I ] Variation in the origin of the coronary orifices

A) Angle of origin
Coronary arteries branch from the aorta at variety of angle.
a) 90 degrees (perpendicular origin)
b) Less than 90 degrees (tangential origin)
c) Zero (intussuception), small portion can be seen embedded in aortic wall (intra mural course)

B) Situation of the coronary orifice
They vary both cross-sectionally and frontally.
1) In the Cross sectional plane
a) Left coronary orifice can originate in the mid third of the sinus (87 %), in the posterior third ( 10 %) or in the anterior third ( 3 %).
b) Right coronary orifice will be located in mid third of sinus (40 %), in the posterior third (59 %) or in the anterior third ( 1%).

2) Frontal plane, the position of the orifice is described in relation to the Sino tubular junction.
a) Low take- off’s Coronary orifices are situated in lowest part of coronary sinus.
b) High take-off’s coronary orifices situated 10 mm above line of Sino tubular junction. Usually seen with the RCA.

High origin of left coronary orifice is associated with long left coronary artery and at greater risk of injury either due to low clamping of aorta or due to incision of the aortic wall during valvular replacement.

Most frequent position of orifice is at the Sino tubular junction or below the junction ( 56% ), followed by high left orifice and a low right orifice or at junction ( 30 %).

C) Number of coronary orifices

1) Multiple orifices with right coronary sinus
Most frequent variation in presence of a accessory orifice is the conal artery called 3rd coronary artery.

2) Multiple orifices in the left aortic sinus
a) Absence of common trunk of the left coronary artery which means that LAD and circumflex have the different origin.
b) Mixed orifices (short gun orifices).

3) Multiple orifices in both aortic sinuses.
Combinations of multiple orifices giving rise to presence of 4 or 5 orifices.

II] Variations in length and distribution of coronary arteries.
1) Left Coronary Artery

a) Common Trunk of Left Coronary Artery
Common trunk is described as long if it is above 15 mm. Short trunk means is equal to or less than 5 mm.
The short common trunk is important clinically as during angiographies an incomplete image of the area of distribution of the left coronary artery may be seen on introducing the catheter into only one of the terminal branches and the other would then not show opacification.

Some authors reported existence of short common trunk and the risk factor for the development of coronary atherosclerosis or as a cause of blockage in the left branch of Bundle of His.

b) Trifurcation into LAD, Ramus and Circumflex artery of the left main is known between 25 to 40 %

2) Ramus (Median) artery is one in which
a) Originates in the vertex of angle between LAD and Circumflex artery or in the 1st mm
b) Has substantial caliber.
c) Has area of distribution extending half way down to free wall of the left ventricle.

3) LAD
Three types
Type I) That doesn’t reach apex.
Type II) Reaches till apex.
Type III) Beyond apex into the posterior interventricular group. Portion of the artery in interventricular posterior group known as a posterior recurrent interventricular artery which may entirely substitute PDA.

Bifurcation of the LAD: - Give rise to 2 arteries which are defined as long and short depending on the length. Bifurcation of the LAD should be distinguished from cases of voluminous diagonal arteries, which course parallel to the LAD. Look for septals and whether it comes to A-V groove distally to differentiate between bifurcating LAD and large diagonal.

4) Circumflex artery
2 points of reference are generally used to localise the termination of the circumflex artery, obtuse margin and the crux cordis. 20-30 % of the time it terminate as OM.

5) Right Coronary Artery
The length of the coronary arteries is variable. Termination points are anatomical border of the heart and crux cordis. More than 70 % of them go beyond the crux.

The point of termination of the circumflex and the right coronary artery in relation to the crux has been used to establish coronary dominance.
48 % have right dominant. 18 % have left dominants and 34 % of balanced circulation.

III] Variation in the route of coronary arteries

Myocardial Bridge was first described by Reyman (1737) and called as coronary mural or the submerged artery.
The left marginal artery in the mid portion of the LAD follows most frequent location seen.
Milking effect of the myocardial bridges on the coronary arteries is postulated as possible cause of myocardial Ischemia in some cases.

Occasionally coronary arteries are intracavitatory.

IV] Variation in the origin of Sino-Atrial nodal artery
Sinus node arteries arises from RCA (58 %), from circumflex (42 %) and both arteries in 2%.

V] Variation in Atrio- ventricular node artery.
Origin from the right 86 % of times and circumflex 12 % of times.