Endovascular repair reduces early and late morbidity compared to open surgery for abdominal aortic aneurysm

PURPOSE

To compare systemic complications between standard surgery and endovascular repair of abdominal aortic aneurysms (AAA) for both primary and late secondary procedures.

METHODS

At a single center between July 1993 and May 2000, 297 patients (255 men; mean age 73.4 +/- 8.1 years, range 50-93) were treated with open surgical repair; beginning in 1996, 200 (166 men; mean age 73.6 +/- 8.0 years, range 45-96) patients were treated with the AneuRx stent-graft. In a comparison of the cohorts, which were similar in terms of age, gender, and aneurysm diameter, the main outcomes were early major systemic morbidity following the primary procedure to treat the aneurysm and late (>30 days) organ system morbidity for any secondary procedures.

RESULTS

Mean length of follow-up for open patients was 20.1 +/- 17.1 months (range 1-150) compared to 12.4 +/- 9.6 months (range 1-60) after endovascular repair (p<0.05). There were 36 (12.1%) systemic complications after the primary open surgery and 15 (7.5%) after endovascular repair (p=NS). There were 43 (14.5%) combined primary and secondary morbidities in the open surgery group versus 15 (7.5%) for patients undergoing endovascular repair (p<0.01). The need for invasive procedures to treat these primary and secondary systemic complications was 4 times greater in the open group (17, 5.7%) than in endograft patients (3, 1.5%) (p<0.05). After secondary procedures (32 in the open group and 30 in the endovascular patients) for graft-related complications, there were 7 (21.9%) adverse events in the open group versus none (0%) for endograft patients (p<0.01). Hospital lengths of stay following both primary and secondary procedures were lower for the endograft patients (p<0.01 and p<0.001, respectively).

CONCLUSIONS

Endovascular stent-graft repair compared to open surgery has reduced the early and late morbidity by half. Complications that require invasive or secondary surgical procedures and hospitalization are reduced with endovascular repair.

Diurnal heart rate reactivity: a predictor of severity of experimental coronary and carotid atherosclerosis

BACKGROUND

Elevated awake resting heart rate (HR) has been shown to be a major risk factor for cardiovascular disease. Since coronary ischaemic events appear to peak during transition from sleep to awake HR, we sought to determine whether the degree of diurnal HR fluctuation (dHRV) is an independent predictor of coronary and peripheral atherogenesis. In this study, we varied both baseline HR and dHRV using sino-atrial node ablation (SNA) in a primate model of diet-induced atherogenesis and determined the degree of plaque formation relative to both HR parameters.

METHODS

HR was recorded continuously for 6 months by an implantable intraaortic sensor/transmitter in 17 active unrestricted male cynomolgus monkeys. In nine monkeys, SNA was employed to create a wide spectrum of dHRV, and the power amplitude of dHRV was determined for the daily HRV cycle with power spectral analysis. After a 6-month diet induction period, percent coronary and carotid stenosis, intimal thickness and area were quantitated in each animal.

RESULTS

Total serum cholesterol and mean HR were no different between high ( n= 10) and low ( n= 7) dHRV groups (866 mg% vs. 740 mg%, P> 0.2 and 130 +/- 22 and 115 +/- 13, P> 0.1, respectively). Percent carotid stenosis was markedly greater in both high HR and dHRV animals ([HR], 54 +/- 19 vs. 35 +/- 10, P< 0.04) and ([dHRV], 54 +/- 17 vs. 32 +/- 10, P< 0.01). Significant increases in all measures of coronary atherogenesis were found in high dHRV animals when compared with those with low dHRV (percent stenosis: 48% +/- 22 vs. 23% +/- 16, P< 0.02), (lesion area: 1.2 +/- 0.8 vs. 0.3 +/- 0.3, P< 0.02), and (intimal thickness: 0.3 +/- 0.1 vs. 0.1 +/- 0.1, P< 0.01), respectively. While there was a trend towards greater coronary atherogenesis in animals with high HR, this did not reach statistical significance.

CONCLUSION

Elevated HR and dHRV are both associated with enhanced experimental atherosclerotic plaque formation. However, a greater degree of carotid and coronary atherogenesis is observed in animals with high dHRV. These findings suggest that elevated dHRV is a stronger predictor for susceptibility to atherogenesis than elevated HR alone. Such a relationship may be attributed to the potential role of dHRV in modulating the frequency of adverse near wall haemodynamic forces, which have been shown to induce atherosclerotic plaques. Lowering of dHRV in humans by exercise or pharmacological agents may have a beneficial role in retarding atherosclerotic plaque induction, progression and complication.

