In vivo analysis of mechanical wall stress and abdominal aortic aneurysm rupture risk

OBJECTIVE: The purpose of this study was to calculate abdominal aortic aneurysm (AAA) wall stresses in vivo for ruptured, symptomatic, and electively repaired AAAs with three-dimensional computer modeling techniques, computed tomographic scan data, and blood pressure and to compare wall stress with current clinical indices related to rupture risk. METHODS: CT scans were analyzed for 48 patients with AAAs: 18 AAAs that ruptured (n = 10) or were urgently repaired for symptoms (n = 8) and 30 AAAs large enough to merit elective repair within 12 weeks of the CT scan. Three-dimensional computer models of AAAs were reconstructed from CT scan data. The stress distribution on the AAA as a result of geometry and blood pressure was computationally determined with finite element analysis with a hyperelastic nonlinear model that depicted the mechanical behavior of the AAA wall. RESULTS: Peak wall stress (maximal stress on the AAA surface) was significantly different between groups (ruptured, 47.7 +/- 6 N/cm(2); emergent symptomatic, 47.5 +/- 4 N/cm(2); elective repair, 36.9 +/- 2 N/cm(2); P =.03), with no significant difference in blood pressure (P =.2) or AAA diameter (P =.1). Because of trends toward differences in diameter, comparison was made only with diameter-matched subjects. Even with identical mean diameters, ruptured/symptomatic AAAs had a significantly higher peak wall stress (46.8 +/- 4.5 N/cm(2) versus 38.1 +/- 1.3 N/cm(2); P =.05). Maximal wall stress predicted risk of rupture better than the LaPlace equation (20.7 +/- 5.7 N/cm(2) versus 18.8 +/- 2.9 N/cm(2); P =.2) or other proposed indices of rupture risk. The smallest ruptured AAA was 4.8 cm, but this aneurysm had a stress equivalent to the average electively repaired 6.3-cm AAA. CONCLUSION: Peak wall stresses calculated in vivo for AAAs near the time of rupture were significantly higher than peak stresses for electively repaired AAAs, even when matched for maximal diameter. Calculation of wall stress with computer modeling of three-dimensional AAA geometry appears to assess rupture risk more accurately than AAA diameter or other previously proposed clinical indices. Stress analysis is practical and feasible and may become an important clinical tool for evaluation of AAA rupture risk.     

Abdominal aortic aneurysm rupture rates: A 7-year follow-up of the entire abdominal aortic aneurysm population detected by screening

Purpose: The goal of the current study was to identify the risk of rupture in the entire abdominal aortic aneurysm (AAA) population detected through screening and to review strategies for surgical intervention in light of this information. Methods: Two hundred eighteen AAAs were detected through ultrasound screening of a family practice population of 5394 men and women aged 65 to 80 years. Subjects with an AAA of less than 6.0 cm in diameter were followed prospectively with the use of ultrasound, according to our protocol, for 7 years. Patients were offered surgery if symptomatic, if the aneurysm expanded more than 1.0 cm per year, or if aortic diameter reached 6.0 cm. Results: The maximum potential rupture rate (actual rupture rate plus elective surgery rate) for small AAAs (3.0 to 4.4 cm) was 2.1% per year, which is less than most reported operative mortality rates. The equivalent rate for aneurysms of 4.5 to 5.9 cm was 10.2% per year. The actual rupture rate for aneurysms up to 5.9 cm using our criteria for surgery was 0.8% per year Conclusion: In centers with an operative mortality rate of greater than 2%, (1) surgical intervention is not indicated for asymptomatic AAAs of less than 4.5 cm in diameter, and (2) elective surgery should be considered only for patients with aneurysms between 4.5 and 6 cm in diameter that are expanding by more than 1 cm per year or for patients in whom symptoms develop. In centers with elective mortality rates of greater than 10% for abdominal aortic aneurysm (AAA) repair, the benefit to the patient of any surgical intervention for an asymptomatic AAA of less than 6.0 cm in diameter is questionable. (J Vasc Surg 1998;28:124-8.)     

A comparative study of aortic wall stress using finite element analysis for ruptured and non-ruptured abdominal aortic aneurysms.

