Abdominal aortic aneurysm morphology in candidates for endovascular repair evaluated with spiral computed tomography and digital subtraction angiography

Endovascular Repair of Small Abdominal Aortic Aneurysms: A Paradigm Shift?

Recent reports have documented poor long-term results following endovascular aneurysm repair (EVAR) of large abdominal aortic aneurysms (AAA). EVAR of small AAAs may result in improved long-term results compared to large AAAs. It is not known whether the frequency of anatomic suitability for EVAR is increased for small compared to large AAAs. This study compared the anatomic suitability of large and small AAAs for EVAR in an unselected patient population. Radiology reports for all computed tomography (CT) scans in a single hospital over a recent 3-year period were reviewed. AAAs diagnosed by contrasted CT scans with cuts >7 mm were excluded. Suitability for EVAR was determined by neck diameter, length, and angulation. In addition, iliac diameters and common iliac distal landing zone lengths were determined. Computerized 3-dimensional (3D) reconstruction was used to measure neck angulation and total aortic tortuosity. One hundred ninety-one patients were found to have AAAs with adequate CT scans for evaluation. Suitability for EVAR was highest in patients with AAA diameters of 3–4 cm and declined with increasing size of the AAA. Dividing AAAs into sizes greater than or less than 5.5 cm revealed that small AAAs had significantly longer necks, less neck angulation, longer common iliac landing zones, and less total aortic tortuosity. Multivariable analysis revealed that maximal aortic diameter was the only independent predictor of suitability for EVAR (p = 0.005, odds ratio 1.67, CI 95% = 1.17 to 2.38). The odds ratio predicts that with each 1 cm increase in size, the likelihood of suitability decreased by 5.3-fold. Small AAAs have less complex anatomy with longer aortic necks, less neck angulation, and less tortuosity. The poor outcomes following the treatment of large AAAs is thought to be due to complex anatomy. EVAR of less anatomically challenging small AAAs may improve longterm outcomes.

Endovascular vs Open AAA Repair: Does Size Matter?

Since the natural tendency of the aorta is to increase in diameter and tortuosity with age and since abdominal aortic aneurysms (AAAs) increase in diameter and length over time, encroaching on the renal and hypogastric orifices, early repair of AAAs (when =4.0 cm) may allow greater applicability of the endovascular option because of more favorable aortoiliac morphology. Patients who present at an older age with larger AAAs should be more likely to be anatomically excluded from endovascular AAA repair. Over a 42-month period, 317 consecutive patients referred with aortoiliac aneurysms (infrarenal AAA =4.0 cm) were evaluated by one of the authors (SGL) for endovascular vs open repair based on computed tomography (CT) and angiographic imaging. The 10 anatomic exclusion criteria were those applicable to the Zenith ® endograft (Cook, Inc), which currently is the most anatomically inclusive of the aortic endografts in commercial use in the United States. Based on their aortoiliac morphology, 212 patients were excluded from endovascular repair and 105 were included as acceptable anatomic candidates. Age, AAA size, and the reason(s) for exclusion were recorded for each patient. By use of Student's t test and logistic and linear regression analyses, the groups were compared by age, AAA size, and age + size. There was no significant difference in patient age or AAA size distribution between the group of patients excluded from endovascular repair based on aortoiliac morphology compared to those who met the inclusion criteria. Patients with small AAAs (4.0–5.4 cm) had similar age distribution as those with large (=5.5 cm) AAAs. The majority of patients (87%) were excluded based on proximal aortic neck morphology. The presence of aortoiliac morphology that precludes endovascular repair is independent of patient age or AAA size at presentation. A patient presenting with a small (4.0–5.4 cm) AAA is not more likely to be a candidate for endovascular repair than a patient with a large AAA.

