Gadolinium-enhanced magnetic resonance angiography of abdominal aortic aneurysms

Purpose: The objective of this study was to assess the usefulness of gadolinum-enhanced magnetic resonance angiography (MRA) for defining anatomic features relevant to performing aortic surgery for aneurysmal disease.Methods: Anatomic data defined by MRA, including abdominal aortic aneurysm (AAA) size and character, as well as the status of the celiac, mesenteric, renal, and iliac arteries, were correlated with angiography, ultrasonography, computed tomography, or operative data in 43 patients. Five MRA sequences were obtained in an hour-long examination optimized for aortoiliac, splanchnic, and renal artery imaging at 1.5 T in a body coil. Four of the sequences were performed during or after infusion of gadolinium to improve image quality.Results: MRA correctly defined the maximum aneurysm diameter, as well as its proximal and distal extent in all patients. MRA detected 33 of 35 significant stenoses among 153 splanchnic, renal, or iliac branches examined (sensitivity = 94% and specificity = 98%). MRA did not resolve the degree of aortic branch stenotic disease sufficiently to precisely grade its severity. MRA did not reliably define the status of the inferior mesenteric artery, lumbar arteries or internal iliac arteries. One ruptured AAA and one inflammatory AAA were correctly diagnosed by MRA. No patient had a contrast reaction or contrast-induced renal toxicity related to administration of gadolinium.Conclusion: Gadolinium-enhanced MRA of AAA provides appropriate, essential anatomic information for aortic reconstructive surgery in a 1-hour examination devoid of contrast-related renal toxicity or catheterization-related complications attending conventional arteriography. (J VASC SURG 1995;21:656-69.)     

The value of screening in siblings of patients with abdominal aortic aneurysm.

OBJECTIVES: This study aimed to determine the incidence of abdominal aortic aneurysm (AAA) in a large group of siblings of Australian AAA patients to determine if screening in this group is justified. METHODS: 1254 siblings of 400 index AAA patients were identified and offered aortic ultrasound screening. An age and sex matched control group was recruited from patients having abdominal CT scans for non-vascular indications. AAA was defined by an infrarenal aortic diameter of > or =3 cm or a ratio of the infrarenal to suprarenal aortic diameter of > or =2.0. A ratio of 1.0-1.5 was considered normal, and a ratio of >1.5 to <2.0 was considered ectatic. Aortic enlargement was defined as ectasia or aneurysm. RESULTS: 276 (22%) siblings could be contacted and agreed to screening or had previously been diagnosed with AAA. All 118 controls had normal diameter aortas. 55/276 siblings had previously been diagnosed with AAA. The remaining 221 siblings underwent ultrasound screening. Overall, 30% (84/276) had enlarged aortas (5% ectasia, 25% aneurysmal); 43% of male siblings (64/150) and 16% of females siblings (20/126). The incidence was 45% in brothers of female index patients, 42% in brothers of male patients, 23% in sisters of female patients, and 14% in sisters of male index patients. CONCLUSIONS: The overall incidence of aortic enlargement of 30% found in this study warrants a targeted screening approach with ultrasound for all siblings of patients with AAA. A similar targeted approach for screening of the children of AAA patients would also seem advisable.     

大、小肾下型腹主动脉瘤的CT形态学特点

目的评价大、小肾下型腹主动脉瘤（AAA）的CT形态学特点。方法对45例肾下型AAA患者行64层螺旋CT血管成像（CTA）,并测定AAA形态学指标。以直径5cm为界,将患者分为大、小AAA两组,比较两组AAA的临床危险因素及形态学差异,分析瘤体大小与其他形态学特点的相关性。结果大AAA患者（n=25）收缩压小于小AAA（n=20）（P〈0．05）,吸烟比例大于小AAA（P〈0．05）。大AAA瘤体长度、近远端瘤颈直径、后壁血栓分布几率及瘤壁钙化积分大于小AAA（P〈0．05）。AAA瘤体长度与近端瘤颈角度（r=0．418,P〈0．01）及近端瘤颈直径呈正相关（r=0．411,P〈0．01）,与入口角度（r=-0．478,P〈0．01）及近端瘤颈长度呈负相关（r=-0．562,P％0．01）。结论肾下型AAA的瘤体大小与其他形态学特点具有一定的相关性。     