BACKGROUND: The decision to repair an asymptomatic abdominal aortic aneurysm (AAA) is currently based on diameter (> or =5.5 cm) alone. However, aneurysms less than 5.5 cm do rupture while some reach greater than 5.5 cm without rupturing. Hence the need to predict the risk of rupture on an individual patient basis is important. This study aims to calculate and compare wall stress in ruptured and non-ruptured AAA. METHODS: The 3D geometries of AAA were derived from CT scans of 27 patients (12 ruptured and 15 non-ruptured). AAA geometry, systolic blood pressure and literature derived material properties, were utilised to calculate wall stress for individual AAA using finite element analysis. RESULTS: Peak wall stress was significantly higher in the ruptured AAA (mean 1.02 MPa) than the non-ruptured AAA (mean 0.62 MPa). In patients with an identifiable site of rupture on CT scan, the area of peak wall stress correlated with rupture site. CONCLUSIONS: Peak wall stress can be calculated from routinely performed CT scans and may be a better predictor of risk of rupture than AAA diameter on an individual patient basis.     

The Natural History of Abdominal Aortic Aneurysm

There is now sufficient published evidence to describe with confidence much but not all of the natural history of AAA. AAA of 4.0–5.5 cm in diameter have a rupture rate of 0.7–1.0% per year and for AAA < 4.0 cm this rate is even lower. Women appear to have a higher rupture rate than men for small aAa, but there is no evidence of this for AAA > 5.5 cm. Median enlargement rate of AAA 4.0–5.5 cm is about 0.3 cm per year. Enlargement rate is influenced by AAA diameter, being approximately half this rate for AAA 3.0–4.0 cm and half again faster for AAA > 5.5 cm. There is, however, considerable individual variability in enlargement rates and a variety of diseases and conditions appear to influence these rates. Rupture rates of AAA > 5.5 cm in fit individuals are unknown and unlikely to be known in the future. However, for unfit individuals with AAA > 5.5 cm, the rupture rate is high, starting at about 10% per year and increasing by several fold in the largest AAA. The search is on for drugs to favorably alter this natural history, and if successful, will doubtless shed much light on the pathophysiology of AAA enlargement.     

Prediction of rupture risk in abdominal aortic aneurysm during observation: wall stress versus diameter

OBJECTIVES: We previously showed that peak abdominal aortic aneurysm (AAA) wall stress calculated for aneurysms in vivo is higher at rupture than at elective repair. The purpose of this study was to analyze rupture risk over time in patients under observation. METHODS: Computed tomography (CT) scans were analyzed for patients with AAA when observation was planned for at least 6 months. AAA wall stress distribution was computationally determined in vivo with CT data, three-dimensional computer modeling, finite element analysis (nonlinear hyperelastic model depicting aneurysm wall behavior), and blood pressure during observation. RESULTS: Analysis included 103 patients and 159 CT scans (mean follow-up, 14 +/- 2 months per CT). Forty-two patients were observed with no intervention for at least 1 year (mean follow-up, 28 +/- 3 months). Elective repair was performed within 1 year in 39 patients, and emergent repair was performed in 22 patients (mean, 6 +/- 1 month after CT) for rupture (n = 14) or acute severe pain. Significant differences were found for initial diameter (observation, 4.9 +/-.1 cm; elective repair, 5.9 +/-.1 cm; emergent repair, 6.1 +/-.2 cm; P <.0001) and initial peak wall stress (38 +/- 1 N/cm(2), 42 +/- 2 n/cm(2), 58 +/- 4 N/cm(2), respectively; P <.0001), but peak wall stress appeared to better differentiate patients who later required emergent repair (elective vs emergent repair: diameter, 3% difference, P =.5; stress, 38% difference, P <.0001). Receiver operating characteristic (ROC) curves for predicting rupture were better for peak wall stress (sensitivity, 94%; specificity,81%; accuracy, 85% [with 44 N/cm(2) threshold]) than for diameter (81%, 70%, 73%, respectively [with optimal 5.5 cm threshold). With proportional hazards analysis, peak wall stress (relative risk, 25x) and gender (relative risk, 3x) were the only significant independent predictors of rupture. CONCLUSIONS: For AAAs under observation, peak AAA wall stress seems superior to diameter in differentiating patients who will experience catastrophic outcome. Elevated wall stress associated with rupture is not simply an acute event near the time of rupture.     

