Relative contribution of wall shear stress and injury in experimental intimal thickening at PTFE end-to-side arterial anastomoses

BACKGROUND

Intimal hyperplastic thickening (IHT) is a frequent cause of prosthetic bypass graft failure. Induction and progression of IHT is thought to involve a number of mechanisms related to variation in the flow field, injury and the prosthetic nature of the conduit. This study was designed to examine the relative contribution of wall shear stress and injury to the induction of IHT at defined regions of experimental end-to-side prosthetic anastomoses.

METHODS AND RESULTS

The distribution of IHT was determined at the distal end-to-side anastomosis of seven canine Iliofemoral PTFE grafts after 12 weeks of implantation. An upscaled transparent model was constructed using the in vivo anastomotic geometry, and wall shear stress was determined at 24 axial locations from laser Doppler anemometry measurements of the near wall velocity under conditions of pulsatile flow similar to that present in vivo. The distribution of IHT at the end-to-side PTFE graft was determined using computer assisted morphometry. IHT involving the native artery ranged from 0.0+/-0.1 mm to 0.05+/-0.03 mm. A greater amount of IHT was found on the graft hood (PTFE) and ranged from 0.09+/-0.06 to 0.24+/-0.06 mm. Nonlinear multivariable logistic analysis was used to model IHT as a function of the reciprocal of wall shear stress, distance from the suture line, and vascular conduit type (i.e. PTFE versus host artery). Vascular conduit type and distance from the suture line independently contributed to IHT. An inverse correlation between wall shear stress and IHT was found only for those regions located on the juxta-anastomotic PTFE graft.

CONCLUSIONS

The data are consistent with a model of intimal thickening in which the intimal hyperplastic pannus migrating from the suture line was enhanced by reduced levels of wall shear stress at the PTFE graft/host artery interface. Such hemodynamic modulation of injury induced IHT was absent at the neighboring artery wall.

Increased flexibility of AneuRx stent-graft reduces need for secondary intervention following endovascular aneurysm repair

PURPOSE

To evaluate the impact of a change in the manufacturing of the AneuRx stent-graft on the long-term results of endovascular abdominal aortic aneurysm (AAA) repair.

METHODS

The first 70 AAA patients treated with the AneuRx stent-graft between October 1996 and December 1998 were reviewed. The early stiff bifurcated design (STIFF) was used in 23 patients (mean age 71.7 +/- 9.3 years, range 45-87) and the current flexible bifurcated design (FLEX) in 47 mean age 75.0 +/- 7.3 years, range 61-96). Data on patient demographics, aneurysm morphology, technical success, complications, secondary procedures, and outcomes were compared using Kaplan-Meier estimates to evaluate patient survival and freedom from surgical conversion, rupture, and secondary interventions at 6, 12, and 24 months.

RESULTS

The 2 groups were equally matched with regard to age, preoperative comorbidities, proximal neck dimensions, and aneurysm diameter. Mean follow-up times were 22.42 +/- 11.72 months (range 1-46) for the STIFF cohort and 18.08 +/- 6.14 months (range 1-30) for the FLEX (p = 0.057). Eleven (48%) of 23 STIFF patients required secondary interventions versus 6 (13%) of 47 FLEX patients (p < 0.05). There were no ruptures. At the 24-month interval, survival estimates were 86% for STIFF and 76% for FLEX (p = NS); freedom from surgical conversion was 100% for STIFF and 97% for FLEX (p = NS) and freedom from secondary interventions was 18% for STIFF and 90% for FLEX (p < 0.05) at 24 months.

CONCLUSIONS

The AneuRx stent-graft was effective in achieving the primary objective of preventing aneurysm rupture in all patients. However, increasing the flexibility of the bifurcated module significantly improved the primary success rate by reducing the need for subsequent secondary interventions.

Impact of endovascular repair on open aortic aneurysm surgical training

PURPOSE

The purpose of this study was to determine the impact of an endovascular stent-graft program on vascular training in open aortic aneurysm surgery.

METHODS

The institutional and vascular surgery fellow experience in aortic aneurysm repair during a 6-year period was reviewed. The 3-year period before introduction of endovascular repair was compared with the 3-year period after introduction of endovascular repair. All patients undergoing abdominal aortic aneurysm (AAA) or thoracoabdominal aortic aneurysm repairs were entered prospectively into a vascular registry and retrospectively analyzed to evaluate the changing patterns in aortic aneurysm treatment and surgical training.

