The coronary sinus is a large venous structure located on the posterior aspect of the left atrium, coursing within the left atrioventricular groove. The function of the coronary sinus is to drain the venous blood from the majority of the heart. It opens into the right atrium between the opening of inferior vena cava, the fossa ovalis and the right atrioventricular orifice. The coronary sinus is often guarded by a thin, semicircular endocardial fold, also known as the Thebesian valve.
The coronary sinus originates from the confluence of the oblique vein (of Marshall) of left atrium and the great cardiac vein, and receives the small and middle cardiac veins, and the posterior vein of the left ventricle as tributaries.
|Drains from||Confluence of the oblique vein (of Marshall) of left atrium and the great cardiac vein|
|Tributaries||Small and middle cardiac veins, the posterior vein of the left ventricle|
|Drains to||Right atrium|
This article will discuss the anatomy and function of the coronary sinus.
Anatomy and course
The coronary sinus is the largest cardiac venous structure. It arises from the confluence of the oblique vein (of Marshall) of left atrium and the great cardiac vein. The sinus then courses for about 2 or 3 cm within the posterior atrioventricular groove, between the left atrium and left ventricle. It then opens into the right atrium between the opening of inferior vena cava, the fossa ovalis and the right atrioventricular orifice.
Aside from the oblique vein of left atrium and the great cardiac vein, the coronary sinus also receives venous blood from the small and middle cardiac veins, and the posterior vein of the left ventricle. This means that the coronary sinus drains most of the cardiac veins, except the smallest cardiac (Thebesian) veins, which drain directly into all four chambers of the heart, and the anterior cardiac veins which drain directly into the right atrium.
The orifice of the coronary sinus is often covered by a thin, semicircular endocardial fold, also known as the Thebesian valve. When present, this valve covers the lower part of the atrioventricular orifice, but it may cover the ostium of the sinus completely, or be absent altogether.
The coronary sinus represents a prominent landmark in the right atrium. It takes part in the demarcation of the triangle (of Koch) of atrioventricular node. The anteromedial margin of the orifice of coronary sinus defines the base, while the subendocardial tendon of Todaro is the superior margin, and the attachment of the septal leaflet of the tricuspid valve is the inferior margin of the triangle. The triangle of Koch is an important surgical landmark that indicates the site of the atrioventricular (AV) node and its atrial connections.
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The tributaries of the coronary sinus can be quite variable. Aside from the usual tributaries, the coronary sinus may also receive the anterior cardiac veins in about 33% of cases, and occasionally the left marginal vein. At times, the coronary sinus can be obliterated or absent. In that case, the cardiac veins drain into the superior vena cava or left brachiocephalic vein via the oblique vein of Marshall. Rarely, the coronary sinus may drain into the left atrium, causing a left-to-right shunt.