The human heart functions as a pump, circulating blood throughout the body to deliver oxygen and nutrients. This muscular organ is divided into four distinct chambers: two upper chambers called atria and two lower chambers called ventricles. These chambers work in a coordinated rhythm to ensure efficient blood flow.
Anatomical Position
The left auricle, also known as the left atrial appendage (LAA), is a small, ear-shaped muscular pouch that extends from the main body of the left atrium. It is located on the anterior-superior aspect of the left atrium, which is positioned more posteriorly and superiorly than the right atrium. This appendage projects forward and to the right, often overlapping the root of the pulmonary artery. Its walls are thin, typically measuring about 1 millimeter in thickness and less than 2.5 centimeters in length.
The interior of the left auricle features a complex, ridged surface due to the presence of pectinate muscles, which contrasts with the smoother walls of the main left atrial chamber. This unique internal structure allows the auricle to hold a variable volume of blood. It lies in a groove between the left atrium and left ventricle and is in close proximity to other cardiac structures. The left auricle is a distinct structure, differing from the rest of the left atrium.
Role in Cardiac Function
The left auricle functions as a reservoir for oxygenated blood returning from the lungs to the heart. This blood enters the left atrium via the pulmonary veins before moving to the left ventricle for distribution. The left auricle’s muscular walls can contract, assisting in the complete emptying of blood into the main left atrial cavity and subsequently into the left ventricle.
While it contributes to the heart’s overall pumping capacity by increasing the volume the left atrium can hold, its contribution to the total cardiac output is relatively small. The left auricle also plays a part in accommodating changes in left atrial volume and pressure, acting as a decompression chamber when left atrial pressure is high. It can release natriuretic peptides, which are proteins that help regulate blood volume and pressure.
Clinical Considerations
The unique anatomical structure of the left auricle has clinical implications, particularly its susceptibility to blood clot formation. Its complex, trabeculated (ridged) interior and narrow opening can lead to stagnant blood flow, especially in conditions like atrial fibrillation (AFib). In individuals with AFib, irregular heartbeats can cause blood to pool and form clots within the left auricle.
These clots can dislodge and travel through the bloodstream to other parts of the body, potentially causing a stroke if they reach the brain. Over 90% of blood clots in patients with non-valvular AFib originate in the left auricle. Due to this risk, the left auricle is a focus in cardiac procedures and imaging studies aimed at preventing stroke.