Morphological classification of abdominal aortic aneurysm in selection of patients for endovascular grafting

Association between blood flow pattern and rupture risk of abdominal aortic aneurysm based on computational fluid dynamics

OBJECTIVES

This study aimed to derive a novel classification of blood flow pattern in AAA based on computational fluid dynamics, and determine the predicting value of flow pattern in abdominal aortic aneurysm (AAA) rupture.

DESIGN

Age, gender matched case-control study MATERIALS: Case patients were identified as those who underwent emergent endovascular or open repair due to ruptured or impending rupture AAA. Control patients were those age and gender matched AAA patients who were asymptomatic and confirmed unruptured from CTA images from the same period.

METHODS

Classification of blood flow pattern (Type I: non-helical main flow channel with multiple vortices; Type II: non-helical main flow channel with single vortices; Type III, helical main flow channel with helical vortices) and hemodynamic parameters [areas of low wall shear stress (A _{low WSS}), aneurysm pressure drop (Δ pressure), etc.] were derived from computational fluid dynamic (CFD) analyses. Multivariate regression was used to determine independent risk factors of AAA rupture. The incremental discriminant and reclassification abilities for AAA rupture were compared among different models.

RESULTS

This study included 53 ruptured and 53 intact AAA patients. Ruptured AAA showed higher prevalence of type III flow pattern (60.38% vs. 15.09%, P<.001) compared to intact AAA. Type III flow pattern was associated with a significantly increased risk of aneurysm rupture (OR 10.22, 95%CI 3.43-30.49). Among all predicting models, combination of AAA diameter, hemodynamic parameters (A _{low WSS} or Δ pressure) and flow pattern showed highest discriminant abilities in both overall population (concordance statistic [c-index] .862) and subgroup patients with AAAs <55mm (c-index .972). Compared to AAA diameter, adding flow pattern could significantly improve the reclassification abilities in both overall population (net reclassification index [NRI] .321; p<.001) and subgroup of AAAs < 55mm (NRI .732, P<.001).

CONCLUSION

Type III flow pattern was associated with a significantly increased risk of AAA rupture. Integration of blood flow pattern may improve the identification of high-risk aneurysms in both overall population and AAAs smaller than 55mm.

Influence of Pulmonary Status and Diabetes Mellitus on Aortic Neck Dilatation following Endovascular Repair of Abdominal Aortic Aneurysms: A EUROSTAR Report

Purpose:

To elucidate the association of impaired pulmonary status (IPS) and diabetes mellitus (DM) with clinical outcome and the incidences of aortic neck dilatation and type I endoleak after elective endovascular infrarenal aortic aneurysm repair (EVAR).

Methods:

In 164 European institutions participating in the EUROSTAR registry, 6383 patients (5985 men; mean age 72.4±7.6 years) underwent EVAR. Patients were divided into patients without versus with IPS or with/without DM. Clinical assessment and contrast-enhanced computed tomography (CT) were performed at 1, 3, 6, 12, 18, and 24 months and annually thereafter. Cumulative endpoint analysis comprised death, aortic rupture, type I endoleak, endovascular reintervention, and surgical conversion.

Results:

Prevalence of IPS was 2733/6383 (43%) and prevalence of DM was 810/6383 (13%). Mean follow-up was 21.1±18.4 months. Thirty-day mortality, AAA rupture, and conversion rates did not differ between patients with versus without IPS and between patients with versus without DM. All-cause and AAA-related mortality, respectively, were significantly higher in patients with IPS compared to patients with normal pulmonary status (31.0% versus 19.0%, p<0.0001 and 6.8% versus 3.3%, p=0.0057) throughout follow-up. In multivariate analysis adjusted for smoking, age, gender, comorbidities, fitness for open repair, co-existing common iliac aneurysm, neck and aneurysm size, arterial angulations, aneurysm classification, endograft oversizing >15%, and type of stent-graft, the presence of IPS was not associated with significantly higher rates of aortic neck dilatation (30.6% versus 38.0%, p>0.05) and did not influence cumulative rates of type I endoleak, endovascular reintervention, or conversion to open surgery (p>0.05). Similarly, the presence of DM did not influence the above-mentioned study endpoints.

