Intravascular Ultrasound to Guide Stenting of an Anomalous Right Coronary Artery Coursing between the Aorta and Pulmonary Artery

Anomalous coronary arteries arising from the opposite sinus of Valsalva (ACAOS) are a rare anomaly associated with increased mortality, particularly when the right coronary artery (RCA) courses between the aorta and pulmonary trunk.^1–4 An anomalous right coronary artery arising from the left coronary sinus under these conditions may give rise to an estimated mortality rate higher than 25%, and anomalous coronary arteries have been thought to be the second leading cause of sudden death in competitive athletes.^2,3,5 Bypass surgery has been suggested as the preferred method of revascularization in symptomatic patients, but these arterial conduits often occlude.⁵ Deployment of a stent to hold open the artery mechanically may be beneficial. We report on the use of intravascular ultrasound (IVUS) to allow optimal sizing and deployment of a drug-eluting stent in a patient with ACAOS. The stent was placed in the ostium of the RCA, spanning the aortic intramural segment as the RCA courses to the right side of the heart. After intervention, there was a considerable increase in the diameter of the ACAOS with abolition of symptoms. Case report. A 28-year-old female presented in 1993 with a 7-month history of classic exertional angina. Cardiac risk factors for conventional vascular disease included smoking, high cholesterol (7.7 mmol/l) and a positive family history. She subsequently had a positive exercise test, with pain and significant inferolateral ST changes. Initial angiography revealed normal left ventricular function and a normal left coronary artery (LCA), but the RCA orifice could not be cannulated. Despite anti-ischemic treatment, the patient continued to experience exertional pain, and angiography was repeated in 1994. Once again, the RCA could not be cannulated despite repeated attempts and it was hypothesized that it came off at an acute angle from the left coronary sinus, probably through a “slit-like” orifice. Due to her limiting symptoms, she was referred for surgery and underwent right internal mammary arterial (IMA) grafting to the RCA. Unfortunately, after presenting again with severe angina one year later, further angiography showed occlusion of the IMA graft. Medical therapy was recommended. The patient re-presented in 2003 with further limiting exertional angina. A magnetic resonance imaging scan was performed to delineate the coronary anatomy, myocardial viability and perfusion response to stress. This confirmed that the take-off of the RCA was at a very acute angle in the left coronary sinus and passed between the aorta and the pulmonary artery, with an aortic intramural tract (Figure 1). The left ventricle was nondilated, with normal global systolic function and no evidence of myocardial hyperenhancement with the “late gadolinium technique”, indicating the absence of myocardial necrosis. Stress MR perfusion was attempted with adenosine, but had to be abandoned after the patient developed severe angina and dyspnea. Repeat angiography was performed, which confirmed the origin and course of the RCA. An AL2 guide catheter was able to engage the anomalous vessel. Subsequently, two hydrophilic wires (“buddy” wires) were carefully passed to the distal vessel using an AL2 guide catheter, and IVUS examination was performed (Figure 2). Many of the features described by Angelini et al.⁶ in their first description of IVUS features of ACAOS were observed: the presence of a “slit-like” orifice, an intramural aortic tract with ovoid appearance, the inter-arterial course (with phasic systolic compression), and the absence of atherosclerotic disease. Interestingly, we also observed possible evidence of a proximal “ridge”, which was absent in their case series. We also noted that the total vessel area of the anomalous vessel’s proximal intramural segment was smaller than that of the more distal “normal” (epicardial) artery,⁷ perhaps indicating that the intramural artery cannot grow normally during adult development. The ischemic mechanism was thought to be a combination of tonic narrowing resulting from the “slit-like” orifice and the intramural passage, along with phasic inter-arterial compression. Measured minimal lumen area (MLA) was 2.3 mm² in systole. Pharmacological test, as proposed by Angelini,⁶ were not carried out due to the previous response to adenosine. The proximal segment was stented using a 3.0 x 12 mm TAXUS™ (Boston Scientific, Natick, Minnesota) deployed at 20 atm. Particular care was used to ensure total coverage of the “slit-like” orifice, placing the stent well proximal to the angiographic image of the