Choice of treatment for the patient with urgent AAA: practical tips

Since the first successful attempts of emergency endovascular aneurysm repair (eEVAR) for patients with ruptured AAAs in the mid 1990s, surgeons have had to decide whether to treat patients by conventional open surgery or by minimally invasive but technically more demanding eEVAR. To date, selection of patients for eEVAR is still heavily debated and factors like hemodynamic instability, fear of treatment delay for patient transfer or imaging procedures and logistic issues often lead to the exclusion of anatomically suitable patients from eEVAR. However, these adverse factors may be overcome by adherence to an appropriate (intention-to-treat) protocol employing the use of a hypotensive hemostatic approach, transfemoral aortic balloon occlusion technique (when needed), different types of devices and an appropriate plan to resolve logistic issues, leaving anatomic suitability as the single most important determinant of suitability for EVAR.

Mortality of ruptured abdominal aortic aneurysm with selective use of endovascular repair

The aim of this review was to examine the results over a seven-year period of treatment for ruptured abdominal aortic aneurysm (RAAA). From 2002 on, our tertiary referral centre offered both open and endovascular (EVAR) treatment modalities for RAAA. All patients with a proven RAAA who were admitted into our hospital were included. Primary outcome measure was surgical mortality. In total 261 patients were admitted with suspicion of acute AAA. Of these, 175 (67%) had a RAAA, confirmed by computed tomography-scanning or at laparotomy. One hundred and fifty-nine patients (90.9%) were treated, 114 by open repair and 45 by EVAR. Overall mortality of patients treated was 25.2%, with an open repair mortality of 27.2%, and EVAR mortality of 20%. EVAR was used more often in patients who were hemodynamically more stable. Evaluation for EVAR and treatment by EVAR increased during the study period. Overall mortality rate for treatment of RAAA in our centre was 25% over the seven-year study period.

Endovascular proximal control of ruptured abdominal aortic aneurysms: the internal aortic clamp

Ruptured abdominal aortic aneurysm (RAAA) is the most common and devastating complication affecting a patient with abdominal aortic aneurysm (AAA). Despite advances in surgery and critical care, the mortality rate associated with RAAA remains largely unchanged. Emergency open repair is the gold standard conventional treatment of RAAA but is associated with a high mortality rate. The physiologic challenges associated with general anaesthetic induction such as loss of the sympathetic vasoconstrictor tone with consequent hypotension, and the anatomic challenges associated with external aortic cross-clamping such as calcification, friability, or poor visualisation of the aneurysm neck, have led to the adoption of endovascular techniques in the surgical treatment of RAAA. Promising results of endovascular repair of ruptured abdominal aortic aneurysm (REVAR) have been reported. In addition, the provision of endovascular aortic control by inflating a compliant aortic occlusion balloon (AOB) proximal to the ruptured aneurysm, as an internal aortic clamp, has been successfully used in haemodynamically unstable patients undergoing either REVAR or emergency open repair of RAAA. An AOB is inserted under local anaesthesia and can be introduced through either the transbrachial or the transfemoral routes, each with its own advantages and disadvantages. This review aimed at providing an up-to-date overview of the current knowledge concerning endovascular proximal aortic control using an AOB with emphasis on the rationale, position, benefits, and drawbacks of its use.

Maximum aortic diameter as a simple predictor of acute type B aortic dissection

OBJECTIVES

To identify the most prognostic predictor of Stanford type B aortic dissection at admission.

PATIENTS AND METHODS

Forty-three patients with Stanford type B aortic dissection were divided into two groups: (1) those who developed dissection-related events later (EV group: n = 18), including the need for surgery (n = 12), rupture (n = 1), dissection-related death (n = 5), and aortic enlargement > or =5 mm in diameter per year (n = 15); (2) those without later events (NoEV group: n = 25). Clinical features, aortic diameters, and blood flow status were compared.

RESULTS

The maximum aortic diameter at admission was 41.5 +/- 1.7 mm for the EV group, which was significantly greater than the NoEV group (34.4 +/- 0.9 mm, p <0.001). A maximum aortic diameter > or =40 mm was found in 11 patients (61%) of the EV group, whereas this maximum was found in 4 (16%) of the NoEV group (p = 0.004). A patent false lumen at admission was found in all patients of the EV group and in 17 (68%) of the NoEV group (p = 0.013). Other factors were not significant. A Cox hazard analysis indicated a maximum aortic diameter > or =40 mm as a significant predictor for dissection-related events (hazard ratio 3.13, p = 0.032). The presence of a patent false lumen did not reach a statistical significance.

CONCLUSION

Our results indicated that a maximum aortic diameter > or =40 mm at admission was the most prognostic factor for developing late dissection-related events, rather than the presence of a patent false lumen.

Traumatic rupture of thoracic aorta in real-world motor vehicle crashes

OBJECTIVE

Traumatic rupture of thoracic aorta (TRA) was reported in the literature to be a major cause of death in motor vehicle crashes. This study aims at evaluating the most relevant risk factors of TRA. It also aims at analyzing the types of TRA as a function of car crash conditions and rib cage fractures.

METHODS

In-depth crash data collected from 1998 to 2006 as part of the Co-operative Crash Injury Study (CCIS) were retrospectively investigated to assess frontal, near-side, and far-side injury risks. This database includes 15,074 occupants with individual detailed autopsy reports. Multivariate statistical analyses were performed. The influence of the following variables on TRA occurrence was studied: gender and age of the involved occupant, ETS, compartment intrusion, and restraint system. Features of TRA and rib cage fractures were described thanks to autopsy data.

RESULTS

Although TRA occurred in only 1.2% of all occupants, TRA victims accounted for 21.4% of all fatalities. The incidence of TRA was found twice higher in side impacts (2.4%) than in frontal ones (1.1%). TRA injury risk increased with ETS, intrusion, and age and decreased with the absence of intrusion regardless of the impact direction. It also decreased for belted occupants in frontal impacts. Except for the site of injury, the TRA features were similar whatever the crash conditions. The multiple ribs fractures were the most common injuries associated with TRA (79.1%) and TRA victims with uninjured or slightly injured (AIS 1) rib cage were significantly younger (p < 0.0001) than other TRA victims. Whatever the impact type, the TRA victims sustained mostly bilateral rib fractures (68%). Results also emphasized a close relationship between the principal direction of force and the body side with more fractured ribs. However, whatever the impact type, the aortic injury site or the side of the thorax, fractures concerned mainly the 2nd up to the 7th ribs of TRA victims.

CONCLUSIONS

This study emphasized four main variables influencing the TRA occurrence: ETS, compartment intrusion, age, and seat belt use. The results suggested that the injury site may be different depending on the occupant or the impact type. However, the typical TRA, i.e., a partial or complete aorta transection within the peri-isthmic region, affected any occupant independently of age and impact type. The high frequency of bilateral rib cage fractures observed in TRA victims and the significant influence of intrusion on TRA occurrence emphasized that the aortic injury mechanism mainly involves a severe direct chest impact or compression.

Ruptured Abdominal Aortic Aneurysms: Endovascular Repair versus Open Surgery—Systematic Review

PURPOSE

To perform a systematic review of studies in which endovascular repair was compared with open surgery in the treatment of patients with a ruptured abdominal aortic aneurysm (AAA).