Wall stress analysis in small asymptomatic, symptomatic and ruptured abdominal aortic aneurysms.

OBJECTIVES: To evaluate the potential of wall stress analysis for the identification of abdominal aortic aneurysm (AAA) at elevated risk of rupture in spite of small diameter. MATERIALS AND METHODS: Thirty patients with small AAA, 10 asymptomatic, 10 symptomatic and 10 ruptured, were included. Demographic data and results from physical examinations were recorded in a retrospective fashion. After CT-evaluation and the creation of a patient specific 3D model, wall stress was calculated using the finite element method. RESULTS: No differences were observed in diameter between asymptomatic, symptomatic or ruptured aneurysms (5.1+/-0.2 cm vs. 5.1+/-0.2 cm vs. 5.3+/-0.2 cm respectively; p=0.57). Peak aortic wall stress at maximal systolic blood pressure is significantly higher in ruptured than asymptomatic aneurysms (51.7+/-2.4 N/cm(2) vs. 39.7+/-3.3 N/cm(2) respectively; p=0.04). Wall stress analysis at uniform blood pressure, performed to correct for higher blood pressure in the symptomatic and rupture group did not result in significant differences in peak wall stress (asymptomatic 31.7+/-2.3 N/cm(2); symptomatic 30.5+/-1.3 N/cm(2); rupture 36.7+/-4.0 N/cm(2); p=0.26). CONCLUSIONS: Wall stress analysis at maximal systolic blood pressure is a promising technique to detect aneurysms at elevated aneurysm rupture risk. Since no significant differences were found at uniform blood pressure, the need for adequate blood pressure control in aneurysm patients is reiterated.     

Size and location of thrombus in intact and ruptured abdominal aortic aneurysms

PURPOSE: This study compared the volume and morphology of intraluminal thrombus (ILT) in intact and ruptured abdominal aortic aneurysms (AAAs). METHODS: ILT volume in 67 intact AAAs and in 31 ruptured AAAs was assessed by using computed tomography (CT) angiography to measure the major and minor diameter of the outer wall and lumen of AAA as outlined by contrast at multiple sites. ILT thrombus morphology was recorded by AutoCAD 2000 software. Four equidistant images traced from the CT scan were recorded along the length of AAA. Thrombus volume was categorized as anterior-eccentric if the calculated area of thrombus was greater anteriorly, posterior-eccentric if greater posteriorly, eccentric-equal if the difference between the anterior and posterior thrombus was 相似文献   

Gender,smoking, body size,and aneurysm geometry influence the biomechanical rupture risk of abdominal aortic aneurysms as estimated by finite element analysis

Objective

Finite element analysis (FEA) has been suggested to be superior to maximal diameter measurements in predicting rupture of abdominal aortic aneurysms (AAAs). Our objective was to investigate to what extent previously described rupture risk factors were associated with FEA-estimated rupture risk.

Effect of intraluminal thrombus on wall stress in patient-specific models of abdominal aortic aneurysm

PURPOSE: The role of intraluminal thrombus (ILT) on abdominal aortic aneurysm rupture is still not clear. Rupture of an aneurysm occurs when the wall stress exceeds the wall strength at any location on the wall. The purpose of this study was to address the hypothesis that the presence of ILT alters the wall stress distribution or wall stress magnitude in AAA. METHODS: Patient-specific 3D AAA geometries were reconstructed from computed tomographic images. Two geometric features, ILT surface ratio (ILT surface area divided by the total AAA surface area) and ILT volume ratio (ILT volume divided by the total AAA volume), were calculated for each AAA. Two models were created for each patient: one with ILT and one without ILT. Systolic pressure measured at the time of computed tomographic imaging was applied to the internal surface of each model. A nonlinear large deformation algorithm was used to compute wall stress distribution with the finite element method. The Wilcoxon matched pairs test was used to compare the peak wall stress between the two models of each patient. RESULTS: Four patients were studied with ILT surface ratios that ranged from 0.29 to 0.72 and ILT volume ratios that ranged from 0.12 to 0.66. The peak wall stress was reduced (range, 6% to 38% reduction; P =.067) for all models with ILT included (range, 28 to 37 N/cm(2)) as compared with models with no ILT (range, 30 to 44 N/cm(2)). Visual inspection also revealed a marked effect of ILT on the wall stress distribution. CONCLUSION: The presence of ILT alters the wall stress distribution and reduces the peak wall stress in AAA.For this reason, ILT should be included in all patient-specific models of AAA for evaluation of AAA wall stresses.     