RESULTS

Between July 1994 and June 2000, a total of 588 patients with AAA or thoracoabdominal aneurysms were treated at Stanford University Medical Center. There were 296 (50%) open infrarenal AAA repairs, 87 (15%) suprarenal AAA repairs, 47 (8%) thoracoabdominal aneurysm repairs, and 153 (26%) endovascular stent-grafts. The total number of aneurysms repaired per year by vascular fellows before the endovascular program was 71.3 +/- 4.9 (range, 68-77) and increased to 124.7 +/- 35.6 (range, 91-162) after introduction of endovascular repair (P <.05). This increase was primarily caused by the addition of endovascular stent-graft repairs by vascular fellows (51.0 +/- 29.0/year [range, 23-81]). There was no change in the number of open infrarenal aortic aneurysm repairs per year, 53.0 +/- 6.6 (range, 48-56) before endovascular repair versus 47.0 +/- 1.7 (range, 46-49) after (P = not significant). There was a significant increase in the number of suprarenal AAA repairs per year by vascular fellows, 10.0 +/- 1.0 (range, 9-11) before endovascular repair compared with 19.0 +/- 6.5 (range, 13-26) after (P <.05). There was no change in the number of thoracoabdominal aneurysm repairs per year between the two groups, 8.0 +/- 3.0 (range, 4-11) before endovascular repair compared with 7.6 +/- 2.3 (range, 5-9) after.

CONCLUSIONS

Introduction of an endovascular aneurysm stent-graft program significantly increased the total number of aneurysms treated. Although the number of open aneurysm repairs has remained the same, the complexity of the open aneurysm experience has increased significantly for vascular fellows in training.

Impact of aortoiliac tortuosity on endovascular repair of abdominal aortic aneurysms: evaluation of 3D computer-based assessment

OBJECTIVE

The purpose of this study was to examine the effect of aortoiliac tortuosity, as assessed by observers and 3-dimensional (3D) computer-based methods, on the conduct and outcome of endovascular repair of abdominal aortic aneurysms.

METHODS

Infrarenal aortoiliac tortuosity was measured in 75 patients (mean follow-up, 14.8 +/- 10.4 months) who underwent endovascular repair of abdominal aortic aneurysms by using the following four methods: (1) grading by 2 experienced observers; (2) tortuosity index measured as the inverse radius of curvature (cm(-1)) at 1-mm intervals along the median luminal centerline (MLC) on 3D reconstructions of computed tomography (CT) angiograms and was calculated as the sum of values greater than 0.3 cm(-1); (3) MLC-straight line length ratio from renal to hypogastric arteries; (4) manual measurement of angles at points of angulation on anteroposterior and lateral projections of 3D CT reconstructions. In evaluating association between these measures, correlation between human observers was accepted as the gold standard.

RESULTS

For rating of overall aortoiliac tortuosity, interobserver correlation (r = 0.67) was comparable with correlation of observers with tortuosity index (r = 0.67 and 0.56), whereas correlations of each observer with MLC-straight line ratio (r = 0.50 and 0.56) and cumulative angulation (r = 0.44 and 0.44) were significant but weaker. For determining the relative tortuosity of right and left aortoiliac access, agreement between observers and tortuosity index (54% and 58%; P < .05; kappa, 0.33 and 0.38) was not as good as between observers (68%; P < .001; kappa, 0.53). This difference was primarily related to evaluation of the aorta, where interobserver correlation (r = 0.71) was better than that between each observer and tortuosity index (r = 0.47 and 0.55), whereas correlations in the iliac arteries were comparable (r = 0.64 and 0.67) (all coefficients P < .01). Increased tortuosity was associated with a more complex endovascular repair, as reflected by longer fluoroscopy time (P = .05), use of more contrast material (P = .03), use of extender modules (P = .04), and more frequent use of arterial reconstruction (P = .01), but was not associated with a higher overall complication rate. Increased tortuosity, when it occurred in the aortic neck, was associated with predischarge endoleak (P = .03) but not with late endoleak, intervention, or aneurysm-related adverse events.