MATERIALS AND METHODS

A search of the English-language literature from January 1994 until March 2006 was performed. Inclusion criteria for studies were that they were about a comparison between patients who underwent endovascular repair and patients who underwent open surgery, that each treatment group included at least five patients, that information about patients' hemodynamic condition at presentation was reported, and that 30-day mortality was reported for each treatment group. Two reviewers independently extracted the data, and discrepancies were resolved by an arbiter. Random-effects models and meta-regression analysis were used to calculate crude and adjusted odds ratios (ORs) for endovascular repair versus open surgery.

RESULTS

Ten studies, in which the results of 478 procedures (n=148 for endovascular repair, n=330 for open surgery) were reported, met the inclusion criteria. All studies were observational; no randomized controlled trials were found. The pooled 30-day mortality was 22% (95% confidence interval [CI]: 16%, 29%) for endovascular repair and 38% (95% CI: 32%, 45%) for open surgery. The pooled rate for total systemic complications was 28% (95% CI: 17%, 48%) for endovascular repair and 56% (95% CI: 37%, 85%) for open surgery. The crude OR for 30-day mortality for endovascular repair compared with open surgery was 0.45 (95% CI: 0.28, 0.72). After adjustment for patients' hemodynamic condition, the OR was 0.67 (95% CI: 0.31, 1.44).

CONCLUSION

In this systematic review, after adjustment for patients' hemodynamic condition at presentation, a benefit in 30-day mortality for endovascular repair compared with open surgery for patients with a ruptured AAA was observed, but it was not statistically significant.

Differential secretion of prostaglandin E(2), thromboxane A(2) and interleukin-6 in intact and ruptured abdominal aortic aneurysms

Ruptured abdominal aortic aneurysm (AAA) contributes largely to aneurysm-related morbidity and mortality. An inflammatory gene, COX-2, was found to be widely expressed in AAA. However, the involvement of COX-2 metabolites and other inflammatory mediators in the disease and particularly in AAA rupture still needs elucidation. The purpose of the present study was to evaluate the secretion of inflammatory mediators and the expression of macrophages in aneurysms and determine their significance in ruptured AAA. Aortic tissue was harvested at time of aortic reconstructive surgery for the group of intact AAA (n=20) and ruptured AAA (n=10) or at time of organ harvest for normal aortic tissue (n=4). Aortic explant cultures were immediately established and the culture medium was collected after 72 h. Specific enzyme-linked immunoassorbent assays were used to quantify COX-2 metabolites and inflammatory cytokines. Inflammatory macrophage cells were also quantified in the corresponding aortic walls immunohistochemically. Differences in the secretory levels of inflammatory metabolites and the macrophage quantity in all groups were assessed. All three explant culture groups secreted detectable levels of studied COX-2 metabolites, including PGE(2), PGF(2alpha), PGI(2) and TxB(2) and inflammatory cytokines, including interleukin (IL)-1beta, IL-6, IL-8 and IL-10. The secretory levels of PGE(2), TXB(2) and IL-6 were highest in the ruptured AAA explant cultures and statistically higher than those in intact AAA cultures (p<0.05). The secretion of those inflammatory mediators and the local expression of macrophages in ruptured aneurysm probably reflects the active inflammatory processes in the aortic lesions. A means of modifying the inflammatory process in the wall of AAAs might play an important role in preventing aneurysm rupture.

Multiple subfailures characterize blunt aortic injury

BACKGROUND

Blunt aortic injuries result from rapid deceleration of the thorax as may occur during automotive impacts and falls from extreme heights. Pathological findings can range from failure of specific vessel layers to immediate vessel wall rupture. The purpose of this investigation was to determine the sequence of local structural events that may lead to aortic wall disruption.

METHODS

Fourteen porcine aorta specimens were opened to expose the intima and longitudinally distracted until rupture. Longitudinal mechanics were quantified and subfailures were identified. Histology was used to examine internal layer subfailure.

RESULTS

Videography demonstrated that subfailures propagated into complete vessel wall rupture. Subfailures occurred before complete vessel rupture in 93% of specimens. Intimal and medial subfailures were present at 74% of the stress and 82% of the strain to rupture. Multiple subfailures were evident in 79% of specimens.

CONCLUSION

Present results supported the clinical theory that nonimmediate death as a result of blunt aortic injury is commonly caused by propagation of lesser lesions, initiating on the intimal layer, into complete vessel rupture including the adventitial layer. This finding, along with histologic evidence of subfailure pathological findings, confirms the presence of an acute window during which recognition and initiation of permissive hypotension may be lifesaving.

Early and Midterm Results After Open and Endovascular Repair of Ruptured Abdominal Aortic Aneurysms in a Comparative Analysis

PURPOSE

To compare early and midterm results of open versus endovascular aortic repair of ruptured abdominal aneurysms (rAAA).

METHODS

A retrospective analysis was performed of 58 consecutive patients with rAAA who were treated with open or endovascular aneurysm repair (EVAR) at a single center between January 2000 and December 2005. Patients without definitive signs of rupture (symptomatic patients) were excluded from the study. Twenty-nine patients (21 men; median age 71 years) were treated using endovascular techniques (EVAR group) and 29 (28 men; median age 71 years) with open repair (OR group). The hemodynamic status at the time of admission was evaluated with respect to blood pressure, pulse rate, and hemoglobin level to reduce selection bias. Patients underwent follow-up by clinical examination and computed tomography.

RESULTS

The 30-day mortality rate was 31% (9/29) in each group (p = 1.0); the morbidity rates also did not differ between groups [16 (55.2%) EVAR vs. 18 (62.1%) OR; p = 0.9]. There was 1 (3.4%) primary conversion in the EVAR group and 7 (24.1%) endoleaks [3 (10.3%) primary; 4 (13.8%) secondary]. There was no difference between the groups with regard to intensive care unit stay (4 days for EVAR vs. 3 days for OR, p = 0.98) or total hospital stay (9 days for EVAR vs. 12 days for OR, p = 0.69). After a mean follow-up of 40.25 months (range 1-70), the midterm mortality rates did not differ [5 (17.2%) EVAR vs. 3 (10.3%) OR, p = 0.41].

CONCLUSION

EVAR of rAAAs is feasible, with equal early and midterm mortality rates compared to open repair. When a defined patient selection is used for rupture, including hemodynamic status, there is no evidence of a better outcome with EVAR in emergency cases.

Ruptured abdominal aortic aneurysm: does trauma center designation affect outcome?

Ruptured abdominal aortic aneurysm (RAAA) continues to be a major cause of mortality in the United States. Rapid diagnosis and uncomplicated surgical repair remain paramount to improving survival in this population. We proposed that the addition of an organized trauma service and subsequent improved management of critically ill patients who present with RAAA would positively impact overall mortality. A retrospective analysis was performed on all patients treated for RAAA at Santa Barbara Cottage Hospital for the years 1985-2004. Patients treated before level II trauma center designation (1985-1999) were compared to those treated after the trauma center was instituted. A total of 76 patients were included in this analysis. The two groups were similar with regard to demographics. However, significant decreases in transport time from the emergency department to the operating room and overall 30-day mortality were seen in patients after the trauma center designation. This designation also led to an increase in the number of cases performed per year, centralizing the treatment for these critically ill patients. Institution of a well-prepared and organized service, such as trauma, improved the outcome for patients treated with RAAA, with a particular benefit in the unstable patient.