Anatomic characteristics of ruptured abdominal aortic aneurysm on conventional CT scans: Implications for rupture risk

OBJECTIVE: The purpose of this study was to analyze anatomic characteristics of patients with ruptured abdominal aortic aneurysms (AAAs), with conventional two-dimensional computed tomography (CT), including comparison with control subjects matched for age, gender, and size. METHODS: Records were reviewed to identify all CT scans obtained at Dartmouth-Hitchcock Medical Center or referring hospitals before emergency AAA repair performed because of rupture or acute severe pain (RUP group). CT scans obtained before elective AAA repair (ELEC group) were reviewed for age and gender match with patients in the RUP group. More than 40 variables were measured on each CT scan. Aneurysm diameter matching was achieved by consecutively deleting the largest RUP scan and the smallest ELEC scan to prevent bias. RESULTS: CT scans were analyzed for 259 patients with AAAs: 122 RUP and 137 ELEC. Patients were well matched for age, gender, and other demographic variables or risk factors. Maximum AAA diameter was significantly different in comparisons of all patients (RUP, 6.5 +/- 2 cm vs ELEC, 5.6 +/- 1 cm; P <.0001), and mean diameter of ruptured AAAs was 5 mm smaller in female patients (6.1 +/- 2 cm vs 6.6 +/- 2 cm; P =.007). Two hundred patients were matched for diameter, gender, and age (100 from each group; maximum AAA diameter, 6.0 +/- 1 cm vs 6.0 +/- 1 cm). Analysis of diameter-matched AAAs indicated that most variables were statistically similar in the two groups, including infrarenal neck length (17 +/- 1 mm vs 19 +/- 1 mm; P =.3), maximum thrombus thickness (25 +/- 1 mm vs 23 +/- 1 mm, P =.4), and indices of body habitus, such as [(maximum AAA diameter)/(normal suprarenal aorta diameter)] or [(maximum AAA diameter)/(L3 transverse diameter)]. Multivariate analysis controlling for gender indicated that the most significant variables for rupture were aortic tortuosity (odds ratio [OR] 3.3, indicating greater risk with no or mild tortuosity), diameter asymmetry (OR, 3.2 for a 1-cm difference in major-minor axis), and current smoking (OR, 2.7, with the greater risk in current smokers). CONCLUSIONS: When matched for age, gender, and diameter, ruptured AAAs tend to be less tortuous, yet have greater cross-sectional diameter asymmetry. On conventional two-dimensional CT axial sections, it appears that when diameter asymmetry is associated with low aortic tortuosity, the larger diameter on axial sections more accurately reflects rupture risk, and when diameter asymmetry is associated with moderate or severe aortic tortuosity, the smaller diameter on axial sections more accurately reflects rupture risk. Current smoking is significantly associated with rupture, even when controlling for gender and AAA anatomy.     

The rupture rate of large abdominal aortic aneurysms: is this modified by anatomical suitability for endovascular repair?

