Where do the coronary arteries arise and what do they supply?
The coronary arteries arise from the sinuses of Valsalva, just beyond the aortic valve. The right coronary artery (RCA) leaves the anterior (right) aortic sinus. The left coronary artery (LCA) leaves the left posterior aortic sinus and, after a short left main stem (LMCA), divides into the left anterior descending (LAD) and the left circumflex (LCx). Together these three vessels are the main epicardial arteries.
Radiology convention names each artery by its territory, not by where it originates. Only the left side has a common stem; the normal LMCA is typically described as having no significant branches of its own before it bifurcates. The LMCA length ranges from about 2 mm to 4 cm, which is why a short or absent stem is one of the recognised anomalies.
| Artery | Course | Main branches | Dependent territory |
|---|---|---|---|
| RCA | Right atrioventricular groove, round the acute margin to the crux | Conus, sinus node, right marginal, AV nodal and posterior interventricular branches | Right atrium and ventricle, SA and AV nodes, inferior part of the septum |
| LAD | Anterior interventricular groove towards the apex (10–13 cm) | Diagonal and septal perforator branches | Anterior wall of the left ventricle and most of the septum |
| LCx | Left atrioventricular groove onto the diaphragmatic surface (5–8 cm) | Obtuse marginal branches; sometimes the posterolateral branch | Lateral wall of the left ventricle |
What are the branches of the right coronary artery?
The RCA passes forwards and to the right between the right auricle and the pulmonary trunk, descends in the right atrioventricular groove, and turns backwards at the acute margin to reach the crux of the heart. Its length is roughly 12–14 cm. A radiology review lists the branches in the order they usually appear.
- Conus branch — first branch in about 50–60% of people; supplies the right ventricular outflow tract. It may arise directly from the aorta instead.
- Atrial branch — runs in the groove between the right auricle and the ascending aorta.
- Sinus node artery — arises from the RCA in about 60–66% of people (from the LCx in the rest) and loops behind the superior vena cava to reach the SA node.
- Right (acute) marginal branch — runs along the acute margin and supplies the right ventricular free wall.
- AV nodal branch — a small branch from the dominant artery to the AV node; in most people it comes from the distal RCA.
- Posterior interventricular (descending) artery — final major branch, in the posterior interventricular groove.
In summary the RCA supplies the right atrium and right ventricle, the sinoatrial and atrioventricular nodes, the interatrial septum, part of the left atrium, the posteroinferior third of the interventricular septum and part of the posterior left ventricle.
What do the LAD, circumflex and ramus intermedius supply?
The LAD continues around the left side of the pulmonary trunk and runs obliquely in the anterior interventricular groove towards the apex. It is usually 10–13 cm long and is divided into proximal, middle and distal thirds at the first septal perforator and the halfway point to the apex. It gives one or two large diagonal branches across the anterior left ventricle and the septal perforators, which supply the anterior two-thirds of the basal septum and the whole septum at mid and apical levels.
The LCx runs in the left atrioventricular groove and usually ends before it reaches the posterior interventricular groove. It is shorter (5–8 cm) and has only two segments, divided by the origin of the first obtuse marginal branch. It supplies the lateral left ventricle and, in left-dominant hearts, also gives the posterior descending artery.
In some hearts the LMCA divides into three vessels: the LAD, the LCx and a ramus intermedius. The ramus behaves like a diagonal or obtuse marginal branch and supplies the lateral and inferior walls. The LAD may also curve round the apex to reach the inferior surface (a wraparound LAD).
What is coronary dominance and how common is each pattern?
Dominance is defined by which artery gives off the posterior descending artery (PDA) — the vessel in the posterior interventricular groove that supplies the inferior wall and the posterior third of the septum. It has nothing to do with which artery is the larger. If the PDA comes from the RCA the heart is right dominant; from the LCx, left dominant; if both contribute, codominant.
| Pattern | PDA arises from | Approximate frequency |
|---|---|---|
| Right dominant | Right coronary artery | About 70–80% |
| Left dominant | Left circumflex artery | About 5–10% |
| Codominant | Both RCA and LCx | About 10–20% |
Published ranges differ slightly: one StatPearls chapter gives 70–80%, 5–10% and 10–20%, while a radiology review quotes roughly 70%, 10% and 20%. For an exam, remember that right dominance is about three-quarters and the other two patterns share the rest. A rare variant in which the LAD continues as the PDA is called 'superdominant'.
Dominance is determined at cardiac catheterisation by injecting contrast into the left main and right coronary ostia. It also guides bypass grafting, because the surgeon must know which vessel supplies the inferior wall before choosing graft targets.
Why does coronary flow peak in diastole?