Extensive spinal cord ischemia following endovascular repair of an infrarenal abdominal aortic aneurysm: a rare complication

Postoperative paraplegia secondary to spinal cord ischemia (SCI) is an extremely rare and devastating complication of endovascular repair in abdominal aortic aneurysm (AAA) surgery. The reported incidence is only 0.21 % worldwide. This case of postoperative paraplegia occurred in a 60-year-old man immediately following endovascular repair of an infrarenal AAA. Postoperative magnetic resonance imaging showed multiple foci of SCI involvement from C5 to L1. However, neither cerebral spinal fluid drainage nor steroid therapy was effective; he was eventually admitted with no improvement in his neurological status. The mechanism remains multifactorial until now and needs more attention in perioperative management. We report the first case involved in the most significantly extensive SCI after endovascular repair of an infrarenal AAA.     

Mechanical properties of the aneurysmal aorta.

The mechanical properties of the abdominal aorta were investigated non-invasively in 30 patients with aortic aneurysm and 11 with peripheral arterial disease. The distensibility of the aorta was measured using M-mode ultrasonography, permitting non-invasive assessment of the pressure--strain elastic modulus or aortic stiffness, Ep. The median Ep value increased from 4.0 N/cm2 in control subjects in their third decade of life (n = 10) to 10.4 N/cm2 in middle age (n = 11) to 14.0 N/cm2 in the elderly (n = 13). In the presence of a normal diameter, peripheral arterial disease with aortic atherosclerosis had little effect on aortic stiffness, median Ep being 16.0 N/cm2. Aneurysmal dilatation was associated with a significant increase in aortic stiffness, median Ep being 31.3 N/cm2 (P < 0.001). For aortas of normal diameter, Ep was at all ages dependent on mean arterial pressure. In patients with aortic aneurysms there was no clear relationship between Ep and mean arterial pressure or aortic diameter. Of the patients studied, 15 underwent aortic reconstruction; increasing aortic stiffness (log Ep) was associated with a decreased medial elastin content of the aortic biopsy (r = -0.63, P < 0.02). This study demonstrates the marked stiffness or inelasticity of dilated or aneurysmal vessels, part of which is attributable to the loss of elastin.     

Computed tomography-detected abnormalities following conventional abdominal aortic aneurysm (AAA) repair

PURPOSE: To determine how time since the operation influences vascular abnormalities following conventional infrarenal abdominal aortic aneurysm (AAA) repair.METHODS: In 47 patients computed tomography was performed 1 to 12 years following the aneurysm repair. Aortic diameters at different levels were measured and other abnormalities recorded.RESULTS: Significant correlation was found between time since operation and diameter of the suprarenal aorta (R=0.51, P<0.001) but not with aortic neck diameter (R=-0.10, P=0.48) or diameter of the prosthetic graft (R=0.07, P=0.66). However, measured diameters of graft and aortic neck showed a significant positive correlation (R=0.40, P=0.005).CONCLUSIONS: Dilatation of the suprarenal aorta has a different pattern from aortic neck dilatation. The latter showed correlation with the diameter of the prosthetic graft. This may be of interest for future design of endovascular stent-grafts.     