BACKGROUND: There are no precise estimates of the rate of rupture of large abdominal aortic aneurysms (AAA). There is recent suspicion that anatomic suitability for endovascular repair may be associated with a decreased risk of AAA rupture. METHODS: Systematic literature review of rupture rates of AAA with initial diameter > or =5 cm in patients not considered for open repair, with stratification by size (<6.0 cm and 6.0+ cm), and gender, combined using random-effects meta-analysis. Proportional hazards regression to analyze factors (including gender, diabetes, initial AAA diameter, aneurysm neck, and sac lengths) associated with rupture in patients anatomically suitable for endovascular repair (EVAR 2 trial). RESULTS: Previous studies (2 prospective, 2 retrospective, and 1 mixed) were identified for meta-analysis and patients with elective repair excluded. The pooled rupture rates was 18.2 [95% confidence interval (CI) 13.7-24.1] per 100 person-years. There was a 2.5-fold increase in rupture rates for patients with AAA of 6.0+ cm versus <6.0 cm, rupture rates = 2.54 (95% CI 1.69-3.85). The pooled rupture rates was nonsignificantly higher in women than men, rupture rates = 1.21 (95% CI 0.77-1.90). For EVAR 2 patients with 6+ cm aneurysms the rupture rates was 17.4 [95% CI 12.9-23.4] per 100 person-years significantly lower than the pooled rate from the meta-analysis, rupture rates = 27.0 [95% CI 21.1-34.7] per 100 person-years, P = 0.026. Patients with shorter neck lengths appeared to have a higher rupture rates than those with longer necks, but this was of borderline significance P = 0.10. CONCLUSIONS: Rupture rates of large AAAs reported in different studies are highly variable. There is emerging evidence that patients anatomically suitable for endovascular repair have lower rupture rates.     

Analysis of expansion patterns in 4-4.9 cm abdominal aortic aneurysms

Our objective was to analyze the growth pattern of 4-4.9 cm infrarenal abdominal aortic aneurysms (AAAs). We used an observational, longitudinal, prospective study design. We followed 4-4.9 cm AAAs with 6-monthly abdominal computed tomographic (CT) scans (January 1988-August 2004). AAA growth was defined as an increase in aortic diameter > or =2 mm in each surveillance period. We established the aortic expansion pattern in AAA with three or more CT scans as continuous, discontinuous. The latter includes at least one period of nongrowth (<2 mm/6 months). We studied the influence of cardiovascular risk factors (CVRFs), comorbidity, and AAA anatomical characteristics using the chi-squared test, t-test, life tables, and Kaplan-Meier for statistical analysis. We included 195 patients: 183 (93.8%) men, age 71 +/- 8.3 years (50-90). The follow-up period was 50 +/- 36.4 months (6.5-193.7). The growth pattern (n =131) was continuous in 15 (11.5%) and discontinuous in 116 (88.5%) AAA. The mean expansion rate was higher in AAAs with continuous expansion (7.92 +/- 3.74 vs. 2.74 +/- 2.94 mm/year, p < 0.0001). No CVRFs or comorbidity influenced the expansion pattern (p > 0.05). The eccentric thrombus was associated with a greater incidence of continuous growth (p = 0.05), with no influence of aortic calcification (p > 0.1). The expansion of 4-4.9 cm AAA is mostly irregular and unpredictable. We have not found any modifiable risk factors which influence their growth pattern. The eccentric distribution of the thrombus is associated with continuous expansion.     

Screening of abdominal aortic aneurysm: a pragmatic approach

In order to evaluate the feasibility of a selective screening programme for abdominal aortic aneurysm (AAA) within an urban setting and assess its impact on the expected increase in workload for the local hospital(s), a population based, prospective study was performed. A total of 4823 men aged 65 years were invited for ultrasound examination of the abdominal aorta between January 1993 and April 1997 as part of a general practice-based aneurysm screening programme covering two districts with a general hospital each. All examinations were carried out by senior radiographers using a portable B mode grey scale machine and a 3.5 MHz curvi-linear array probe. Patients with a maximum aortic diameter of over 3 cm were annually recalled, those with over 4 cm were referred to hospital for an out-patient's appointment. Those with AAA greater than 5 cm were considered for surgery. Of those approached, 3497 (72.5%) took part in the study, 1206 (25%) did not attend and 120 (2.5%) were excluded by their general practitioners (GPs) on medical grounds. Of the men taking part, 3130 (89.5%) had an aortic diameter equal to or less than 2.5 cm, 196 (5.6%) between 2.6 and 3.0 cm, and 171 (4.9%) had aortic diameters greater than 3 cm--29 of whom had AAA greater than 5 cm with a mean diameter of 6.0 cm (range 5.1-9.0 cm). Of 127 men with an initial diameter of 3.1-4.0 cm (mean progression in size of 2.3 mm/year), 22 enlarged to > 4 cm and 3 to > 5 cm. Of 24 men with an initial diameter of 4.1-5.0 cm, 6 enlarged to > 5 cm. Some 69 (2%) patients were referred to hospital requiring a total of 125 consultations (1.8 consultations per patient); 21 underwent surgery and one died from rupture whilst awaiting surgery. Five patients refused their operation and two failed to attend the clinic (all > 5 cm) but remain well to date. No patient died following surgery. We conclude that, screening for AAA in men at age 65 years within an urban setting is feasible and well received by patients and GPs. Screening does not lead to a huge increase in terms of outpatient appointments and operations for AAA.     

