88

Sunday, March 21, 199910:10 am-12:00 noon

10:10 amOpening Ceremony

Or. Gary J. Becker Young Investigator Award

Plenary Session-Aortic Stent GraftsModerator: Curtis Bakal) MD

10:30 am

Computed Tomographic Angiography Before andAfterAorticSren~GnUting

Geoffrey D. Rubin) MDStanford UniversityStanford, Calilfornia

Until approximately 6 years ago, direct surgical repairwas the only treatment available for aortic aneurysms.The recent development of endovascular prostheses orstent-grafts for the percutaneous treatment of aortic an­eurysms, however, has allowed aneurysm repair in asignificantly broader range of patients, particularly thosetoo frail to undergo standard operative repair 0-5).

Advantages of endovascular repair include treatmentunder local or limited epidural anesthesia, lack of aorticcross-clamping, and brief total aottic occlusion time.Anatomic requirements for stent-graft placement are de­vice specific and continually evolving. Although endo­vascular repair of abdominal aortic aneurysms (AAAs)was limited to the 10-15% of AAAs with a neck greaterthan 10 mm proximal to the iliac artery bifurcation, theintroduction of bifurcated stent-grafts (3,6-8) and thedevelopment of a combined single aortoiliac stent-graft,contralateral iliac artery occluder, and surgical femoralartery to femoral artelY bypass (9) broadened the selec­tion criteria for endovascular repair. Complication ratevariations within populations of AAA are associated withthe morphologic characteristics of the aneurysm (0).Based on an assessment of 168 AAAs, Armon and col­leagues (11) estimated that 131 (80%) were potentiallysuitable for endoluminal repair assuming that 1 of 756possible combinations of proximal and distal graft diam­eters (2-mm increments) and graft lengths (in I-em in­crements) are available. Although the measurementtechniques used in this study were limited, the resultsunderscore the marked morphologic variability presentin AAA and the importance of an accurate and repro­ducible method for sizing the aorta and iliac arteriesbefore device deployment. The table lists complicationsthat may occur after endovascular repair of aneurysmsand the quantitative and qualitative features of the anat­omy that influences the likelihood of these complica­tions.

As a result, the planning of endovascular treatment ofaortic aneUlysms puts greater requirements on pre­operative imaging than any previous application

(1,9,12,18,19), because stent-grafts must conform to theaortic lumen, and refinement of vascular measures, graftsizing, and alterations in suturing technique typicallymade under direct visualization in the operating roomare not an option (11).

Aortoillac Characterization Before Stent-GraftDeploymentConventional angiography has long been considered thegold standard for vascular imaging. Conventional an­giography is limited, however, by its inability to showthrombosed regions of aneurysms and the effects ofprojection, magnification, and parallax on the accuracyof measurements. Conventional angiography is three orfour times more expensive than computed tomography(CT) and is invasive and uncomfortable.

Transverse CT measurements have been used to quan­tify aortic aneurysm diameters, but these measurementscan substantially overestimate dimensions because of arte­rial obliquity. Furthermore, significant interobserver vari­ability for both aneulysmal and nonaneurysmal aortic mea­surements from transverse CT sections has been reported(20). Determining the appropriate length of the endovas­cular prosthesis is as important as device diameter; how­ever, cranial-caudal dimensions substantially underesti­mate true vessel length by failing to account for obliquity.Nevertheless, transverse measurements of aortic diameterand cranial caudal dimensions of aortic length are usedroutinely for aOltic quantification before endovascular re­pair (21,22). One approach to improving arterial cross­section measurements is the creation of oblique multipla­nar reformations, perpendicular to the longitudinal axis ofthe aorta. This approach to improving CT measurementsbefore endovascular repair of aortic aneurysms has beenimplemented manually by at least two groups of investiga­tors; however, the measurements have not been validatedagainst a reference standard, and variability has not beenassessed (11,23,24).

For the purpose of pre-stent-graft planning, we di­vide the aorta into four primary zones-the proximalneck, aneurysm body, distal neck, and access route,indicated in Table 1. Pertinent data differs among thesezones. Critical assessments of the proXimal and distalaneurysm necks include true cross-sectional diametermeasurements (orthogonal to the median axis of theaorta), length along the medial axis of the aorta, angu­lation relative to adjacent segments, mural atheroma/thrombus, and degree of tapering. The aneurysm body isassessed primarily for length and patent branches, suchas accessory renal arteries or unusually large lumbar orinferior mesenteric arteries originating from the aneurys­mal segment. The access route (typically one of the iliacarteries) is assessed for minimal diameter, tortuosity, andextent of calcification. Although these three factors likelyinfluence the ease with which the device can be ad­vanced to its deployment position with minimal compli­cations, the relative contribution of these three iliac