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.

Improved survival after introduction of an emergency endovascular therapy protocol for ruptured abdominal aortic aneurysms

BACKGROUND

The study was conducted to demonstrate improved survival (30-day mortality) after the introduction of an emergency endovascular therapy protocol for ruptured abdominal aortic aneurysms (rAAA). Numerous authors have successfully demonstrated reduced mortality in patients with rAAA using endovascular techniques. Comparison of endovascular aneurysm repair (EVAR) with open repair for rAAA may be misleading, however, because EVAR cannot be performed on all patients, and selection bias may explain the superior performance of any given surgical or endovascular strategy. We developed a model to predict mortality in patients before the introduction of EVAR (preprotocol population), applied this model to predict 30-day mortality among prospective patients (postprotocol population), and compared observed vs expected results.

METHODS

We assessed 126 patients with rAAA. Primary outcome was 30-day mortality. Potential confounding variables were age, sex, presurgical lowest recorded systolic blood pressure (SBP), and glomerular filtration rate (GFR). A logistic regression model incorporating significant confounders was used to evaluate changes in 30-day mortality for all patients with rAAA after introduction of the EVAR protocol. Separate logistic regressions were done to compare 30-day mortality for preprotocol vs patients receiving EVAR and preprotocol vs patients receiving postprotocol open repair. Cumulative sum (CUSUM) analysis was used to assess shifts in the performance of the rAAA program over time.

RESULTS

Significant confounders were SBP, absence of SBP, and GFR. Logistic regression found evidence of lower mortality after the protocol was introduced, 17.9% vs 30.0% (odds ratio [OR], 0.385; 95% confidence interval [CI], 0.141 to 0.981; P = .046). Comparison of all open repairs (preprotocol and postprotocol) and EVAR demonstrated decreased risk for EVAR of 5.0% vs 28.3% (OR, 0.109; 95% CI, 0.013 to 0.906; P = .0084). Unstable patients (SBP <or=80) showed a trend towards improved survival with EVAR relative to open repair (14.3% vs 56.0%, P = .061). Comparison of preprotocol surgery with open repair after the introduction of the protocol found no evidence of a difference between mortality rates for the open procedures-30.0% (preprotocol) vs 25.0% (postprotocol; OR, 0.688; 95% CI, 0.335 to 1.415, P = .3031)-demonstrating that the improved performance observed with CUSUM analysis was related to the introduction of the EVAR protocol.

CONCLUSION

Our predictive model using "weighted" CUSUM analysis (a measure of performance over time) demonstrated that a predefined strategy of management of rAAA that includes EVAR is associated with improved (P < .05) mortality. Unstable patients with rAAA may be particularly benefited by EVAR and should not be excluded from repair. Appropriate patients with rAAA who are undergoing treatment in experienced vascular centers should be offered EVAR as the treatment of choice.

Endovascular repair versus open surgery in patients with ruptured abdominal aortic aneurysms: clinical outcomes with 1-year follow-up

OBJECTIVE

To compare the clinical outcomes of treatment after endovascular repair and open surgery in patients with ruptured infrarenal abdominal aortic aneurysms (AAAs), including 1-year follow-up.

METHODS

All consecutive conscious patients with ruptured infrarenal AAAs who presented to our tertiary care teaching hospital between January 1, 2001, and December 31, 2005, were included in this study (n = 55). Twenty-six patients underwent endovascular repair, and 29 patients underwent open surgery. Patients who were hemodynamically too unstable to undergo a computed tomography angiography scan were excluded. Outcomes evaluated were intraoperative mortality, 30-day mortality, systemic complications, complications necessitating surgical intervention, and mortality and complications during 1-year follow-up. The statistical tests we used were the Student t test, chi2 test, Fisher exact test, and Mann-Whitney U test (two sided; alpha = .05).

RESULTS

Thirty-day mortality was 8 (31%) of 26 patients who underwent endovascular repair and 9 (31%) of 29 patients who underwent open surgery (P = .98). Systemic complications and complications necessitating surgical intervention during the initial hospital stay were similar in both treatment groups (8/26 [31%] and 5/26 [19%] for endovascular repair, respectively, and 9/29 [31%] and 8/29 [28%] for open surgery, respectively; P > .40). During 1-year follow-up, two patients initially treated with endovascular repair died as a result of non-aneurysm-related causes; no death occurred in the open surgery group. Complications during 1-year follow-up were 1 (5%) of 20 for endovascular repair and 4 (16%) of 25 for open surgery (P = .36).

CONCLUSIONS

On the basis of our study with a highly selected population, the mortality and complication rates after endovascular repair may be similar compared with those after open surgery in patients treated for ruptured infrarenal AAAs.

Effects of ethanol on limited resuscitation in a model of traumatic brain injury and hemorrhagic shock

Object

Limited resuscitation following uncontrolled hemorrhagic shock (HS) has been associated with improved outcomes in various animal models, although it has not been previously studied in the setting of traumatic brain injury (TBI) and ethanol intoxication. The aim of the present study was to determine the effects of ethanol intoxication in a model of experimental TBI and HS treated with limited resuscitation.

Methods

After induction of anesthesia and the placement of instruments, swine were subjected to a fluid-percussion injury of 3 atm. Simultaneously, hemorrhage was induced from an arterial catheter via a computerized roller pump to a mean arterial blood pressure (MABP) of 50 mm Hg, at which time uncontrolled hemorrhage was induced by the creation of an aortic tear. When the MABP decreased to 30 mm Hg, limited resuscitation to a MABP of 60 mm Hg was begun. After 60 minutes, animals were aggressively resuscitated to baseline MABP levels. Two groups of animals were studied: those receiving tap water by gastrostomy tube and those receiving ethanol (4 g/kg) by gastrostomy tube. Animals were monitored for 180 minutes after TBI. Hemorrhage volumes were significantly greater in ethanol-infused animals (mean ± standard deviation, 41 ± 34 mm Hg) compared with tap water–infused animals (17 ± 18 mm Hg; p = 0.048). Resuscitation requirements were significantly higher and metabolic parameters significantly worse in the ethanol group. Survival time was also significantly decreased in the animals infused with ethanol (81 ± 60 minutes) compared with those infused with tap water (130 ± 51 minutes; p = 0.035).

Conclusions

Ethanol intoxication led to increased hemorrhage volume and worsened hemodynamic and metabolic profiles in this model of limited resuscitation after TBI and HS. Ethanol-exposed animals had increased resuscitation requirements and decreased survival times.

