Venous Drainage of the Heart
The heart's venous drainage occurs primarily through three systems: the coronary sinus system (which drains approximately 60-85% of myocardial venous blood into the right atrium), the anterior cardiac veins (which drain directly into the right atrium), and the smallest cardiac veins (Thebesian veins, which drain directly into all cardiac chambers). 1, 2
Primary Venous Drainage Systems
The Coronary Sinus System (Major Cardiac Venous System)
The coronary sinus is the largest cardiac vein, receiving blood from the great cardiac vein, middle cardiac vein (posterior interventricular vein), small cardiac vein (when present), posterior vein of the left ventricle, and oblique vein of the left atrium 1, 2
The coronary sinus opens into the right atrium between the orifice of the inferior vena cava and the tricuspid valve, with its ostium typically located in a circle-like arrangement with other venous openings 1
Intramural collecting chambers or sinuses exist just before the opening of cardiac veins into the right atrium, which facilitate venous return from the myocardium 1
The Anterior Cardiac Veins (Minor Cardiac Venous System)
These veins drain directly into the right atrium through multiple small openings between the pectinate muscles, bypassing the coronary sinus entirely 1, 2
The right marginal vein joins the anterior cardiac vein system in 64% of cases rather than draining into the coronary sinus via a small cardiac vein (which exists in only 36% of cases), making the anterior cardiac vein system more functionally important than traditionally recognized 1
The Smallest Cardiac Veins (Thebesian Veins)
- These are minute vessels that drain directly into all four cardiac chambers, representing the compound cardiac venous system 2
Anatomical Variations and Clinical Significance
Common Variations
The small cardiac vein is absent in 64% of hearts, with its territory instead drained by the anterior cardiac vein system 1
Intramural courses of the great cardiac vein occur, which can cross coronary arteries and create potential obstacles for catheterization procedures 1
Ostial valves of varying efficiency are present at the openings of cardiac veins and the coronary sinus, which can affect venous drainage and catheter access 1, 2
Congenital Anomalies
Unroofed coronary sinus occurs in association with persistent left superior vena cava in 54% of cases with coronary sinus abnormalities, frequently associated with atrial appendage isomerism and atrioventricular septal defects 3
Coronary sinus orifice atresia results in drainage via a left superior caval vein or a coronary sinus to left atrial window 3
In hearts with discordant atrioventricular connections, the coronary sinus receives all morphologically right ventricular veins plus the posterior interventricular vein in 87% of cases, while morphologically left ventricular veins frequently drain directly into the morphologically right atrium 4
Critical Clinical Considerations
Surgical and Interventional Implications
Before any procedure involving the coronary sinus or left superior vena cava (such as ligation, transcatheter coil embolization, or venous redirection), coronary sinus drainage patterns must be thoroughly evaluated to avoid inadvertent impairment of coronary venous return 3
Extensive intra-atrial maneuvers risk damaging direct venous drainage pathways between pectinate muscles, potentially leading to postoperative intra-atrial thrombosis 4
The presence of a substantial branch supplying the right ventricular outflow tract (found in 61% of hearts with discordant connections) can restrict ventriculotomy placement 4
Catheterization Considerations
Semicircular venous sinuses in the right atrial wall, intramural venous tunnels, and variable ostial valve efficiency all represent potential anatomical hindrances to coronary sinus catheterization and selective cardiac vein access 1, 2
Anomalous connections between the coronary venous system and superior vena cava have been documented and may represent either congenital variants or iatrogenic tracts from repeated interventions 5