Left Atrial Appendage
The left atrial appendage (LAA) is the finger-like outpouching of atrial tissue that contains more than 90% of atrial thrombi in patients with atrial fibrillation and is associated with arrhythmia generation. 1, 2
Anatomic Characteristics
The LAA is a distinct cardiac structure with unique features that differentiate it from the main left atrium:
It originates as a finger-like extension from the main body of the left atrium, with developmental, ultrastructural, and physiological characteristics distinct from the left atrium proper 2, 3
The LAA is derived from the left wall of the primary atrium during the fourth week of embryonic development, making it embryologically distinct from other atrial structures 3
It lies within the pericardium in close relation to the free wall of the left ventricle, which significantly affects its emptying and filling patterns 3
Role in Thromboembolism
The LAA is the predominant source of cardiac thrombi in atrial fibrillation:
More than 90% of cardiac-based emboli originate from the LAA, particularly in patients with atrial fibrillation 1, 4
At least 90% of left atrial thrombi discovered in AF patients are localized to the LAA 4
The pathogenesis involves relative stasis within the appendage due to its shape, trabeculations, and reduced contractility during AF 2, 3
Imaging Assessment
Cardiac CT provides optimal visualization of LAA anatomy:
Cardiac CT allows detailed anatomic assessment of the LA and LAA, with several parameters identified as predictors of AF and thromboembolic stroke 5
The high spatial resolution and excellent 3-dimensional definition of cardiac CT has made it the method of choice for LAA evaluation in AF patients 5
3D echocardiography provides "en-face" views of atrial structures from both right and left atrial perspectives, though the LAA poses technical challenges for strain imaging due to its complex anatomy 6
Clinical Implications
Understanding LAA anatomy is critical for multiple interventions:
LAA exclusion or occlusion is considered in selected AF patients with elevated thromboembolic risk, particularly those with contraindications to oral anticoagulation 4
Percutaneous LAA exclusion has been developed to limit cardioembolic events, with benign healing occurring without adverse hemodynamic effects 1
Optimal imaging is essential before cardioversion and with transcatheter therapies including pulmonary vein isolation and LAA occlusion device implantation 2