Patency of distal false lumen in acute dissection: extent of resection and prognosis

We assessed the hypotheses that extension of aortic replacement would reduce the patency of the false lumen of the descending aorta and that postoperative patency of the false lumen would result in poor prognosis. One hundred and twenty-four consecutive patients underwent surgical repair for acute type A acute dissection on an emergency basis. Among the 124 patients, 89 patients had De Bakey type I dissection. Among the patients with De Bakey type I dissection, the false lumen of the descending aorta was preoperatively patent in 52 patients. Distal extent of aortic replacement was ascending aorta in 16 patients, hemiarch in 15 patients, partial arch in seven patients, and total arch in 11 patients. Patency of the false lumen was not influenced by distal extent of the aortic replacement. In a one-year follow-up, the maximum diameter of the descending aorta with patent false lumen had increased significantly than that with closed false lumen. Survival rates were 96% at one year and 67% at five years in the patients with patent false lumen and no mortality in the patients with closed false lumen. Patency of the false lumen was not influenced by extension of aortic replacement and associated with poor prognosis.

A single-center experience in open and endovascular treatment of hemodynamically unstable and stable patients with ruptured abdominal aortic aneurysms

OBJECTIVE

To retrospectively compare a single center's immediate and mid-term outcomes of ruptured abdominal aortic aneurysm open and endovascular repair (EVAR) for two patient groups-hemodynamically stable and unstable patients-in the same time period.

METHODS

Patients presenting at our center with confirmed rupture of an abdominal aortic aneurysm between December 1999 and April 2006 were considered according to an intention-to-treat model with EVAR. Patients with symptomatic or acute (but not ruptured) AAAs were not included in this study. Thirty-three patients underwent EVAR, and 91 underwent open repair. Seventy-two patients (EVAR, 45%; open, 63%) were classified as hemodynamically unstable at arrival, and 52 were classified as stable (EVAR, 55%; open, 37%). Ninety-seven percent of EVAR procedures commenced under local anesthesia, and 100% of open repairs occurred with general anesthesia. Overall successful graft deployment, 30-day mortality, overall reintervention rate, and complications were the study primary end points.

RESULTS

Overall successful graft deployment for EVAR was 91%; for open repair, it was 96%. Overall 30-day mortality for EVAR was 30% (unstable, 53%; stable, 11%), and the rate was 46% for open repair (unstable, 61%; stable, 21%). The EVAR postoperative reintervention rate (within 30 days) was 15% (unstable, 20%; stable, 11%), and for open repair it was 10% (unstable, 9%; stable, 15%). We recorded a 27% severe complication rate for EVAR patients (unstable, 40%; stable, 17%), and for patients treated with open repair, it was 33% (unstable, 35%; stable, 29%). Our overall EVAR eligibility rate was 52%, and our overall EVAR treatment rate was 27%.

CONCLUSIONS

Our study's overall results for EVAR remain encouraging when compared with those of conventional repair, but large randomized trials are required to confirm the efficacy of the procedure.

Study of potential mechanisms of traumatic rupture of the aorta using insitu experiments

Traumatic rupture of the aorta (TRA) is an important transportation-related injury. This study investigated TRA mechanisms using in situ human cadaver experiments. Four quasi-static tests and one dynamic test were performed. The quasi-static experiments were conducted by perturbing the mediastinal structures of the cadavers. The mechanisms investigated included anterior, superior, and lateral displacement of the heart and aortic arch. The resulting injuries ranged from partial tears to complete transections. All injuries occurred within the peri-isthmic region. Intimal tears were associated with the primary injuries. The average failure load and stretch were 148 N and 30 percent for the quasi-static tests. This study illustrates that TRA can result from appropriate application of nominal levels of longitudinal load and tension. The results demonstrate that intraluminal pressure and whole-body acceleration are not required for TRA to occur. The results suggest that the role of the ligamentum arteriosum is likely limited, and that TRA can occur in the absence of pulmonary artery injury. Tethering of the descending thoracic aorta by the parietal pleura is a principal aspect of this injury.

An Experimental Cadaveric Study for a Better Understanding of Blunt Traumatic Aortic Rupture

BACKGROUND

Blunt traumatic aortic rupture (BTAR) is a common catastrophic injury leading to death. Considerable uncertainty remains regarding the pathogenic cause. This study examines the comportment of the heart and the aorta during a frontal deceleration.

METHODS

Accelerometers were placed in the right ventricle of the heart, the aorta, the sternum, and the spine of six trunks removed from human cadavers. Different vertical decelerations were applied to cadavers and the relative motion of these organs was studied (19 tests).

RESULTS

The deceleration recorded in the isthmus of the aorta was always higher that the one recorded in the heart (p < 0.05). The difference of deceleration was 17% and increased with the speed's fall (extremes 5-25%). There was no significant difference of deceleration between the bony structures of the thorax. These results experimentally demonstrate for the first time that the fundamental mechanism of BTAR is sudden stretching of the isthmus of the aorta.

CONCLUSION

Four mechanisms are suspected to explain the location of the rupture: two hemodynamic mechanism (sudden increase of intravascular pressure and the water-hammer effect), and two physical mechanisms (sudden stretching of the isthmus and the osseous pinch). A greater understanding of the mechanism of this injury could improve vehicle safety leading to a reduction in its incidence and severity. Future work in this area should include the creation of an inclusive, dynamic model of computer-based modeling systems. This study provides for the first time physical demonstration and quantification of the stretching of the isthmus, leading to a computerized model of BTAR.

Computer simulation and validation of the Archimedes Lever hypothesis as a mechanism for aortic isthmus disruption in a case of lateral impact motor vehicle crash: a Crash Injury Research Engineering Network (CIREN) study

OBJECTIVES

Can aortic isthmus disruption occurring in a lateral motor vehicle crash (LMVC) be explained by the Archimedes Lever Hypothesis, where the intrathoracic aorta, super-pressurized by the thoracic impact force, functions as a rigid lever system? The long arm of this lever system is the proximal aorta-aortic arch, the short arm is the aortic isthmus fixed distally at the descending aorta, and the fulcrum is at the great vessels, especially the left subclavian artery.

METHODS

The theory was tested by a simulation technique using a computer-based finite element numerical model system. This simulation model included the dynamics of the crashed vehicles, the direction of force impact, and the structure of the thorax and intrathoracic viscera, including the entire intrathoracic aorta. The specific patient whose data were entered into the model was chosen from a study of 34 LMCV aortic injuries (AIs). The model was constrained by patient and vehicle data from this surviving case.

RESULTS

Three sequential lateral thoracic levels impacted by the vehicle side structures were selected. At each level, the maximum mean intra-aortic pressure was 50 to 100 ms after impact, the structure dynamics of the actual crash and the resultant vehicle deformation were simulated; only when the lateral impact was induced in a transverse plane including the first 4 ribs at the level of the aortic arch/isthmus system, with intra-aortic pressures from 200 to 500 mm Hg, were AI-compatible stresses and deformations in the aortic wall achieved at the isthmus.

CONCLUSIONS

In LMVC AI, the simulation suggests that the aorta functions as an Archimedes Lever System in which the magnified force mediated by the long lever arm produces sufficient strain on the short lever arm to rupture the aorta at the isthmus.

