Anomalous coronary arteries are frequently seen in conjunction with certain other congenital cardiac defects and may even be considered inherent in some anomalies, such as in transposition of the great vessels. These abnormalities, which may be called secondary coronary artery anomalies, will be discussed in brief at the end of this chapter.
Abnormalities of the origin or the course of coronary arteries in the absence of other congenital cardiac defects, the so-called primary or isolated congenital coronary anomalies, constitute a separate category of congenital cardiac defects.
Primary Congenital Coronary Anomalies
Classification
In view of the great “normal” variability in the coronary anatomy, the division between normal and abnormal anatomy is subject to a certain degree of subjectivity. Furthermore, some relatively common anomalies are generally believed to have no pathologic significance and are therefore classified as “normal variations.” This approach is the basis of a World Health Organization working group classification that divides coronary anomalies into primarily two categories ( Box 58.1 ):
- 1.
Normal variations or anomalies (benign anomalies).
- 2.
Abnormal variations , that is, anomalies generally considered to have clinical relevance.
Normal variations include:
- •
Separate origin of the left anterior descending and left Cx arteries from the left sinus of Valsalva
- •
Large conus branch with separate origin in the right sinus
- •
Abnormal origin of the first septal branch (eg, from the first diagonal branch or right coronary artery [RCA])
- •
Dual left anterior descending arteries
- •
Cx originating from the right sinus or from the proximal RCA and coursing behind the aorta
- •
Most variations in the course of normally originating coronary arteries
Abnormal variations include:
- •
Origin of the coronary artery or main branch from the opposite sinus or from the opposite coronary artery
- •
High takeoff of a coronary artery
- •
Single coronary artery
- •
Origin of left coronary artery or RCA from the pulmonary artery
- •
Tunneling or extensive myocardial bridging of a coronary artery
As will be discussed later, the clinical significance of many anomalies is still unclear, and therefore the second category may be divided into anomalies that unequivocally have pathologic significance (also called malignant or serious anomalies) and those that may have pathologic significance under certain circumstances (also called potentially malignant or serious anomalies).
Several proposals have been made to classify coronary artery anomalies on an anatomic basis. Undoubtedly, a gross anatomic classification is useful, as discussed previously. However, these anomalies are very rare, and proposals for detailed anatomic classification systems comprising many categories may be more confusing than helpful. Most importantly, proper interpretation and evaluation of coronary anomalies is of great clinical importance, irrespective of the merits and limitations of various classification schemes.
Prevalence
Most large studies on the prevalence of congenital coronary anomalies are based on reviews of data obtained at coronary angiography (CAG) in which the reported prevalence ranges from about 0.3% to 2% . The differences between studies may in part be explained by different definitions of abnormal anatomy. If benign variations such as abnormal origin of the circumflex (Cx) artery and separate origin of the left anterior descending and left Cx arteries in the left sinus are excluded, then the prevalence of anomalies is well below 1% in all studies.
In the last decade there has been an exponential increase in the use of computed tomographic coronary angiography (CTCA), in part because it requires no arterial catheterization and is therefore often called a “noninvasive” technique, although it still requires infusion of contrast material. CTCA is eminently suitable for depicting congenital coronary anomalies because of the typical three-dimensional (3D) representations and the visualization of surrounding structures. It is therefore not surprising that this technique has contributed to an increased interest in the diagnosis and management of congenital coronary anomalies. When comparing prevalence data obtained by CTCA with data obtained by CAG, a correction should be made for the presence of myocardial bridging or tunneling, which may be defined as a band of cardiac muscle overlying a segment of a coronary artery. CTCA can visualize these bands, whereas CAG only indirectly demonstrates their presence if they cause systolic narrowing of the arterial lumen, which seems to happen in very few cases. Therefore CTCA studies show a relatively high prevalence of myocardial bridging but most of these cases appear to be benign variations.
Table 58.1 lists the prevalence of congenital coronary artery anomalies according to CTCA studies published after 2011. In most studies the prevalence of potentially harmful anomalies is around 1% and on average, slightly higher than in CAG studies.
| First Author | Year of Publication | No. of Patients | No. of Congenital Coronary Anomalies | % of Congenital Coronary Anomalies |
|---|---|---|---|---|
| Tariq | 2012 | 900 | 14 (8) | 1.56 (0.89) |
| Xu | 2012 | 12,145 | 124 (106) | 1.02 (0.87) |
| Park | 2013 | 1582 | 18 (17) | 1.14 (1.07) |
| Ghadri | 2014 | 1759 | 138 (79) | 7.85 (4.49) |
| Namgung | 2014 | 8864 | 103 (85) | 1.16 (0.96) |
| Graidis | 2015 | 2572 | 60 (39) | 2.33 (1.51) |
| Total | 27,822 | 457 (334) | 1.64 (1.20) |
We must be cautious to extrapolate the data obtained by CAG or CTCA to the population at large. Data obtained by CAG are based on findings in patients who were candidates for coronary arteriography, which introduces a selection bias. However, it may be argued that most patients underwent CAG for evaluation of coronary atherosclerosis and the presence or suspicion of a congenital coronary anomaly was practically never a selection criterion. It is therefore unlikely that the prevalence of congenital coronary anomalies in these patients is much different from the prevalence in unselected populations. Because the threshold for examination by CTCA appears to be lower than for CAG (CTCA has even been proposed as a screening tool for high-risk persons), one might expect that this modality more accurately reflects the true prevalence. However, in most centers, a substantial number of patients undergoing CTCA were referred for a more precise analysis of a congenital coronary anomaly that was detected at CAG, which introduces another selection bias. An exception is a study by Park et al. that examined an unselected group of police officers and found about the same prevalence of congenital coronary artery anomalies as reported in other studies (see Table 58.1 ).
