The auricles of the heart are small, ear-shaped muscular pouches extending from the upper chambers, the atria. Also known as atrial appendages, these structures contribute to the heart’s overall function and are implicated in significant disease states. Their unique structure and location make them important, particularly the left auricle, which is a major clinical concern in the context of stroke prevention.
Structure and Location
There are two auricles in the human heart, one attached to the right atrium and one attached to the left atrium. The term “auricle” is derived from the Latin word for ear, reflecting their characteristic external appearance as small, wrinkled outpouchings on the surface of the atria. The right auricle is typically a broad, triangular pouch.
The internal walls of both auricles have a highly irregular and rough surface. This texture is created by an intricate network of muscular ridges known as pectinate muscles. These muscles are more extensive within the right auricle, but they are also present in the left auricle, which is often a more narrow, tubular structure. The auricles are essentially remnants of the primitive atria from embryonic development, and this internal complexity contrasts sharply with the generally smooth walls of the main atrial chambers.
Normal Physiological Role
The auricles serve a modest but functional purpose in a healthy cardiovascular system, primarily acting as minor volume reservoirs. Their distensible, muscular structure allows the atria to accommodate a small increase in blood volume. This extra capacity helps relieve pressure within the chamber and manages the flow of blood returning to the heart before it is pumped into the ventricles.
Beyond their mechanical function, the auricles play a role in endocrine regulation through the release of Atrial Natriuretic Peptide (ANP). Specialized muscle cells within the atrial wall synthesize and store this hormone. When the atrial walls stretch due to increased blood volume or pressure, ANP is secreted into the bloodstream. This hormone acts on the kidneys to promote the excretion of salt and water (natriuresis and diuresis). This mechanism provides a rapid countermeasure to high blood pressure and volume overload, helping the body maintain fluid balance.
The Left Atrial Appendage and Stroke Risk
The Left Atrial Appendage (LAA) is the most clinically significant auricle due to its direct link to ischemic stroke. In patients with Atrial Fibrillation (AFib), the normal contraction of the atria is replaced by a rapid, chaotic quiver. This disorganized movement causes the blood within the left atrium, especially in the LAA, to slow down significantly.
The highly irregular, trabeculated structure of the LAA, created by the pectinate muscles, becomes a liability in this scenario. The slow-moving, or stagnant, blood pools in the numerous crevices of the LAA wall, a condition known as stasis. This stasis creates an environment highly prone to clotting (thrombus formation).
In patients with non-valvular AFib who experience a stroke, over 90% of the responsible blood clots originate within the LAA. If a clot breaks free, it enters the left ventricle and is pumped into the systemic circulation. These emboli travel to the brain, where they can block an artery, leading to an ischemic stroke. The LAA is often described as the primary source of these life-threatening clots.
Clinical Interventions for Clot Prevention
Managing stroke risk in AFib patients begins with standard medical therapy, typically involving oral anticoagulant medications (blood thinners). These medications prevent the blood from clotting, mitigating the risk of thrombus formation inside the LAA. However, many patients cannot tolerate long-term anticoagulation due to a high risk of major bleeding, frequent falls, or other medical contraindications.
For patients who cannot tolerate anticoagulation, physicians employ structural interventions to physically close off the LAA. The most common non-surgical procedure is Left Atrial Appendage Occlusion (LAAO), performed using transcatheter devices. These devices, such as the Watchman and the Amulet, are delivered through a catheter inserted via a vein in the groin and deployed to seal the LAA opening.
The goal of LAAO is to permanently isolate the LAA from the main bloodstream, preventing any clots that form inside from escaping and causing a stroke. During open-heart surgery for another condition, a surgeon may perform a surgical exclusion or ligation, where the LAA is either excised or tied off from the rest of the atrium. Both non-surgical and surgical approaches aim to eliminate the LAA as a source of emboli, offering an alternative to lifelong blood thinner use for high-risk individuals.