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I./1.3.: Left coronary artery (a. coronaria sinistra)
I./1.3.1.: Left coronary artery (a. coronaria sinistra) – in general
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The left coronary artery (LCA) arises from the left aortic sinus; its initial main stem courses horizontally in the postero-lateral direction between the base of the pulmonary trunk and the left atrial appendage embedded in subepicardial areolar fatty connective tissue. Its inner diameter at the origin measures 4.21 mm on average. The main stem then curves around the pulmonary trunk and turns ventrally; and beneath the left auricle it bifurcates into two major branches, the left anterior descending and the left circumflex arteries.
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Study the images, and analyze what you see!
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4. fotó: A jobb fülcse bal pitvar illetve kamra a bal artéria koronáriával - Molnár Attila és Balogh Attila).
(1) Auricula dextra; (2) Crista terminals; (3) Atrium sinistrum; (4) Truncus pulmonalis; (5) Arteria coronaria sinistra; (6) Arteria circumflexa; (7) Arteria interventricularis anterior; (8) Ventriculus sinister
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Occasionally, the main stem splits into three or four branches. The left descending artery, a direct continuation of the left main stem, descends obliquely forward and left in the anterior interventricular groove and in majority of cases reaches the apex of the heart. The circumflex artery, the second main branch, originates perpendicularly from the main stem and its initial section runs under the left auricle, in the left atrioventricular groove, and around the left ventricular margin toward the crux. In right dominant hearts, the circumflex artery terminates between the obtuse margin of the left ventricle and crux region.
I./1.3.2.: Segments of the LCA
Clinicians separate the LAD into three segments; however the inter-segmental borders are described differently. The first diagonal branch or the first major perforating septal branch is used as a landmark in designating the different segments of the LAD. The proximal segment is the region between the origin of the LAD and the origin of D1 or the first perforating artery . The segment between the D1 or S1 and the D2 is the mid-LAD. The most distal third of the LAD is called the distal segment.
There are clinicians who used to divide the circumflex artery into three segments: proximal (from vessel origin to first major obtuse marginal branch), mid (between obtuse marginal branch one and two), and distal (the vessel distal to the second obtuse marginal).
I./1.3.3.: Branches of the LCA
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1.: Main stem of the LCA (truncus proximalis arteriae coronariae sinistrae)
The main stem varies in length from 3 mm up to 30 mm. This segment has usually no branches. Rarely, an atrial branch or a left sinuatrial artery may arise from the left main stem.
2.: Anterior interventricular artery – left anterior descending artery (a. interventricularis anterior)
As the largest branch of the LCA, its inner diameter at its origin is 3.32 mm on average. This appears to be in the similar range of that of the right coronary main stem (3.39 mm). It reaches the apex in most cases. One third terminates at the apex, but the majority turn into the posterior interventricular sulcus, and travel towards the terminal branch of the posterior descending artery. About half of the backward turning arteries terminate 10 to 25 mm from the apex, while the other half extend further back up to 55 mm from the apex. Occasionally the LAD bifurcates and the two vessels run parallel on the sides of the anterior interventricular groove towards the apex.
Branches of the LAD
2.1.: Left conus branch (r. sinister coni arteriosi)
A usually small branch, the left conus artery arises from the initial portion of the LAD (often as a first branch) and curves over the infundibulum of the right ventricle to meet the right conus artery forming an anastomosis known as the Vieussens’ arterial ring. Sometimes, this small branch does not course over the right outflow tract, but instead courses behind anastomosing with the vasa vasorum of the pulmonary artery and the aorta.
2.2.: Diagonal branches (rr. diagonales)
The left ventricular branches of the LAD are known as the diagonal branches, because they branch off at acute angles and extend over the sternocostal aspect of the left ventricle in a diagonal fashion toward the obtuse margin. They run parallel to one another and are highly variable in number (2 to 9). The first diagonal branch tends to be the most prominent. Diagonal branches supply the sternocostal aspect of the left ventricle.
2.3.: Right anterior ventricular branches (rr. anteriores ventriculi dextri)
Right ventricular branches of the LAD, when present (one or two), are usually short and extend over the adjacent right ventricular surface, usually meeting right ventricular branches originating from the RCA. The right anterior ventricular area supplied by these vessels is negligible.
