samples were collected from the femoral vein, left atrium, and LAA in each patient. The levels of blood parameters were tested for each blood sample. The cauliflower‐type LAA was associated with elevated platelet P‐selectin expression, and interleukin‐6 levels and with lower NO levels in LAA blood samples (P<0.05) independent of LAA flow velocity and LAA volume. LAA flow velocity, which was lowest in the cauliflower‐type LAA, was the only independent predictor of von Willebrand factor antigen and plasminogen activator inhibitor‐1 levels in LAA blood samples. In femoral vein blood samples, no significant difference was detected in the above blood parameters among the four LAA morphological types. In all blood samples, the levels of thrombin‐antithrombin complex, D‐dimer, fibrinogen, and tissue plasminogen activator were comparable among the four LAA morphological types.

Conclusions

In patients with atrial fibrillation, LAA morphological types might be associated with local platelet activity, fibrinolysis function, endothelial dysfunction, and inflammation.

Impact of left atrial appendage location on risk of thrombus formation in patients with atrial fibrillation

Most strokes in patients with atrial fibrillation (AF) are thought to arise from thrombus formation in the left atrial appendage (LAA). Assessing the hemodynamics in LAA and left atrium (LA) may provide some insights in the evaluation of the risk of thrombus formation. This study aims to find out the impact of different LAA locations with respect of LA on the risk of thrombus formation within LAA in patients with AF. Three different LAA locations at LA were modeled and a fully coupled fluid-structure interaction analysis was performed. A discrete phase method was used for particle residence analysis to evaluate risk of the thrombus formation. The results showed that LAA positions on the LA affected the LAA flow velocity distribution, passive contraction ability, and particle residence. In particular, the left pulmonary veins (PVs) had a greater influence on the LAA hemodynamics than the right PVs. The LAA had the lowest contractibility when it was located between left superior and left inferior PVs, and in this case, a larger number of particles were resided, which indicated a higher risk of thrombus formation. The present work provides a quantitative way to evaluate the risk of thrombus formation within LAA in patients with AF.

Morphology of the Left Atrial Appendage: Introduction of a New Simplified Shape-Based Classification System

BACKGROUND

The left atrial appendage (LAA) is a heart structure with known prothrombogenic and pro-arrhythmogenic properties.

AIM

The aim of this study was to evaluate the specific anatomy of the LAA and to create a simple classification system based on the shape of its body.

METHOD AND RESULTS

This study investigated 200 randomly selected autopsied human hearts (25.0% females, 46.6±19.1 years old). Three (3) types of LAAs were distinguished: the cauliflower type (no bend, limited overall length, compact structure [36.5%]); the chicken wing type (substantial bend in the dominant lobe [37.5%]), and the arrowhead type (no bend, one dominant lobe of substantial length [26.0%]). Additional accessory lobes were present in 55.5% of all LAAs. Significant variations between category types were noted in LAA length (chicken wing: 35.7±9.8 mm, arrowhead: 30.8±10.1 mm, cauliflower: 22.3±9.6 mm [p<0.001]) and in the thickness of pectinate muscles located within the LAA apex (arrowhead: 1.2±0.7 mm; cauliflower: 1.1±0.6 mm; chicken wing: 0.9±0.6 mm [p<0.001]). Left atrial appendage volume and orifice size were not affected by the type of LAA shape. The age of the donor was positively correlated with LAA volume (r=0.29, p=0.005), body length (r=0.26, p=0.012), and area of the orifice (r=0.36, p<0.001). Donors with an oval LAA orifice were significantly older than those with round orifices (50.2±16.6 vs 43.7±20.4 years [p=0.014]) and had significantly heavier hearts (458.2±104.8 vs 409.6±114.1g [p=0.002]).

CONCLUSIONS

This study delivered a new simple classification system of the LAA based on its body shape. An increase in age and heart weight was associated with LAA enlargement and a more oval-shaped orifice. Results of current study may help to estimate the different thrombogenic properties associated with each LAA type and be an assistance during planning and performing interventions on LAA.

Assessment of the left atrial appendage morphology in patients after ischemic stroke - The ASSAM study

BACKGROUND

The ASSAM study was designed to evaluate the association between left atrial appendage (LAA) morphology and stroke risk in patients with atrial fibrillation (AF).

METHODS

The study included 85 randomly chosen AF patients with acute ischemic stroke matched with 84 AF without stroke. All patients had left atrial (LA) computed tomography performed to analyze LAA anatomy.

RESULTS

Patients in the stroke group had a larger LAA volume (10.22 [7.83-13.62] vs. 9.33 cm³ [7.33-11.47], p = 0.046], greater distance from LAA ostium to the first LAA bend (9.25 ± 3.85 vs. 7.23 ± 2.95 mm, p = 0.0002), and more frequently had round LAA ostium shape (11.8 vs. 1.2%, p = 0.005). According to a multivariable model, significant predictors of ischemic stroke were distance from LAA ostium to the first LAA bend (OR 1.202 [1.065-1.356], p = 0.003), LAA ostium round shape of (OR 16.813 [1.857-152.231], p = 0.012), LAA ostium surface area (OR 0.612 [0.457-0.819], p = 0.009), and cactus LAA morphology (OR 2.739 [1.176-6.380], p = 0.016). After adjusting for CHA₂DS₂-VASc score, only the distance from LAA ostium to the first LAA bend remained a significant risk factor for stroke (OR 1.154 [1.014-1.314], p = 0.03).

CONCLUSIONS

The distance from LAA ostium to the first bend of the LAA was independently associated with stroke risk in patients with AF. Whether this parameter may help improve identification of patients at risk of ischemic stroke, needs to be confirmed in larger studies.

The predictive value of a concise classification of left atrial appendage morphology to thrombosis in non-valvular atrial fibrillation patients

Background

The complexity of left atrial appendage (LAA) in patients with nonvalvular atrial fibrillation (NVAF) is closely related to LAA thrombosis and stroke incidence. But the classification of LAA morphology is not uniform and controversial.

Hypothesis

This study divided the LAA into two categories according to the LAA morphology to investigate the risk of thrombosis related to the LAA structural complexity in NVAF patients.

Methods

A total of 336 NVAF patients were enrolled continuously in this study. The patients were divided into thrombosis group and non‐thrombosis group according to whether the thrombus presence in LAA. Through computer LAA three‐dimensional reconstruction, LAA morphology was divided into the complex type and simple type according to with or without the clearly lobulated structure judged by imaging experts. The relationship between LAA thrombosis and various potential risk factors was analyzed.

Results

A total of 19 potential risk factors for LAA thrombosis in NVAF patients were enrolled into statistical analysis. The coincidence rate of LAA morphology classification was 96.4% (324/336) between two imaging experts. Multivariate logistic regression analysis showed that complex LAA morphology (OR 4.168, 95% CI 1.871‐9.288, P < .001) was associated with the presence of LAA thrombus, independently of other enrolled risks.

Conclusions

It is a concise and reliable method to divide the LAA morphology into complex type and simple type according to whether with the clearly lobulated structure. The complex LAA is an independent risk factor for LAA thrombosis in NVAF patients.