Use of cine magnetic resonance angiography in quantifying aneurysm pulsatility associated with endoleak

OBJECTIVE: Persistent aneurysm perfusion or endoleak is associated with pulsatility of abdominal aortic aneurysm (AAA) after endovascular repair. However, the resultant pulsatile change in aneurysm diameter may be difficult to quantify, and therefore its significance is unknown. In this study cine magnetic resonance angiography (MRA) was used to quantify aneurysm wall motion during the cardiac cycle and to correlate it with the presence and type of endoleak. METHODS: Cine MRA was performed in 16 patients undergoing endovascular repair of AAA. A 1.5 T magnet and post-processing with GEMS 4.0 Fiesta computerized video image analysis software were used to calculate maximum aortic diameter during systole and diastole. Changes in aortic diameter were determined from these measurements. Cine MRA was performed on aneurysms before treatment and in patients with and without endoleak after endovascular repair. Type of endoleak was confirmed at angiography in all cases. Four patients had antegrade (type I) endoleak, and eight patients had retrograde (type II) endoleak; no endoleak was present in four patients. Endovascular grafts with stent support throughout the entire length of the graft (Talent) were used in all cases (14 bifurcated grafts, 2 tube grafts). RESULTS: Cine MRA demonstrated significantly greater wall motion and resultant change in aneurysm diameter in patients with type I endoleak compared with patients without endoleak (type I, 2.14 +/- 1.28 mm vs no endoleak, 0.12 +/- 0.09 mm, P =.001). Change in aneurysm diameter in patients with type II endoleak was not significantly greater than in patients with no endoleak (type II, 0.26 +/- 0.21 mm vs no endoleak, 0.12 +/- 0.09 mm, P = NS). Untreated aneurysms demonstrated the greatest change in diameter during the cardiac cycle (3.51 +/- 0.79 mm). CONCLUSION: Cine MRA may be used to accurately quantify AAA wall motion before and after endovascular stent-graft treatment. The extent of change in diameter corresponds to the type of endoleak, with antegrade (type I) endoleak generating greater pulsatile change in diameter than retrograde-collateral (type II) endoleak or no endoleak. Cine MRA may provide a noninvasive means of assessing the success of endovascular treatment of AAA. Further studies will be necessary to confirm the utility and efficacy of cine MRA in postoperative assessment of endovascular aneurysm repair.     

The incidence of small abdominal aortic aneurysms and the change in normal infrarenal aortic diameter: implications for screening.

AIM: to study the incidence of small abdominal aortic aneurysms (AAA), and to investigate what proportion of normal infrarenal aortic diameters (IAD) expand with age. METHODS: longitudinal follow-up in a population-based aneurysm screening programme. The infrarenal aortic diameter (IAD) was measured by ultrasound. A second scan was performed in subjects with a normal aorta after an average of 5.5 years. RESULTS: data were analysed from 4072 subjects, 464 with a small AAA and 3608 with a normal aorta. The infrarenal aorta expanded in 15% of subjects, but significant growth (>5 mm) occurred in only 7%. Age and initial diameter were independent predictors for aortic dilatation. The effect of diameter at first screen was non-linear. The relative risk for expansion increased dramatically for IADs over 2.5 cm (test for departure of trend: chi2=52, p<0.0001). The effect of age was also non-linear, the risk of expansion was highest in the 60-69 year old age group; test for departure of trend (chi2=13, p=0.002). The incidence of new aneurysms was 3.5 per 1000 person-years (py) (95% CI: 2.8-4.4). The highest incidence of new aneurysms was found in the 60 to 69 year old age group. CONCLUSION: only a small proportion of the population is prone to aortic dilatation. Patients over 70 with an IAD <2.5 cm can be discharged from follow-up.     

Carotid Atherosclerosis and Relation to Growth of Infrarenal Aortic Diameter and Follow-up Diameter: The Tromsø Study

