Thromboembolism in Atrial Fibrillation: Role of the Left Atrial Appendage

The correlation between ultrasonographic morphology and structure of the left atrial appendage, blood flow velocity, and plasma galectin-3 levels with thrombus formation in the left atrial appendage of patients with atrial fibrillation

Background

To explore the correlation between left atrial appendage morphology, blood flow velocity and plasma galectin-3 and thrombosis in patients with atrial fibrillation.

Methods

Patients with atrial fibrillation who received treatment and completed ultrasound examination in hospital from 2022 to December 2023 were enrolled. According to whether there was left atrial appendage thrombosis, the patients were divided into a control group (no left atrial appendage thrombosis was found) and a study group (left atrial appendage thrombosis was found). The morphology and structure of the left atrial appendage, blood flow velocity and plasma galectin-3 level were recorded exploring its correlation with left atrium thrombosis.

Results

A total of 330 patients with atrial fibrillation were enrolled, including 278 in the control group and 52 in the study group. Left group and the control group of morphological structure differences (P < 0.05). The main lobe length, ostial area, longest diameter, shortest diameter, left atrial appendage volume and left atrial volume in the study group were higher than those in the control group (P < 0.05). The left atrial appendage emptying velocity, filling velocity and left ventricular ejection fraction of the study group were lower than those of the control group, and the left ventricular end-diastolic diameter was higher than that of the control group (P < 0.05). Group of white blood cell count, neutrophils/lymphocyte ratio, plasma galactose lectin-3 levels were higher than control group (P < 0.05). ROC curve analysis of left atrial appendage emptying velocity, left atrial appendage filling velocity, left atrial enddiastolic diameter and left atrial ejection fraction had higher diagnostic value (P < 0.05).

Conclusions

Left atrial appendage morphology, blood flow velocity and plasma galectin-3 level are important factors to evaluate the risk of left atrial appendage thrombosis in patients with atrial fibrillation. This study improves the understanding of thrombosis, further elucidates the risk factors for thrombosis, and improves patient prognosis.

A highly-detailed anatomical study of left atrial auricle as revealed by in-vivo computed tomography

The left atrial auricle (LAA) is the main source of intracardiac thrombi, which contribute significantly to the total number of stroke cases. It is also considered a major site of origin for atrial fibrillation in patients undergoing ablation procedures. The LAA is known to have a high degree of morphological variability, with shape and structure identified as important contributors to thrombus formation. A detailed understanding of LAA form, dimension, and function is crucial for radiologists, cardiologists, and cardiac surgeons. This review describes the normal anatomy of the LAA as visualized through multiple imaging techniques such as computed tomography (CT), magnetic resonance imaging (MRI), and echocardiography. Special emphasis is devoted to a discussion on how the morphological characteristics of the LAA are closely related to the likelihood of developing LAA thrombi, including insights into LAA embryology.

An Observational Study: Clinical Manifestations and Prognosis of Left Atrial Thrombosis in Atrial Fibrillation

We did this study to find out the clinical manifestations and prognosis of left atrial thrombosis in different types of atrial fibrillation and the relationship with systemic thromboembolism, hoping to find a better therapy strategy. A single-center retrospective study enrolled patients with definite diagnosis of atrial fibrillation complicated with left atrial thrombosis. Data of general clinical information, anticoagulation medications, thromboembolism events, and thrombosis prognosis were recorded and analyzed. A total of 103 patients were enrolled. Compared with non-valvular atrial fibrillation (NVAF), thrombosis outside the left atrial appendage (LAA) was much more common in valvular atrial fibrillation (VAF) with p=0.003. Total prevalence of systemic thromboembolism was 33.0%. Thrombi disappeared in 78 cases (75.7%) under anticoagulation treatment within 2 years. There was no significant difference between warfarin, dabigatran, and rivaroxaban on thromboembolism events and thrombosis prognosis in NVAF, with p=0.740 and 0.493, respectively. Atrial fibrillation patients with LA thrombosis have a high risk of systemic thromboembolism events. Compared with NVAF, patients with VAF had higher incidence of thrombosis outside the LAA. Standard stroke-preventing doses of anticoagulants might not be sufficient to deplete all LA thrombi. There was no statistically difference between warfarin, dabigatran, and rivaroxaban for depleting LA thrombi in NVAF patients.

PLXND1-mediated calcium dyshomeostasis impairs endocardial endothelial autophagy in atrial fibrillation

Left atrial appendage (LAA) thrombus detachment resulting in intracranial embolism is a major complication of atrial fibrillation (AF). Endocardial endothelial cell (EEC) injury leads to thrombosis, whereas autophagy protects against EEC dysfunction. However, the role and underlying mechanisms of autophagy in EECs during AF have not been elucidated. In this study, we isolated EECs from AF model mice and observed reduced autophagic flux and intracellular calcium concentrations in EECs from AF mice. In addition, we detected an increased expression of the mechanosensitive protein PLXND1 in the cytomembranes of EECs. PLXND1 served as a scaffold protein to bind with ORAI1 and further decreased ORAI1-mediated calcium influx. The decrease in the calcium influx-mediated phosphorylation of CAMK2 is associated with the inhibition of autophagy, which results in EEC dysfunction in AF. Our study demonstrated that the change in PLXND1 expression contributes to intracellular calcium dyshomeostasis, which inhibits autophagy flux and results in EEC dysfunction in AF. This study provides a potential intervention target for EEC dysfunction to prevent and treat intracardiac thrombosis in AF and its complications.