Flow Dynamics in Expansions Characterizing Abdominal Aorta Aneurysms

Our purpose was to identify and quantify hemodynamic factors contributing to the generation, proliferation, and rupturing of abdominal aorta aneurysms (AAAs) using a computational investigation of steady laminar and turbulent flow in AAA models. Steady laminar and turbulent flows were computed using the incompressible Navier-Stokes equations. Flow fields in symmetric shapes of different extents and degrees of expansion are presented first. Two representative cases of asymmetric AAAs are considered next: an aneurysm with an elliptic cross section and an aneurysm with preferential expansion in one direction. For symmetric aneurysms, parametric studies are presented. For asymmetric aneurysms, flow fields are computed only for high flow rates representative of systolic flow. For all cases, a recirculating flow region was found in the expanded part of the AAA. Recirculation is accompanied by a minor increase in pressure but a significant increase in wall shear stress. For cases where turbulent flow was considered, it was found that the recirculation zone diminishes but the computed wall shear stress reaches levels higher than laminar flow. The levels of wall shear stress reached in turbulent flow may cause lesions of the aneurysmal wall. The minor variation of pressure within the aneurysms with smooth expansions indicates that the structural properties of the arterial wall tissue may play a significant role for the generation and subsequent proliferation of the aneurysm. However, the high values of the wall shear stress in AAAs appear to be an important hemodynamic factor that may contribute to wall degeneration and eventual rupturing. The recirculating flow in AAAs may explain the generation of intraluminal thrombi. Furthermore, the asymmetry and complexity of the flow in asymmetric AAAs may explain the frequently observed asymmetric thrombi distribution.

Biomechanical properties of ruptured versus electively repaired abdominal aortic aneurysm wall tissue

OBJECTIVE

The purpose of this study was to evaluate and compare the biomechanical properties of abdominal aortic aneurysm (AAA) wall tissue from patients who experienced AAA rupture with that of those who received elective repair.

METHODS

Rectangular, circumferentially oriented AAA wall specimens (approximately 2.5 cm x 7 mm) were obtained fresh from the operating room from patients undergoing surgical repair. The width and thickness were measured for each specimen by using a laser micrometer before testing to failure with a uniaxial tensile testing system. The force and deformation applied to each specimen were measured continuously during testing, and the data were converted to stress and stretch ratio. The tensile strength was taken as the peak stress obtained before specimen failure, and the distensibility was taken as the stretch ratio at failure. The maximum tangential modulus and average modulus were also computed according to the peak and average slope of the stress-stretch ratio curve.

RESULTS

Twenty-six specimens were obtained from 16 patients (aged 73 +/- 3 years [mean +/- SEM]) undergoing elective repair of their AAA (diameter, 7.0 +/- 0.5 cm). Thirteen specimens were resected from nine patients (aged 73 +/- 3 years; P = not significant in comparison to the electively repaired AAAs) during repair of their ruptured AAA (diameter, 7.8 +/- 0.6 cm; P = not significant). A significant difference was noted in wall thickness between ruptured and elective AAAs: 3.6 +/- 0.3 mm vs 2.5 +/- 0.1 mm, respectively (P < .001). The tensile strength of the ruptured tissue was found to be lower than that for the electively repaired tissue (54 +/- 6 N/cm2 vs 82 +/- 9.0 N/cm2; P = .04). Considering all specimens, no significant correlation was noted between tensile strength and diameter (R = -0.10; P = .55). Tensile strength, however, had a significant negative correlation with wall thickness (R = -0.42; P < .05) and a significant positive correlation with the tissue maximum tangential modulus (R = 0.76; P < .05).

CONCLUSIONS

Our data suggest that AAA rupture is associated with aortic wall weakening, but not with wall stiffening. A widely accepted indicator for risk of aneurysm rupture is the maximum transverse diameter. Our results suggest that AAA wall strength, in large aneurysms, is not related to the maximum transverse diameter. Rather, wall thickness or stiffness may be a better predictor of rupture for large AAAs.

Spinal fluid dynamics during thoracic- and thoracoabdominal aortic surgery

AIM

The intention was to investigate cerebrospinal fluid pressure (CSFP) and volume of cerebrospinal fluid (CSF) drained during and after thoracic- and thoracoabdominal aneurysm repair. The findings were related to the occurrence of postoperative neurologic deficits.

METHODS

Twenty-nine patients (12 with thoracic and 17 with thoracoabdominal aortic aneurysm) were operated without shunting or extracorporeal circulation. For monitoring of CSFP an intrathecal catheter was placed in all patients. The volume of CSF withdrawn intraoperatively, on the day of operation as well as on the 1st and 2nd postoperative day was recorded.

RESULTS

Twenty-six patients had no postoperative neurologic sequelae. One patient had postoperative paraplegia while 2 had paraparesis. The three patients with neurologic sequelae had higher CSFP intraoperatively than those without neurologic symptoms (P=0.04). Median CSFP during aortic cross-clamping was 19 mmHg and 10 mmHg and the median volumes of CSF drained on the day of operation 210 and 85 mL in the two groups, respectively. There was a significant positive correlation between CSFP and central venous pressure.

CONCLUSIONS

A higher intraoperative CSFP was observed in patients with neurologic sequelae following thoracic- and thoracoabdominal aneurysm repair. Further, there was a tendency of higher volumes of CSF drained in this group of patients. Although, the series is too small to allow firm conclusions, it supports the view that CSFP monitoring and drainage is beneficial during thoracic- and thoracoabdominal aneurysm repair.

Introduction to biomechanics related to endovascular repair of abdominal aortic aneurysm

Biomechanical issues of practical relevance to the physician in the clinical management of patients undergoing endovascular repair (EVR) of their abdominal aortic aneurysms (AAA) is discussed. Following a brief description of key terms in vascular biomechanics, background on the current state of knowledge in the biomechanics of AAA pathogenesis and rupture is provided. This is followed by a discussion of key issues of biomechanical relevance in EVR such as the mechanics of endotension, the notion of intraaneurysmal sac pressure and potential pitfalls of techniques used to measure them, mechanics of graft fracture/kinking, and graft migration. The discussions are intended to provide an overview of this field to physicians.

Strain estimation in abdominal aortic aneurysms from 2-D ultrasound

The rupture risk of abdominal aortic aneurysms (AAAs) is routinely inferred from the maximum diameter of the AAA. However, clinical experience indicates that this criterion has poor accuracy and that noninvasive assessment of the elastic properties of the vessel might give better correspondence with the rupture risk. We have developed a method for analysis of circumferential strain in AAAs from sequences of cross-sectional ultrasound B-mode images. The algorithm is fast, semiautomatic and well-suited for real-time applications. The method was developed and evaluated using data from 10 AAA patients. The preliminary results demonstrate that the method is sufficiently accurate and robust for clinically acquired data. An important finding is that local strain values may exceed the circumferential average strain significantly. Furthermore, the calculated strain shows no apparent covariation with the diagnosed diameter. This implies that the method may give new and essential information on the clinical condition of the AAA.

Biomechanical determinants of abdominal aortic aneurysm rupture

Rupture of abdominal aortic aneurysm (AAA) represents a significant clinical event, having a mortality rate of 90% and being currently ranked as the 13th leading cause of death in the US. The ability to reliably evaluate the susceptibility of a particular AAA to rupture on a case-specific basis could vastly improve the clinical management of these patients. Because AAA rupture represents a mechanical failure of the degenerated aortic wall, biomechanical considerations are important to understand this process and to improve our predictions of its occurrence. Presented here is an overview of research to date related to the biomechanics of AAA rupture. This includes a summary of results related to ex vivo and in vivo mechanical testing, noninvasive AAA wall stress estimations, and potential mechanisms of AAA wall weakening. We conclude with a demonstration of a biomechanics-based approach to predicting AAA rupture on a patient-specific basis, which may ultimately prove to be superior to the widely and currently used maximum diameter criterion.

