Blood Supply (Dominance) Type Concept
In diagnostic radiology, the type of coronary dominance is determined by which specific blood vessel gives rise to the posterior descending artery (posterior descending artery, PDA), which supplies the posterior interventricular septum.
- Right-dominant type (Right dominant): The PDA originates from the right coronary artery. This is a normal variant for 80% of the population. The circumflex branch is small in this case.
- Left-dominant type (Left dominant): The PDA arises from the circumflex branch of the left coronary artery. Found in 10%. In this case, the right coronary artery is initially short, and the right coronary sulcus remains empty.
- Co-dominant type (Co-dominant): Observed in the remaining 10% of cases.
Determining the type is critically important in clinical practice as it helps avoid misdiagnosis of occlusion. For example, an inexperienced specialist might mistake an empty right sulcus in a left-dominant heart for a complete occlusion of the right artery.
Anatomy of the Right Coronary Artery (RCA)
The right coronary artery originates from the right Valsalva sinus and descends along the right atrioventricular sulcus. Its major branches can be traced in detail on transverse CT reconstructions:
- Conus branch (conus branch) — runs along the right ventricular outflow tract.
- Atrioventricular branch — extends posteriorly toward the sinuatrial node.
- Acute marginal branches (acute marginal) — run along the free wall of the right ventricle.
- Posterior descending branch (PD) — descends into the posterior interventricular sulcus.
- Posterolateral branch (PL) — is the distal continuation of the main trunk.
Anatomy of the Left Coronary Artery (LCA)
The left main coronary artery (LM) originates from the left Valsalva sinus. In rare cases (1%), the trunk is absent, and the arteries originate from separate ostia. Normally, the trunk divides into two main vessels:
- Left anterior descending artery (LAD). Runs in the anterior interventricular sulcus. It gives off septal branches vertically downward and diagonal branches (D) to the anterolateral wall of the left ventricle.
- Circumflex artery (Cx). Runs along the left atrioventricular sulcus. It forms obtuse marginal branches (OM) that supply the lateral free wall. Notably, the obtuse marginal branch often appears larger on reconstructions than the circumflex artery itself, which is completely normal.
Principles of CT Assessment and Nomenclature
To accurately describe the location of stenoses, anatomical segment names (proximal, middle, and distal thirds) should be used, as an abundance of numerical classifications can cause confusion.
The primary vascular analysis during CT coronary angiography must be performed strictly on original axial (transverse) slices. Only these provide an objective picture without distortion. Additional methods, such as 3D Volume-Rendered CT or curved multiplanar reconstructions (Curved MPR), are used only for a rapid spatial overview or evaluation of tortuous segments in a single plane.
Venous System of the Heart on Tomograms
In addition to arteries, elements of the venous system are clearly visible on CT images. The main collector is the coronary sinus (Coronary sinus). It collects blood from the great cardiac vein (GCV), the anterior and posterior interventricular veins, the left marginal vein, and the posterior left ventricular vein. The exception is the right atrial vein, which empties blood directly into the right atrium, bypassing the sinus.
Briefly: answers to topical questions
What branches does the right coronary artery give off?
The right coronary artery gives off a series of branches supplying the right heart chambers and the posterior wall of the left ventricle. Its main branches include:
- Conus branch (r. coni arteriosi / conus branch) — runs along the right ventricular outflow tract.
- Sinuatrial nodal branch (r. nodi sinuatrialis) — heads toward the sinuatrial node.
- Right marginal branch / acute marginal branches (r. marginalis dexter / acute marginal branches) — run along the free wall of the right ventricle.
- Intermediate atrial branch (r. atrialis intermedius) — supplies the posterior wall of the right atrium and ventricle.
- Atrioventricular nodal branches (rr. nodi atrioventricularis) — supply the corresponding node.
- Posterior interventricular branch / posterior descending branch (r. interventricularis posterior / posterior descending branch) — runs in the posterior interventricular sulcus.
- Posterolateral branch (posterolateral branch) — is the continuation of the artery in the left atrioventricular sulcus.
What branches does the circumflex branch of the left coronary artery form?
The circumflex branch of the left coronary artery gives off:
- Obtuse marginal branches (obtuse marginal branches, OM) — typically 1 to 3 branches supplying the lateral free wall of the left ventricle.
- Sinuatrial nodal artery — in approximately 1/3 of the population, it originates from the circumflex branch of the left coronary artery.
Which cardiac veins drain directly into the right atrium, bypassing the coronary sinus?
The right atrial vein (right atrial vein) drains directly into the right atrium.
Which myocardial regions are supplied by the posterior descending artery?
The posterior descending artery, or posterior interventricular branch, supplies:
- the posterior part of the interventricular septum;
- the posterior wall of the left ventricle;
- the posterior wall of the right ventricle.
It gives off interventricular septal branches. The posterior interventricular branch itself dips into the myocardium at approximately the border of the middle and lower thirds.
To avoid confusing the marginal branches: the RIGHT coronary artery gives off ACUTE marginal branches (mnemonic "RA"), while the LEFT circumflex branch gives off OBTUSE marginal branches (mnemonic "LO").
Class and exam questions
What is the advantage of invasive coronary angiography over CT?
Invasive angiography is the gold standard due to its highest resolution. It allows visualization of the true vessel lumen, and its quality is not degraded by dense calcifications in plaques, which often hinder CT.
What is the intermediate artery and where to find it?
The ramus intermedius is an anatomical variant found in one-third of patients. It originates from the left main coronary artery and lies on the left ventricular wall strictly between the anterior descending and circumflex branches.
How to distinguish a left-dominant blood supply from occlusion of the right artery?
In left-dominant circulation, the posterior descending artery originates from the circumflex branch. Meanwhile, the right coronary sulcus appears empty, and the right artery itself is very short — this is normal topography for this type, not an occlusion.
What else to study on this topic
- Topography and Functions of the Aortic Valve Sinuses of Valsalva
- Standard Projections for Left Ventricular Orientation on CT
- Anatomical Variations of Sinuatrial Nodal Artery Origin
- Functional Assessment of Heart Valves Using MRI and Echocardiography
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