ObjectivesThis research aims to study how carotid atherosclerosis is related to growth of infrarenal aortic diameter and aneurysmal formation.DesignPopulation-based follow-up study.Materials and methodsAt baseline, ultrasound examination of the carotid artery and the abdominal aorta was performed in 4241 persons from a general population with no evidence of abdominal aortic aneurysm (AAA). The burden of atherosclerosis was assessed as carotid total plaque area (TPA). After a mean follow-up of 6.3 years, a new ultrasound examination was performed and measurements of the aortic diameter and carotid TPA were repeated. The effects on aortic diameter progression, follow-up diameter and risk for AAA were assessed in multiple linear and logistic regression models according to carotid TPA, adjusted for known risk factors.ResultsWhen analysing AAA as a dichotomous variable, a borderline association between atherosclerosis and AAA could be demonstrated. When modelling aortic diameter as a continuous variable, a 1-SD increase in 5 years' carotid plaque area (ΔTPA) was associated with a 0.12-mm growth in infrarenal aortic diameter (standard error (SE) 0.04) and a 0.20-mm wider aorta at follow-up (SE 0.06). No independent relation was seen for baseline atherosclerosis.ConclusionsCarotid plaque progression was positively related to growth in infrarenal aortic diameter and aortic diameter at follow-up. Whether this co-variation between plaque growth and aortic diameter growth is causally related or independent events is still an open question.     

Aminoterminal propeptide of type III procollagen and matrix metalloproteinases-2 and -9 failed to serve as serum markers for abdominal aortic aneurysm.

OBJECTIVES: Matrix-metalloproteinase (MMP)-2 and -9 and aminoterminal propeptide of type III collagen (NIIINP) have been reported to be elevated in patients with abdominal aortic aneurysm (AAA). The aim of our study was to test NIIINP, MMP-2 and -9 as potential serum markers for AAA in a large population group at risk for AAA. METHODS: Fifty-five to 70 year old men were screened for AAA by abdominal ultrasound. Simultaneously, blood samples were taken and the patients were interviewed for known risk factors for AAA. Patients with a dilatation of the infrarenal aorta of > or =25mm (Group 1, n=76) were compared to randomly assigned patients with normal aortic diameters (Group 2, n=83). A third group consisted of patients scheduled for operation of AAA (n=19). RESULTS: A total of 987 men were investigated with ultrasound. Seventy-six (7.7%) had an aortic dilatation > or =25mm. Aortic dilatation was correlated with age (P=0.0001). However, serum levels of NIIINP and MMP 2 were not different between the three groups of patients. For MMP-9 there was a weak inverse correlation with lower serum levels in patients with aortic dilatation (P=0.043). CONCLUSIONS: Both MMP-2 and -9 and NIIINP failed to show relevance as serum markers for aortic dilatation. Our results are, therefore, in contradiction to previous published results. AAAs cannot be diagnosed with a simple blood test.     

Serum concentrations of elastin-derived peptides in patients with specific manifestations of atherosclerotic disease.

OBJECTIVE: To measure serum concentrations of elastin-derived peptides (S-EDP) in patients with aneurysmal, occlusive and ulcerative manifestations of atherosclerotic disease. MATERIALS AND METHODS: S-EDP concentrations were measured by a competitive enzyme-linked immunosorbent assay in 10 patients with infrarenal aneurysms 5cm in diameter (AAA), 10 patients with distal aortic occlusive disease (AOD), 10 patients with symptomatic carotid stenosis (>or=70%) and plaque ulceration (SCS) and a control group of 10 patients with no similar specific manifestations of atherosclerotic disease (NAM). RESULTS: S-EDP concentrations (median, range) were significantly higher in patients with AAA (42ng/ml, 35-52, p<0.001) and SCS (49ng/ml, 37-60, p<0.001) but not AOD (28ng/ml, 22-38, p=0.240) compared to NAM (26ng/ml, 19-36) patients. CONCLUSION: Increased concentrations of S-EDP were associated with aneurysmal and ulcerative, but not occlusive, manifestations of atherosclerosis.     

Growth rate and associated factors in small abdominal aortic aneurysms.