Early and sustained medial cell activation after aortocaval fistula creation in mice

BACKGROUND

The response of endothelial cells to altered flow conditions has been studied extensively. However, the indirect effects of shear stress on medial smooth muscle cells (SMCs) have been less well characterized and a murine model of high shear stress has not been available.

MATERIALS AND METHODS

The hemodynamic changes that occur in a mouse aorta proximal to an aortocaval fistula (ACF) were characterized by measuring blood flow, aortic diameter, and calculating wall shear stress. This model was next used to evaluate cellular activation by assessing beta-galactosidase expression in fos-lacZ transgenic mice. Aortic specimens were examined by a chemiluminescent beta-galactosidase assay, cross-sectional histology, and Hautchen prep en face histology.

RESULTS

Immediately after ACF construction, aortic diameter remained unchanged and wall shear stress increased 2.6-fold (49.57 +/- 5.89 to 134.93 +/- 15.69 dyn/cm(2), P < 0.05). Flow-induced aortic enlargement occurred gradually (0.61 +/- 0.03 to 1.18 +/- 0.05 mm at 21 days, P < 0.5) such that by 21 days after ACF, wall shear stress had returned to baseline (56.97 +/- 8.62 dyn/cm(2), P = ns compared to control). Aortas from fos-lacZ mice demonstrated increased beta-gal activity at 6 h and up to 7 days after ACF (1.81 +/- 0.22 rlu/microg in controls vs 41.41 +/- 16.28 rlu/microg at 6 h and 15.17 +/- 1.1 rlu/microg at 7 days, P < 0.5) On histologic evaluation, there was a significant increase in medial SMC staining that was most prominent in cells near the intima (2 +/- 0.3% positive cells in controls vs 67 +/- 10% at 6 h and 11 +/- 7.6 at 7 days, P < 0.5). Endothelial cells, evaluated by en face methods, did not demonstrate significant amounts of beta-gal positivity at the times studied.

CONCLUSIONS

These in vivo findings using a new high shear stress model suggest that early and sustained activation of medial SMCs is a critical component of flow-induced enlargement. Further evaluation of these events may provide important insights into the mechanisms of pathologic arterial remodeling.

Arterial enlargement in response to high flow requires early expression of matrix metalloproteinases to degrade extracellular matrix

This study investigated the effects of high flow and shear stress on the expression of matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinase-2 (TIMP-2) during flow-induced arterial enlargement using a model of arteriovenous fistula (AVF) creation on the carotid artery with the corresponding jugular vein in Japanese white male rabbits. Flow increased 8-fold 7 days after AVF. Endothelial cells (EC) and smooth muscle cells (SMC) proliferated with internal elastic lamina (IEL) degradation in response to high flow and shear stress. Expression of MMP-2 mRNA peaked at 2 days (1700-fold) and maintained high level expression. MMP-9 mRNA gave a 10.8-fold increase within 2 days and decreased later. Their proteins were detected in EC and SMC. Membrane type-1-MMP (MT1-MMP) mRNA increased 121-fold at 3 days and maintained high expression. TGF-beta1 was increased after AVF. Two-peak up-regulation of Egr-1 mRNA was recognized at 1 and 5 days of AVF. These results suggest that high flow and shear stress can mediate EC and SMC to express MMP-2 and MMP-9, which degrade cell basement membranes and IEL to induce arterial enlargement. The disproportional increase in MT1-MMP and TIMP-2 might contribute to MMP-2 activation. Egr-1 and TGF-beta1 might play important roles in this process.

Biphasic response of tropoelastin at the poststenotic dilation segment of the rabbit aorta

OBJECTIVE

The purpose of this study was to assess the time course of tropoelastin gene expression in the poststenotic dilatation segment of rabbit aorta with experimental coarctation.

METHODS

Midthoracic aortic coarctation was created in rabbits to produce a PSD. The time points of the study after coarctation were 1, 3, and 7 days and 2, 4, and 8 weeks (n = 3 each). Additional animals (n = 6) were subjected to hypercholesterolemia for analysis of tropoelastin expression in intimal lesions. Northern and Western blot analyses were used to quantitate tropoelastin messenger RNA (mRNA) and protein, and immunohistochemistry was used to analyze tropoelastin distribution.