CONCLUSION

Aortoiliac tortuosity is associated with increased complexity of endovascular aneurysm repair and with predischarge endoleak but does not appear to affect intermediate-term results. Computer-based 3D measurement of aortoiliac tortuosity is feasible and clinically meaningful. Its ultimate role in relation to human assessment must be further defined in future studies.

Type-II endoleaks following endovascular AAA repair: preoperative predictors and long-term effects

PURPOSE

To determine the significance of persistent type-II endoleaks and whether they can be predicted preoperatively in patients with abdominal aortic aneurysms (AAA).

METHODS

The charts of all AAA patients treated with the AneuRx stent-graft at a single center from 1996 to 1998 were reviewed. Patients with <12-month follow-up or type-I endoleaks were excluded. The presence or absence of type-II endoleaks was determined from duplex imaging and computed tomographic angiography. Three groups were identified and compared: 16 patients with persistent type-II endoleaks (PE), 14 patients with transient type-II endoleaks (TE), and 16 patients with no endoleak (NE).

RESULTS

The groups did not differ with regard to age, preoperative comorbidities, follow-up time, and AAA neck diameter and length. AAA diameters were 57.1 +/- 9.0 mm for NE, 63.4 +/- 11.4 mm for TE, and 55.6 +/- 4.2 mm for PE. The inferior mesenteric artery (IMA) was patent in 5 (31%) NE patients, 6 (43%) TE patients, and 13 (81%) PE patients (p < 0.01). The number of patent lumbar arteries visualized preoperatively was 0.5 +/- 1.0 in NE, 1.3 +/- 0.8 in TE, and 2.4 +/- 0.6 in PE (p < 0.0001). Patent IMAs (RR 0.82, p < 0.01) and >2 lumbar arteries (RR 0.40, p < 0.0001) were identified as independent preoperative risk factors for persistent endoleaks. There were no changes in mean diameter or volume in aneurysms with persistent endoleaks.

CONCLUSIONS

No adverse clinical events were related to the presence of type-II endoleaks, but there was no decrease in aneurysm size in patients with persistent type-II leaks. Patients with a large, patent IMA, or >2 lumbar arteries on preoperative CT angiography are at higher risk for persistent type-II endoleaks.

Prediction of aortoiliac stent-graft length: comparison of measurement methods

PURPOSE

To determine the accuracy of helical computed tomography (CT), projectional angiography derived from CT angiography, and intravascular ultrasonographic withdrawal (IUW) length measurements for predicting appropriate aortoiliac stent-graft length.

MATERIALS AND METHODS

Helical CT data from 33 patients were analyzed before and after endovascular repair of abdominal aortic aneurysm (Aneuryx graft, n = 31; Excluder graft, n = 2). The aortoiliac length of the median luminal centerline (MLC) and the shortest path (SP) that remained at least one common iliac arterial radius away from the vessel wall were calculated. Conventional angiographic measurements were simulated from CT data as the length of the three-dimensional MLC projected onto four standard viewing planes. These predeployment lengths and IUW length, available in 24 patients, were compared with the aortoiliac arterial length after stent-graft deployment.

RESULTS

The mean error values of SP, MLC, the maximum projected MLC, and IUW were -2.1 mm +/- 4.6 (SD) (P =.013), 9.8 mm +/- 6.8 (P <.001), -5.2 mm +/- 7.8 (P <.001), and -14.1 mm +/- 9.3 (P <.001), respectively. The preprocedural prediction of the postprocedural aortoiliac length with the SP was significantly more accurate than that with the MLC (P <.001), maximum projected MLC (P <.001), and IUW (P <.001).

CONCLUSION

The shortest aortoiliac path length maintaining at least one radius distance from the vessel wall most accurately enabled stent-graft length prediction for 31 AneuRx and two Excluder stent-grafts.

