The term “left auricle” is the informal name for a small, ear-shaped pouch of muscle extending from the main body of the left atrium, which is officially called the Left Atrial Appendage (LAA). This structure is an embryological remnant from heart development. The name “auricle” comes from the Latin word auricula, meaning “little ear,” reflecting its appearance as a small, wrinkled flap of tissue attached to the left upper chamber. The LAA has become the focus of significant medical attention due to its unique anatomical properties.
Precise Anatomical Positioning
The Left Atrial Appendage projects forward and to the side from the superolateral wall of the left atrium, the chamber that receives oxygenated blood from the lungs. It is tucked into the atrioventricular groove, also known as the coronary sulcus, which is the boundary between the left atrium and the left ventricle below it. The LAA often drapes over the proximal segment of the left main coronary artery and the left circumflex artery. Its position is generally anterior and lateral to the left superior pulmonary vein, meaning it sits externally on the heart’s surface, making it an accessible target for surgeons.
Physical Characteristics and Internal Structure
The Left Atrial Appendage is a highly variable structure, differing significantly in shape and size from person to person. Researchers classify its general appearance into several categories:
- Chicken wing
- Windsock
- Cactus
- Cauliflower
The most common shape is the “chicken wing,” describing an LAA with a distinct bend. Internally, the LAA is typically multi-lobed and lined with irregular, crisscrossing muscle bundles called pectinate muscles. This rough, trabeculated interior sharply contrasts with the relatively smooth walls of the rest of the left atrium.
Clinical Relevance and Blood Clot Risk
The unique anatomical structure of the Left Atrial Appendage makes it the primary site for the formation of blood clots in patients with certain heart rhythm disorders. Its rough, intricate interior and narrow entrance promote the stagnation of blood flow, known as stasis. This blood stasis is especially pronounced in individuals suffering from Atrial Fibrillation (A-fib), the most common sustained irregular heart rhythm. During A-fib, the left atrium quivers instead of contracting effectively, causing the blood inside the LAA to pool and move sluggishly. Over 90% of stroke-causing blood clots that originate in the left atrium in non-valvular A-fib patients form within the LAA. Consequently, specialized medical procedures, such as LAA occlusion or closure, are designed to seal off or remove the appendage to prevent these thromboembolic events.