Regional distribution of wall thickness and failure properties of human abdominal aortic aneurysm

The regional distribution of wall thickness and failure properties in human abdominal aortic aneurysm (AAA) was explored. Three unruptured and one ruptured AAA were harvested as a whole during necropsy. Thickness was measured at about every 1.5 cm(2) wall surface area for an average of 100 measurement sites per AAA. Multiple longitudinally oriented rectangular specimen strips were cut at various locations from each AAA for a total of 48 strips. The strips were subjected to uniaxial extension until failure. Wall thickness varied regionally and between AAA from as low as 0.23 mm at a rupture site to 4.26 mm at a calcified site (median=1.48 mm). Wall thickness was slightly lower in the posterior and right regions. The failure tension (ultimate) of specimen strips varied regionally and between AAA from 5.5 N/cm close to a blister site in the ruptured AAA to 42.3N/cm at the undilated neck of a 4 cm diameter unruptured AAA (median=14.8 N/cm). Failure stress (ultimate) varied from 33.6 to 235.1N/cm(2) (median=126.6N/cm(2)). There was no perceptible pattern in failure properties along the circumference. Failure tension of specimen strips at or close to blisters was mostly low. The rupture site in the ruptured aneurysm had the lowest recorded wall thickness of 0.23 mm with only slightly higher readings within a 1cm radius. The failure tension of the specimen strip close to the rupture site was low (11.1 N/cm) compared to its neighborhood in the ruptured aneurysm.

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.

Fluid-structure interaction effects on sac-blood pressure and wall stress in a stented aneurysm

An aneurysm is a local artery ballooning greater than 50% of its nominal diameter with a risk of sudden rupture. Minimally invasive repair can be achieved by inserting surgically a stent-graft, called an endovascular graft (EVG), which is either straight tubular curved tubular or bifurcating. However post-procedural complications may arise because of elevated stagnant blood pressure in the cavity, i.e., the sac formed by the EVG and the weakened aneurysm wall In order to investigate the underlying mechanisms leading to elevated sac-pressures and hence to potentially dangerous wall stress levels and aneurysm rupture, a transient 3-D stented abdominal aortic aneurysm model and a coupled fluid-structure interaction solver were employed. Simulation results indicate that, even without the presence of endoleaks (blood flowing into the cavity), elevated sac pressure can occur due to complex fluid-structure interactions between the luminal blood flow, EVG wall, intra-sac stagnant blood, including an intra-luminal thrombus, and the aneurysm wall. Nevertheless, the impact of sac-blood volume changes due to leakage on the sac pressure and aneurysm wall stress was analyzed as well. While blood flow conditions, EVG and aneurysm geometries as well as wall mechanical properties play important roles in both sac pressure and wall stress generation, it is always the maximum wall stress that is one of the most critical parameters in aneurysm rupture prediction. All simulation results are in agreement with experimental data and clinical observations.

Endovascular repair of the descending thoracic aorta: evidence for the change in clinical practice

The purpose was to review outcome data following endovascular repair of the descending thoracic aorta from reports published between 1994 and 2004. To accomplish this task, 1,518 patients underwent endovascular repair for thoracic aortic disease; 810 thoracic aortic aneurysms, 500 type B thoracic aortic dissections, and 106 traumatic ruptures. The 30-day mortality rate was 5.5% and 6% for late postoperative deaths. The primary technical success rate was 97%, with only 15 patients requiring open conversion. Neurologic deficits occurred in 29 patients. In total, 118 endoleaks were reported; 29 were restented, and the remainder required surgical intervention. Graft infection occurred in 6 cases, and migrations were detected in 10. The conclusion reached is that endovascular repair of descending thoracic aortic disease is feasible and can be achieved with low rates of perioperative morbidity and mortality. As few long-term data exist on the durability of thoracic stent grafts, lifelong surveillance remains necessary.

Serum lactate and base deficit as predictors of mortality after ruptured abdominal aortic aneurysm repair

OBJECTIVE

Whole body hypoperfusion and lower torso ischaemia-reperfusion contribute to post-operative organ dysfunction in patients undergoing repair of ruptured abdominal aortic aneurysm (AAA). Serum lactate and base deficit are markers of tissue ischaemia and are used to assess the adequacy of resuscitation. This study examines the prognostic value of immediate post-operative levels of serum lactate and base deficit in ruptured AAA.

METHODS

Thirty patients (24 men and 6 women of median age 74, range 51-85, years) who survived to at least 12h after ruptured AAA repair were studied retrospectively. The relationship between immediate post-operative lactate, base deficit and mortality was determined.

RESULTS

Fifteen patients (50%) died, all from organ failure. An elevated lactate (>2.1 mmol/l) and base deficit (<-2 mmol/l) were present in 20 (67%) and 27 (90%) patients, respectively. Lactate (p<0.001) and base deficit (p=0.003) were significantly higher in non-survivors compared with survivors. Lactate (p=0.021) and base deficit levels (p=0.028) were independently significant for predicting mortality and a significant interaction existed between lactate and base deficit levels for predicting mortality (p=0.027). The sensitivity and specificity of lactate > or =4.0 mmol/l was 13 of 15 (87%) and 12 of 15 (80%), respectively, and base deficit < or =-7 mmol/l was 12 of 15 (80%) and 12 of 15 (80%), respectively. The likelihood ratios for a positive result with the defined cut-off values for lactate and base deficit were 4.3 and 4.0, respectively. Lactate > or =4.0 mmol/l and base deficit <or =-7 mmol/l were associated with a 94.5% probability of death while lactate < or =4.0 mmol/l and base deficit > or =-7 mmol/l were associated with a 4% probability of death.

CONCLUSION

These data demonstrate that an immediate post-operative serum lactate > or =4.0 mmol/l and base deficit < or =-7 mmol/l are good predictors of outcome after ruptured AAA repair. The prognostic value of these simple and inexpensive tests require corroboration in a larger prospective study.

A Review of Biological Factors Implicated in Abdominal Aortic Aneurysm Rupture

Abdominal aortic aneurysm (AAA) rupture is the 13th commonest cause of death in the Western World. Although considerable research has been applied to the aetiology and mechanism of aneurysm expansion, little is known about the mechanism of rupture. Aneurysm rupture was historically considered to be a simple physical process that occurred when the aortic wall could no longer contain the haemodynamic stress of the circulation. However, AAAs do not conform to the law of Laplace and there is growing evidence that aneurysm rupture involves a complex series of biological changes in the aortic wall. This paper reviews the available data on patient variables associated with aneurysm rupture and presents the evidence implicating biological factors in AAA rupture.

A new wall stress equation for aneurysm-rupture prediction

Aneurysms, especially in the abdominal aorta (AAA), are prone to rupture, and hence a reliable and easy-to-use predictor is most desirable. Based on clinical observations and numerical analyses, a semi-empirical equation for the peak AAA-wall stress has been developed. It can be readily used for AAA-rupture predictions or can be integrated into more elaborate AAA-assessment models.

