A Rare Type of Dual Left Anterior Descending Artery Distribution Demonstrated by Multislice Cardiac Computerized Tomography in a

Case Report. A 45-year-old male underwent coronary angiography 2 weeks after non-ST-elevation anterior wall MI. Electrocardiography showed inverted T-waves in leads V2–V5. Echocardiography revealed mild hypokinesia of the mid and apical segments of the septum and anterior wall. Coronary angiography showed normal bifurcation of the LMCA, with a nondominant left circumflex artery. The LAD ran in the anterior interventricular sulcus (AIVS) until its mid-part, giving 2 short diagonals, but no septal branches during the course, and had a 99% stenosis in the proximal part. The right coronary artery (RCA) showed a normal origin from the right aortic sinus. Close to the origin of the RCA from the sinus, a vessel originated, which coursed inferiorly to reach the posterior part of interventricular septum initially, and then anerosuperiorly. After reaching the upper septum, the aberrant vessel coursed parallel and posterior to the LAD originating from the LMCA (Figures 1 and 2). Multiple septal perforators originated from this vessel during its long septal course. The lesion in the proximal LAD was stented, with a good result (Figure 3). Subsequent 64-slice CT confirmed the dual LAD distribution and the septal course of the aberrant vessel (Figures 4 and 5).

Discussion. Spindola-Franco et al provided an angiographic description of the four variants of a dual LAD as follows:²

Type I. The shorter LAD runs in the AIVS, which is generally the source of all the major proximal septal perforators. The longer counterpart descends on the left ventricular side of the AIVS, and then reenters the distal AIVS in order to reach the apex.
Type II. The shorter LAD is the same as in Type I. The longer LAD descends over the right ventricular side before reentering the AIVS.
Type III. The shorter LAD is consistent with that described in Types I and II. The longer LAD travels intramyocardially in the ventricular septum. Type IV. The LAD proper is very short, giving the major septal perforators and the diagonal branches. The longer LAD arising from the RCA shows a septal course. The dual LAD distribution in our case closely mimics this more common variant, except that the anomalous branch had a separate ostium close to the RCA origin and the LAD proper did not give any major septals.
The first description of a Type IV LAD was in 1939, by Waterson et al, in the case of Sir James Mackenzie, who had this binary distribution in addition to ischemic heart disease.³ Since then, only a few cases of this anomaly with an aberrant vessel from the proximal RCA have been reported.^4–9 In a recent large series involving 70,850 unselected patients, a Type IV LAD was noted only in 3 out of 171 (1.8%) patients with major congenital coronary anomalies.⁹ The origin of the aberrant vessel from the right aortic sinus, rather than the RCA in a Type IV LAD distribution, was described only in one case thus far in the literature.¹ Apart from being an angiographic curiosity, the higher likelihood of missing such an anomaly during an angiographic study and the technical issues involved in the angioplasty of ostial RCA lesions, if required, make it a separate clinical entity.
A paucity of distribution of vessels in the apical LAD territory with a small LAD proper during angiography of the left coronary system should alert the angiographer to this as one of the likely possibilities. An anomalous LAD arising from the right coronary sinus or artery often follows either a septal or conal course, which can be differentiated in two-dimensional coronary angiography by the “dot and eye method”.¹⁰ In a 30º RAO view, before turning to the apex at the midseptum, the LAD will pass left and upward (forming the upper half of the “eye”) in an anterior free wall or conal course, while it will pass left and downward (forming the lower half of the “eye”) in a septal course (Figure 1). The septal course is also recognized by the presence of multiple septal perforators throughout its course.
A multislice CT also confirmed the septal course in the index case. As compared to conventional angiography, the information obtained from cross-sectional imaging using multidetector CT permitted better definition of the origin and anatomic course of the aberrant vessel in our case. The use of multislice CT for the depiction of dual LAD distribution has been reported only once before in the literature.¹¹
The presence of this uncommon coronary distribution per se offers no additional risk to the patient. On the other hand, the binary distribution from either coronary system probably limits the extent of anterior wall ischemic insult, as in our case. However, inadvertent incorrect placement of an arteriotomy due to nonrecognition of the anomaly, difficulties in identification and grafting of a short LAD proper and the intramyocardial course of the aberrant vessel are of concern during surgical revascularization.¹² During angiography, a total occlusion of either of the dual arteries may be underecognized as well. Hence, it is important for both angiographers and surgeons be aware of the anatomic variants of this rare coronary anomaly.

References

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