2.4.: Anterior septal branches (rr. interventricularis septalis anteriores)
Numerous (up 12) septal branches, also known as septal perforating branches in clinical practice, arise from the LAD and travel down and posteriorly in the interventricular septum toward the shorter posterior septal rami proceeding anteriorly and upward from the posterior descending artery. The anterior septal vessels usually supply about the ventral two-thirds of the septum. The first septal perforating artery characteristically arises perpendicular to the LAD. In some cases this branch plays the functionally important role of exclusively supplying the atrioventricular node and/or to bundle of His with blood.
Atrioventricular block usually develops following LAD occlusion, as a result of extensive septal necrosis involving the bundle branches. The second or third septal perforating artery is the longest and exhibits the largest inner diameter (up to 2.2 mm) among the septal perforators. It is known as the main septal perforator, or the moderator, or the left descending septal artery. The middle portion of the septum is supplied by this artery and it sends one or two vertically descending fine branches to the moderator band in the septomarginal trabecule, and their terminal twigs loop up into the anterior papillary muscle of the right ventricle.
3.: Circumflex artery (r. circumflexus) - Segments of the circumflex artery
Originating from the left main, the left circumflex artery has a diameter 2.99 mm on average at its root. It curves left in the atrioventricular sulcus travelling round the left cardiac margin into the posterior portion of the sulcus and terminates left of the crux in the right dominant hearts. This is found in most hearts. Clinicians distinguish three segments: the proximal segment extends from origin of the circumflex artery to the first obtuse marginal branch; the mid-segment extends from the first obtuse marginal branch to the second one; and the third distal segment extends from the second obtuse marginal to the termination.
Branches of the circumflex artery:
3.1.: Lateral diagonal branches (rr.diagonales laterales)
They supply the lateral wall of the left ventricle and the anterolateral (anterior) papillary muscle of the bicuspid valve. Their numbers are variable.
3.2.: Left marginal branch – obtuse marginal branch (rr. marginalis sinistri)
The circumflex artery curving around the obtuse margin gives rise to the marginal branches (1 to 3 branches) that descend toward the apex and curve slightly toward the posterior surface of the heart supplying the anterolateral (anterior) papillary muscle with marginal tributaries. However, the posterior papillary muscle along with the posterior wall is entirely perfused either by the left ventricular branches of the RCA or by the third obtuse marginal branch. It is also noteworthy that the type of blood supply of the posterior papillary muscle seems to be independent of the coronary dominance.
3.3.: Posterior branch of the left ventricle (r. posterior ventriculi sinistri)
This branch supplies or contributes to the blood supply of the posterior papillary muscle of the bicuspid valve and the posterior diaphragmatic left ventricular wall with the branches derived from the RCA.
Atrial branches
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3.4.: Left sinuatrial nodal artery (r. nodi sinuatrialis [sinister])
As the strongest atrial vessel, it displays usually a large average diameter of 1.32 mm. Its course to the sinus node is highly variable in length and shape. The left sinuatrial artery may arise from the proximal, middle or distal segments of the circumflex artery, respectively.
Numerous small atrial vessels are described (up to 250) supplying the left atrium. However, in right dominant hearts, twigs from the RCA are also involved in the nourishment of the left atrium:
3.5.: Left lateral atrial branches (rr. atriales sinistri laterales)
3.6.: Left marginal atrial branch (r. atrialis sinister marginalis)
3.7.: Left posterior atrial branches (rr. atriales sinistri posteriores)
3.8.: In left dominant coronary systems
At the crux, the left circumflex artery extends into the posterior interventricular groove to become the posterior descending artery (posterior interventricular artery). Moreover, the left atrioventricular nodal artery may also arise from the circumflex artery in the crux region.
I./1.3.3.4.: Intermediate branch(es)
In 25 % of hearts, the left main artery trifurcates or quadrifurcates. The supplementary, so called intermediate branch(es) or left diagonal branch(es) originate from the angle between the left anterior descending and circumflex arteries. This (these) vessel(s) proceed to the anterolateral wall of the left ventricle displaying a long intramural course; they participate in the blood supply of the sternocostal and lateral aspect of the left ventricle.
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