Catheter ablation of atrial fibrillation: cardiac imaging guidance as an adjunct to the electrophysiological guided approach

Catheter ablation is increasingly utilized to treat patients with atrial fibrillation (AF). Despite progress in technology and procedural strategy, there remain significant limitations with suboptimal outcomes. The role of imaging has continued to evolve, and multimodality imaging now presents an important opportunity to make substantial progress in the safety and efficacy of ablation. In this review, we discuss the history of imaging in the ablation of AF with a specific focus on the ability of cardiac computed tomography and magnetic resonance imaging to characterize anatomy, arrhythmogenic substrate, and guide ablation strategy. We will review the progress that has been made and highlight many of the limitations as well as future directions for the field.

Malignant Left Atrial Appendage Morphology: Current Classification vs H-L System

INTRODUCTION

In previous studies the risk of stroke recurrence has been associated with the left atrial appendage (LAA) morphology (non-chicken wing (NCW)), knowing those with a greater risk as malignant LAA. Recently, a simpler morphological classification has been suggested with two categories: Low-risk (LAA-L) and High-risk (LAA-H); which could be easier to apply and may correlate better with the risk of embolic stroke.

METHODS

Retrospective analysis from a registry of patients with recurrent cardioembolic strokes despite appropriate anticoagulant therapy, in which LAA morphology was studied with cardiac CT scan. LAA morphology was classified according to the four current categories and H-L morphology by the same cardiologist. Other variables associated with a high risk of stroke were also assessed, such as CHA₂DS₂-VASc score and left atrial (LA) size.

RESULTS

Twenty-six cases were included in the analysis. We identified 22 (84.6%) chicken wing (CW), 1 (3.8%) windsock and 3 (11.5%) cactus by the current classification system, while 15 (57.7%) were classified as LAA-H and 11 (42.3%) as LAA-L by the new system. Half of the 22 cases with CW morphology were considered LAA-H, whereas all NCW were also classified as LAA-H. LA diameter and area were significantly higher in cases with LAA-H morphology (p=0.03 and 0.014), and also in those CW and LAA-H, compared to those CW with LAA-L (p=0.035).

CONCLUSIONS

With this new classification system more than half of the cases of our malignant LAAs were classified as high-risk morphology. This morphology was also associated with an increased LA size.

Evaluating the novel parameters for assessing the LAA function and thrombus formation with nonvalvular atrial fibrillation

The dysfunction of left atrial appendage (LAA) is prone to form thrombus when atrial fibrillation (AF) sustained more than 48 h. Traditional 2D-TEE (transesophageal echocardiography) can not accurate evaluate the function of LAA. The purpose of this study is to analyze the relationship of LAA function parameters and thrombus formation in patients with non-valvular atrial fibrillation (NVAF) by real-time three-dimensional transesophageal echocardiography (RT-3D-TEE). High risk patients can be identified according to the characteristics of ultrasonic index in patients with left atrial appendage thrombosis, which has important clinical value and significance in the risk assessment, guiding treatment and judging prognosis. We examined the relationship between the echocardiographic parameters of LAA function and the incidence of thrombus in 102 NVAF patients. They underwent RT-3D-TEE and left atrial appendage thrombus (LAAT)/severe spontaneous echocardiographic contrast (SSEC) was found in 67 patients (thrombus group) but absent in the remaining 35 patients (non-thrombus group). After measured by QLAB software, the LAA functional parameters were significantly associated with LAAT/SEC formation. Univariate analysis indicated that AF time, LAD, LVEF, LAA-OAmax, LAAVmax, LAAVI and LAAEF demonstrated a positive association (P < 0.05). However, logistic regression analysis identified that AF time (OR:1.73, P < 0.05)、LAAEF (OR:4.09, P < 0.01)and LAAVI (OR:3.28, P < 0.01) were independent predictors of LAAT/SSEC. In patients with nonvalvular atrial fibrillation, echocardiographic parameters of LAA function are significantly associated with LAAT/SSEC.

Acute Mesenteric Ischemia With Secondary Thromboembolism: A Rare Complication

Acute mesenteric ischemia presents a clinical challenge due to its subtle presentation and high mortality rate, which can mimic a variety of other conditions. Acute mesenteric ischemia requires a high index of suspicion, especially in those with comorbidities and risk factors such as hypertension, diabetes, atrial fibrillation, and peripheral arterial disease. The inciting thrombus commonly originates in the left atrial appendage or left atrium, embolizing to occlude mesenteric vessels, with resulting gut ischemia. Patients commonly present with post-prandial abdominal pain as mesenteric vascular demands increase, though diarrhea and gastrointestinal bleeding may be the presenting symptom. CT angiography of the abdomen and pelvis provides rapid confirmation of the diagnosis and visualization of the thrombus, aiding vascular surgical management. The authors present a novel case of a 69-year-old female with an acute mesenteric ischemia of her superior mesenteric artery and a second acute arterial thromboembolism to the right axillary artery visualized from her left atrial appendage.