The heart has the highest oxygen consumption per unit mass of any organ, yet the coronary circulation receives only about 5% of cardiac output. In most tissues flow peaks in systole; in the coronaries it is paradoxical and peaks in diastole. During systole the contracting myocardium compresses the intramural vessels, most strongly in the subendocardial layer of the thick left ventricle, and flow can even reverse transiently. Diastolic relaxation removes that compression.
At rest the myocardium extracts 60–70% of the oxygen from coronary blood, so extraction has little reserve; extra demand must be met by increased flow. Regulation is multifactorial. Metabolites (such as carbon dioxide) set resting flow, adenosine matters mainly in ischaemia, nitric oxide responds to shear stress, prostacyclin adds a minor dilator effect, and endothelin is a potent constrictor. Sympathetic effects are relatively minor.
| Reduction in diameter | Functional effect |
|---|---|
| About 50% | Loss of the ability to respond to increased metabolic demand (reserve lost) |
| 80% or more | Substantial enough to reduce flow at rest |
Nitrates and calcium-channel blockers relieve ischaemia partly by dilating the large epicardial arteries. Hypertension raises oxygen demand (muscle hypertrophy from the higher afterload) while reducing flow, widening the mismatch. For related respiratory and cardiac physiology see oxygen-haemoglobin dissociation curve and types of hypoxia.
How does the heart drain — coronary sinus and its tributaries?
The coronary sinus is the largest cardiac vein: 3–5 cm long and about 1 cm in calibre. It lies in the left posterior atrioventricular groove and opens into the posteroinferior right atrium, medial to the inferior vena cava orifice and above the septal leaflet of the tricuspid valve. Its origin is marked by the junction of the great cardiac vein with the oblique vein of the left atrium (of Marshall).
| Vein | Course | Travels with |
|---|---|---|
| Great cardiac vein | Apex up the anterior interventricular groove, round the left margin to the posterior surface | Anterior interventricular (LAD) artery |
| Middle cardiac vein | From the posterior apex in the posterior interventricular groove | Posterior descending artery |
| Small cardiac vein | Coronary groove between right atrium and ventricle | Right marginal branch of the RCA |
| Posterior vein of the left ventricle | Inferior and lateral left ventricular wall, between the middle and great veins | — |
| Oblique vein of the left atrium | Posterior left atrium | — |
Every tributary except the oblique vein has a valve at its junction with the sinus. The Vieussens valve marks the start of the sinus, and the Thebesian valve at its right atrial orifice prevents regurgitation from the atrium in diastole. Do not confuse Thebesian valve (coronary sinus orifice) with Thebesian veins (tiny veins opening directly into the heart chambers).
| Route | Approximate share | Drains into |
|---|---|---|
| Coronary sinus | About 55% | Right atrium |
| Anterior cardiac veins (2–5) | About 35% | Right atrium directly |
| Thebesian veins | About 10% | Any of the four chambers |
Another StatPearls chapter groups the veins as a greater system (coronary sinus, marginal and anterior veins) returning about three-quarters, and a smaller system (Thebesian veins) returning about one-quarter. The fractions differ between sources, so learn the principle — the coronary sinus carries most of the venous return — and use the 55/35/10 split only if the question gives it. Embryologically the sinus is derived from the left horn of the sinus venosus.
Which clinical conditions and anomalies depend on this anatomy?
- Retrograde cardioplegia — cardioplegic solution is delivered backwards through the coronary sinus during cardiac surgery, usually together with antegrade delivery so that tight arterial stenoses do not block distribution. A persistent left SVC is a limitation, because solution may reach the systemic circulation, and coronary sinus rupture is a rare complication.
- Cardiac resynchronisation therapy — in a biventricular pacemaker for advanced heart failure with ejection fraction below 35%, the left ventricular lead is usually placed in a coronary sinus tributary and the right lead in the right ventricle.
- Persistent left superior vena cava — the left brachiocephalic vein fails to form, so left arm and head venous blood drains into the coronary sinus. It is silent alone but often accompanies other cardiac defects.
- Unroofed coronary sinus — an atrial septal defect-type communication between the coronary sinus and the left atrium.
- Myocardial bridging — a segment of coronary artery, most often the proximal LAD, runs within the myocardium and is compressed in systole. Most cases are asymptomatic.
- Anomalous origin of the LAD or left coronary artery from the pulmonary artery — very rare and dangerous; about 90% of untreated affected infants die in the first year. An anomalous artery that passes between the aorta and pulmonary trunk (inter-arterial course) carries a risk of sudden cardiac death.
For the fetal side of cardiac development see fetal circulation, and for valve lesions that change coronary perfusion pressure see valvular heart disease and murmurs.