RESULTS

Thoracic aortic coarctation produced a moderate stenosis, which resulted in PSD. mRNA levels in the PSD segment decreased at days 1 and 3, followed by an increase at 2 and 4 weeks (P <.05 versus controls). This biphasic change in tropoelastin mRNA was associated with increase in tropoelastin protein levels at 2 and 4 weeks (P <.05 versus controls). PSD diameter reached a maximum at 4 weeks and did not increase significantly thereafter. The number of medial elastic laminae in PSD was reduced slightly, but media thickness was unchanged. Intimal lesions were much smaller in the PSD segment than in the proximal segment in animals with hypertension superimposed with hypercholesterolemia. Moreover, tropoelastin protein distributed not only in the intima but also in the media of the PSD.

CONCLUSION

Tropoelastin gene expression is regulated in a biphasic pattern and precedes PSD formation. The differential distribution of tropoelastin in the media suggests a role for tropoelastin in the poststenotic adaptation response, which may provide increased elasticity to the PSD wall.

Quantification of vessel wall cyclic strain using cine phase contrast magnetic resonance imaging

In vivo quantification of vessel wall cyclic strain has important applications in physiology and disease research and the design of intravascular devices. We describe a method to calculate vessel wall strain from cine PC-MRI velocity data. Forward-backward time integration is used to calculate displacement fields from the velocities, and cyclic Green-Lagrange strain is computed in segments defined by the displacements. The method was validated using a combination of in vitro cine PC-MRI and marker tracking studies. Phantom experiments demonstrated that wall displacements and strain could be calculated accurately from PC-MRI velocity data, with a mean displacement difference of 0.20 +/- 0.16 mm (pixel size 0.39 mm) and a mean strain difference of 0.01 (strain extent 0.20). A propagation of error analysis defined the relationship between the standard deviations in displacements and strain based on original segment length and strain magnitude. Based on the measured displacement standard deviation, strain standard deviations were calculated to be 0.015 (validation segment length) and 0.045 (typical segment length). To verify the feasibility of using this method in vivo, cyclic strain was calculated in the thoracic aorta of a normal human subject. Results demonstrated nonuniform deformation and circumferential variation in cyclic strain, with a peak average strain of 0.08 +/- 0.11.

Aneurysm-related death: primary endpoint analysis for comparison of open and endovascular repair

PURPOSE

The purpose of this study was to utilize an objective endpoint analysis of aneurysm treatment, which is based on the primary objective of aneurysm repair, and to apply it to a consecutive series of patients undergoing open and endovascular repair.

METHOD

Aneurysm-related death was defined as any death that occurred within 30 days of primary aneurysm treatment (open or endovascular), within 30 days of a secondary aneurysm or graft-related treatment, or any death related to the aneurysm or graft at any time following treatment. We reviewed 417 consecutive patients undergoing elective infrarenal aortic aneurysm repair: 243 patients with open repair and 174 patients with endovascular repair.

RESULTS

There was no difference between the groups (open vs endovascular) with regard to mean age +/- standard deviation (73 +/- 8 years vs 74 +/- 8 years) or aneurysm size (64 +/- 2 mm vs 58 +/- 10 mm) (P = not significant [NS]). The 30-day mortality for the primary procedure after open repair was 3.7% (9/243) and after endovascular repair was 0.6% (1/174, P <.05). The 30-day mortality for secondary procedures after open repair was 14% (6/41) compared to 0% after endovascular repair (P <.05). The aneurysm-related death rate was 4.1% (10/243) after open surgery and 0.6% (1/174) after endovascular repair (P <.05). Mean follow-up was 5 months longer following open repair (P <.05). Secondary procedures were performed in 41 patients following open surgery and 27 patients following endovascular repair (P = NS). Secondary procedures following open repair were performed for anastomotic aneurysms (n = 18), graft infection (n = 6), aortoenteric fistula (n = 5), anastomotic hemorrhage (n = 4), lower extremity amputation (n = 4), graft thrombosis (n = 3), and distal revascularization (n = 1). Secondary procedures following endovascular repair consisted of proximal extender cuffs (n = 11), distal extender cuffs (n = 11), limb thrombosis (n = 3), and surgical conversion (n = 2). The magnitude of secondary procedures following open repair was greater with longer operative time 292 +/- 89 minutes vs 129 +/- 33 minutes (P <.0001), longer length of stay 13 +/- 10 days vs 2 +/- 2 days (P <.0001) and greater blood loss 3382 +/- 4278 mL vs 851 +/- 114 mL (P <.0001).

