What is the function of the left atrial auricle (left atrial appendage)?

From the Guidelines

The left atrial auricle, also known as the left atrial appendage (LAA), is not useless but serves several critical functions in the heart, including acting as a decompression chamber and contributing to cardiac output, as highlighted in the context of atrial fibrillation management 1. The LAA plays a significant role in normal cardiac physiology, and its functions are essential for maintaining optimal heart performance. Some of the key functions of the LAA include:

• Acting as a decompression chamber during left atrial pressure overload
• Contributing to cardiac output by its contractile function, which can add to the heart's pumping capacity
• Producing atrial natriuretic peptide (ANP), which helps regulate blood pressure and fluid balance However, in certain cardiac conditions like atrial fibrillation, the LAA can become problematic, and its reduced contractility can lead to blood stasis and clot formation, increasing stroke risk, as noted in the management guidelines for atrial fibrillation 1. In such cases, LAA closure or removal is sometimes performed in patients with atrial fibrillation who cannot take anticoagulants, as per the 2024 ESC guidelines for the management of atrial fibrillation 1. Despite its potential to cause problems in specific pathological conditions, the LAA plays meaningful roles in normal cardiac physiology, and its benefits should not be overlooked. The most recent guidelines, such as the 2024 ESC guidelines, emphasize the importance of considering LAA occlusion as a therapeutic option for preventing ischemic stroke in patients with atrial fibrillation 1.

From the Research

Left Atrial Appendage Function and Importance

• The left atrial appendage (LAA) is not a useless appendage, but rather a complex structure with important functions in the human body 2.
• It is a major site of origin for atrial fibrillation in patients undergoing ablation procedures 3.
• The LAA has a high degree of morphological variability, with shape and structure identified as important contributors to thrombus formation 3.

Role in Thromboembolism

• The LAA is the main source of intracardiac thrombi, which contribute significantly to the total number of stroke cases 3.
• It is estimated that the LAA accounts for more than 90% of thrombus formation in patients with atrial fibrillation (AF) 4.
• The risk of thromboembolism events in patients with AF depends on clinical comorbidities and structural and physiologic parameters of atria, especially LAA 4.

Anatomical and Physiological Characteristics

• The LAA has unique anatomy which allows it to serve special functions in the human body 2.
• Assessing the hemodynamics in LAA and left atrium (LA) may provide some insights in the evaluation of the risk of thrombus formation 5.
• The location of the LAA with respect to the LA affects the LAA flow velocity distribution, passive contraction ability, and particle residence, which can impact the risk of thrombus formation 5.

Clinical Implications

• Closing the LAA has been shown to decrease the risk of thromboembolic events in patients who cannot tolerate anticoagulation 2.
• Anticoagulation therapy, including warfarin and non-vitamin K antagonist oral anticoagulants (NOACs), can effectively resolve left atrial thrombus or sludge in patients with nonvalvular atrial fibrillation (NVAF) or atrial flutter (AFL) 6.
• Increasing the duration of anticoagulation, determining the optimal dosage of anticoagulants, and switching to another anticoagulant when necessary could be considered to improve treatment effectiveness 6.