Blood flow decrease induces apoptosis of endothelial cells in previously dilated arteries resulting from chronic high blood flow

We investigated apoptosis of endothelial cells during the arterial narrowing process in response to reduction in flow. The decrease in flow was created in the carotid artery by closure of an arteriovenous fistula (AVF), which had been established for 28 days in rabbits. The endothelial cell apoptosis in the carotid artery was studied at 1, 3, 7, and 21 days of flow reduction after closure of the AVF by use of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) with laser scanning confocal microscopy and transmission and scanning electron microscopy. After AVF closure, arterial lumen diameter was reduced by 36%, and compared with endothelial cells before the closure, the number of endothelial cells was decreased by 45% at 21 days. Endothelial cell apoptosis was observed at 1 day, peaked at 3 days (381.3+/-87.1 cells per square millimeter), and decreased at 7 days. These cells had irregular protrusions under scanning electron microscopy and were characterized by fragmented nuclei under transmission electron microscopy. Apoptotic cells were mainly beneath the endothelium and were occasionally within smooth muscle cells and endothelial cells. The results suggest that apoptosis of endothelial cells may play a role in the arterial remodeling in response to a reduction in flow.

Outcome after unilateral hypogastric artery occlusion during endovascular aneurysm repair

PURPOSE

The purpose of this study was to determine the long-term functional outcome after unilateral hypogastric artery occlusion during endovascular stent graft repair of aortoiliac aneurysms.

METHODS

During a 41-month period, 157 consecutive patients underwent elective endovascular stent graft repair of aortoiliac aneurysms with the Medtronic AneuRx device. Postoperative computed tomography scans were compared with preoperative scans to identify new hypogastric artery occlusions. Twenty-three (15%) patients had unilateral hypogastric occlusion, and there were no cases of bilateral occlusions. Telephone interviews about past and current levels of activity and symptoms were conducted, and pertinent medical records were reviewed. All 23 (100%) patients were available for the telephone interview. A disability score (DS) was quantitatively graded on a discrete scale ranging from 0 to 10 corresponding to "virtually bed-bound" to "greater-than-a-mile" exercise tolerance. Worsening or improvement of symptoms was expressed as a difference in DS between two time points (-, worsening/+, improving).

RESULTS

Among the 23 patients, two groups were identified: 10 patients (43%) had planned and 13 patients (57%) had unplanned or inadvertent occlusions. The patients in the two groups did not differ significantly in the mean age (73.4 vs 73.7 years), sex (male:female, 9:1 vs 10:3), and duration of follow-up (15.6 vs 14.4 months). Nine (39%) of the 23 patients, five patients in the planned and four patients in the unplanned group, reported significant symptoms of hip and buttock claudication ipsilateral to their occluded hypogastric arteries. The mean decrement from baseline of these nine patients in their DS postoperatively was -3.3. The symptoms were universally noted on postoperative day 1. Although most patients improved (89%), one (11%) never got better. Among those whose symptoms improved, the mean time to improvement was 15 weeks, but with a plateau thereafter resulting in a net decrement of DS of -2.3 from baseline. Finally, when questioned whether they would undergo the procedure again, all 23 patients unanimously answered, "Yes."

CONCLUSIONS

A significant number (39%) of patients who sustain hypogastric artery occlusion after endovascular aneurysm repair have symptoms. Although most patients with symptoms have some improvement, none return to their baseline level of activity. Despite this, all patients in retrospect would again choose endovascular repair over conventional open repair.

Vascular complications in high-performance athletes

PURPOSE

The purpose of this study was to evaluate our experience with the diagnosis and management of vascular injuries in a group of high-performance athletes.

METHODS

Between June 1994 and June 2000, we treated 26 patients who sustained vascular complications as a result of athletic competition. Clinical presentation, type of athletic competition, location of injury, type of therapy, and degree of rehabilitation were analyzed retrospectively.

RESULTS

The mean age of the patients was 23.8 years (range, 17-40). Twenty-one (81%) patients were men, and five (19%) were women. Athletes included 8 major-league baseball players, 7 football players, 2 world-class cyclists, 2 rock climbers, 2 wind surfers, 1 swimmer, 1 kayaker, 1 weight lifter, 1 marksman, and 1 volleyball player. There were 14 (54%) arterial and 12 (46%) venous complications. Arterial injuries included 7 (50%) axillary/subclavian artery or branch artery aneurysms with secondary embolization, 6 (43%) popliteal artery injuries, and 1 (7%) case of intimal hyperplasia and stenosis involving the external iliac artery. Subclavian vein thrombosis (SVT) accounted for all venous complications. Five of the seven patients with axillary/subclavian branch artery aneurysms required lytic therapy for distal emboli, and six required operative intervention. All popliteal artery injuries were treated by femoropopliteal bypass graft with autogenous saphenous vein. The external iliac artery lesion, which occurred in a cyclist, was repaired with limited resection and vein patch angioplasty. All 12 patients with SVT were treated initially with lytic therapy and anticoagulation. Eight patients required thoracic outlet decompression and venolysis of the subclavian vein. Thirteen arterial reconstructions have remained patent at an average follow-up of 31.9 months (range, 2-74). One patient with a popliteal artery injury required reoperation at 2 months for occlusion of his bypass graft. Eleven of the patients with an arterial injury were able to return to their prior level of competition. All of the patients with SVT have remained stable without further venous thrombosis and have returned to their usual level of activity.

