The coronary sinus is the main venous channel of the heart, lying in the posterior atrioventricular groove. It is formed at the junction of the great cardiac vein and the oblique vein of Marshall and drains into the right atrium through the coronary sinus ostium, guarded by the Thebesian valve. It receives the great cardiac vein (anterior interventricular groove), middle cardiac vein (posterior interventricular groove), small cardiac vein, and several posterior left ventricular veins.
The coronary sinus is the primary access route for cardiac resynchronisation therapy (CRT) lead placement: a left ventricular pacing lead is advanced through the coronary sinus and positioned in a lateral or posterolateral cardiac vein to resynchronise left ventricular contraction in heart failure with bundle branch block. The coronary sinus ostium in the right atrium is also the landmark for retrograde cardioplegia delivery during cardiac surgery. Coronary sinus defect produces left-to-right shunting in unroofed coronary sinus syndrome.
Advancement of a coronary sinus lead into a small or acutely angled lateral cardiac vein risks perforation of the thin venous wall, producing pericardial effusion or tamponade requiring drainage; careful fluoroscopic technique and use of over-the-wire lead delivery reduces this risk.
A rare congenital defect in the wall between the coronary sinus and the left atrium creates a left-to-right shunt with associated persistent left superior vena cava draining to the coronary sinus, producing right heart volume overload and requiring surgical repair.