Hopefully, data will become available from screening by noninvasive methods of large asymptomatic populations that will allow a more accurate estimate of the true prevalence of congenital coronary anomalies. In this respect, echocardiography may appear to be a suitable diagnostic modality and has been shown to be useful in certain circumstances, but at present, echocardiographic evaluation cannot replace radiographic methods.
We may conclude that there still is some uncertainty about the prevalence of coronary artery anomalies in the population at large, but that there can be no doubt that these anomalies are rare, which is even truer for (potentially) serious anomalies.
In this chapter, anomalies that have the greatest practical significance are discussed in the most detail. Because most anomalies are detected at CAG or CTCA, we will focus on these diagnostic modalities without detracting from the merit of other less frequently used methods such as magnetic resonance imaging (MRI) and ultrasound studies.
Ectopic Coronary Arteries
Definition
Coronary arteries that do not arise normally from the right or left sinus of Valsalva are usually called ectopic. Well-known variants are:
- 1.
A Cx artery arising from the right sinus of Valsalva or proximal right coronary artery (RCA)
- 2.
Coronary arteries arising from opposite sinus of Valsalva (left coronary artery [LCA] arising from the right sinus or RCA arising from the left sinus)
- 3.
High takeoff of a coronary artery
- 4.
A coronary artery arising from the “noncoronary” sinus
- 5.
The origin of LCA or RCA in the pulmonary artery
Various origins in the aorta or subclavian and bronchial arteries have also been described in case reports.
Circumflex Artery Arising From the Right Sinus of Valsalva or Proximal Right Coronary Artery
A Cx artery arising from the right sinus or proximal RCA is the most common variant of ectopic coronary arteries and is generally considered to have no practical consequences. The anomalous Cx runs behind the aortic root to supply the posterior left ventricular wall ( Fig. 58.1 ). This anomaly is easy to recognize but is occasionally missed at CAG because the catheter is advanced too far in the RCA to opacify the origin of the Cx artery.
Origin of Coronary Arteries in the Opposite Sinus
In various respects, the most important group of anomalies concerns coronary arteries or coronary artery branches arising from the opposite sinus, that is, the LCA arising from the right sinus of Valsalva (or the proximal RCA) or the RCA artery arising from the left sinus of Valsalva or proximal LCA. Until the introduction of CTCA, this was also the group that presented the greatest diagnostic problems because assessment of the course of the artery with anomalous origin visualized by CAG can be cumbersome, although not impossible in most cases with sufficient experience and knowledge of anatomic features. Today CTCA is generally considered the method of choice to accurately depict the origin and course of these arteries in detail.
Anatomy and Physiological Consequences
Left Coronary Artery Arising From the Right Sinus of Valsalva
If the LCA originates in the right sinus of Valsalva, it may, before it divides into the left anterior descending and left Cx arteries, follow one of the following courses: (1) in the interventricular septum, the intraseptal (or intramyocardial) course; (2) between the aorta and pulmonary artery, the interarterial course; (3) anterior to the pulmonary artery, the anterior course; (4) posterior to the aorta, the posterior course ( Fig. 58.2 ).
The intraseptal course is the most common variant; in this case the left main coronary artery (LMCA) crosses the superior aspect of the crista supraventricularis, then passes a variable distance through the interventricular septum where it gives off one or more septal branches, and finally reaches an epicardial position where it divides into the left anterior descending and left Cx arteries. This is generally considered to be a benign anomaly, but occasionally this anomaly is held responsible for symptoms such as arrhythmias.
The interarterial course , in which the LMCA courses between the aorta and pulmonary artery, is the most malignant variant and often considered the most malignant anomaly of all. This anomaly may be the cause of sudden death, especially after strenuous exercise. Compression of the LMCA between the aorta and pulmonary artery was previously thought to be the mechanism underlying sudden death. Currently, most investigators assume that the sharp angle between the aorta and ectopic LCA with interarterial course, which is associated with a slitlike orifice and easily collapsible proximal portion of the LCA, is responsible in most cases. Collapse of the LMCA in a valvelike manner, for example by stretching of the aortic wall during vigorous exercise and concomitant rise of blood pressure, may cause occlusion of the LMCA and cause sudden death. This situation is most likely to occur if a relatively long portion of the LMCA is embedded in the aortic wall ( Fig. 58.3 ). In addition, in this situation the origin or proximal portion of the LMCA is often hypoplastic.