CONCLUSIONS

Athletes are susceptible to a variety of vascular injuries that may not be easily recognized. A high level of suspicion, a thorough workup including noninvasive studies and arteriography/venography, and prompt treatment are important for a successful outcome.

Molecular mechanisms of aortic wall remodeling in response to hypertension

OBJECTIVE

The molecular basis of vascular response to hypertension is largely unknown. Both cellular and extracellular components are critical. In the current study we tested the hypothesis that there is a balance between vascular cell proliferation and cell death during vessel remodeling in response to hypertension.

METHODS

A midthoracic aortic coarctation was created in rats to induce an elevation of blood pressure proximal to the coarctation. The time course was 1 and 3 days and 1, 2, and 4 weeks for the study of the proximal aorta. Ribonuclease protection assay and Western blot analysis were used to evaluate gene expression of growth and apoptosis-related cytokines with two sets of multiple probes, rCK-3 and rAPO-1. Cell proliferation was determined with BrdU (5-bromo-2'-deoxyuridine) incorporation. Apoptosis was examined with TUNEL (transferase-mediated dUTP nick end-labeling). Morphometry was performed on histologic sections.

RESULTS

Coarctation produced hypertension in the proximal aorta, 118 +/- 9 mm Hg versus 94 +/- 6 mm Hg in controls (P <.002). Both messenger RNA and protein levels of transforming growth factor (TGF)-beta1 and TGF-beta3 were increased (P <.005 vs controls). Messenger RNA and protein of Bcl-xS and Fas ligand, known as proapoptotic factors, were both reduced after coarctation (P <.005 vs controls). There was increased BrdU incorporation at 3 days and 1 and 2 weeks (P <.001 vs controls). There were no remarkable changes in the apoptosis rate until 4 weeks later.

CONCLUSION

Cell proliferation was stimulated at 3 days, and apoptosis was halted until 4 weeks. These changes were associated with upregulation of TGF-beta and downregulation of Bcl-xS and Fas ligand gene expression. These findings suggest that a coordinated regulation of cell proliferation and cell death contributes to arterial remodeling in response to acute sustained elevation of blood pressure. Cell proliferation precedes apoptosis by 2 weeks in this procedure.

Eccentric stent graft compression: an indicator of insecure proximal fixation of aortic stent graft

PURPOSE

The purpose of this study was to determine whether radiographically demonstrated proximal stent graft contour can be used as a marker for security of proximal neck fixation after endovascular aneurysm repair.

METHODS

Stent graft structure was examined in 100 consecutive patients with abdominal aortic aneurysms who were treated with the stent graft. Stent graft integrity, stent contour, angulation, compression, and position were assessed by use of plain abdominal radiography, and the results were correlated with contrast computed tomography (CT) scanning, clinical findings, and outcomes. Repeated imaging was carried out during follow-up of 3 to 38 (mean, 12) months.

RESULTS

Stent graft repair was successful in all 100 patients. No stent fractures were identified. Concentric compression of the proximal portion of the stent graft was visible in 69% of patients and reflected deliberate oversizing of the stent graft at the time of implantation. In 5% of patients, a short eccentric compression deformity of the proximal stent was observed. This finding was associated with an increased risk of stent graft migration (P <.01) and with an increased risk for development of a late proximal (type I) endoleak (P <.01). Compared with CT scanning, abdominal radiography was less useful for assessment of short distances of migration (sensitivity 67%; specificity 79%). However, they provided better definition of the stent graft in relation to bony landmarks and better visualization of aortic calcification than CT with three-dimensional reconstruction.

CONCLUSION

Plain abdominal radiographs are important in the postoperative evaluation of patients with aortic stent grafts. They allow for more precise evaluation of the structural elements of the stent graft than CT scanning and may disclose inadequate proximal fixation by demonstration of an eccentric compression deformity. They are less useful for assessment of migration.