Functional outcome after open repair of ruptured abdominal aortic aneurysm

BACKGROUND

Outcome after operative repair of ruptured abdominal aortic aneurysm (AAA) has traditionally been assessed in terms of survival. This study examines the functional outcome of patients who survive operation.

METHODS

Consecutive patients who survived open repair over an 18-month period were entered into a prospective case-control study. Age- and sex-matched controls were identified from patients undergoing elective AAA repair. The Short Form-36 health survey was administered to both groups of patients at 6 months after operation. Results were compared with the expected scores for an age- and sex-matched normal UK population.

RESULTS

Fifty-seven patients underwent open repair of a ruptured AAA, and 30 survived; no patient was lost to follow-up. There were no significant differences in quality of life between patients who had an emergency repair and those who had an elective repair. Both of these groups had poorer health-related quality of life outcomes than the matched normal population. Surprisingly, compared with the normal population, patients after elective repair had poorer outcomes in more health domains than patients who survived emergency operation.

CONCLUSIONS

Survivors of ruptured AAA repair have a good functional outcome within 6 months of operation.

Factors promoting rupture of abdominal aortic aneurysms

The risk for rupture of an abdominal aortic aneurysm is widely believed to be related to its maximum diameter. Rupture occurs at the site of maximum wall stress, when it exceeds the tensile strength of the aortic wall. Basic research confirmed that peak wall stress and aortic wall biodegradation contribute to the mechanism of aneurysm rupture. In order to highlight the role of loss in wall strength and increase in focal peak stress, the authors reviewed recent literature. The clinical relevance of these recent insights in the etiopathogenesis of aneurysm rupture is analysed.

Selective inducible nitric oxide synthase (iNOS) inhibition attenuates remote acute lung injury in a model of ruptured abdominal aortic aneurysm

OBJECTIVE

Abdominal aortic aneurysm rupture is associated with a systemic inflammatory response syndrome and acute lung injury. Using a selective inducible nitric oxide synthase (iNOS) inhibitor, N(6)-(iminoethyl)-lysine (L-NIL), we explored the role of iNOS in the early pro-inflammatory signaling and acute lung injury in experimental abdominal aortic aneurysm rupture.

MATERIALS AND METHODS

Anesthetized rats were randomized to sham control or shock and clamp (s + c) groups, which underwent one hour of hemorrhagic shock, followed by 45 minutes of supramesenteric aortic clamping, and then two hours resuscitated reperfusion. Animals in s + c were randomized to receive intravenous L-NIL at 50 microg/kg/h or saline at the start of reperfusion. Pulmonary permeability to (125)I-labeled albumin, myeloperoxidase (MPO) activity, cytokine levels, and semi-quantitative RT-PCR for mRNA were indicators of microvascular permeability, leuco-sequestration, and pro-inflammatory signaling, respectively.

RESULTS

Lung permeability index were significantly increased in s + c compared to sham (4.43 +/- 0.96 versus 1.30 +/- 0.17, P < 0.01), and attenuated by L-NIL treatment (2.14 +/- 0.70, P < 0.05). Lung tissue MPO activity was significantly increased in s + c compared to sham (2.80 +/- 0.32 versus 1.03 +/- 0.29, P < 0.002), and attenuated by L-NIL treatment (1.50 +/- 0.20, P < 0.007). Lung tissue iNOS activity was significantly increased in s + c compared to sham animals (P < 0.05), and attenuated by L-NIL treatment (P < 0.05). Lung tissue iNOS mRNA was upregulated 8-fold in s + c compared to sham (P < 0.05). Data represents mean +/- standard error mean, comparisons with ANOVA.

CONCLUSIONS

These data suggest that in our model of ruptured abdominal aortic aneurysm iNOS plays a crucial role in reperfusion lung injury. Selective inhibition of iNOS during early reperfusion prevents neutrophil mediated acute lung injury.

Chronobiology of rupture and dissection of aortic aneurysms

A growing body of evidence suggests that the occurrence of cardiovascular events is not evenly distributed over time, but shows peculiar temporal patterns that vary with time of day, day of the week, and month (season) of the year. These patterns coincide with the temporal variation in the pathophysiologic mechanisms that trigger cardiovascular events and the physiologic changes in body rhythms. These two factors in combination contribute to the periodicity in susceptibility to acute cardiovascular events. The classic assumption of epidemiologic studies that there is a constancy in risk for disease during the various time domains has now been challenged by the emerging new concept of chronorisk. In the last two decades temporal patterns (circadian, weekly, seasonal) have been identified for several acute cardiovascular diseases, such as acute myocardial infarction, sudden death, pulmonary embolism, and stroke, with peak incidence for most in the morning and during winter. One of the most life-threatening cardiovascular emergencies, aortic aneurysm rupture or dissection, also demonstrates periodicity, characterized by a similar temporal distribution, which suggests a common pathophysiologic mechanism or triggers similar to other cardiovascular acute emergencies. We review the data on chronobiology of acute aortic rupture or dissection, and discuss various pathophysiologic mechanisms that account for this variability. It is likely that identification of consistent recurring patterns in the underlying risk mechanisms could provide potential new insights for more precise diagnosis and efficacious therapeutic intervention.

Endovascular treatment of abdominal aortic aneurysm

BACKGROUND

Endovascular repair of abdominal aortic aneurysm has become widely used. Supporters claim high success rates, few complications and a dramatically reduced hospital stay. However, endoleak, endotension and reports of endoprosthesis rupture are causes of concern.

METHODS

A Medline search was undertaken to identify articles on endovascular repair of abdominal aortic aneurysm. Additional papers were identified by manual scanning of the references from key articles.

RESULTS AND CONCLUSION

Endoleak is a potentially serious complication of the endovascular technique and occurs in a significant proportion of patients. It is still not possible to judge whether the presence of an endoleak alone signifies failure of treatment, and the long-term durability of prosthetic covered stents is unknown. However, endovascular repair does appear to confer a degree of protection from rupture although patients must be advised of the need for life-long imaging surveillance and, perhaps, further intervention.

The utility of commercially available endografts in the treatment of contained ruptured abdominal aortic aneurysm with hemodynamic stability

PURPOSE

Food and Drug Administration-approved endografts are suitable for the elective repair of abdominal aortic aneurysms (AAAs) with favorable aneurysm anatomy. Our aim is to illustrate the feasibility and versatility of commercially available endografts for emergency AAA repair in hemodynamically stable AAA rupture.

METHODS

From June 2001 to July 2002, five patients presented with severe abdominal pain and were diagnosed with contained rupture of an infrarenal AAA. In all cases, patients were deemed unfit to withstand conventional open repair by both the referring outside medical center as well as our center's team. All patients were hemodynamically stable on arrival at our medical center. Measurement and selection of endovascular devices were based on computed tomography (CT) scans performed emergently at the outside referring center. The required emergently procured endografts were obtained within 2 to 4.5 hours (mean, 3.1 hours) of presentation. Complex anatomy at the proximal and distal fixation zones or difficult access was present in every case.

