Percutaneous Repair of a Left Internal Mammary Graft Entrapped Under Sternal Wires

Injury to a left internal mammary artery (LIMA) bypass graft is a known complication of repeat cardiothoracic surgical intervention. This report details the percutaneous intervention to an entrapped LIMA graft to the left anterior descending artery (LAD). Case Report. Five weeks prior to the intervention, a 50-year-old male with a history of hypertension, diabetes mellitus and COPD, presented with an anterior ST-segment elevation myocardial infarction. He underwent emergent cardiac catheterization, which revealed three-vessel disease, including a long 95% complex lesion in the LAD that involved the origin of a large diagonal branch. He was emergently taken to coronary artery bypass surgery where vein grafts to the first diagonal, obtuse marginal and posterior descending were placed. The LIMA was used as an in situ graft to the LAD. His postoperative course was complicated by an episode of COPD exacerbation and pneumonia which resolved with a course of steroids and antibiotics. The patient presented to the emergency room one month after discharge with sterile dehiscence of the sternum. The sternum was reapproximated with Robby Check Weave, closed with double wires, and he was discharged home. Four days later, he presented to the emergency department with chest pain, shortness of breath and syncope. The electrocardiogram showed diffuse ST-segment depression. The initial troponin-I was elevated. He underwent cardiac catheterization, which showed the native LAD to be occluded in the mid segment, and the distal LAD filled via retrograde flow from the first diagonal which was supplied by a patent saphenous vein graft. The LIMA injection revealed abrupt interruption of flow in the mid segment of the LIMA graft (Figure 1). It appeared that the LIMA was entrapped under the recently placed sternal wires. A ventriculogram revealed normal contraction of the anterior wall. Given the high risk of re-operation, a percutaneous interventional approach was chosen. There were two viable approaches to this case. An attempt could be made to restore flow down the native LAD, or an attempt could be made to open the LIMA graft. The native LAD had a very complex lesion involving the origin of the first diagonal branch. The LIMA graft appeared to have a short segment that was occluded by external compression. Therefore, we opted to attempt balloon dilatation of the LIMA graft. The LIMA graft was engaged with a 7 French LIMA guiding catheter, and a 0.014 inch ChoICE® PT (Boston Scientific, Natick, Massachusetts) extra support guidewire was passed down the LIMA and across the occluded segment into the distal LAD. Multiple views under fluoroscopy showed the course of the guidewire to pass under two loops of sternal wire (Figure 2). A balloon catheter could not be advanced beyond the point of wire entrapment. In the cardiac catheterization laboratory, under sterile conditions, the cardiothoracic surgeons removed the entrapping sternal wires under fluoroscopic guidance. Repeat angiography showed persistent interruption of flow in the LIMA graft (Figure 3). The mid and distal LIMA segments were serially dilated with a 2.5 mm x 18 mm NC Raptor™ balloon (Cordis Corporation, Warren New Jersey). Each inflation resulted in transient antegrade flow down the LIMA, followed by reocclusion. The distal anastamosis was then dilated with a 2.0 mm x 15 mm OpenSail® balloon (Guidant Corporation, Santa Clara, California). The distal segment of the LIMA was stented with a 2.5 mm x 18 mm Velocity stent. TIMI 3 flow was restored down the LIMA. The mid segment of the LIMA graft that was previously entrapped under the wires had a 60% hazy lesion, suggestive of edema, bruising and possible thrombus. This segment was stented using a 2.75 mm x 23 mm BX Velocity™ stent (Cordis Corporation) deployed proximal to, and overlapping, the first stent. Final angiography showed a patent LIMA graft with TIMI 3 flow (Figure 4). The patient was discharged in stable condition with a plan to perform a pectoral flap reconstruction of his sternum. Discussion. Injury to the LIMA graft should be considered as a possible cause of myocardial ischemia, especially following repeat cardiothoracic surgery. LIMA grafts have been shown to increase 10-year survival over that of saphenous vein grafts.1–3 For this reason, a majority of coronary bypass procedures use one or both mammary arteries as in situ bypass conduits. Despite their excellent long-term patency, flow through a LIMA graft may be compromised. The most common location for impaired flow in a LIMA graft is the distal anastamotic site. Early on, this can be due to suboptimal surgical technique, but over time, a proliferative lesion can develop in this location. Ostial and mid-graft lesions are less commonly seen. Unobstructed flow in the vessel receiving the LIMA graft has been reported to cause atresia of the LIMA.4 The course of this vessel along the anterior chest wall makes it susceptible to injury during repeat surgical procedures in the chest, including repeat CABG, valve surgery and in this case, repair of sternal dehiscence. Despite careful surgical technique, there have been prior reports of damage to LIMA grafts caused by sternal wires.5 Our patient presented with acute coronary syndrome caused by entrapment of the LIMA graft in the sternal wires shortly after undergoing sternal reapproximation. This complication can be suspected on clinical grounds, diagnosed by angiography and is usually corrected surgically. In this report, we have described a novel multidisciplinary cath lab-based approach for the management of this complication.

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