From the Guidelines
An atrial appendage forms during embryonic heart development, specifically around the fourth week, as small, ear-shaped pouches extending from the main chambers of the left and right atria. The atrial appendages, also called atrial auricles, develop as the primitive atrium divides into right and left sides. As the heart continues to develop, these sac-like structures maintain their distinct trabeculated appearance, characterized by pectinate muscles lining their inner walls.
Key Developmental Features
- The appendages develop a unique muscular, ridged internal structure that distinguishes them from the smoother walls of the main atrial chambers.
- This trabeculated structure results from the incomplete regression of the primitive atrium during development, as noted in studies on cardiac development 1.
- The right atrial appendage typically has a broader base and is more triangular in shape, while the left atrial appendage is usually narrower, more tubular, and has a more complex, multi-lobed structure.
Clinical Relevance
These anatomical differences arise from the asymmetrical development of the heart chambers during embryogenesis and are crucial for understanding the role of the atrial appendages in conditions like atrial fibrillation, where the left atrial appendage is a common site for thrombus formation 1.
Developmental Timeline
- The formation of the atrial appendages is an early event in heart development, occurring around the fourth week of embryonic development.
- As the heart develops further, the appendages maintain their distinct structure and function, playing a role in the heart's electrical and mechanical activities. Given the provided evidence, the formation of the atrial appendage is a critical aspect of embryonic heart development, with significant implications for understanding cardiac structure and function, as well as the management of conditions like atrial fibrillation 1.
From the Research
Formation of the Atrial Appendage
- The left atrial appendage (LAA) is derived from the left wall of the primary atrium, which forms during the fourth week of embryonic development 2.
- The morphogenesis of the left atrium, including the left atrial appendage, has been studied in human embryos and early fetuses using high-resolution imaging techniques 3.
- The left atrial appendage forms as a lobe-like structure with a large volume in the center, extending to the periphery 3.
- The left atrial appendage orifice increases in area and tends to become flatter with growth 3.
Developmental Characteristics
- The LAA has developmental, ultrastructural, and physiological characteristics distinct from the left atrium proper 2.
- The LAA lies within the confines of the pericardium in close relation to the free wall of the left ventricle, and its emptying and filling may be significantly affected by left ventricular function 2.
- The physiological properties and anatomical relations of the LAA render it ideally suited to function as a decompression chamber during left ventricular systole and during other periods when left atrial pressure is high 2.
Related Studies
- Studies have focused on the anatomy and function of the LAA, as well as the pathogenetic mechanisms of LAA thrombosis in patients with atrial fibrillation 4.
- Research has also explored the efficacy and safety of new oral anticoagulants, such as apixaban, compared to warfarin in patients with atrial fibrillation 5, 6.