Atherosclerotic enlargement of the human abdominal aorta

Aortic aneurysms usually develop in the atherosclerosis prone infrarenal abdominal aorta. To assess the role of atherosclerosis in aortic enlargement, we studied the relation between plaque formation and aortic size in 30 pressure-fixed male cadaver aortas (age 40-95 years, mean age 67 years). Morphometric analysis of transverse sections of the mid-thoracic and the mid-abdominal aortas included measurement of intimal plaque area, lumen area, plaque and media thicknesses. The area encompassed by the internal elastic lamina area (IEL area) was taken to be an index of aortic size. IEL area increased with age at both the thoracic (r=0.77, P<0.01) and abdominal (r=0.54, P<0.01) aortic levels. The aorta also enlarged with increasing plaque area at the thoracic (r=0.73, P<0.01) and abdominal (r=0.79, P<0.01) levels. Regression analysis of IEL area on age, body weight, height and plaque area revealed that the primary predictor of thoracic aortic size was age, whereas the primary predictor of abdominal aortic size was plaque area. Plaque thickness in the abdominal aorta was greater than in the thoracic aorta (P<0.01). Increased plaque area was associated with a significant decrease in media thickness in the abdominal aorta (r=-0.75, P<0.01) but not in the thoracic aorta. Aortas with relatively enlarged abdominal segments, i.e. those with a thoracic to abdominal ratio of <1.2 (n=13), were compared to those with a normal ratio (> or =1.2, n=17). Relatively large abdominal aortas had twofold greater plaque area (P<0.001), reduced medial thickness (P<0.05), fewer medial elastic lamellae (P<0.01) and greater mural tensile stress (P<0.05) than relatively normal abdominal aortas. We conclude that plaque formation in the infrarenal abdominal aorta in humans is associated with aortic enlargement and decreased media thickness. These changes may be predisposing factors for the preferential development of subsequent aneurysmal dilation in the abdominal aorta.

The AneuRx stent graft: four-year results and worldwide experience 2000

OBJECTIVE

The objective was to review the current results of endovascular abdominal aortic aneurysm repair with the AneuRx stent graft and to determine the effectiveness of the device in achieving the primary objective of preventing aneurysm rupture.

METHODS

The outcome of all patients treated during the past 4 years in the U.S. AneuRx clinical trial was determined, and the worldwide clinical experience was reviewed.

RESULTS

A total of 1192 patients were treated with the AneuRx stent graft during all phases of the U.S. Clinical Trial from June 1996 to November 1999, with follow-up extending to June 2000. Ten (0.8%) patients have had aneurysm rupture, with most ruptures (n = 6) occurring in 174 (3.4%) patients treated with an early stiff bifurcation stent graft design used in phase I and in the initial stages of phase II. Since the current, flexible, segmented bifurcation stent graft design was introduced, four (0.4%) ruptures have occurred among 1018 patients treated. Of these, one was during implantation, two were placed too far below the renal arteries, and one patient refused treatment of a type I endoleak. Kaplan-Meier analysis of all 1192 patients treated with the AneuRx stent graft including both stent graft designs revealed the patient survival rate to be 93% at 1 year, 88% at 2 years, and 86% at 3 years, freedom from conversion to open repair to be 98% at 1 year, 97% at 2 years, and 93% at 3 years, and freedom from secondary procedure to be 94% at 1 year, 92% at 2 years, and 88% at 3 years. Freedom from aneurysm rupture with the commercially available segmented bifurcation stent graft was 99.7% at 1 year, 99.5% at 2 years, and 99.5% at 3 years. The presence or absence of endoleak on contrast computed tomography scanning after stent graft placement was not found to be a significant predictor of long-term outcome measures. Worldwide experience with the AneuRx device now approaches 10,000 patients.

CONCLUSIONS

Endovascular management of abdominal aortic aneurysms with the AneuRx stent graft has markedly reduced the risk of aneurysm rupture while eliminating the need for open aneurysm surgery in 98% of patients at 1 year and 93% of patients at 3 years. The device was effective in preventing aneurysm rupture in 99.5% of patients over a 3-year period. The overall patient survival rate was 93% at 1 year and 86% at 3 years.