Proteolysis of the abdominal aortic aneurysm wall and the association with rupture.

PURPOSE: to investigate proteolysis of the abdominal aortic aneurysm (AAA) wall and the association with rupture. METHODS: levels of matrix metalloproteinases (MMP-2 and MMP-9) and tissue inhibitor of metalloproteinases (TIMP-1 and TIMP-2) were measured in the walls of medium-sized (5-7 cm in diameter) ruptured AAA (rAAA) (n =30) and large (> or = 7 cm in diameter) asymptomatic AAA (aAAA) (n=30). RESULTS: MMP-2 levels (median, range) were significantly higher in the walls of large aAAA (165 ng/g AAA tissue, 50-840) than from medium-sized rAAA (110 ng/g AAA tissue, 47-547, p=0.007). MMP-9 levels were significantly higher in the walls of medium-sized rAAA (107 ng/g AAA tissue, 19-582) than from large aAAA (55 ng/g AAA tissue, 11-278, p=0.012). TIMP-1 and TIMP-2 levels were equivalent. There was a positive correlation between MMP-2 and the diameter of aAAA (r=0.54, p=0.002), but a negative correlation with MMP-9 (r= -0.44, p=0.017). No significant correlations were found between aAAA diameter and TIMP-1 or TIMP-2. CONCLUSION: AAA rupture is associated with higher levels of MMP-9. There is no association with TIMP-1 or TIMP-2 levels. MMP-2 levels are positively, whereas MMP-9 levels are negatively, correlated with aAAA size. MMP-9 may play a role in the progression towards rupture, whereas MMP-2 may play a role in expansion.     

Wall stress distribution on three-dimensionally reconstructed models of human abdominal aortic aneurysm

PURPOSE: Abdominal aortic aneurysm (AAA) rupture is believed to occur when the mechanical stress acting on the wall exceeds the strength of the wall tissue. Therefore, knowledge of the stress distribution in an intact AAA wall could be useful in assessing its risk of rupture. We developed a methodology to noninvasively estimate the in vivo wall stress distribution for actual AAAs on a patient-to-patient basis. METHODS: Six patients with AAAs and one control patient with a nonaneurysmal aorta were the study subjects. Data from spiral computed tomography scans were used as a means of three-dimensionally reconstructing the in situ geometry of the intact AAAs and the control aorta. We used a nonlinear biomechanical model developed specifically for AAA wall tissue. By means of the finite element method, the stress distribution on the aortic wall of all subjects under systolic blood pressure was determined and studied. RESULTS: In all the AAA cases, the wall stress was complexly distributed, with distinct regions of high and low stress. Peak wall stress among AAA patients varied from 29 N/cm(2) to 45 N/cm(2) and was found on the posterior surface in all cases studied. The wall stress on the nonaneurysmal aorta in the control subject was relatively low and uniformly distributed, with a peak wall stress of 12 N/cm(2). AAA volume, rather than AAA diameter, was shown by means of statistical analysis to be a better indicator of high wall stresses and possibly rupture. CONCLUSION: The approach taken to estimate AAA wall stress distribution is completely noninvasive and does not require any additional involvement or expense by the AAA patient. We believe that this methodology may allow for the evaluation of an individual AAA's rupture risk on a more biophysically sound basis than the widely used 5-cm AAA diameter criterion.     