OBJECTIVE: To study the growth rate and factors influencing progression of small infrarenal abdominal aortic aneurysms (AAA). DESIGN: Observational, longitudinal, prospective study. PATIENTS AND METHODS: We followed patients with AAA <5 cm in diameter in two groups. Group I (AAA 3-3.9 cm, n = 246) underwent annual ultrasound scans. Group II (AAA 4-4.9 cm, n = 106) underwent 6-monthly CT scans. RESULTS: We included 352 patients (333 men and 19 women) followed for a mean of 55.2+/-37.4 months (6.3-199.8). The mean growth rate was significantly greater in group II (4.72+/-5.93 vs. 2.07+/-3.23 mm/year; p<0.0001). Group II had a greater percentage of patients with rapid aneurysm expansion (>4 mm/year) (36.8 vs. 13.8%; p<0.0001). The classical cardiovascular risk factors did not influence the AAA growth rate in group I. Chronic limb ischemia was associated with slower expansion (< or = 4 mm/year) (OR 0.47; CI 95% 0.22-0.99; p = 0.045). Diabetic patients in group II had a significantly smaller mean AAA growth rate than non-diabetics (1.69+/-3.51 vs. 5.22+/-6.11 mm/year; p = 0.032). CONCLUSIONS: The expansion rate of small AAA increases with the AAA size. AAA with a diameter of 3-3.9 cm expand slowly, and they are very unlikely to require surgical repair in 5 years. Many 4-4.9 cm AAA can be expected to reach a surgical size in the first 2 years of follow-up. Chronic limb ischemia and diabetes are associated with reduced aneurysm growth rates.     

Abdominal aortic aneurysm neck remodeling after open aneurysm repair

PURPOSE: Proximal endovascular aortic graft fixation and maintenance of hemostatic seal depends on the long-term stability of the aortic neck. Previous investigations of aortic neck dilation mostly focused on the infrarenal aortic diameter. Fenestrated and branched stent grafts facilitate suprarenal graft fixation and may thereby improve the long-term integrity of the aortic attachment site. For these devices, the natural history of the suprarenal aortic segment is also of interest. We investigated the natural history of the supra- and infrarenal aortic segment after open abdominal aortic aneurysm (AAA) repair. METHODS: For this retrospective analysis, we reviewed the preoperative and the initial postoperative as well as the most recent CT series that were obtained from 52 patients undergoing conventional repair of an infrarenal abdominal aortic aneurysm between January 1998 and December 2002. Measurements were performed using electronic calipers on a "split screen", allowing direct comparison of subsequent CT series at corresponding levels along the vessel. Main outcome measures were changes in postoperative measures of the supra- and infrarenal aortic diameters. RESULTS: The first postoperative exam was at a mean (+/-SD) of 7.0 +/- 3.5 months, and the final exams were at 44.4 +/- 21 months. Over this time period, the estimated rate of change in suprarenal diameter was 0.18 mm/ y with 95% confidence interval (CI) from 0.08 to 0.27. The estimated rate of change for the infrarenal diameter was 0.16 (95% CI: 0.05 to 0.27). A clinically relevant diameter increase of >or=3 mm was observed in seven patients (13%). There was evidence of larger diameter increases associated with larger AAA diameters (P = .003 and <.001 for suprarenal and infrarenal diameters), an inverted funnel shape (P = .002 and <.001), and marginal evidence of association with a history of inguinal hernia (P = .043 and .066). CONCLUSIONS: Although there is statistically significant evidence of increases in the supra- and infrarenal aortic diameters after conventional AAA repair, mean annual increases tended to be small and clinically relevant increases of 3 mm or more were observed in only a small proportion of cases.     

Cigarette smoking increases aortic dilatation without affecting matrix metalloproteinase-9 and -12 expression in a modified mouse model of aneurysm formation

