Rationale for Postoperative Surveillance

Late adverse events after endovascular repair are part of the natural history of the therapy and a well-recognized complication. The incidence is time dependent, meaning that the longer the period of observation, the greater the likelihood of an event. Adverse events can be broadly categorized as device-related and anatomic. Device-related events are self-explanatory, and they include material fatigue (graft tears or erosions, stent fractures) and stent graft kinking, compression, or infolding leading to thrombosis or vascular compromise. Anatomic issues include endoleaks, degeneration or enlargement of landing zones, obstruction of branch vessels, and/or continued expansion of the sac. Although fortunately many of the device-related events occur less often than they used to with early generation devices, they have not been completely eliminated. For most of these complications, prophylactic intervention before a clinically symptomatic event such as rupture or end-organ ischemia is safer and easier to manage than intervention after the fact. Therefore, the purpose of postoperative surveillance is timely detection of impending problems and prevention of serious complications before they occur.

Elements of Complete Surveillance

Proper surveillance after endovascular aortic repair shares many features of any postoperative evaluation after a major surgical procedure. In the first postoperative visit, history-taking should focus on fevers and other systemic symptoms, new-onset claudication, hypertension, and azotemia, which could suggest iliac or renovascular compromise. Physical examination should be directed at the groins and other vascular access sites, femoral pulses, and aortic pulsatility in cases of abdominal aortic aneurysms. While pulsatility in isolation is a relatively nonspecific finding, a change from a nonpulsatile to a pulsatile examination during follow-up often indicates a new type I or III endoleak (Figure 1). Any serious access site problems such as infections, seromas, or pseudoaneurysms will manifest themselves within the first 30 days.

Unique to endovascular repair are types of imaging that form an integral part of the surveillance regimen. Available imaging modalities include computed tomography angiography (CTA), magnetic resonance angiography (MRA), plain multiview x-ray, duplex ultrasound with or without sonographic contrast, and intrasaccular pressure monitoring. No single modality is sufficient or necessary for each follow-up, and each should be considered complementary depending on the segment of the aorta treated, the pathology, the device’s construction, and the patient’s physiology. The purpose of imaging includes measurement of aortic size and detection of endoleak or device migration (Figure 2) and impaired endograft patency (including kinking and/or compression) and device integrity. Secondary findings include associated vascular problems such as iliac stenosis or dissection, branch vessel compromise or graft infection, and nonvascular pathologies that can masquerade as aortic symptoms and malignancies. Regardless of which modality, any new finding or serial dimensional measurement (e.g., length, distance, diameter) should be compared or performed using the same modality performed the same way, such as aneurysm diameter measured on orthogonal centerline reconstruction.

Computed Tomography Angiography

The CT angiogram remains the gold standard for postoperative surveillance after endovascular aortic repair. This is a result of its widespread availability, familiarity with interpretation of vascular structures by nonradiologists, turnkey consistency in producing quality images, spatial resolution, and data acquisition speed using multidetector array scanners. It is relatively more resistant to metallic artifact, especially nitinol, and the study is not restricted by any type of body implants. As three-dimensional (3-D) postprocessing software becomes more commonplace, images can be rendered into a variety of formats such as multiplanar reformat (MPR) and maximum-intensity projection (MIP) to look for intravascular abnormalities and stent morphology and integrity. Principal disadvantages are radiation exposure, whose cumulative lifetime dose for a younger patient may be significant, and risk of contrast nephropathy, especially in those with mild to moderate chronic kidney disease and/or diabetes.

Typical acquisition technique should include chest–abdomen–pelvis after thoracic repair, abdomen–pelvis after abdominal repair, and a three-phase scan consisting of noncontrast (5-mm collimation), arterial-phase (intravenous timed-bolus contrast infusion at ≤2-mm collimation), and delayed phase (60 to 90 seconds at 5-mm collimation). Ideally, the dataset should be stored in DICOM format digital media to be able to be viewed on a personal or PACS workstation so that the contrast and brightness can be properly adjusted (windowing) and direct dimensional analysis can be performed using digital measurement tools.

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