Aneurysmal and occlusive atherosclerosis of the human abdominal aorta

PURPOSE

The purpose of this study was to assess atherosclerotic plaque deposition and aortic wall responses in the abdominal aorta in relation to the development of aneurysmal and occlusive disease in the infrarenal aorta.

METHODS

Morphologic differences at five standardized locations in the infrarenal aorta in 67 pressure perfusion-fixed male cadaver aortas (aged, 41-98 years; mean, 66 years) were studied and compared with the supraceliac segment. Quantitative computer-assisted morphometry of histologic sections included measurement of plaque area, lumen area, lumen diameter, media thickness, number of medial elastic lamellae, and the area encompassed by the internal elastic lamina that best represents the artery size of each segment. The ratio of the supraceliac segment to the midabdominal segment (normally greater than 1.3) was used to define three groups: Group I (normal): ratio greater than or equal to 1.30 (n = 31); Group II (intermediate): ratio greater than or equal to 1.20 but less than 1.30 (n = 20); and Group III: ratio less than 1.20 (n = 16), which represented dilated midabdominal aortas. There was no significant difference in age among the groups.

RESULTS

Group I had minimal intimal plaque and little gross evidence of atherosclerosis. Group II had increased intimal plaque compared with Group I (P <.01) and gross evidence of atherosclerosis, which was maximally localized in the distal aorta; there was no aortic enlargement or thinning of the media underneath the plaque. Group III had more intimal plaque than Group I (P <.01) and Group II (P <.01) and was associated with localized aortic enlargement and media thinning compared with Group I (P <.05) and Group II (P <.01). Increasing intimal plaque in Group III correlated with an increase in lumen diameter (r = 0.61, P <.05), but this relationship was not significant in Group I and Group II. The aortic media in Group III had a reduced number of medial elastic lamellae, was reduced in thickness, and was more exposed to increased wall stress than the aortas in Groups I and II.

CONCLUSION

These results suggest that there may be different local responses to atherosclerosis in the abdominal aorta in human beings. Plaque deposition associated with localized dilation, thinning of the media, and loss of medial elastic lamellae may predispose that segment of aorta to subsequent aneurysm formation. Plaque deposits without media thinning, without loss of elastic lamellae, and without artery wall dilation may predispose the aorta, in the event of continuing plaque accumulation, to the development of lumen stenosis.

Quantitative determination of age-related geometric changes in the normal abdominal aorta

PURPOSE

We conducted a novel quantitative three-dimensional analysis of computed tomography (CT) angiograms to establish the relationship between aortic geometry and age, sex, and body surface area in healthy subjects.

METHODS

Abdominal helical CT angiograms from 77 healthy potential renal donors (33 men/44 women; mean age, 44 years; age range, 19-67 years) were selected. In each dataset, orthonormal cross-sectional area and diameter measurements were obtained at 1-mm intervals along the automatically calculated central axis of the abdominal aorta. The aorta was subdivided into six consecutive anatomic segments (supraceliac, supramesenteric, suprarenal, inter-renal, proximal infrarenal, and distal infrarenal). The interrelated effects of anatomic segment, age, sex, and body surface area on cross-sectional dimensions were analyzed with linear mixed-effects and varying-coefficient statistical models.

RESULTS

We found that significant effects of sex and of body surface area on aortic diameters were similar at all anatomic levels. The effect of age, however, was interrelated with anatomic position, and gradually decreasing slopes of significant diameter-versus-age relationships along the aorta, which ranged from 0.14 mm/y (P <.0001) proximally to 0.03 mm/y (P =.013) distally in the abdominal aorta, were shown.

CONCLUSION

The abdominal aorta undergoes considerable geometric changes when a patient is between 19 and 67 years of age, leading to an increase of aortic taper with time. The hemodynamic consequences of this geometric evolution for the development of aortic disease still need to be established.

Does complete aneurysm exclusion ensure long-term success after endovascular repair?

PURPOSE

To examine whether complete aneurysm exclusion is a reliable marker for successful long-term endovascular abdominal aortic aneurysm (AAA) repair.