CONCLUSIONS

The aneurysm-related death rate combines early and late deaths and should be used as the primary outcome measure to objectively compare the results of open and endovascular repair in the treatment of infrarenal abdominal aortic aneurysms. In our experience, endovascular aneurysm repair reduced the overall aneurysm-related death rate when compared to open repair. Secondary procedures are required after both open and endovascular repair. However, the magnitude, morbidity, and mortality of secondary procedures are reduced significantly with endovascular repair.

Introduction of endovascular aneurysm repair into community practice: initial results with a new Food and Drug Administration-approved device

PURPOSE

The purpose of this study was to determine the outcome of endovascular aneurysm repair in a defined geographic region during the first 2 years after Food and Drug Administration approval of a new endovascular device.

METHOD

Clinical results of all attempted endovascular aneurysm repairs from 1999 to 2001 with the AneuRx stent graft in the northern California/Nevada region were reviewed. All cases performed in 23 hospitals by 21 endovascular treatment teams were included on an intent-to-treat basis. Community physician training, proctoring, and assistance in case selection was provided by the manufacturer, with outcome monitored by external physician observers and clinical vascular specialists. Results in 22 community hospitals were compared with concurrent results in the regional university hospital training center and with results from the controlled, multicenter AneuRx clinical trial.

RESULTS

Endovascular aneurysm repair was attempted in 257 patients by 20 endovascular teams working in 22 community hospitals. The mean number of cases per team was 13 +/- 2 (range, 1 to 36). Patient age was 74.1 +/- 6.5 years (89% men and 11% women), and 29% of patients were not candidates for open surgical repair because of multiple medical comorbidities. Mean aneurysm diameter was 5.7 +/- 0.8 cm. The endoluminal stent graft was successfully deployed in 254 patients (98.8%). In two patients, iliac access could not be obtained, and in one case, the iliac limb was misdeployed and the patient underwent successful open surgical repair. The surgical conversion rate was two of 257 patients (0.8%). The 30-day mortality rate was 1.2%, with one patient dying of stroke, one of multisystem organ failure, and one of cerebral hemorrhage. No device-related deaths occurred. Secondary procedures were performed in 8% of patients. Primary graft patency rate was 98%, and secondary graft patency rate was 100%. Concurrent university training center experience with 100 patients with similar characteristics and aneurysm size was not statistically different (deployment success rate, 100%; 30-day mortality rate, 0%; surgical conversion rate, 0%; secondary procedure rate, 8%). No aneurysm ruptures and no late surgical conversions have been seen in either the community or university experience, with follow-up periods extending to 2 years.

CONCLUSION

Early results of endovascular aneurysm repair introduced into community practice are favorable. Initial community experience, with clinical support from the manufacturer, does not appear to differ significantly from concurrent results in the university training center or from results reported from the multicenter controlled clinical trial with the same device.

Changes in aneurysm volume after endovascular repair of abdominal aortic aneurysm

OBJECTIVE

The purpose of this study was to define changes in aneurysm volume after endovascular repair of abdominal aortic aneurysm.

METHODS

A total of 154 consecutive patients who underwent endovascular repair of abdominal aortic aneurysm with the Medtronic AneuRx stent graft at Stanford University Hospital were evaluated. During a mean follow-up period of 15.8 +/- 11.3 months, serial computerized measurements of aneurysm volume and orthogonal maximal diameter were performed on helical computed tomographic scan data sets and maximal transverse diameter was measured manually from transverse computed tomographic images. Aortoiliac length (renal to hypogastric artery origin) was measured along the median luminal centerline and along the straight line.

RESULTS

Aneurysm volume increased immediately after endovascular repair (from 180.2 +/- 69.9 mL to 187.9 +/- 71.6 mL; P <.001), but orthogonal and transverse diameter and aortoiliac length did not change significantly. During the follow-up period, mean volume decreased to 171.9 +/- 70.2 mL (P <.05) and straight-line and centerline aortoiliac length remained unchanged from preoperative values. Overall, volume decreased at a rate of 1.7 +/- 5.9 mL/mo (P <.001). During periods without endoleak, the rate of decrease was 3.2 +/- 5.5 mL/mo (P <.001), and during periods with endoleak, aneurysm volume increased at a rate of 2.0 +/- 5.3 mL/mo (P <.005), without a difference between types of endoleak. Predictive values for the presence of endoleak were similar for transverse and orthogonal diameter and volume. Logistic regression analysis showed volume to be most closely associated with the presence of endoleak.

