Placement of a Sirolimus-coated Stent in the Distal Left Internal Mammary Artery of an 8-year-old Boy

Coronary artery revascularization in the pediatric population is rare. Revascularization of the coronary arteries has been carried out with percutaneous transluminal coronary angioplasty (PTCA), stent delivery, and coronary artery bypass grafting (CABG). The left internal mammary artery (LIMA) graft is the graft of choice for a coronary artery bypass graft in pediatric cardiac surgery because it has the best long-term patency rate of available options. Although the 10-year LIMA patency rate is greater than 95%,¹ early stenoses or graft failure have been observed. These early stenotic lesions can occur at anastomotic site or body of the graft. Lesions in the proximal or anastomotic sites appearing soon after the surgery and may be caused by kinking of the LIMA during surgical mobilization² or by a surgical clip. The lesions in the body may occur as a result of mechanical injury during vessel harvesting.³ Acute dissection of left internal mammary artery may occur during the deployment of stents in the artery.4 PTCA may be performed in early or late LIMA graft stenosis. Case Report. We present an eight year-old child with initial diagnosis of D-transposition of the great vessels. He underwent Jatene vessel switch as a neonate. He did fine for four years, but then developed shortness of breath and atypical chest pain. Transthoracic echocardiogram showed left ventricular dilatation and moderate aortic insufficiency. A year later his symptoms worsened and a repeat transthoracic echocardiogram showed further increase in the left ventricular diameter, measuring 4.6 cm, and progressive aortic insufficiency. He underwent aortic valve replacement with 13 mm aortic Synergraft valve. In the operating room he was found to have occlusion of the left main coronary artery (LMCA). We dissected what we thought to be the left anterior descending (LAD) and circumflex left (LCX). The LCX was thought to be the larger vessel and therefore the LIMA was harvested and anastomosed to the LCX. The patient did well for 4 months and then started complaining of atypical chest pain. He underwent cardiac catheterization, which demonstrated that the LCX actually originated from the right coronary artery and that the LIMA was anastomosed to the LAD. Most significantly, this catheterization revealed a 99% lesion in the distal segment of the LIMA that extended into the anastomosis to the LAD. Balloon angioplasty was performed successfully, and the patient became asymptomatic for the following 8 months. He presented again with atypical chest pain with ST-T changes on EKG and indeterminant elevation in the troponin I level. Repeat coronary angiography revealed a significant stenosis at the previous angioplasty site in the LIMA. Six months later, his repeat left heart catheterization revealed mild to moderate (40%) residual stenosis at the anastomotic site but PTCA was not performed and patient was followed medically. The patient presented again to the hospital with chest pain. Repeat coronary angiography showed a significant stenosis in the distal segment of the LIMA at the site of the previous balloon angioplasty (Figures 1 and 2). PTCA of the LIMA was performed this time using a 2.0 x 15 mm balloon Cross sail™ (Guidant Corporation, Santa Clara, Calif.) inflated to 8, 10, 12, and 14 atmospheres and a 2.5 x 15 mm balloon inflated at 10, 12 and 14 atmospheres. Despite this, significant recoil was observed and a decision was made to stent the vessel. A 2.5 x 18 mm Cypher™ stent (Cordis, Miami, Fla.) was deployed at 9 atmospheres in the distal LIMA (Figure 3). The final angiographic results revealed TIMI III flow and 0% residual stenosis (Figures 4 and 5). No complication was observed during the procedure. Post intervention CK-MB and troponin were normal. The patient was given clopidogrel and aspirin and was discharged from the hospital the day after the procedure. At thirteen months following placement of the drug eluting stent in the LIMA, the patient is symptom free. The follow-up transthoracic echocardiogram showed reduction of the ventricular diameter from 4.6 cm to 4.1 cm and the ejection fraction remained unchanged. Discussion. Among the adult population, stenosis of coronary arteries is acquired as a result of coronary atherosclerosis. In the pediatric population, isolated congenital coronary artery stenosis is extremely rare. Most of the time, coronary artery stenosis is associated with other congenital heart diseases, commonly William’s syndrome and pulmonary atresia with intact ventricular septum.⁵ The most common acquired disease of the coronary arteries in children is Kawasaki disease.⁶ Other acquired conditions associated with coronary stenoses include post-operative congenital heart disease, coronary artery disease following transplant, and homozygous lipid disorders.⁷ In the pediatric population, PTCA has been used to treat various conditions including Kawasaki disease,⁸ tissue conduit stenosis after surgical repair of anomalous coronary artery⁹ and a case of a LIMA that was bypassed to anomalous coronary artery arising from the pulmonary artery.¹⁰ Even in the adult population there are limited long-term outcome data of patients undergoing stenting of the LIMA conduit. A retrospective study revealed higher one-year target lesion revascularization (TLR) rate in the stented lesions than lesion treated with angioplasty alone. The higher TLR rate in the stented lesions was apparently at the anastomotic site (25.0% vs 4.2% p = 0.006).¹¹ Recently, new drugs have been evaluated in the development of drug-coated stents. These drugs include paclitaxel (anticancer drug), sirolimus (an immunosuppressant), everolimus and tacrolimus. The two major trials to reference are SIRIUS and TAXUS that show the significant reduction in stent stenosis at one-year follow up.^12,13 Patients with recurrence of in-stent stenosis following placement of drug-coated stent usually have more benign pattern of restenosis that can be treated with balloon angioplasty. If restenosis events continue to recur after one or two more balloon angioplasties then repeat bypass surgery with re-attachment of left internal mammary artery to the left anterior descending coronary artery could be attempted. Very limited data are available on the outcomes of drug eluting stents being used to treat saphenous vein, or LIMA conduits. Data are also needed to determine the outcome with these stents in the pediatric population. To our knowledge this is the first drug-eluting stent used in the LIMA of a pediatric patient. This case is unique in the sense that it is first case to be reported in which there was successful placement of drug eluting stent in left internal mammary artery in 8-year-old boy with good angiographic result and clinical outcome up to thirteen months.

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