Correlation of CT aortography measurements of infrarenal aortic aneurysms and body mass index in preprocedural evaluation for endovascular repair

The aim of this study is to analyze the morphological differences of infrarenal aortic aneurysms and common iliac arteries that are important for endovascular management between patients of different body mass index using 64 slice multidetector row CT aortography. This was a multicenter study of 100 patients (50 Europeans and 50 Japanese). All patients had risk factors, manifest symptoms, and ultrasound verified aneurysmal dilation of the infrarenal aorta. All examinations were performed on the same CT platform using the same post-processing protocols. Due to the heterogeneity of the population, several statistical models were used. Significant differences were found in morphological parameters of infrarenal aorta in relation to BMI. In over one out of three patients with BMI less than 23, endovascular treatment is contraindicated due to the dimensions of the aneurysmal neck. Relative to BMI value, differences were found in transverse diameters of the medium part of the aneurysm and in the length of common iliac arteries. CT aortography performed on a 64 slice multidetector row CT platform provides precise and numerous data for the analysis of anatomical and pathological differences of infrarenal aortic aneurysms that are of crucial importance for the planning of treatment and the analysis of the differences relating to body habitus.

Endovascular Repair of Infrarenal Abdominal Aortic Aneurysms in High-Risk-Surgical Patients

PURPOSE

Following the publication of a prospective randomized trial (EVAR2) that questioned the benefit of endovascular repair of abdominal aortic aneurysms (AAA) for high-surgical-risk patients, we evaluated our own initial and long-term results with endovascular AAA repair for this patient population.

MATERIAL AND METHODS

Between January 2000 and December 2005, 115 patients with an AAA managed by an aortic endograft were entered in a registry. Data concerning diagnosis, operative risk, treatment, and follow-up were analyzed on an intention-to-treat basis for all patients considered to be poor candidates for surgery. Patients with a ruptured AAA and those who were good surgical candidates were excluded from analysis. The main goal was evaluation of the operative mortality and the long-term survival of these patients. Secondary goals were determination of the frequency of secondary operations, the outcome of the aneurysm sac, and primary and secondary patency rates after aortic endograft placement.

RESULTS

A total of 92 high-surgical-risk patients treated by an endograft were entered in this study. Sixty-seven patients (73%) were classed ASA III and 18 (20%) were ASA IV (20%). Mean aneurysm diameter was 58 mm+/-9 mm. The technical success rate was 99%. Operative mortality was 4.3% (4 cases). Four patients required re-intervention during the mean follow-up of 18 months. The survival rate at 3 yr was 85%. One type I endoleak (1%) and 9 type II endoleaks (9.7%) occurred during the follow-up period. Primary and secondary patency rates at 3 yr were respectively 96% and 100%.

CONCLUSION

Our initial and long-term results with endograft repair of AAA in high-surgical-risk patients were satisfactory. These results appear to justify endovascular repair for this patient population.

Should usual criteria for intervention in abdominal aortic aneurysms be "downsized," considering reported risk reduction with endovascular repair?

Two randomized trials have demonstrated the safety of waiting until abdominal aortic aneurysm (AAA) diameter reaches 5.5 cm for repair in most patients. Other recent randomized trials have demonstrated lower perioperative mortality and morbidity with endovascular aneurysm repair (EVAR) compared to open surgery. Therefore, it is logical to assume that endovascular repair may change the appropriate threshold for intervention. However, endovascular repair is not as durable as open surgery and is associated with ongoing risks of rupture and reintervention. Decision analysis based on data available in 1998 showed that endovascular repair should not change the threshold for intervention. Since that time retrospective data have emerged to suggest that outcomes with endovascular repair are improved in smaller AAAs, although this may simply represent selection bias and the natural history of small AAAs. Randomized trials are appropriate to determine whether improved endovascular outcomes in small AAAs reduce late rupture and reintervention enough to justify early intervention in patients with appropriate anatomy. In the absence of data from these trials, the threshold for intervention should not be changed.

Aortic Aneurysm Morphology in Asians:Features Affecting Stent-Graft Application and Design

PURPOSE

To determine the morphological features of abdominal aortic aneurysms (AAA) in an Asian cohort in order to identify unique features relevant to stent-graft planning and application.