METHODS

The medical records, computed tomographic (CT) scans, and duplex examinations of all the patients who underwent endovascular AAA repair at a single institution and had at least 12 months of follow-up were reviewed. Sixty-seven patients (58 men; mean age 74 years, range 57-87) were identified. Complete aneurysm exclusion was defined by the absence of an endoleak at any time before an adverse event. The primary endpoint included all major adverse events that occurred during the postoperative period, including aneurysm expansion, acute symptoms referable to the AAA, late secondary procedures, ruptures, and deaths from ruptures and all other causes.

RESULTS

There were 44 adverse events (8 expanding aneurysms, 4 acute symptoms, 17 secondary procedures, and 15 deaths from other causes) in 28 (42%) patients. Among 36 (54%) patients who had initial complete aneurysm exclusion (no endoleak), 12 (33%) experienced adverse events, compared with 16 (52%) events in 31 patients who had endoleak (chi2 = 1.59, p = 0.21).

CONCLUSIONS

There was no statistically significant difference in adverse events based on the presence or absence of endoleak. Complete aneurysm exclusion as defined by absence of an endoleak does not indicate an event-free postoperative course. A better marker of clinical success of endovascular AAA repair is needed.

Duplex ultrasound scanning versus computed tomographic angiography for postoperative evaluation of endovascular abdominal aortic aneurysm repair

OBJECTIVE

The purpose of this study was to compare duplex ultrasound scanning and computed tomographic (CT) angiography for postoperative imaging and surveillance after endovascular repair of abdominal aortic aneurysm (AAA).

METHODS

One hundred consecutive patients with AAA underwent endovascular (Medtronic AneuRx, stent graft) aneurysm repair and were imaged with both CT angiography and duplex ultrasound scanning at regular intervals after the procedure. Each imaging modality was evaluated for technical adequacy and for documentation of aneurysm size, endoleak, and graft patency. In concurrent scan pairs, accuracy of duplex scanning was compared with CT.

RESULTS

A total of 268 CT scans and 214 duplex scans were obtained at intervals of 1 to 30 months after endovascular aneurysm repair (mean follow-up interval, 9+/-7 months). All CT scans were technically adequate, and 198 (93%) of 214 duplex scans were technically adequate for the determination of aneurysm size, presence of endoleak, and graft patency. Concurrent (within 7 days of each other) scan pairs were obtained in 166 instances in 76 patients (1-6 per patient). The maximal transverse aneurysm sac diameter measured with both methods correlated closely (r = 0.93; P <.001) without a significant difference on paired analysis. In 92% of scans, measurements were within 5 mm of each other. Diagnosis of endoleak on both examinations correlated closely (P <.001), and compared with CT, duplex scanning had a sensitivity of 81%, a specificity of 95%, a positive predictive value of 94%, and a negative predictive value of 90%. Discordant results occurred in 8% of examinations, and in none of these was the endoleak close to the attachment sites or associated with aneurysm expansion. An endoleak was demonstrated on both tests in all eight patients who had an endoleak judged severe enough to warrant arteriography. Graft patency was documented in each instance, without discrepancy, with both modalities.

CONCLUSIONS

High-quality duplex ultrasound scanning is comparable to CT angiography for the assessment of aneurysm size, endoleak, and graft patency after endovascular exclusion of AAA.

Hypercholesterolemia superimposed by experimental hypertension induces differential distribution of collagen and elastin

We studied the mural distribution of collagen types I and III and tropoelastin in enhanced experimental atherogenesis induced in rabbits by hyperlipidemia superimposed by hypertension. Animals were fed a high-cholesterol diet for 5 weeks and also subjected to midthoracic aortic coarctation for 4 weeks. Serum cholesterol levels were increased and blood pressure was elevated proximal to the coarctation. Foam cell lesions developed in the aorta proximal to the coarctation. In situ hybridization and immunohistochemistry showed that gene expression of collagen types I and III and tropoelastin was upregulated, with a differential distribution across the arterial wall. New collagen type I was mainly distributed in the intima, the outer media, and the adventitia. New collagen type III was spread more uniformly across the wall, including the adventitia, whereas tropoelastin was mainly localized in intimal foam cell lesions. Morphometric data showed an increase in wall thickness. These results suggest that collagen types I and III play a role in remodeling of the aortic wall in response to hypertension. The remarkable involvement of the adventitia in this response indicates that the adventitia is an important component of the arterial wall. Tropoelastin is closely associated with foam cell lesion formation, suggesting a role for this component in atherogenesis as well.