Conclusion:

In contrast to observations regarding the natural course of AAAs, impaired pulmonary status does not negatively influence aortic neck dilatation, while the presence of diabetes does not protect from these dismal events after EVAR.

Abdominal Aortic Aneurysm Morphology in Candidates for Endovascular Repair Evaluated with Spiral Computed Tomography and Digital Subtraction Angiography

Purpose:

To analyze the morphology of abdominal aortic aneurysms (AAAs) and to study the usefulness of spiral computed tomography (CT) versus digital subtraction angiography (DSA) in the evaluation of patients for endovascular repair.

Methods:

Of 133 AAA patients (120 men, mean age 67 years, range 52 to 84) evaluated preoperatively with CT imaging, 77 endograft candidates (68 men) were also assessed with intra-arterial DSA. Arterial parameters were measured on axial CT scans and angiographic films for comparison.

Results:

Mean maximum AAA diameter was 58 ± 11 mm (range 39 to 95). Aneurysmal neck diameter was consistently smaller on DSA than on CT (20.7 ± 3.6 mm versus 23.0 ± 3.5 mm, p < 0.0001). The distance from the most distal renal artery to the aortic bifurcation was longer on angiography than on CT (mean difference 10.0 mm, p < 0.0001). There was a positive correlation between the maximum AAA diameter and the AAA length (r = 0.49, p < 0.0001) and an inverse relationship between the neck length and the neck diameter (r = −0.36, p < 0.0001). No correlation was found between the maximum AAA diameter and maximum iliac diameter, angulation, or length.

Conclusions:

AAA anatomy varies widely and independently of the aneurysm size. Therefore, the maximum size of the aneurysm is a poor predictor of whether or not an aneurysm is suitable for endovascular repair. The discrepancy between angiographic and axial CT measurements suggests that neither alone is sufficient as a preoperative imaging technique when evaluating a patient for an endovascular graft procedure.

Treatment possibility for AAA of the visceral branches region

The authors describe a promising abdominal aortic aneurysm treatment--a combined endovascular/surgical approach--used in two cases of aneurysm taking the aortic visceral branches region.

Banding in aortic stent-graft fixation in EVAR

The authors describe the method of surgical aortic banding for better stent-graft fixation in cases of problematic aortic neck in the endovascular infrarenal aneurysms repair.

AAA elective treatment indication tactics in EVAR era

The authors describe their indication tactics for AAA elective treatment. Based on one-month morbidity and mortality they evaluate the results obtained in the past six years and compare the methods of open surgery, endovascular repair and combined strategy in AAAs elective repair.

Endovascular treatment of abdominal aortic aneurysms--6 years of experience with Ella stent-graft system

PURPOSE

Evaluation of 6-year results of abdominal aortic aneurysm (AAA) treatment by Ella stent-grafts with regard to safety and effectivity in relation to morphology of the aneurysm.

METHODS

From a group of 172 patients with AAA, in whom elective endovascular treatment was considered, 120 of them (69.8%) were found to be suitable for this type of therapy. The bifurcated type of stent-graft was implanted in 97 patients, uniiliacal type in 19 patients and only four patients were found to be suitable for tubular type of stent-graft. Additional necessary procedures (internal iliac artery occlusion or contralateral common iliac artery occlusion in a group of patients with uniiliacal type of stent-graft) were performed surgically during the stent-graft implantation. CT and US controls were performed at 3, 6 and 12 months after implantation, later every 12 months.