OBJECTIVE: The development of abdominal aortic aneurysms (AAA) is presumed to result from multiple genetic and environmental factors, with exposure to tobacco smoke the single largest known factor predisposing to aneurysm growth. We have attempted to adapt the elastase-perfused animal model to determine whether tobacco exposure can lower the threshold of aortic injury necessary for AAA development. METHODS: Adult C57BL/6 mice underwent transient perfusion of the infrarenal aorta with an active solution of elastase: high-dose (HDE, 0.19 U/mL, n=9), standard-dose (SDE, 0.16 U/mL, n=21) or low-dose (LDE, 0.07 U/mL, n=24). Control animals (n=24) were treated with heat inactivated elastase (HIE). Twenty LDE perfused mice were exposed to cigarette smoke (LDE-S) beginning 2 weeks before perfusion and continuing until aortic harvest. Aortic diameter (AD) was measured preperfusion, postperfusion, and at harvest on day 14. AAA was defined as %DeltaAD>or=100% between preperfusion and harvest. Aortas from each group (except HDE) were analyzed for matrix metalloproteinase-9 (MMP-9) and MMP-12 expression by real-time polymerase chain reaction normalized to glyceraldehyde-3-phosphate dehydrogenase. RESULTS: All SDE mice developed large AAA by %DeltaAD (189.3%+/-16.9%, mean+/-standard error of the mean), but control mice had only a small dilatation (69.7%+/-3.7%, P<.01). Higher doses of elastase did not produce larger aneurysms in HDE mice. In contrast, only 63% of LDE mice showed aneurysmal dilatation, and these were significantly smaller (104.3%+/-4.2%, P<.01). When exposed to cigarette smoke, LDE animals developed significantly larger aneurysms (%DeltaAD, 134.5%+/-7.9%, P=.0021). There was no difference in normalized aortic MMP-9 and MMP-12 expression between elastase doses or between smoke-exposed and unexposed animals. Histologic analysis revealed that smoking increased the extent of aortic elastin degradation when compared with LDE-S animals. CONCLUSION: Aneurysm development in the elastase model is dependent on the quantity of active elastase infused. Exposure of animals to tobacco smoke after a relatively minor aortic elastase injury produces increases in elastin degradation and aneurysm size without affecting MMP-9 or MMP-12 expression. To our knowledge, this is the first demonstration in an animal model that smoking can act as a synergistic factor in AAA development. Further understanding of the relationship between smoking and AAA in this model may help unveil the pathophysiologic pathways involved between cigarette smoke and AAAs.     

肾动脉水平以下腹主动脉瘤的诊断和治疗(附261例报告)

为提高腹主动脉瘤手术的安全性，对１９６０年１月～１９９７年１２月２６１例肾动脉水平以下腹主动脉瘤的处理进行了分析。１９７０年以前手术切除７３例，其中５０例经主动脉造影确诊。１９８７年以来的１７８例由Ｂ超和ＣＴ确诊，５例行动脉造影或数字减影造影（ＤＳＡ）、５例经磁共振血管成像明确了动脉瘤上界和肾动脉的关系。结果：患者均行动脉瘤切除人造血管移植，手术死亡率３．８％，５年存活率７４．４１％。腹主动脉瘤诊断中最为关键的是确定动脉瘤上界与肾动脉间的距离，若Ｂ超与ＣＴ不能肯定，主动脉造影或ＤＳＡ极有帮助。提示：手术操作和麻醉技术的改进使腹主动脉瘤修补术变得更为迅速、安全和方便。     