METHODS

Spiral computed tomography (CT) and angiographic assessment of AAA morphology was performed on 65 ethnic Chinese (58 men; mean age 74 years, range 50-87) who underwent endovascular AAA repair. Morphological parameters were compared with published data from American and European patients. The eligibility and potential concerns referable to 4 current stent-graft designs were addressed.

RESULTS

Both common iliac arteries (CIA) measured significantly shorter in Asians, particularly on the right side. The mean RCIA and LCIA lengths were 29.9 mm and 34.2 mm, respectively (25.7 and 34.1 mm for CIAs <20 mm in diameter), compared to >50-mm in Caucasians (p<0.001). The distance between the lowest renal artery and the CIA bifurcation averaged 20 mm shorter in Asians: 148 mm on the right side and 153 mm for the left. The CIAs were also wider, averaging 20.2 mm for the right and 17.9 mm for the left. Other linear measurements did not show a population difference. The AAAs in this series were slightly larger (p<0.001), with a shorter neck (mean 23 mm, p<0.001). No correlation was found between the morphological parameters and body build. Internal iliac artery coverage with or without embolization was necessary in 51% of endovascular repairs due to short or aneurysmal CIAs.

CONCLUSIONS

These differences in AAA morphology pose unique challenges for endovascular repair in Asians. Preoperative angiography is more often necessary. The need for an accurate landing in a short CIA and insufficient length for maneuvering placed constraints on 2-piece graft designs with long main body lengths. A 3-piece endograft with wider aortic and iliac diameters is currently the most attractive option.

Multidetector CT Angiography Versus Digital Subtraction Angiography for Aortoiliac Length Measurements Prior to Endovascular AAA Repair

PURPOSE

To assess observer variation between calibrated-catheter digital subtraction angiography (DSA) and software-enhanced multidetector computed tomography angiography (CTA) in measuring vessel length prior to endovascular aortic aneurysm repair (EVAR).

METHODS

Thirty patients (25 men; mean age 65 years, range 61-85) scheduled for EVAR underwent CTA in 4x2-mm collimation using advanced vessel analysis software. CTA measurements were performed twice by 2 blinded readers in random order with at least a 4-week interval between readings. Nine patients were found unsuitable for endovascular repair after the CTA, so DSA was performed in 21 patients for morphometric evaluation of the abdominal aorta and the iliac arteries. The following segments were measured: H1 (aneurysm neck), H2 (lower renal artery to distal aspect of the aneurysm), H3 (lower renal artery to aortic bifurcation), and H4a/H4b (lower renal artery to iliac bifurcations). Length measurements on DSA were made by (1) following the catheter path in the aortic lumen and (2) dividing tortuous vessel anatomy into segments and measuring each segment along an idealized centerline. Addition of the various segments allowed comparison with data obtained from CTA measurements.

RESULTS

CTA was performed with good intraobserver agreement for all length parameters except H3 in reader 2 (p<0.05). While good interobserver agreement was demonstrated for CTA over long aortoiliac distances (H4a, H4b), higher interobserver agreement was obtained with DSA for shorter segments (H1, H2). Considerable differences were observed between CTA and DSA for the lengths H2 and H4b.

CONCLUSIONS

CTA produces better intra and interobserver correlations in measuring vessel length than DSA. It has the potential to replace DSA as an imaging method before EVAR.

Diameter of abdominal aortic aneurysm and outcome of endovascular aneurysm repair: does size matter? A report from EUROSTAR

OBJECTIVES

This study was undertaken to determine the effect of the preoperative diameter of abdominal aortic aneurysms on the midterm outcome after endovascular abdominal aneurysm repair (EVAR).

