Computed tomography coronary angiography (CTCA) of anomalous coronary vasculature

Invasive coronary angiography has long been used to map coronary arterial anatomy and associated disease. In this procedure, a contrast agent is instilled into a coronary artery via a catheter inserted into the opening (ostium) of that artery within an aortic sinus. The fluoroscopic images that are acquired have a high spatial and temporal resolution and are of benefit in patient diagnosis and treatment, but they are two-dimensional (2D). In marked contrast, computed tomography (CT) is a non-invasive imaging modality that can demonstrate the anatomy and relations of a region of interest in 3D.

Despite the benefits afforded by CT, the cross-sectional imaging community used to regard the heart as an ‘object of mystery’ because of the rapidity of its movements and the limited speed of the available technology. Recent advances in the temporal resolution of CT scanners and associated radiation dose have enabled the development of computed tomography coronary angiography (CTCA), which is able to capture motion-free, essentially ‘freeze-frame’, 3D images of the heart and coronary vasculature. Image quality can still be adversely affected by the presence of a tachycardia: in such cases image quality can be enhanced using a pharmacological intervention to reduce heart rate or by timing (gating) scans to end diastole or end systole, when the coronary arteries and associated cardiac structures show the least movement. The simplicity of image capture and quality improves as technology develops: the latest generation of CT scanners are now fast enough to acquire diagnostic images even in patients with tachycardia ( ).

After volumetric dataset acquisition using CTCA, post-processing with 3D reconstruction tools such as volume rendering and multiplanar reformatting enables visualization of the course, origin and anatomical relationships of the coronary arteries to neighbouring structures in a level of detail unmatched by other modalities. A relatively new post-processing technique, cinematic rendering, provides striking photorealistic images from CTCA datasets ( ). While standard volume rendering is able to demonstrate anatomy and anatomical relationships in three dimensions, the overall quality achieved with cinematic rendering is much higher (see Commentary I.4 and Fig. 7.2.7C–D for a comparison of standard 3D volume rendering of the coronary arteries with cinematic rendering).

Classification of coronary artery anomalies

While there is no universal definition for the division between coronary artery variants and anomalies, a simple, robust and commonly used threshold defines variants as differences occurring in >1% of the population, and anomalies as differences occurring in ≤1% of the population ( , ). Variants and anomalies may be asymptomatic and only of relevance during cardiac surgery or may cause chest pain, shortness of breath, or serious cardiovascular sequelae ( , ). Coronary artery anomalies can be grouped into three broad categories: anomaly of origin and course; anomaly of intrinsic anatomy (absence, atresia or duplication); and anomaly of termination. Some anomalies are asymptomatic and discovered incidentally, whereas others require treatment for symptomatic relief or to ensure continued cardiac function. CTCA is an important clinical tool for the diagnosis and detailed mapping of anomalies and the addition of photorealistic cinematic rendering further enhances its quality and utility for surgical and procedural planning and research, especially in cases of complex aberrant anatomy.

An exhaustive list of all the documented coronary anomalies is not possible in a single article. The cases in this commentary demonstrate a mixture of both the most common and most serious anomalies and have been selected to highlight the sometimes extreme deviations from normal coronary artery anatomy that can occur. Many permit survival to adulthood, and although extremely rare, the physician should be aware of their existence in clinical practice.

Anomalies of origin and course

Anomalies of coronary artery origin and course are the most commonly encountered of the three categories of anomalous vessels. The left coronary artery, anterior interventricular branch or circumflex branch of the left coronary artery, or the right coronary artery, can all arise from ectopic positions, which include a non-conventional aortic sinus, the ascending aorta, pulmonary trunk or other coronary arteries. The proximal part of an anomalous coronary artery follows one of five paths (pre-pulmonic, retro-aortic, inter-arterial, trans-septal or retro-cardiac) to access its more usual distal course and designated perfusion territory ( Fig. 7.2.1 ). The pre-pulmonic and retro-aortic paths pass anterior to the pulmonary trunk and posterior to the ascending aorta, respectively, whereas the inter-arterial path passes between the ascending aorta and pulmonary trunk. The trans-septal path is subpulmonic, traversing anteriorly and inferiorly through the myocardium of the interventricular septum; the retro-cardiac path passes around the heart within the atrioventricular (coronary) sulcus ( ).

Depending on their location and initial path, a proportion of anomalous coronary arteries are associated with functional ischaemia and are the second most common cause of sudden cardiac death among young athletes ( ). Anomalous vessels taking the inter-arterial path are most frequently associated with sudden cardiac death, perhaps due to the exercise-related expansion of the ascending aorta and pulmonary trunk and the consequent increase in angulation and decrease in luminal diameter of the anomalous vessel ( ) ( Fig. 7.2.2 ). Sudden cardiac death is more likely with an inter-arterial anomalous left coronary artery or anterior interventricular artery because of the larger volume of subtended myocardium at risk during an associated cardiac event ( ). Other paths are not commonly associated with haemodynamic compromise because they are not associated with luminal narrowing ( Fig. 7.2.3 ), but their location may complicate surgery.

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