RESULTS

All patients survived endograft repair and had successful exclusion of their aneurysm sac on the basis of intraoperative arteriography and postoperative CT surveillance. All were discharged to home at baseline function within a mean of 6.8 days (range, 2-13 days). There were no deaths. There was one postoperative pulmonary embolism, one myocardial infarct, and one type 2 endoleak. Mean operative time and blood loss were 4.67 hours and 217 mL, respectively. At a mean follow-up of 18 months, CT scans showed stable or shrinking aneurysm sacs.

CONCLUSIONS

In patients with contained ruptured AAAs who present with hemodynamic stability and comorbidities that preclude open surgery, commercially available endografts are a versatile treatment option even in the face of complicated aneurysm anatomy.

A finite element model of blunt traumatic aortic rupture1

OBJECTIVE

Blunt traumatic aortic rupture has a scene survival of 2-5% and is present in 20% of all automobile fatalities. The manner in which the forces from a range of thoracic impacts are transduced through the thoracic cavity to produce consistent injury to the aortic isthmus remains uncertain. Our objective was to create and evaluate a computer based finite element (FE) model of the aorta and observe its behavior during blunt traumatic impacts.

METHODS

A finite element model of the thorax including details of the heart, aorta and pertinent thoracic structures was created and run under the FE code LS-DYNA3D. The motion response of the heart following a simulated thoracic impact was extracted from the thorax model and applied in a second more detailed model of the heart and aorta in order to investigate the stresses acting through the aortic isthmus during simulated thoracic impacts.

RESULTS

Simulated impact studies show that the predicted peak chest compression of the thorax model matched the measured responses from non-embalmed human cadaver impact studies by Kroell et al., 1974. The more detailed heart-aorta model predicted maximum stresses at the isthmus and pulmonary artery bifurcation the sites of most common trauma injury.

CONCLUSIONS

Analysis of the response of the finite element heart-aorta model during blunt thoracic trauma demonstrates its potential for predicting major vessel injury. The model will be helpful in the design of impact protection systems.

Predicting aneurysm enlargement in patients with persistent type II endoleaks

OBJECTIVE

The clinical significance of type II endoleaks is not well understood. Some evidence, however, indicates that some type II endoleaks might result in aneurysm enlargement and rupture. To identify factors that might contribute to aneurysm expansion, we analyzed the influence of several variables on aneurysm growth in patients with persistent type II endoleaks after endovascular aortic aneurysm repair (EVAR).

METHODS

In a series of 348 EVARs performed during a 10-year period, 32 patients (9.2%) developed type II endoleaks that persisted for more than 6 months. Variables analyzed included those defined by the reporting standards for EVAR (SVS/AAVS) as well as other endoleak characteristics. Univariate, receiver operating characteristic curve, and Cox regression analyses were used to determine the association between variables and aneurysm enlargement.

RESULTS

The median follow-up period was 26.5 months (range, 6-88 months). Thirteen patients (41%) had aneurysm enlargement by 5 mm or more (median increase in diameter, 10 mm), whereas 19 (59%) had stable or shrinking aneurysm diameter. Univariate and Cox regression analyses identified the maximum diameter of the endoleak cavity, ie, the size of the nidus as defined on contrast computed tomography scan, as a significant predictor for aneurysm enlargement (relative risk, 1.12; 95% confidence interval, 1.04-1.19; P =.001). The median size of the nidus was 23 mm (range, 13-40 mm) in patients with aneurysm enlargement and 8 mm (range, 5-25 mm) in those without expansion (Mann-Whitney U test, P <.001). Moreover, receiver operating characteristic curve and Cox regression analyses showed that a maximum nidus diameter greater than 15 mm was particularly associated with an increased risk of aneurysm enlargement (relative risk, 11.1; 95% confidence interval, 1.4-85.8; P =.02). Other risk factors including gender, smoking history, hypertension, need of anticoagulation, aneurysm diameter, type of endograft used, and number or type of collateral vessels were not significant predictors of aneurysm enlargement.

CONCLUSIONS

In patients with persistent type II endoleaks after EVAR, the maximum diameter of the endoleak cavity or nidus is an important predictor of aneurysm growth and might indicate the need for more aggressive surveillance as well as earlier treatment.

Complement C5a receptor antagonist attenuates multiple organ injury in a model of ruptured abdominal aortic aneurysm

OBJECTIVE

Abdominal aortic aneurysm (AAA) rupture is associated with a systemic inflammatory response syndrome, characterized by increased microvascular permeability and neutrophil sequestration, leading to multiorgan dysfunction. We examined the role of a novel complement factor 5a (C5aR) receptor antagonist, the cyclic peptide AcF-(OpdChaWR), in attenuation of pathologic complement activation and tissue injury in a model of AAA rupture.

METHODS

Anesthetized rats were randomized to sham (control) or shock and clamp (s+c) groups. Animals in the s+c group underwent 1 hour of hemorrhagic shock (mean arterial blood pressure < or =50 mm Hg), followed by 45 minutes of supramesenteric aortic clamping, then 2 hours of resuscitated reperfusion. Animals in the s+c group were randomized to receive an intravenous bolus of C5aR antagonist at 1 mg/kg or saline solution control at the end of hemorrhagic shock. Intestinal and pulmonary permeability to iodine 125-labeled albumin was measured as an indicator of microvascular permeability. Tissue myeloperoxidase activity, proinflammatory cytokine tissue necrosis factor-alpha (TNF-alpha) protein and mRNA, and C5aR mRNA levels were measured as indicators of neutrophil sequestration and inflammatory signaling, respectively.

RESULTS

Lung permeability index was significantly increased in the s+c group compared with the sham group (4.43 +/- 0.96 vs 1.30 +/- 0.17; P <.01), and prevented with treatment with C5aR antagonist (1.74 +/- 0.50; P <.03). Lung myeloperoxidase activity was significantly increased in the the s+c group compared with the sham group (2.41 +/- 0.34 U/mg vs 1.03 +/- 0.29 U/mg; P <.009), and significantly attenuated with treatment with C5aR antagonist (1.11 +/- 0.09 U/mg; P <.006). Lung TNF-alpha protein levels were significantly elevated in both s+c groups, whereas lung TNF-alpha mRNA expression was significantly downregulated in both s+c groups compared with the sham group. Intestinal permeability index was significantly increased in animals in the s+c groups during reperfusion, compared with sham (P <.001), which was attenuated in early reperfusion with treatment with C5a receptor antagonist. Data represent mean +/- SEM, group comparisons with analysis of variance and post hoc Scheffé test.

CONCLUSIONS

These results indicate that a potent antagonist of C5a receptor protects the rat intestine and lung from neutrophil-associated injury in a model of AAA rupture. These data suggest that complement-mediated inflammation can be modulated at the C5a receptor level, independent of proinflammatory TNF-alpha production, and prevent acute local and remote organ injury.

Aortic regurgitation secondary to back-and-forth intimal flap movement of acute type A dissection

We present an unusual case of acute type A dissection complicated with severe aortic valve insufficiency caused by prolapse of the tubular intimal flap into the left ventricular outflow tract, which was shown legibly by transesophageal echocardiography in the diastolic phase and by intraoperative macroscopic findings. The dissected ascending aorta was excised completely and replaced without any repairing of the aortic valve, resulting in a favorable outcome for the patient. Prolapse of an intimal flap from the aorta into the left ventricle represented a rare pathophysiology of aortic regurgitation in patients with aortic dissection.