Coronary artery anomalies encompass a diverse range of pathological and non-pathological deviances from the normal arrangement. Variations are commonly seen in the coronary ostia, ramifications of the coronary arteries and courses of the coronary arteries (Figure 1).
Anomalies in Origin
Absent left main (LM) or separate origin of left anterior descending (LAD) and left circumflex (LCx) from the left sinus of Valsalva has been found to be the most common anomaly of coronary artery origin, followed by anomalous origin of the LCx from the right coronary artery (RCA) or right coronary cusp[3]. Other anomalies of origin, such as single origin (figure 2), are seen to be significantly rarer with reported incidence of up to 0.066%[7].
Anomalous origin of the right coronary artery has been reported to be present in 0.25% of the population[5] (figures 3, 4). This is a particularly critical variant of note, due to many of these cases demonstrating an inter-arterial course of the anomalous RCA that carries a potentially serious risk of sudden cardiac death from luminal compression (discussed further in the subsequent section). Conversely, origin of the LAD from the right coronary cusp is far less common, with prevalence of 0.03% reported[3], but can pose an equal threat if the artery runs an inter-arterial course. Anomalous ostial morphology itself can also render luminal constriction (figure 5).
Origin from a non-coronary cusp is exceedingly rare; LM origin from the posterior cusp is seen in 0.0008% and RCA origin from the posterior cusp in 0.003%[3] (figure 6).
Anomalous Origin of the Left Coronary Artery from the Pulmonary Artery (ALCAPA), also known as Bland-White-Garland syndrome, is an incredibly rare variant (figure 7), reportedly 0.00003% of the population[6]. In this anomaly, there is hypoperfusion of the myocardium in the critical region of the interventricular septum and left ventricle with subsequent development of ischemia and infarction.
Anomalies in Course
Anomalies in the coronary artery course are typically defined as malignant and non-malignant, relating to the risk of physiological sudden cardiac death, typically exercise-induced. There has been purported attribution to not just the inter-arterial nature of its course (and thus the subsequent risk of compression between the major vessels) but additional further factors, such as acute angle take-off and intra-mural course[7]. Other texts describe origin of the ostia in relation to the location of the pulmonary valve as potentially problematic – above the valve most at risk of compression due to simultaneous dilatation of the aorta and pulmonary trunk from rapid blood flow in systole[8].
Of all the anomalous courses, malignant courses are by far less common; figures from an extensive case study of 126,595 patients demonstrated 81% of coronary artery anomalies were indeed benign[3].
Classic examples of malignant coronary course include inter-arterial course of anomalous RCA from the left coronary cusp (figure 8) and inter-arterial course of anomalous LAD from the right coronary cusp (figure 9). Inter-arterial RCA course is relatively common when compared to prevalence of inter-arterial course of the left coronary artery (reported at around 0.23% vs 0.03% incidence respectively)[9].
In contrast, the pre-pulmonic anterior course of an anomalous coronary artery from the opposite coronary sinus (figures 10, 11) is benign given the absence of compression. Similarly, the retro-aortic course of anomalous LCx from the right coronary cusp (figure 12), a common anomaly with a 0.37% prevalence[3], is also benign in nature.
Another common variant seen is intra-mural course (figures 13, 14), with a prevalence rate of up to 23% of the population demonstrated. Given the intra-muscular nature of the course, there is evidence demonstrating that dynamic compression occurs in a high proportion of cases, seen in around 19.1% of patients with this anomaly, with ranging degree of luminal narrowing and symptomatology [10]. Intra-cavitary courses are contrastingly rarer, with a case study reporting 0.9% prevalence for the LAD and 0.4% prevalence for the RCA (figure 15)[11].
Anomalies in Ramifications
The most common benign anomaly is trifurcation of the LM with a third branch, the ramus intermedius, which has a reported prevalence of up to 31% of the general population[12] (figure 16).
Dual systems are usually of the RCA (figure 17) or LAD (figure 18); these anomalies are generally benign, but recognition is important for surgical/angiographic procedural planning. Split RCA has been reported to be seen in up to 1% of the population[13] and dual LAD in up to 0.68% of the population[14]).
There are multitudes of possible variations in ramifications of the major coronary arteries and their branches, such as anomalous posterior descending artery (PDA) origin from the coronary cusp (figure 19), and LCx extension from the RCA (figure 20).
Anomalies in Terminations
Coronary arterio-venous fistulae (figure 21) are rare (prevalence 0.002%), mostly congenital, and vary in calibre. Many small fistulae do not cause any serious cardiac compromise and may go undetected, but those of larger calibre are often problematic and require monitoring and intervention[15]. Extra-cardiac terminations are even rarer and vary in not just range and spectrum but also pathological risk.
Coronary artery arcades are quite uncommon with minimal case studies and limited data on exact prevalence, although one case report states an incidence of 1 in 500 cases, or 0.05%[16]. They are distinct from the microscopic collaterals seen normally, differentiated by calibre (>1mm)[17].