Variation of infrarenal aortic diameter: A necropsy study

PURPOSE: To determine anatomicomorphological changes in the infrarenal portion of the abdominal aorta, we performed 645 dissections of the segment in corpses undergoing necropsy. METHODS: The aortas were removed from the corpses with a surgical technique; by means of a device that we designed, the external diameter of the artery was measured after luminal pressure was reestablished. This way, it was possible to avoid underestimation of the arterial diameter postmortem. The influence of age, sex, body size, arterial hypertension, chronic obstructive pulmonary disease, and coronary disease on the aortic diameter and the influence of different degrees of sclerosis on the infrarenal aorta wall were analyzed. Considering the diameters, aortas were regarded as "normal" when they did not present any ectasia, arteriomegaly, aneurysm, or hypoplasia. RESULTS: The sample involved 645 subjects whose ages ranged from 19 to 97 years (mean age, 55.8 years). Of the 645 subjects, 65.5% (423) were men, 34.5% (222) were women, 81% (523) were white, and 19% (122) were of another race. The diameters of arteries showing no anomalous dilatation (ectasis, arteriomegaly, or aneurysm) varied according to subject age, sex, body length, and the degree of atherosclerosis on the aorta wall (P <.01). Aortic diameters of those subjects with arterial hypertension, coronary disease, and chronic obstructive pulmonary disease were compared with the aortic diameters of control subjects, and significant differences were not shown (P >.05). Twenty-nine aneurysms were found (4.5% prevalence). Four were ruptured aneurysms, and all occurred in aortas with diameters larger than 5.0 cm. CONCLUSION: The infrarenal aortic diameter enlarges with aging, and this enlargement occurs earlier in men than in women. Those subjects who had a longer body length and advanced sclerosis on the aorta wall had larger aortic diameters. There was a high prevalence of infrarenal aneurysms (4.5%), with rupture found solely in aortas with diameters larger than 5.0 cm.     

Mechanical deterioration underlies malignant behavior of aneurysmal human ascending aorta

OBJECTIVE: The human ascending aorta becomes markedly prone to rupture and dissection at a diameter of 6 cm. The mechanical substrate for this malignant behavior is unknown. This investigation applied engineering analysis to human ascending aortic aneurysms and compared their structural characteristics with those of normal aortas. METHODS: We measured the mechanical characteristics of the aorta by direct epiaortic echocardiography at the time of surgery in 33 patients with ascending aortic aneurysm undergoing aortic replacement and in 20 control patients with normal aortas undergoing coronary artery bypass grafting. Six parameters were measured in all patients: aortic diameter in systole and diastole, aortic wall thickness in systole and diastole, and blood pressure in systole and diastole. These were used to calculate mechanical characteristics of the aorta from standard equations. Aortic distensibility reflects the elastic qualities of the aorta. Aortic wall stress reflects the disrupting force experienced within the aortic wall. Incremental elastic modulus indicates loss of elasticity reserve. RESULTS: Aortic distensibility falls to extremely low levels as aortic dimension rises toward 6 cm (3.02 mm Hg(-1) for small aortas versus 1.45 mm Hg(-1) for aortas larger than 5 cm, P < .05). Aortic wall stress rises to 157.8 kPa for the aneurysmal aorta, compared with 92.5 kPa for normal aortas. For 6-cm aortas at pressures of 200 mm Hg or more, wall stress rises to 857 kPa, nearly exceeding the known maximal tensile strength of human aneurysmal aortic wall. Incremental elastic modulus deteriorates (1.93 +/- 0.88 MPa vs 1.18 +/- 0.21 MPa, P < .05) in aneurysmal aortas relative to that in normal aortas. CONCLUSION: The mechanical properties of the aneurysmal aorta deteriorate dramatically as the aorta enlarges, reaching critical levels associated with rupture by a diameter of 6 cm. This mechanical deterioration provides an explanation in engineering terms for the malignant clinical behavior (rupture and dissection) of the aorta at these dimensions. This work adds to our fundamental understanding of the biology of aortic aneurysms and promises to permit future application of engineering measurements to supplement aneurysm size in clinical decision making in aneurysmal disease.     

Changes of the Infrarenal Aortic Segment After Conventional Abdominal Aortic Aneurysm Repair

OBJECTIVES: to delineate the natural history of the residual infrarenal aortic segment after conventional abdominal aortic aneurysm (AAA) repair. DESIGN: open prospective study. PATIENTS AND METHODS: between 1990 and 1997, 100 patients, who underwent conventional infrarenal AAA repair at our department, were followed annually by means of colour duplex ultrasonography. Data from 76 patients who had at least 3 scans were analysed. RESULTS: mean duration of follow-up was 4.7 years (range: 3-8 years). The residual infrarenal aorta dilated a mean of 0.57 mm annually. No patient required reoperation. There was no significant correlation between dilatation and any of the recorded risk factors except for the initial neck diameter (p=0.03). CONCLUSIONS: conventional AAA surgery is durable so that surveillance, during the first 5 postoperative years, is not justified in terms of cost-effectiveness. The impact of such a dilatation on endovascular AAA repair requires further investigation.     