Expansion rates and outcomes for the 3.0-cm to the 3.9-cm infrarenal abdominal aortic aneurysm

OBJECTIVE: This study was performed for the determination of the expansion rates and outcomes and for recommendations for the surveillance of the 3.0-cm to 3.9-cm abdominal aortic aneurysm (AAA). DESIGN: The study was observational with data from patients screened with ultrasound scanning for AAA at five Veterans Affairs Medical Centers for enrollment in the Aneurysm Detection and Management Trial. The eligibility requirements included: AAA from 3.0 cm to 3.9 cm in diameter and at least one repeat ultrasound scan more than 90 days after the initial screening. Patients also completed a questionnaire for demographic data and the determination of the presence of risk factors associated with AAA. The study endpoints included: 1, both mean and median expansion rates; 2, moderate expansion (>4 mm/year); 3, no expansion; 4, all causes of death; 5, AAA rupture; 6, expansion to 4 cm or more; 7, expansion to 5.0 cm or more; and 8, operative repair. RESULTS: Ultrasound scan screening results identified 1445 patients with 3.0-cm to 3.9-cm AAAs. Seven hundred ninety men met the ultrasound scan criterion of having at least two ultrasound scan studies during the study period, and these 790 men were used for this study. Mean AAA size was 3.3 cm, with an average follow-up period of 3.89 +/- 1.93 years. The median expansion rate was 0.11 cm/year. Expansion rates were significantly different (P <.001) between 3.0-cm and 3.4-cm cm AAA and 3.5-cm and 3.9-cm AAA. There were no reported AAA ruptures during the study period, although cause of death data were available in only 43% of the patients. Few 3.0-cm to 3.9-cm AAAs expanded to 5.0 cm or more during the study period. The patients with 3.0-cm to 3.9-cm AAAs who underwent operative repair during the study period were younger, had larger initial AAA diameters, and had more rapid expansion rates. CONCLUSION: AAAs of 3.0 cm to 3.9 cm expanded slowly, did not rupture, and rarely had operative repair or expanded to more than 5.0 cm in our study of male patients. Expansion rates and the incidence rate of operative repair are more common in the 3.5-cm to 3.9-cm AAA when compared with the 3.0-cm to 3.4-cm AAA.     

The risk of rupture in untreated aneurysms: the impact of size,gender, and expansion rate

OBJECTIVE: The purpose of this study was to establish the risk of rupture as related to size of abdominal aortic aneurysm (AAA), gender, and expansion of the aneurysm. METHODS: Between 1976 and 2001, 476 patients with conditions considered unfit for surgery with AAA 5.0 cm or more were followed with computed tomographic scans every 6 months until rupture, surgery, death, or deletion from follow-up. Surgery was performed for rupture (n = 22), improved medical condition (n = 37), increase in size (n = 95), symptoms (n = 17), and other reasons (n = 24). RESULTS: Fifty ruptures occurred during the follow-up period. The average risk of rupture (and standard error) in male patients with 5.0-cm to 5.9-cm AAA was 1.0% (0.01%) per year, in female patients with 5.0-cm to 5.9-cm AAA was 3.9% (0.15%) per year, in male patients with 6.0-cm or greater AAA was 14.1% (0.18%) per year, and in female patients with 6.0-cm or greater AAA was 22.3% (0.95%) per year. CONCLUSION: The risk of rupture in male patients with AAA 5.0 to 5.9 cm is low. The four-time higher risk of rupture in female patients with AAA 5.0 to 5.9 cm suggests a lower threshold for surgery be considered in fit women. The data regarding risk of rupture in patients with AAA 6.0 cm or more may allow more appropriate decision analysis for surgery in patients with unfit conditions with large AAA.     

Variables that affect the expansion rate and outcome of small abdominal aortic aneurysms