METHOD

The data for 4392 patients who had undergone EVAR were analyzed. Patients were enrolled over 6 years to June 2002 in the EUROSTAR database. Outcomes were compared between three groups defined by the preoperative diameter of the aneurysm: group A (n = 1962), 4.0 to 5.4 cm; group B (n = 1528), 5.5 to 6.4 cm; and group C (n = 902), 6.5 cm or larger. Patient characteristics, details of aortoiliac anatomy, operative procedures, old or current device generation, and postoperative complications in the three patient groups were compared. Outcome events included aneurysm-related death, unrelated death, conversion, and post-EVAR rupture of the aneurysm. Life table analysis and log-rank tests were used to compare outcome in the three study groups. Multivariate Cox models were used to determine whether baseline and follow-up variables were independently associated with adverse outcome events.

RESULTS

Patients in group C were significantly older than patients in groups A and B (73 years vs 70 and 72 years, respectively; P =.003 - P <.0001 for different group comparisons), and more frequently were at higher operative risk (American Society of Anesthesiologists classification >or=3; 63% vs 48% and 54%; P =.0002-P <.0001). Device-related (type I) endoleaks were more frequently observed at early postoperative arteriography in group C compared with groups A and B (9.9% vs 3.7% and 6.8%; P =.01-P <.0001). Postoperatively systemic complications were more frequently present in group C (17.4% vs 12.0% in group A and 12.6% in group B; P <.0001 and.001). The first-month mortality was approximately twice as high in group C compared with the other groups combined (4.1% vs 2.1%; P <.0001). Late rupture was most frequent in group C. Follow-up results at midterm were less favorable in groups C and B compared with group A (freedom from rupture, 90%, 98%, and 98% at 4 years in groups C, B, and A, respectively; P <.0001 for group C vs groups A and B). Aneurysm-related death was highest in group C (88% freedom at 4 years, compared with 95% in group B and 97% in A; P =.001 and P <.0001, respectively; group B vs A, P =.004). The annual rate of aneurysm-related death in group C was 1% in the first 3 years, but accelerated to 8.0% in the fourth year. Incidence of unrelated death also was higher in groups C and B than in group A (76% and 82% freedom at 4 years vs 87%; P <.0001 for both comparisons). Ratio of aneurysm-related to unrelated death was 23%, 21%, and 50% in groups A, B, and C, respectively. Cox models demonstrated that the correlation between large aneurysms (group C) and all assessed outcome events was independent and highly significant. Older generation devices had an independent association with aneurysm-related and unrelated deaths (P =.02 and P =.04, respectively). However, this correlation was less strong than large aneurysm diameter (P =.0001 and P =.0009, respectively).

CONCLUSIONS

The midterm outcome of large aneurysms after EVAR was associated with increased rates of aneurysm-related death, unrelated death, and rupture. Reports of EVAR should stratify their outcomes according to the diameter of the aneurysm. Large aneurysms need a more rigorous post-EVAR surveillance schedule than do smaller aneurysms. In small aneurysms EVAR was associated with excellent outcome. This finding may justify reappraisal of currently accepted management strategies.

Aortoiliac morphologic correlations in aneurysms undergoing endovascular repair

PURPOSE

The feasibility of endovascular aneurysm repair depends on morphologic characteristics of the aortoiliac segment. Knowledge of such characteristics is relevant to safe deployment of a particular device in a single patient and to development of new devices for use in patients with a broader spectrum of anatomic variations.

METHODS

We evaluated findings on computed tomography scans for 277 patients being considered for endovascular aneurysm repair. Aortic neck length and angulation estimates were generated with three-dimensional trigonometry. Specific centerline points were recorded, corresponding to the aorta at the celiac axis, lowest renal artery, cranial aspect of the aneurysm sac, aortic terminus, right hypogastric artery origin, and left hypogastric origin. Aortic neck thrombus and calcium content were recorded, and neck conicity was calculated in degrees. Statistical analysis was performed with the Spearman rank correlation. Data are expressed as median and interquartile range.

