Coronary Sinus — Position, Course and Tributaries
Overview
The coronary sinus is the largest vein of the heart. It drains most of the venous blood from the heart wall and returns it to the right atrium.
- Length: ~3 cm
- Essentially a widened, short venous channel — the continuation of the great cardiac vein
Position
Lies in the left posterior part of the coronary sulcus (atrioventricular groove), on the diaphragmatic surface of the heart, between the left atrium above and the left ventricle below.
Course
Runs from left to right within the posterior coronary sulcus, covered by a muscular fold of the left atrium.
Termination
Opens into the posterior wall of the right atrium, between:
- The opening of the inferior vena cava (to its right)
- The right atrioventricular (tricuspid) orifice (anteriorly)
Guarded by a rudimentary, non-functional semilunar valve — the valve of the coronary sinus (Thebesian valve).
Tributaries (5 Named)
| Tributary | Accompanies | Joins Sinus at | Notes |
|---|---|---|---|
| Great cardiac vein | Anterior interventricular artery (then circumflex artery) | Left end of coronary sinus | Largest tributary; begins at apex, ascends in anterior interventricular groove, turns left in coronary sulcus |
| Middle cardiac vein | Posterior interventricular artery | Middle part of coronary sinus | Ascends in posterior interventricular groove from apex |
| Small cardiac vein | Right coronary artery | Right end of coronary sinus | Runs in right posterior coronary sulcus; right marginal vein may drain into it |
| Posterior vein of left ventricle | — | Coronary sinus (middle part) | Runs on diaphragmatic surface of left ventricle |
| Oblique vein of left atrium (vein of Marshall) | — | Left end of coronary sinus | Small vein on posterior surface of left atrium |
Variable Tributaries
| Vein | Drainage |
|---|---|
| Left marginal vein | Accompanies left marginal artery → drains into coronary sinus |
| Right marginal vein | Accompanies right marginal artery → drains into small cardiac vein OR directly into right atrium |
Development of the Oblique Vein of Left Atrium
The oblique vein of Marshall develops from the left common cardinal vein (duct of Cuvier). Normally it regresses almost completely. Occasionally the left common cardinal vein persists as a left superior vena cava, which drains into the coronary sinus (instead of the right atrium). This is the most common congenital venous anomaly of the thorax.
Clinical Correlations
Cardiac resynchronisation therapy (CRT): In heart failure with left bundle branch block, a pacing lead is placed in a lateral branch of the coronary sinus (to pace the left ventricle). Anatomical knowledge of the coronary sinus tributaries is essential for lead placement.
Retrograde cardioplegia: During cardiac surgery (cardiopulmonary bypass), cardioplegic solution is infused in a retrograde direction through a cannula placed in the coronary sinus — protecting the myocardium during aortic cross-clamping.
Persistent left superior vena cava: If the left common cardinal vein persists, it forms a left SVC draining into the coronary sinus → the coronary sinus becomes markedly dilated. Visible as a large shadow lateral to the aortic knuckle on CXR.