CONCLUSION

Aneurysm volume increases immediately after endovascular repair. After repair, aneurysm volume gradually decreases and aortoiliac length remains unchanged. Changes in volume parallel changes in maximal aneurysm diameter, and their association with the presence of an endoleak does not appear to be appreciably stronger.

Expression of TGF-beta1 and beta3 but not apoptosis factors relates to flow-induced aortic enlargement

BACKGROUND

Cell proliferation and apoptosis are both involved in arterial wall remodeling. Increase in blood flow induces arterial enlargement. The molecular basis of flow-induced remodeling in large elastic arteries is largely unknown.

METHODS

An aortocaval fistula (ACF) model in rats was used to induce enlargement in the abdominal aorta. Aortic gene expression of transforming growth factors beta (TGF-beta) and apoptosis-related factors was assessed at 1 and 3 days and 1, 2, 4, and 8 weeks. Expression levels were determined using a ribonuclease protection assay and western blotting. Cell proliferation and apoptosis were analyzed using BrdU incorporation and TUNEL techniques.

RESULTS

Blood flow increased 5-fold immediately after ACF (P<0.05). Lumen diameter of the aorta was 30% and 75% larger at 2 and 8 weeks respectively than those of controls (P<0.05). mRNA levels of TGF-beta1 and TGF-beta3 increased after ACF, peaked at 3 days (P<0.05) and returned to normal level at 1 week and thereafter. Western blotting showed enhanced expression of TGF-beta1 at 3 days and TGF-beta3 at 1 and 3 days and 1 week (P<0.05). mRNA levels of Bcl-xS initially decreased at 1 day, 3 days and 1 week, followed a return to baseline level at 2 weeks. Cell proliferation was observed at all time points after ACF (P<0.001 vs. controls) with proliferation in endothelial cells more significant than smooth muscle cells. Apoptosis was not significant.

CONCLUSIONS

Gene expression of TGF-beta1 and beta3 precedes arterial enlargement. Expression of apoptosis related factors is little regulated in the early stage of the flow-induced arterial remodeling.

Duplex ultrasound criteria for defining the severity of carotid stenosis

Duplex ultrasound scan (DUS) criteria for grading >50% carotid artery stenosis is typically divided into broad categories such as 50-79% stenosis, 80-99% stenosis, and occlusion. The purpose of this study is to validate DUS criteria for stratifying 50 to 100% carotid stenosis into 10% intervals using digital substraction cerebral angiography (DSCA) as the standard of comparison. Between 1996 and 2001, 163 patients were evaluated with duplex ultrasound and angiography. A total of 326 carotid arteries were studied using DUS in an accredited ICAVL vascular laboratory. Threshold velocity criteria for determining the degree of carotid stenosis was defined according to seven categories: <50%, 50-59%, 60-69%, 70-79%, 80-89%, 90-99%, and occlusion. Treatment decisions were based on the angiographic findings. In cases where the degree of stenosis as defined by duplex velocity criteria did not correlate with angiographically defined stenosis, each record was reviewed to determine whether the angiographic findings altered the surgeon's treatment decision. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for DUS-defined degree of stenosis as compared to angiographically defined stenosis were determined. There was a high correlation (R = 0.96) between duplex scan and angiography in 93% (302/326) of the cases. Clinical management was altered in only 3% (10/326) of the cases because of the results of angiography. The DUS velocity criteria to grade the severity of carotid disease in 10% intervals is reliable and accurate. Clinical management of patients with carotid stenosis can be based solely on carotid DUS in 97% of patients considered for treatment of carotid artery disease.

Open versus endovascular AAA repair in patients who are morphological candidates for endovascular treatment

PURPOSE

To compare the outcomes of open versus endovascular repair of abdominal aortic aneurysm (AAA) in a cohort of patients who fulfill morphological criteria for endovascular repair.

METHODS

A retrospective review of 229 consecutive AAA patients treated over a 3-year period identified 149 patients who were candidates for endovascular repair based on preoperative computed tomography and angiography. Of the 149 patients, 79 (68 men; mean age 74 +/- 8 years) underwent endovascular repair with the AneuRx stent-graft; the remaining 70 (56 men; mean age 72 +/- 8 years) had open repair. Short-term outcome measures were 30-day mortality and procedure-related morbidity, length of stay in the intensive care unit and hospital, intraoperative blood loss, interval to oral diet, and time to ambulation. Long-term outcome measures included death and secondary procedures.