RESULTS

Median diameter of the aneurysms was 52 mm (interquartile range, 48-59 mm) in minor axis and 56 mm (interquartile range, 51-64 mm) in major axis, and median length was 88 mm (interquartile range, 74-103 mm). Median proximal aortic neck diameter was 26 mm (interquartile range, 22-29 mm), and median neck length was 30 mm (interquartile range, 18-45 mm). The common iliac arteries were similar in diameter (right artery, 16 mm [interquartile range, 13-20 mm]; left artery, 15 mm [interquartile range, 11-18 mm]) and length (right, 59 mm [interquartile range, 50-69 mm]; left, 60 mm [interquartile range, 49-70 mm]). Median angulation of the infrarenal aortic neck was 40 degrees (interquartile range, 29-51 degrees), and median angulation of the suprarenal segment was 45 degrees (interquartile range, 36-57 degrees). By gender, sac diameter, proximal neck diameter, and iliac artery diameter were significantly larger in men. Significant linear associations were identified between sac diameter and sac length, neck angulation, and iliac artery diameter. As the length of the aneurysm sac increased the proximal aortic neck length decreased. Conversely, as the sac length decreased sac eccentricity increased. Mural thrombus content within the neck increased with increasing neck diameter.

CONCLUSIONS

There is considerable variability in aortoiliac morphologic parameters. Significant associations were found between various morphologic variables, links that are presumably related to a shared pathogenesis for aberration in aortoiliac diameter, length, and angulation. Ultimately this information can be used to develop new endovascular devices with broader applicability and improved long-term results.

Disparate outcome after endovascular treatment of small versus large abdominal aortic aneurysm

OBJECTIVES

The size of an abdominal aortic aneurysm is the most important parameter for determining whether repair is appropriate. This decision, however, must be considered in the context of long-term outcome of treatment, balancing risk for rupture with mortality from the initial procedure and all subsequent secondary procedures necessary when durability is not ideal. Information on the results of endovascular repair of small versus large aneurysms has not been available.

METHODS

Preoperative imaging studies and postoperative outcome were assessed in 700 patients who underwent endovascular repair of abdominal aortic aneurysm over 6 years at a single institution. Patients were divided into two groups: 416 patients (59.4%) with aneurysms smaller than 5.5 cm in diameter and 284 patients (40.6%) with aneurysms 5.5 cm or larger in diameter. Outcome variables were assessed with the Kaplan-Meier method and the log-rank test.

RESULTS

Patients with small and large aneurysms were comparable with regard to all baseline parameters assessed, with the single exception of a small increase in age (2.3 years) in patients with large aneurysms (P =.031). While there were no differences in rate of type II endoleaks, mid-term changes in sac diameter, or aneurysm rupture between the two groups, at 24 months patients with large aneurysms had more type I leaks (6.4% +/- 2.3% vs 1.4% +/- 0.6%; P =.011), device migration (13% +/- 4.0% vs 4.4% +/- 1.8%; P =.006), and conversion to open surgical repair (8.2% +/- 3.2% vs 1.4% +/- 1.1%; P =.031). Of greatest importance, at 24 months patient survival was diminished (71% +/- 4.6% vs 86% +/- 2.8%; P <.001) and risk for aneurysm-related death was increased (6.1% +/- 2.6% vs 1.5% +/- 1.0%; P =.011) in the group with large aneurysms.

CONCLUSIONS

Outcome after endovascular repair of abdominal aortic aneurysm depends on size; results appear inferior in patients with larger aneurysms. These differences attain importance when choosing between observation and repair, balancing risk for rupture against size-dependent outcome.

Nature, frequency, and predictors of secondary procedures after endovascular repair of abdominal aortic aneurysm

OBJECTIVES

Endovascular stent grafting offers a potentially less invasive option for treatment of abdominal aortic aneurysm. Clinical benefit has been demonstrated with respect to early parameters such as blood transfusion, return of gastrointestinal function, and length of hospital stay. Endovascular repair, however, has been criticized on the basis of inferior long-term outcome. Secondary procedures may be necessary to address durability issues such as migration, high-pressure endoleak, graft limb thrombosis, and degeneration of the stent-fabric structure itself, issues that may compromise the primary goal of aneurysm repair, protection from rupture.