RESULTS

Primary technical success was achieved in 109 of the 120 patients (91%). Primary endoleak was recorded in 11 patients (primary endoleak type Ia in seven patients, type Ib in three patients and type IIIa in one patient). Assisted technical success after reintervention or spontaneous seal was 98.3%. Surgical conversion was indicated in two patients (1.7%). Perioperative mortality rate was 3.3%. Total average follow-up period was 20.7 months (range from 2 to 60 months). In nine patients (7.5%) secondary endoleak type II was found at control CT or US, in three patients partial thrombosis of the stent-graft was found. There was no aneurysm rupture during follow-up.

CONCLUSION

Treatment of AAA with Ella stent-graft system is effective and safe. Bifurcated stent-graft is the most frequently used type. Uniiliacal type of stent-graft is used by us only in cases of complicated morphology.

Femoral - internal iliac bypass in aortoiliac aneurysms endovascular repair

The authors describe femoral - internal iliac bypass creation to remove ischemic complications in aortoiliac aneurysm endovascular repair. Based on a good experience with bypass in 6 patients they recommend its preventive indication when both internal iliac arteries are overstented.

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

PURPOSE

To analyze the morphology of abdominal aortic aneurysms (AAAs) and to study the usefulness of spiral computed tomography (CT) versus digital subtraction angiography (DSA) in the evaluation of patients for endovascular repair.

METHODS

Of 133 AAA patients (120 men, mean age 67 years, range 52 to 84) evaluated preoperatively with CT imaging, 77 endograft candidates (68 men) were also assessed with intra-arterial DSA. Arterial parameters were measured on axial CT scans and angiographic films for comparison.

RESULTS

Mean maximum AAA diameter was 58 +/- 11 mm (range 39 to 95). Aneurysmal neck diameter was consistently smaller on DSA than on CT (20.7 +/- 3.6 mm versus 23.0 +/ 3.5 mm, p < 0.0001). The distance from the most distal renal artery to the aortic bifurcation was longer on angiography than on CT (mean difference 10.0 mm, p < 0.0001). There was a positive correlation between the maximum AAA diameter and the AAA length (r = 0.49, p < 0.0001) and an inverse relationship between the neck length and the neck diameter (r = -0.36, p < 0.0001). No correlation was found between the maximum AAA diameter and maximum iliac diameter, angulation, or length.

CONCLUSIONS

AAA anatomy varies widely and independently of the aneurysm size. Therefore, the maximum size of the aneurysm is a poor predictor of whether or not an aneurysm is suitable for endovascular repair. The discrepancy between angiographic and axial CT measurements suggests that neither alone is sufficient as a preoperative imaging technique when evaluating a patient for an endovascular graft procedure.

Role of magnetic resonance angiography for assessment of abdominal aortic aneurysm before endoluminal repair

BACKGROUND

A detailed knowledge of the morphology of the aorta and iliac arteries is an important prerequisite for successful endoluminal abdominal aortic aneurysm (AAA) repair. The best method of preoperative evaluation remains to be determined.

METHODS

A prospective study was undertaken between January 1994 and July 1995 to assess the ability of computed tomography (CT), magnetic resonance angiography (MRA), colour duplex imaging and intra-arterial digital subtraction angiography (IA-DSA) to visualize AAA morphology.

RESULTS

Eighty-two consecutive patients (64 men, 18 women) with AAA were assessed with MRA, contrast-enhanced CT, colour duplex imaging and IA-DSA. Median age was 74 (range 59-87) years and median AAA diameter was 5.7 (range 3.5-9.7) cm. Five patients were unable to tolerate CT or MRA examination. Seventy-seven patients underwent both CT and MRA. Of these, 55 also had a colour duplex scan and 32 underwent arteriography. The scans were assessed by an independent blinded observer. MRA was significantly better (P < 0.01) at visualizing AAA morphology compared with CT and colour duplex imaging. There was no statistically significant difference between MRA and arteriography.

CONCLUSION

MRA is useful in patient selection for endoluminal AAA repair, as it avoids use of iodinated contrast medium and ionizing radiation.