Seventy-three patients with small (less than 6 cm in diameter) abdominal aortic aneurysms (AAAs) were selected for nonoperative management and followed up with sequential ultrasound size measurements. Fifty-four men and 19 women, 51 to 89 years of age (mean 70 years), had an initial mean AAA size of 4.1 cm (anteroposterior) x 4.3 cm (lateral) diameter, with a calculated elliptic cross-sectional area of 14.3 cm2. After a mean of 37 months of follow-up, AAA area increased at a mean rate of 20% per year (3 cm2 yr; 0.4 to 0.5 cm/yr diameter). Expansion rate was not affected by initial aneurysm size. During follow-up, only 3 patients (4%) required urgent operation (1 died), 26 patients (36%) died of non-AAA causes, and 26 patients (36%) underwent elective AAA repair because of progressive size increase (1 died). Elective operations were performed at the rate of 10% per year, when mean AAA size had increased to 22 cm2 (5.1 cm in diameter). Multiple regression analysis of clinical parameters available at presentation indicated that subsequent elective AAA repair was predicted by younger age at diagnosis and larger initial aneurysm size. As anticipated, patients who underwent surgery had more rapid aneurysm expansion (5.3 cm2/yr) compared with patients who did not undergo surgery (1.6 cm2/yr; p less than 0.05). This difference was caused by more rapid expansion during later follow-up intervals among patients selected for operation and was not predicted by the change in aneurysm size observed during initial ultrasonographic follow-up. Final aneurysm size was predicted by initial size, duration of follow-up, and both systolic and diastolic pressure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Risk factors for rupture of abdominal aortic aneurysm based on three-dimensional study

PURPOSE: Factors influencing the development or rupture of abdominal aortic aneurysms (AAAs) have not yet been confirmed. This study delineated the risk factors for rupture of AAAs as evaluated by means of a combination of three-dimensional (3D) reconstruction and clinical data analysis. METHODS: The study population comprised Japanese patients in whom an atherosclerotic AAA had been diagnosed between January 1980 and December 1997. We obtained 3D-based data by means of computer-aided 3D reconstruction from computed tomography studies of AAAs. The data included the tortuosity of the aneurysm, maximum transverse diameter, length of the aneurysm, aneurysmal volume, aneurysmal surface area, largest aneurysmal cross-sectional area, ratio of transverse aneurysmal diameter to the length of the aneurysm (T/L), and amount of mural thrombus. Clinical data were collected from patient files. All data were assessed by means of multivariate analysis for their predictive value for expansion or rupture of AAA. RESULTS: The most efficient predictor of annual expansion rate of maximum transverse diameter (EX-D) was a combination of largest aneurysmal cross-sectional area, tobacco use, and tortuosity. The most efficient predictor of annual expansion rate of aneurysmal volume (EX-V) was a combination of aneurysmal volume and blood urea nitrogen level. The most efficient predictors of aneurysmal rupture was a combination of EX-D, diastolic blood pressure, and T/L. CONCLUSION: Three-dimensional-based data on aneurysmal morphology, including T/L, largest aneurysmal crosssectional area, and aneurysmal volume, had strong predictive value for expansion and rupture of AAAs.     

Optimal interval screening and surveillance of abdominal aortic aneurysms.

OBJECTIVES: to determine safe and optimal intervals of rescreening and surveillance for AAA. METHODS: hospital-based mass screening of 6339 65-73-year-old men from 1994-98. 76.4% attended. One hundred and ninety-one (4%) had AAA53 cm. Twenty-four (0.5%) were initially >5 cm and referred for surgery, while the rest were offered annual control scans to check for expansion. Later, all 348 (7.5%) men who 3 to 5 years ago had an ectatic aorta (infrarenal aortic diameter of 25-29 mm or distal/renal aortic diameter ratio >1.2) were offered rescreening. Of these, 62 (18%) died before rescanning, while 248 of the survivors attended rescreening (87%). Furthermore, a random sample of 380 of those with non-ectatic aortas were offered rescreening. Of these, 49 (13%) died before rescreening (p=0.06), while 275 (83%) of the survivors attended re-screening. RESULTS: none of the controls had developed AAA. Of those who initially had an 25-29 mm aorta, 29% had developed AAA (size range 30-48 mm) with expansion rates varying from 1.0 to 4.7 mm/year. Only 3.5% with a ratio >1.2 developed AAA (size range: 30-34 mm) with expansion rates from 1.3 to 2.4 mm/year. During the fourth year of surveillance some AAA initially sized below 3.5 cm expanded to above 5 cm, while some sized 3.5-3.9 cm did so during the second year, >4 cm did so during the first year of surveillance. CONCLUSION: rescreening for AAA can be restricted to initially ectatic aortas sized 25-29 mm at 5-year intervals. Surveillance of small AAA can be restricted to 1-4 year intervals.