RESULTS

There was no difference in the 30-day mortality between endovascular repair (2, 2.5%) and open repair (2, 2.9%), even though endovascular patients had more comorbidities (p<0.05). Overall length of stay was reduced for endovascular patients (3.9 +/- 2.4 days versus 7.7 +/- 3.1 days for surgical patients, p<0.0001). Fewer endograft patients had complications (24% versus 40% for open repair, p<0.05), and the severity of these complications was less, as evidenced by the shorter hospital stays for endovascular patients with complications compared to conventionally treated patients with complications (6.7 +/- 2.4 days versus 22.5 +/- 35.2 days, p<0.05). There were no aneurysm ruptures or late surgical conversions in either group.

CONCLUSIONS

Patients with AAA who were endograft candidates but who were treated with open repair experienced more morbidity and had more complications than patients treated with stent-grafts. Despite increased comorbidities in the endograft patients, there was no increase in mortality compared to open repair. Both treatments required secondary procedures and appeared to be equally effective in preventing aneurysm rupture up to 3 years.

The first 150 endovascular AAA repairs at a single institution: how steep is the learning curve?

PURPOSE

To determine whether increasing experience with endovascular abdominal aortic aneurysm (AAA) repair in a single institution will result in improved outcome.

METHODS

A retrospective review was undertaken of 150 consecutive cases of endovascular AAA repairs performed using the AneuRx device between October 1996 and April 2000 in a university-based medical center. The population was divided into early and late groups of 75 patients each. Endpoints included technical success; complications; early (< or =30-day) morbidity, mortality and rupture; endoleak at discharge and at 1 month; early secondary intervention; proximal neck and iliac tortuosity; extender cuff placement; femoral reconstructions beyond primary repair; total fluoroscopy time; and contrast load.

RESULTS

Baseline patient and aneurysm characteristics were similar between the 2 groups. Technical success was 98.7%; 2 cases were converted intraprocedurally owing to difficult iliac access (early group) and a severely angulated proximal neck (late group). There was a tendency toward more frequent use of intraoperative proximal extender cuffs in the early group (12% versus 4% in the late group, p=0.13). Femoral reconstructions were more frequent in the early group (36% versus 19%, p<0.025). While total contrast volume was similar (111 +/- 56 versus 105 +/- 45 mL, p=NS), total fluoroscopy time was significantly reduced (p<0.05) between the early and late groups.

CONCLUSION

With attention to detail and careful patient selection, successful endovascular AAA repair can be achieved with very few conversions and low perioperative mortality even during the center's early experience. Evidence indicates, however, that a learning curve definitely exists, as shown by fewer access site problems, more accurate device deployments, and decreased fluoroscopy times as proficiency is attained.

In vivo validation of numerical prediction of blood flow in arterial bypass grafts

In planning operations for patients with cardiovascular disease, vascular surgeons rely on their training, past experiences with patients with similar conditions, and diagnostic imaging data. However, variability in patient anatomy and physiology makes it difficult to quantitatively predict the surgical outcome for a specific patient a priori. We have developed a simulation-based medical planning system that utilizes three-dimensional finite-element analysis methods and patient-specific anatomic and physiologic information to predict changes in blood flow resulting from surgical bypass procedures. In order to apply these computational methods, they must be validated against direct experimental measurements. In this study, we compared in vivo flow measurements obtained using magnetic resonance imaging techniques to calculated flow values predicted using our analysis methods in thoraco-thoraco aortic bypass procedures in eight pigs. Predicted average flow rates and flow rate waveforms were compared for two locations. The predicted and measured waveforms had similar shapes and amplitudes, while flow distribution predictions were within 10.6% of the experimental data. The average absolute difference in the bypass-to-inlet blood flow ratio was 5.4 +/- 2.8%. For the aorta-to-inlet blood flow ratio, the average absolute difference was 6.0 +/- 3.3%.

Gender differences in endovascular abdominal aortic aneurysm repair with the AneuRx stent graft

OBJECTIVE

The objective of this study was to evaluate gender differences in the selection, procedure, and outcome of endovascular abdominal aortic aneurysm repair (EVAR).

PATIENTS

Between October 1996 and January 2001, 378 patients were evaluated for EVAR and 189 patients underwent EVAR with the Medtronic AneuRx stent graft at a single center.

