In a recent article in Cath Lab Digest, Cooper1 reported a “typical case” of a patient with unstable, recent-onset angina, who had a “high-risk” coronary artery anomaly (CAA) that the author deemed to “require surgical treatment.” He stated that the best treatment for this condition was coronary bypass surgery and proximal ligation of the anomalous artery, which were indeed carried out.

After reviewing the coronary catheter angiographic images and computerized axial tomographic angiographic (CTA) images that nicely illustrate Cooper’s article, I have concluded that even the most attractive images, including these, may lead to incorrect interpretation of a CAA. Indeed, this particular anomaly is commonly considered benign, and the case study deserves careful discussion. I will briefly attempt to clarify several fundamental principles, based on a recently updated body of evidence,2,3 for diagnosing and treating CAAs.

In human beings, there are only a few “high-risk” types of CAAs. Not all anatomic coronary variants are potentially life-threatening, although, when referring to CAAs in general, the nonspecialized medical literature generally implies that they are. In fact, only one type of CAA has been associated with sudden death in athletes4 or military recruits.5 That CAA is anomalous coronary artery originating from the opposite sinus of Valsalva (ACAOS) and having “a course between the aorta and pulmonary artery.”6,7 Recently, my group and others2-4 have elucidated the types and mechanisms of high-risk CAAs, which are summarized as follows:

• Ectopic coronary origin. An abnormal location of the coronary ostium results in an abnormal coronary course, but, by itself, is not a sufficient indicator of clinical severity; rather, it is the associated intramural course of the proximal ectopic coronary trunk that leads to stenosis of variable severity (Figure 1) and, hence, to the possibility of adverse clinical events.

In cases of ectopic origin of the left coronary artery, the differential diagnosis of an intraseptal versus an intramural course is a recurrent challenge, both in the literature1 and in clinical practice. Table 1 sets forth sound, readily available criteria for diagnosing a CAA by means of coronary catheter angiography or tomographic imaging (CTA or magnetic resonance angiography [MRA]). The correct differential diagnosis of the CAA type can be reliably made by using both of these methods (Figure 1).

Current volume-rendered images that are derived electronically from tomographic images do not significantly enhance diagnostic accuracy regarding either the intramural coronary course or the severity of stenosis. In terms of cross-sectional imaging, CTA and MRA have a spatial resolution of 10% to 20% in comparison with intravascular ultrasonography (IVUS),2 and both CTA and MRA are unable to clarify the severity of obstruction in cases involving an intraseptal course.

In the case reported by Cooper,1 the CAA’s course was labeled as “between the aorta and the pulmonary outflow tract,” which was assumed to entail a high risk of sudden death. However, there is no doubt that it was actually an intraseptal course (Figures 1 and 2), a well-recognized benign condition without a malignant mechanism of stenosis. Furthermore, ligation of the proximal left main artery, even in the context of coronary artery bypass grafting, is not a totally benign intervention, as it entails a 5% to 10% risk of disastrous graft failure. Such ligation is not the currently preferred surgical treatment, even in cases involving an intramural course; instead, unroofing procedures are favored, being regarded as better than reimplantation.2,3

I will readily acknowledge that CAAs are neither a well-defined nor a fully understood aspect of cardiology.2,4 In particular, besides factors involved in sudden cardiac death (maximal exertion seems to be one of these factors), other, more common clinical manifestations (dyspnea, chest pain, syncopal symptoms) might be indications for selective intervention.2,3 Still, the unsolved critical question is this: Can the severity of the baseline stenosis of the intramural variant, both in itself and as assessed by IVUS, indicate the clinical implications of a given case and be used to indicate the necessity for intervention?4 My group has proposed that the severity of the stenosis of the intramural segment be described by means of IVUS according to the following quantitative parameters (Figure 2):

1. Hypoplasia, as measured by the ratio of the stenotic-segment circumference to the reference-distal-vessel circumference (the hypoplasia index).

2. Lateral compression of the intramural segment, as manifested by an ovaloid cross-section in which the longest diameter is similar to, or longer than, the diameter of the reference distal vessel, and the shortest diameter is usually half that of the reference vessel. On IVUS images, the reference distal vessel quickly regains a normal circular cross-section (Figure 2).

3. Worsening of the lateral compression during systole, leading to a variable increase in the severity of stenosis at each heart beat, and also during exercise (especially owing to an increase in the stroke volume and simultaneous tachycardia). This phenomenon is quantified by the pulsatility index (the systolic cross-sectional area divided by the diastolic cross-sectional area). My group is in the process of elaborating data designed to establish clinical correlations for such IVUS-based parameters of functional stenosis. Obviously, larger arteries (e.g., the left coronary artery versus the smaller right coronary artery, or the whole coronary artery versus only the left anterior descending, as in Cooper’s case) are more likely to have a clinical impact when affected by this type of CAA.

In conclusion, although angiography (performed by a trained observer) can detect the presence of an intramural course, only IVUS can clarify the severity of an individual case involving an intramural course.

Dr. Angelini can be contacted at pangelini@leachmancardiology.com