The cardiac venous system drains deoxygenated blood from the myocardium. The majority of cardiac veins drain into the coronary sinus, which empties into the right atrium. A small proportion drains directly into the cardiac chambers via Thebesian veins.
Coronary Sinus
The coronary sinus is the largest cardiac vein, measuring approximately 3-5 cm in length and 8-12 mm in diameter. It is located in the posterior atrioventricular groove on the diaphragmatic surface of the heart.
Course
The coronary sinus begins at the junction of the great cardiac vein and the oblique vein of the left atrium (ligament of Marshall). It runs rightward along the posterior atrioventricular groove and empties into the right atrium through the coronary sinus orifice, located between the inferior vena cava and the tricuspid valve.
Ostium
Location: Posterior wall of the right atrium, between the Eustachian valve (valve of the IVC) and the tricuspid annulus
Thebesian Valve: A semilunar valve that covers the coronary sinus orifice in approximately 70% of hearts. It is usually small but can be large enough to impede catheterization.
Triangle of Koch: The coronary sinus orifice forms the posterior border of the triangle of Koch (landmark for the AV node).
Tributaries of the Coronary Sinus
| Vein | Origin | Course | Drainage Territory |
|---|---|---|---|
| Great cardiac vein | Apex (anterior interventricular groove) | Ascends in anterior interventricular groove, curves into left atrioventricular groove | Anterior LV, septum, apex |
| Middle cardiac vein | Apex (posterior interventricular groove) | Ascends in posterior interventricular groove | Posterior LV, posterior septum |
| Small cardiac vein | Right acute margin | Ascends in right atrioventricular groove | Right ventricle, right atrium |
| Posterior vein of LV | Posterior LV wall | Drains directly into coronary sinus | Posterolateral LV |
| Left marginal vein | Left obtuse margin | Drains into great cardiac vein or directly into coronary sinus | Lateral LV |
| Oblique vein of LA | Left atrium (ligament of Marshall) | Joins coronary sinus origin | Left atrium |
Great Cardiac Vein
The great cardiac vein (GCV) is the longest cardiac vein. It accompanies the LAD in the anterior interventricular groove and then the LCx in the left atrioventricular groove.
Course:
- Begins at the apex (anastomosing with the middle cardiac vein)
- Ascends with the LAD in the anterior interventricular groove
- Curves posteriorly around the obtuse margin
- Continues in the left atrioventricular groove
- Joins the coronary sinus at the ligament of Marshall
Tributaries: Left marginal vein, anterior interventricular veins, left atrial veins
Clinical significance: The GCV is used for left ventricular lead placement during cardiac resynchronization therapy (CRT).
Middle Cardiac Vein
The middle cardiac vein (MCV) accompanies the posterior descending artery in the posterior interventricular groove.
Course:
- Begins at the apex
- Ascends in the posterior interventricular groove
- Drains into the coronary sinus at or near its termination in the right atrium
Tributaries: Posterior septal perforating veins
Clinical significance: The MCV is used for pacing and defibrillator leads.
Small Cardiac Vein
The small cardiac vein (SCV) accompanies the RCA in the right atrioventricular groove.
Course:
- Begins at the acute margin of the heart
- Ascends in the right atrioventricular groove
- Drains into the coronary sinus near its termination
Note: The SCV is absent in approximately 20% of hearts.
Anterior Cardiac Veins
The anterior cardiac veins drain the anterior right ventricular wall directly into the right atrium, bypassing the coronary sinus.
Characteristics:
- 2-5 veins
- Course across the right atrioventricular groove
- Empty directly into the right atrium
- Visible on the anterior surface of the heart
Thebesian Veins (Venae Cordis Minimae)
The Thebesian veins are small valveless channels that drain directly from the myocardium into the cardiac chambers.
Characteristics:
- 20-50 small channels
- Most numerous in the right atrium and right ventricle
- Provide direct myocardial drainage into the chambers
- May contribute to physiologic shunting
Physiologic significance:
- Normally minimal flow (1-5% of coronary blood flow)
- Increase in disease states (hypertrophy, ischemia)
- Contribute to myocardial turgor during diastole
- May provide collateral circulation in coronary occlusion
Venous Drainage Patterns
| Cardiac Region | Venous Drainage |
|---|---|
| Left ventricle (anterior, lateral) | Great cardiac vein, left marginal vein |
| Left ventricle (posterior) | Posterior vein of LV, middle cardiac vein |
| Interventricular septum (anterior) | Great cardiac vein |
| Interventricular septum (posterior) | Middle cardiac vein |
| Right ventricle (anterior) | Anterior cardiac veins |
| Right ventricle (posterior) | Small cardiac vein, middle cardiac vein |
| Left atrium | Oblique vein, left atrial veins |
| Right atrium | Small cardiac vein, anterior cardiac veins, Thebesian veins |
| Apex | Great cardiac vein, middle cardiac vein |
Clinical Significance
Coronary Sinus Catheterization
The coronary sinus is accessed for:
- Cardiac resynchronization therapy (CRT): Left ventricular lead placement via the great cardiac vein or posterolateral vein
- Electrophysiology studies: Mapping of left-sided accessory pathways
- Retrograde cardioplegia: Delivery of cardioplegic solution during cardiac surgery
- Coronary sinus sampling: Measurement of cardiac biomarkers (e.g., troponin, BNP)
Coronary Sinus Anatomy for CRT
Successful left ventricular lead placement requires understanding of:
- Coronary sinus anatomy and variants
- Target vein selection (posterolateral vein is preferred)
- Thebesian valve obstruction
- Coronary sinus dissection risk
Coronary Sinus Trauma
The coronary sinus can be injured by:
- Blunt chest trauma
- Cardiac surgery (especially reoperations)
- Catheter manipulation during electrophysiology procedures
- Pacemaker lead placement
Coronary Sinus Abnormalities
Coronary sinus enlargement:
- Persistent left superior vena cava
- Anomalous pulmonary venous drainage
- Right heart volume overload
Coronary sinus atresia:
- Absent coronary sinus orifice
- Cardiac veins drain via a left superior vena cava
- Associated with persistent left SVC
Coronary Sinus in Congenital Heart Disease
- Atrial septal defects: Coronary sinus ASD (unroofed coronary sinus)
- Persistent left SVC: Drains into coronary sinus, causing enlargement
- Anomalous pulmonary veins: May drain into coronary sinus