RESULTS

Women constituted 17% of patients considered for EVAR. Their eligibility rate (49%) did not differ significantly from that of men (57%), and they constituted 14% of patients who underwent EVAR (26/189). Women who underwent EVAR were older (77.9 +/- 6.3 years versus 73.1 +/- 8.1 years; P <.005) with a higher rate of chronic obstructive lung disease (50% versus 28%; P <.05). Maximal aneurysm diameter (57.2 +/- 10.9 mm versus 57.8 +/- 9.4 mm; not significant) did not differ between men and women. Mean diameters of the proximal neck (20.4 +/- 2.3 mm versus 22.3 +/- 2.0 mm; P <.01), common iliac arteries (11.4 +/- 1.2 mm versus 13.5 +/- 3.6 mm; P <.001), and external iliac arteries (7.9 +/- 0.7 mm versus 9.4 +/- 1.4 mm; P <.001) were all smaller in women, and abdominal aortic aneurysm/neck diameter ratio was larger (2.82 +/- 0.59 versus 2.60 +/- 0.49; P <.05). The length of the proximal aortic neck was shorter in women (20.7 +/- 8.2 mm versus 24.5 +/- 11.8 mm; P <.05). Women had significantly more intraoperative complications (31% versus 13%; P <.05), primarily related to arterial access, and needed more frequent arterial reconstruction (42% versus 21%; P <.05), without a difference in postoperative mortality rate (0/26 versus 2/163; not significant) and complication rate (23% versus 20%: not significant). During a follow-up period of 13.8 +/- 11.7 months, no gender-related difference was found in survival rate, endoleak rate, or reintervention rate or in the rate of change in aneurysm diameter or volume.

CONCLUSION

Eligibility rates of women for EVAR are similar to those of men. Women are at an increased risk for access-related complications during EVAR, but outcome is equivalent to that of men.

Nature and significance of endoleaks and endotension: summary of opinions expressed at an international conference

OBJECTIVE

Endoleaks and endotension are critically important complications of some endovascular aortic aneurysm repairs (EVARs). For the resolution of controversial issues and the determination of areas of uncertainty relating to these complications, a conference of 27 interested leaders was held on November 20, 2000.

METHODS

These 27 participants (21 vascular surgeons, five interventional radiologists, one cardiologist) had previously answered 40 key questions on endoleaks and endotension. At the conference, these 40 questions and participant answers were discussed and in some cases modified to determine points of agreement (consensus), near consensus (prevailing opinion), or disagreement.

RESULTS

Conference discussion added two modified questions for a total of 42 key questions for the participants. Interestingly, consensus was reached on the answers to 24 of 42 or 57% of the questions, and near consensus was reached on 14 of 42 or 33% of the questions. Only with the answers to four of 42 or 10% of the questions was there persistent controversy or disagreement.

CONCLUSION

The current endoleak classification system with some important modifications is adequate. Types I and II endoleak occur after 0 to 10% and 10% to 25% of EVARs, respectively. Many (30% to 100%) type II endoleaks will seal and have no detrimental effect, which never or rarely occurs with type I endoleaks. Not all endoleaks can be visualized with any technique, and increased pressure (endotension) can be transmitted through clot. Aneurysm pulsatility after EVAR correlates poorly with endoleaks and endotension. An enlarging aneurysm after EVAR mandates surgical or interventional treatment. These and other conclusions will help to resolve controversy and aid in the management of these vexing complications and should also point the way to future research in this field.

Gene expression of tropoelastin is enhanced in the aorta proximal to the coarctation in rabbits

To assess elastin biosynthesis in the aortic wall in response to acute elevation of blood pressure, we studied the aortic gene expression of tropoelastin in a rabbit midthoracic aortic coarctation model. The time points of the study were 1, 3, and 7 days and 2, 4, and 8 weeks after coarctation. Additional animals were subjected to hypercholesterolemia for analysis of tropoelastin expression in the intimal lesion. mRNA for tropoelastin was quantitated by Northern blot analysis and its distribution was revealed by in situ hybridization. The 65-kDa tropoelastin was analyzed by Western blotting and immunohistochemistry. Tropoelastin mRNA proximal to the coarctation was increased at 2 weeks and returned to baseline by 8 weeks (P < 0.05 versus control). Changes in 65-kDa tropoelastin corresponded to those of mRNA. Tropoelastin gene was expressed mainly in the intima and in the outer media at the proximal region to the stenoses, which was particularly remarkable in the intimal lesion. The results indicate that tropoelastin gene expression was enhanced in the early remodeling response to elevated blood pressure. The distribution of newly synthesized tropoelastin in the outer media suggests a reenforcement role of tropoelastin, which preserves mechanical resiliency in response to changes in tensile stress.

