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Ann Thorac Surg 2004;78:1456-1458
© 2004 The Society of Thoracic Surgeons
a Division of Cardiology, Baltimore, Maryland, USA
b Department of Cardiac Surgery, The Johns Hopkins Hospital, Baltimore,, USA
c National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
Accepted for publication July 10, 2003.
* Address reprint requests to Dr Hirsch, NHLBI/NIH, 10 Center Dr, MSC-1061, Bldg 10, Room B1D-416, Bethesda, MD 20892-1061, USA
ghirsch{at}jhmi.edu
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A 60-year-old man with a history of diabetes mellitus, hyperlipidemia, smoking, and four-vessel coronary artery bypass (CAB) 20 years previously underwent emergent repair of an abdominal aortic aneurysm at a referring institution. His postoperative course was complicated by multiple episodes of bacteremia with Enterococcus faecalis and Staphylococcus aureus, sepsis, and acute respiratory distress syndrome. In addition, the patient had hemorrhagic pancreatitis and ischemic colitis develop, which required a distal pancreatectomy, splenectomy, and partial bowel resection. He returned to the operating room for lysis of adhesions to relieve a postoperative small bowel obstruction. Two months after his initial abdominal aortic aneurysm repair, he was transferred to our hospital for further management. On arrival he remained ventilator dependent and critically ill with multiple abdominal abscesses and an entero-cutaneous fistula. Over the following month his condition slowly improved with antibiotics, percutaneous drainage of his abdominal abscesses, and intense nutritional support. He was subsequently weaned from the ventilator. Despite more than 1 month of antibiotic therapy, the patient remained febrile with temperatures exceeding 38°C. Nevertheless he remained hemodynamically stable and was transferred out of the intensive care unit.
One day later, the patient had chest pain develop while moving from his bed to the chair. It was the first time he had experienced anginal symptoms since his CAB 20 years previously. Sublingual nitroglycerin was given to the patient, which resolved his pain and electrocardiographic changes. Serum cardiac enzyme levels were normal. Echocardiography revealed no regional wall motion abnormality, but a large anterior mediastinal mass compressing the right ventricle was present (Fig 1). To evaluate this mass, computed tomography of the thorax was performed that revealed a 6.0 x 3.0 cm calcified aneurysm of the SVG to the left anterior descending artery (LAD). Blood flow was maintained through a narrowed but patent graft lumen (Fig 2). Magnetic resonance imaging of the thorax revealed the presence of layered intraluminal thrombus within the aneurysm and a patent graft lumen (Fig 3).
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Our case is unusual because the mycotic aneurysm developed many years after graft placement and because it occurred outside the setting of postoperative mediastinitis or sternal wound infection. The patient in the present case report had an aneurysm that likely developed after multiple bacteremic episodes that complicated the postoperative course of his abdominal aortic aneurysm resection. Despite the abundant amount of purulent fluid found intraoperatively, we were unable to identify a causative organism in this case, probably from sterilization of the aneurysm fluid by a prolonged course of broad-spectrum antibiotics. Of the 4 previously reported patients, 3 of the causative organisms were Staphylococcus aureus and Aspergillus was the isolated cause in the other patient [1–4].
Typically SVG aneurysms present with ischemic symptoms secondary to graft occlusion or distal embolization from intraluminal thrombus, or as asymptomatic chest masses detected during chest imaging. As described by Lupetin and colleagues [5], the triad of chest pain, mediastinal mass, and previous bypass surgery should raise concern of an SVG aneurysm. The most common graft involved is the SVG to the LAD. This is important because aneurysms of this graft are usually not seen on standard chest roentgenograms, whereas SVGs to the RCA or obtuse marginal branches may often be seen.
True aneurysms and pseudoaneurysms of SVGs occur with the same frequency, but they are pathologically different. True aneurysms typically are fusiform and involve the body of the graft and also commonly result from graft arteriosclerosis. Pseudoaneurysms, in contrast, are saccular, they usually present at the anastomotic site, and they are often related to technical issues [6].
In a review of 50 cases of SVG aneurysm by Kalimi and colleagues [6], the mean length of time post-CAB aneurysms were diagnosed was 10 years after surgery (range, 7 days to 21 years). As SVGs age, they become more susceptible to have aneurysms develop secondary to accelerated arteriosclerosis, and the inability of the thin venous wall to prevent dilatation. Our case, although extremely rare, illustrates that patients with previous CAB and bacteremia are at risk for mycotic aneurysm formation.
Once an SVG aneurysm is detected, computed tomography or magnetic resonance imaging of the chest should be performed to determine patency of the graft lumen, as well as the precise location of the graft within the mediastinum to guide the surgical approach. Before operation, a diagnostic cardiac catheterization should also be performed to evaluate potential distal targets for revascularization. In the review of 50 SVG aneurysms by Kalimi and colleagues [6], 31 patients underwent surgical ligation of the SVG aneurysm. Of these, 29 patients had simultaneous revascularizations of the affected vessel. The 2 patients who did not suffered large anterior wall myocardial infarctions postoperatively indicative of the importance of simultaneous revascularization in this setting. Embolization using coils placed percutaneously is another therapeutic option; however, no simultaneous revascularization occurs during this procedure. Kalimi and colleagues [6] suggest embolization should be reserved for patients deemed too high risk for repeat CAB.
This article describes a rare case of a mycotic SVG aneurysm that developed in a patient more than 20 years after CAB surgery in the setting of multiple episodes of bacteremia. Management of SVG aneurysms (mycotic or otherwise) depend on recognition of the disease, subsequent evaluation with computed tomography or magnetic resonance imaging of the chest to delineate the location of the aneurysm and patency of the graft lumen. This should be followed by cardiac catheterization to locate target areas for revascularization. The appropriate timing of surgery in patients with an SVG aneurysm is not known. However, we would advocate urgent surgical revascularization of symptomatic or suspected mycotic aneurysms. A more conservative, observational approach for asymptomatic patients is reasonable for SVG aneurysms less than 1 cm in diameter and with brisk graft flow. The observational strategy could be performed noninvasively by using either magnetic resonance imaging, computed tomography or angiography. For those patients with SVG aneurysms greater than 1 cm in diameter or with diminished graft flow, prompt surgical revascularization would be recommended. Ligation or resection of SVG aneurysms with simultaneous revascularization appears to be the optimal therapy, but intravascular embolization of the graft with coils may be an option for high-risk patients.
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