ostium. Postdilation and “flaring” were performed with a 3.25 balloon at 20 atm. Further IVUS examination was used to check the results: optimal coverage was confirmed with a MLA of 7.1 mm², partial correction of the ovoid appearance and abolition of systolic phasic distortion (Figure 3). The patient was discharged home the next day and is currently asymptomatic one month after the procedure. Discussion. While ACAOS are reported to be rare, it is not uncommon for interventionists to deal with these patients. Being generally young and with atypical symptoms, they pose serious diagnostic and therapeutic challenges. Firstly, the exact mechanism of ischemia in such cases is unclear, and a correlation between symptoms and signs is rarely found. The intramural tract of the ACAOS tends not to have any atherosclerotic intimal build-up.^6,7 A slit-like orifice causes a reduction in arterial flow, particularly on exertion, an aortopulmonary scissors effect, with pressure from the aorta squeezing the intramural segment of the ACAOS against the pulmonary artery, and an aortic hinge effect where the artery is wedged between the aortic wall and the intramyocardial arterial bed may be possible, causing intermittent reduction in blood supply and thus ischemia.^6–9 Therapeutic options: Surgery or (drug-eluting) stents? Visualization of anomalous arteries using angiography may be difficult^9,10 and due to the unusual anatomical situation, obtaining a proper intubation and alignment of a catheter can be very time-consuming or even impossible. This, together with a perceived lack of efficacy and restenosis risk, have limited the use of percutaneous techniques to treat ACAOS, and bypass surgery has been considered the therapy of choice. However, grafting is often unsuccessful as the grafts are prone to occlude,^11,12 as occurred in our patient. This is likely to be secondary to unfavorable hemodynamics such as lack of a pressure drop across the proximal part of the grafted vessel and competitive flow resulting from a phasic flow obstruction. Other surgical techniques have been attempted; surgical re-implantation of the ectopic vessel has been tried, but is complicated by difficulty in fashioning the proximal anastomosis and avoiding aortic valve impairment.^13,14 Another recently suggested method involves surgical translocation of the pulmonary artery in order to solve the problem of an aortopulmonary scissors mechanism.¹⁵ Unroofing of the intramural portion of the AOCA to relocate the ostia in the appropriate sinus is another alternative.^16,17 Stenting may thus offer considerable benefit over surgical revascularization in patients with ACAOS, particularly in the drug-eluting stent era. Concerns have been expressed regarding a possible increased restenosis rate as a high rate of restenosis is observed in stenting for muscular bridges, which are anatomically close to the ACAOS situation,^18,19 perhaps due to extrinsic crushing of the stent that causes an exaggerated intimal reaction. Aside from a low restenosis rate, modern stents have features of flexibility to adapt to unusual anatomies, but also structural rigidity that can protect against intramural compression by the major vessels and can correct the ostial slit-like lumen of the anomalous artery. So far, however, the experience with stenting is very limited: the largest reported case series of stenting for ACAOS (excluding atherosclerosis) refers to 14 patients,²⁰ and 2 other patients have been reported by Angelini,⁷ with reasonable long-term success. Role of IVUS guidance. IVUS features of ACAOS have been comprehensively described,⁷ but only one case of IVUS-guided ACAOS stenting has been reported.⁶ This technique is certainly useful for research purposes, but can also be practically employed in the single patient to diagnose the specific relevance of the anomaly, sometimes using pharmacological challenge.⁶ When stenting is chosen as the approach, IVUS can accurately determine the size of the required stent. In the intramural segment, where no adventitia is present, accurate sizing may also reduce the theoretical risk of traumatic aortic dissection. We also used IVUS to check the optimal deployment across the intramural segment and ostium, which is very difficult to judge due to the hazy angiographic appearance. Conclusion. We report the first use of IVUS to deploy a drug-eluting stent in a patient with ACAOS in whom surgical revascularization had failed. Stenting, particularly with drug-eluting stents, offers a number of advantages over surgical revascularization in addition to offering direct therapy to the proximal part of the anomalous artery causing the symptoms.

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