Subnormal shear stress-induced intimal thickening requires medial smooth muscle cell proliferation and migration

Arterial intimal thickening is consisted of predominately smooth muscle cells (SMC). The source of these SMCs and mechanisms response for their changes have not been well cleared. Using a model of rabbit common carotid artery (CCA) shear induced intimal thickening, we sought to identify and describe the source of SMCs in intima. The enlarged CCA 28 days after arteriovenous fistula (AVF) creation was subjected to subnormal wall shear stress (WSS) for 1, 3, and 7 days by closure of the AVF. To determine SMC proliferation, BrdU pulse labeling of SMCs was performed. BrdU-labeled SMCs were tracked over time to further confirm SMC migration. In response to subnormal WSS intimal thickening developed progressively. BrdU-labeled SMCs localized in the subendothelial area. When the BrdU-labeled medial SMCs were tracked 1 day after AVF closure, progenies of these BrdU-incorporated SMCs increased by 4.8-fold with 75% of them in the intima. They were 12-fold increased with 83% in the intima 7 days after. En face examination showed an accumulation of SMCs in internal elastic lamina gap after AVF closure, which later migrated into subendothelial area. In situ hybridization revealed increased TGF-beta1 mRNA expression in intimal SMCs. This study demonstrates that the medial SMCs are the predominant cells in subnormal WSS-induced intimal thickening. Early expression of TGF-beta1 may play an important role in the process of intimal thickening.

Measurement of vessel wall strain using cine phase contrast MRI

PURPOSE

To determine the feasibility of using magnetic resonance imaging (MRI) to non-invasively measure strain in the aortic wall.

MATERIALS AND METHODS

Cine phase contrast MRI was used to measure the velocity of the aortic wall and calculate changes in circumferential strain over the cardiac cycle. A deformable vessel phantom was used for initial testing and in vitro validation. Ultrasonic sonomicrometer crystals were attached to the vessel wall and used as a gold standard.

RESULTS

In the in vitro validation, MRI-calculated wall displacements were within 0.02 mm of the sonomicrometer measurements when maximal displacement was 0.28 mm. The measured maximum strain in vitro was 0.02. The in vivo results were on the same order as prior results using ultrasound echo-tracking.

CONCLUSION

Results of in vivo studies and measurement of cyclic strain in human thoracic and abdominal aortas demonstrate the feasibility of the technique.

Late endoleak after endovascular repair of an abdominal aortic aneurysm with multiple proximal extender cuffs

Late onset graft or attachment site-related endoleaks may be hazardous, and early identification of patients at risk is important. We describe a patient who underwent implantation of a bifurcated stent graft 5.5 cm below the renal arteries because of a technical error with three extender cuffs implanted proximally to bridge the gap. During the 1st year, aneurysm diameter decreased from 68 to 52 mm. After 1 year, the patient had an acute endoleak develop, which originated between two of the extender cuffs and which was accompanied by severe abdominal pain and reexpansion of the aneurysm. This endoleak was treated with insertion of an additional bifurcated stent graft within the extender cuff segment. The patient has been subsequently followed for 6 months and has had no endoleak or symptoms, and aortic diameter has decreased once again to 55 mm.

"Pseudoendoleak"--residual intrasaccular contrast after endovascular stent-graft repair

PURPOSE

To present a unique demonstration of postoperative perigraft contrast masquerading as an endoleak following endovascular abdominal aortic aneurysm (AAA) repair.

CASE REPORT

A 66-year-old man underwent endovascular stent-graft repair of a 4.6-cm infrarenal AAA. The procedure was uncomplicated, and intraoperative completion angiography demonstrated good proximal and distal fixation of the stent-graft without an endoleak. A spiral computed tomographic (CT) angiogram obtained on postoperative day 2 revealed a large amount of extrastent contrast along the posterior aspect of the aneurysm sac. This defect had the appearance of an endoleak, but it was also present on the non-contrast images. A color-flow duplex examination performed on the same day showed a widely patent stent-graft with no evidence of extrastent flow.

CONCLUSIONS

Contrast trapped in the aneurysm sac during endovascular aneurysm repair may be misinterpreted as an endoleak on postprocedural CT scans. "Pseudoendoleaks" can be distinguished from true endoleaks by examination of prebolus, noncontrast CT images, as well as by duplex ultrasound scanning.