METHODS

Between 1996 and 2002, 703 patients underwent endovascular treatment of infrarenal abdominal aortic aneurysm at The Cleveland Clinic Foundation. During this time, five devices were used: Ancure, AneuRx, Excluder, Talent, and Zenith. Outcome was assessed with physical examination, lower extremity arterial studies, plain abdominal radiography, and computed tomography at discharge, at 1, 6, and 12 months postoperatively, and annually thereafter. Secondary procedures were defined as any procedure, exclusive of diagnostic angiography, performed after stent graft implantation, directed at treatment of aneurysm-related events. Multivariable statistical techniques for censored data (Cox proportional hazards modeling) were used to determine baseline parameters associated with need for secondary procedures over follow-up, with calculation of hazards ratio (HR) and 95% confidence interval (CI).

RESULTS

Patient follow-up averaged 12.2 +/- 11.7 months. Patient survival was 90% +/- 1.4% at 1 year, 78% +/- 2.6% at 2 years, and 70% +/- 3.8% at 3 years. Aneurysm rupture occurred in 3 patients (0.4%), accounting for rupture risk of 1.4% over the first 2 years of follow-up (Kaplan-Meier method). Overall, 128 secondary procedures were required in 104 patients (15%), with a cumulative risk of 12% +/- 1.5% at 1 year, 24% +/- 2.8% at 2 years, and 35% +/- 4.4% at 3 years after stent graft implantation. Among the secondary procedures, new stent grafts and extensions were placed in 34 patients (27%), embolization of endoleak was performed in 33 patients (26%), and open surgical conversion was undertaken in 11 patients (9%). Periprocedural mortality of secondary procedures was 8% overall, but was 18% for patients undergoing open surgical conversion. Multivariable modeling identified the date the procedure was performed (HR, 1.53 per 3-month period of study; CI, 1.22-1.92; P <.001) and aneurysm size (HR, 1.35 per centimeter of minor axis; CI, 1.13-1.60; P <.001) as independent predictors of need for secondary procedures.

CONCLUSIONS

Current endovascular devices are associated with a relatively high rate of complications over mid-term follow-up, culminating in frequent need for secondary remedial procedures. With strict follow-up imaging compliance, however, risk for rupture and aneurysm-related death remain exceedingly low. Newer technology may achieve improved durability and a lower requirement for secondary procedures, while maintaining the minimally invasive nature of presently available devices.

Prediction of aortoiliac stent graft length: comparison of a semiautomated computed tomography angiography method and calibrated aortography

OBJECTIVE

The aim of this study is to compare multislice computed tomography (MSCT) in combination with a newly developed semiautomated software program with calibrated aortography in patients who are scheduled for endovascular aortic stent graft placement.

METHODS

From November 2000 until December 2001, seven patients with an abdominal aortic aneurysm (AAA) underwent both calibrated aortography and MSCT for preoperative endovascular stent graft planning. Both studies were performed within 14 days. Further, length measurements were performed with a semiautomated computerized tomographic angiography (CTA) calibration method and a conventional calibrated aortography technique using three differently configured tubes with variable tortuosity. The AAA length measurements of the semiautomated CTA calibration method and the calibrated aortography were compared.

RESULTS

Statistical analysis included linear regression analysis and revealed a probability value of 0.000381 and an r2 value of 0.93. Using phantoms, it is proven by the authors that the accuracy of the semiautomated CTA calibration method increases with increasing tortuosity when compared with the conventional calibrated aortography technique.

CONCLUSIONS

Our preliminary results show that the semiautomated CTA calibration method has a potentially advantageous role in preoperative stent graft planning regarding the aortic length measurements and seems to be more accurate than calibrated aortography, especially in extremely tortuous vessels. Further studies have to be performed, however.