Initial results of ultrasound screening for aneurysm of the abdominal aorta in Western Australia: relevance for endoluminal treatment of aneurysm disease

BACKGROUND: Increased life expectancy in men during the last thirty years is largely due to the decrease in mortality from cardiovascular disease in the age group 29--69 yr. This change has resulted in a change in the disease profile of the population with conditions such as aneurysm of the abdominal aorta (AAA) becoming more prevalent. The advent of endoluminal treatment for AAA has encouraged prophylactic intervention and fueled the argument to screen for the disease. The feasibility of inserting an endoluminal graft is dependent on the morphology and growth characteristics of the aneurysm. This study used data from a randomized controlled trial of ultrasound screening for AAA in men aged 65--83 yr in Western Australia for the purpose of determining the norms of the living anatomy in the pressurized infrarenal aorta. AIMS: To examine (1) the diameters of the infra-renal aorta in aneurysmal and non-aneurysmal cases, (2) the implications for treatment modalities, with particular reference to endoluminal grafting, which is most dependent on normal and aneurysmal morphology, and (3) any evidence to support the notion that northern Europeans are predisposed to aneurysmal disease. METHODS: Using ultrasound, a randomized control trial was established in Western Australia to assess the value of a screening program in males aged 65--83 yr. The infra-renal aorta was defined as aneurysmal if the maximum diameter was 30 mm or more. Aortic diameter was modelled both as a continuous (in mm) and as a binary outcome variable, for those men who had an infra-renal diameter of 30 mm or more. ANOVA and linear regression were used for modelling aortic diameter as a continuum, while chi-square analysis and logistic regression were used in comparing men with and without the diagnosis of AAA. FINDINGS: By December 1998, of 19,583 men had been invited to undergo ultrasound screening for AAA, 12,203 accepted the invitation (corrected response fraction 70.8%). The prevalence of AAA increased with age from 4.8% at 65 yr to 10.8% at 80 yr (chi(2)=77.9, df=3, P<0.001). The median (IQR) diameter for the non-aneurysmal group was 21.4 mm (3.3 mm) and there was an increase (chi(2)=76.0, df=1, P<0.001) in the diameter of the infra-renal aorta with age. Since 27 mm is the 95th centile for the non-aneurysmal infra-renal aorta, a diameter of 30 mm or more is justified as defining an aneurysm. The risk of AAA was higher in men of Australian (OR=1.0) and northern European origin (OR=1.0, 95%CL: 0.9, 1.2) compared with those of Mediterranean origin (OR=0.5, 95%CL: 0.4, 0.7). CONCLUSION: Although screening has not yet been shown to reduce mortality from AAA, these population-based data assist the understanding of aneurysmal disease and the further development and use of endoluminal grafts for this condition.     

Elastin metabolism of the infrarenal aorta

Aortic tissue elastase and alpha 1-antitrypsin were assayed in 67 patients with different types of infrarenal aortic disease; occlusive disease, elective abdominal aortic aneurysms (AAAs), multiple aneurysms, and ruptured aneurysms. Elastase modified by alpha 1-antitrypsin (elastase/alpha 1-antitrypsin) increased significantly as the type of aortic disease changed from occlusive to aneurysmal disease. Aortic elastase was significantly higher in patients with AAAs, multiple aneurysms, and ruptured AAAs compared with occlusive disease. The alpha 1-antitrypsin, was significantly lower in patients with multiple aneurysms and ruptured AAAs. These data suggest that the ratio between elastase and its major serum inhibitor, alpha 1-antitrypsin, is significantly altered in the aortic wall in different types of infrarenal aortic disease. In addition, the ratio between these two enzyme systems changes in favor of more proteolytic activity as the type of infrarenal disease changes from occlusive to aneurysmal.