Surgical Anatomy
With the exception of the Leiden convention,8 attempts categorising the variations in coronary arterial patterns have foundered either because of incompleteness or undue complexity. The Leiden convention itself is less than perfect, failing to account for the course of the coronary arterial stems relative to the arterial roots. Nor does it recognise that, on occasion, the coronary arteries themselves may be absent or duplicated. This does not mean that it should be discarded. Nor does it necessitate the addition of new codes.9 On the contrary, it retains its major value in accounting adequately for the origin of the coronary arteries from the aortic valvar sinuses. It is an easy matter then to account for additional features in descriptive fashion.
The convention is based on the anticipated presence of the three major coronary arteries, each with well-recognised areas of myocardial supply. The right coronary artery supplies the right ventricular myocardium and, when dominant, a variable portion of the diaphragmatic wall of the left ventricle. The circumflex artery supplies the obtuse marginal wall of the left ventricle. If dominant, this artery can supply part of the diaphragmatic wall of the right ventricle. The anterior interventricular artery supplies the anterior walls of both ventricles, along with the anterior part of the ventricular septum. The variations found in the setting of transposition can then almost always be understood on the basis of “marriage of convenience” between the arteries and the aortic valvar sinuses.6 Thus, the coronary arteries typically arise from one or other, but usually both, of the aortic sinuses adjacent to the pulmonary trunk (Figure 1A). The Leiden approach distinguishes between these sinuses irrespective of the variations in relationship between the roots themselves, and irrespective of which sinus gives rise to which particular artery or arteries. The observer, figuratively speaking, stands upright in the non-adjacent sinus of the aortic root and looks towards the pulmonary root. One of the adjacent aortic valvar sinuses is then to the right hand of the observer, and the other to the left hand (Figure 1A). These positions are retained irrespective of the relationships of the arterial roots (Figure 1B).
In the commonest pattern found in transposition, the right coronary artery arises from the left-handed sinus, while the main stem of the left coronary artery, branching into anterior interventricular and circumflex arteries, arises from the right-handed sinus (Figure 2A). In the second commonest pattern, the circumflex artery arises from the left-handed sinus, taking a retro-pulmonary course (Figure 2B). Distinguishing the sinuses in handed fashion might seem to be illogical because the right coronary artery often arises from the left-handed sinus. The convention, however, does no more than distinguish between the adjacent sinuses. The approach popular amongst cardiac surgeons is to nominate the right-handed sinus as #1, and the left-handed sinus as #2. In a minority of cases, furthermore, the main stem of the left coronary artery does arise from the left-handed sinus (#2). It then passes behind the pulmonary trunk to branch and fulfil its marriages of convenience (Figure 2C). The right coronary artery in this pattern arises from the right-handed sinus (#1), taking an antero-aortic course to reach the right atrioventricular groove.
When all three major arteries are present, assuming they arise from the adjacent sinuses, there are only eight potential patterns of sinusal origin. All have now been described. One is particularly rare, since it breaks the concept of marriage of convenience. In this rarest variant, two of the major arteries cross from their sinusal origin as they extend to supply their myocardial territory.7 In all the other variants, the arteries course from the most appropriate sinus to their myocardial territory. On occasion, however, as shown, the arterial stems course loop the pulmonary root, or else loop in front of the aortic root. Such looping is a constant feature when all the coronary arteries arise from one or other of the adjacent sinuses, with the other adjacent sinus bereft of a coronary arterial origin (Figures 2 E,F).5 Such looping, tethering the coronary arteries to the arterial roots, can create significant problems for the surgeon. In presence of a significant arterial stem, however, such looping does not necessarily produce problems (Figure 2C). A greater surgical problem is encountered when single sinus origin (Figure 3A) is the consequence of an intramural course of one or more of the major arteries.16 Intramural arteries pass between the arterial roots, extending through the wall of the aortic valvar sinus, and usually cross the valvar commissure adjacent to the pulmonary trunk (Figure 3B). Also of potential significance is whether the arteries take individual origin from the valvar sinuses, or whether there is a confluent origin and stem for two of the major branches, or for all three in the setting of a solitary coronary artery.5Additional features of potential significance are the origins of the artery to the sinus node and the infundibular artery (Figure 2). Any of the three major coronary arteries can also be absent or duplicated. Exceedingly rarely, one or more of the coronary arteries can arise from the non-adjacent sinus of the aortic root. This can be a contra-indication to the arterial switch procedure.29A further variation is mismatch between the commissures of the arterial valves (Figures 2A, F).30 If extreme, this variation can complicate safe transfer during the arterial switch.