RESUMEN
PURPOSE: To determine whether the introduction of a policy of adjunctive stent insertion based on preoperative CT assessment or completion angiography reduced the incidence of limb occlusion after stent-graft implantation for endovascular aneurysm repair (EVAR). METHODS: A tertiary referral unit's endovascular database was retrospectively interrogated to compare the incidence of endograft limb occlusion in Zenith grafts following the introduction of a policy of selective adjunctive stent insertion. Group A included 288 limbs at risk in 146 patients (134 men; mean age 74+/-8 years) treated prior to August 2005 in whom adjunctive stents were inserted on an ad hoc basis only. Group B included 293 limbs at risk in 149 patients (127 men; mean age 76+/-7 years) treated after this date in whom a more aggressive adjunctive stenting strategy was adopted. Kaplan-Meier analysis was employed to compare outcomes. RESULTS: In total, 295 patients underwent EVAR involving 581 iliac vessels, of which 11 (1.8%) occluded at a median of 24 months (0-27). Of 65 limbs extended into the external iliac segment, 5 (7.6%) subsequently occluded; in the remaining 516 limbs, there were 6 (1.1%) occlusions (p = 0.004). Across the study group, 38 (6.5%) adjunctive stents were deployed in limbs deemed at risk; 1 (2.6%) of these occluded. In the remaining 543 unstented limbs, 10 (1.8%) occlusions occurred (p = 0.15). There were 11 occlusions in group A, in which 5 (1.7%) adjunctive stents had been deployed, but none in group B, which had received 33 (11.2%) stents (p<0.0001). Kaplan-Meier survival curves identified primary patency rates at 36 months of 96% and 100%, respectively (p = 0.001). CONCLUSION: Adjunctive stenting significantly reduces the risk of postoperative stent-graft limb occlusion without obvious compromise to the aneurysm repair.
Asunto(s)
Aneurisma de la Aorta Abdominal/cirugía , Implantación de Prótesis Vascular/instrumentación , Prótesis Vascular , Oclusión de Injerto Vascular/prevención & control , Arteria Ilíaca/cirugía , Stents , Anciano , Anciano de 80 o más Años , Aneurisma de la Aorta Abdominal/diagnóstico por imagen , Aortografía/métodos , Implantación de Prótesis Vascular/efectos adversos , Distribución de Chi-Cuadrado , Femenino , Oclusión de Injerto Vascular/etiología , Humanos , Arteria Ilíaca/diagnóstico por imagen , Estimación de Kaplan-Meier , Masculino , Persona de Mediana Edad , Diseño de Prótesis , Estudios Retrospectivos , Medición de Riesgo , Factores de Riesgo , Factores de Tiempo , Tomografía Computarizada por Rayos X , Resultado del TratamientoRESUMEN
PURPOSE: To investigate in an in vitro model the ability of different covered and uncovered stents to resist displacement/migration of a fenestrated stent-graft. METHODS: Three different types (2 covered, 1 bare) of commonly used 7-mm balloon-expandable stainless steel stents (Jostent, Advanta V12, and Palmaz Genesis) were investigated in a testing rig consisting of 2 overlapping tubes with 2 sets of 7-mm holes representing bilateral renal artery fenestrations and ostia. The rig was attached to a tensile tester via pneumatic clamps. The stents were deployed without flaring to 7 mm through the overlapping holes. The rig was moved apart at a constant rate of 12 mm/min up to a maximum displacement of 6 mm; force versus displacement values were recorded while stent deformation was observed. Tests were repeated at least 6 times for each stent type at room temperature. The median force required to cause a 25%, 50%, or 75% reduction in cross-sectional area of the bilateral "renal artery" stents was determined. RESULTS: The median force (interquartile range) required to cause a 50% reduction in cross-sectional area of identical bilateral "renal artery" stents securing fenestrations was 25.1 N (8.1) for a covered Jostent, 9.3 N (0.9) for a covered Advanta V12 stent, and 7.5 N (0.7) for a bare Palmaz Genesis stent. The differences were statistically significant (p<0.01) between stents at each of the 3 levels of cross-sectional area reduction. CONCLUSION: There is a significant difference in the ability of different commercial "non-dedicated" stents to withstand a crushing force when deployed within endograft fenestrations, which has important implications for clinical practice.
Asunto(s)
Aorta/cirugía , Implantación de Prótesis Vascular/instrumentación , Prótesis Vascular , Migración de Cuerpo Extraño/etiología , Falla de Prótesis , Arteria Renal/cirugía , Stents , Distinciones y Premios , Implantación de Prótesis Vascular/efectos adversos , Análisis de Falla de Equipo , Humanos , Diseño de Prótesis , Estrés MecánicoRESUMEN
This article reports the investigation and treatment of 24 women presenting with recurrent lower limb varicosities secondary to reflux within the pelvic venous circulation. Diagnosis based on selective retrograde pelvic phlebography enabled precise identification and classification of sites of incompetence. A total of 74 veins were treated by embolization with platinum coils and glue prior to repeat surgery to the lower limb veins. At 4-year follow-up, signs of stasis had disappeared in all patients. Repeat phlebography revealed no evidence of recurrent reflux at the sites of treatment. One patient developed recurrent varices due to incomplete embolization of incompetent pelvic veins. Endovascular occlusion of incompetent pelvic veins is an effective treatment for varicose veins secondary to pelvic venous incompetence.
Asunto(s)
Pelvis/irrigación sanguínea , Várices/terapia , Adulto , Anciano , Embolización Terapéutica/métodos , Femenino , Humanos , Vena Ilíaca/fisiopatología , Pierna/irrigación sanguínea , Persona de Mediana Edad , Ovario/irrigación sanguínea , Pelvis/diagnóstico por imagen , Flebografía/métodos , Recurrencia , Flujo Sanguíneo Regional/fisiología , Reoperación , Resultado del Tratamiento , Várices/diagnóstico , Várices/cirugía , Insuficiencia Venosa/fisiopatologíaRESUMEN
PURPOSE: To determine whether fenestrated stent-grafts provide better stability to resist migration than standard non-fenestrated stent-grafts. METHODS: Truncated fenestrated stent-grafts with a single fenestration were deployed in bovine aortic segments with a side branch. Balloon-expandable stents were then delivered into the branches. Similarly, standard stent-grafts of the same dimensions were deployed for comparison. The aorta was pressurized to achieve stent-graft oversizing of 5%, 10%, or 20%. The force required to cause distal migration was recorded by a digital force gauge attached to the stent-graft. RESULTS: Displacement of the stent-grafts occurred in 2 distinct phases: an initial yield during which the barbs embedded in the aortic wall and a final displacement leading to significant migration and dislodgement of the device. The displacement force that initiated each phase was dependent upon the degree of oversizing of the stent-graft relative to the aortic diameter. For 5%, 10%, and 20% oversizing, the mean displacement forces in the initial displacement phase were 3.39+/-0.37, 4.32+/-0.63, and 7.69+/-1.18 N, respectively, in non-fenestrated grafts and 10.48+/-1.23, 11.45+/-1.48, 12.12+/-1.42 N in fenestrated grafts. The displacement forces in the final displacement phase were 8.10+/-0.92, 10.76+/-1.74, and 16.82+/-0.92 N for non-fenestrated and 22.56+/-1.60, 28.24+/-1.56, and 33.01+/-1.75 N for fenestrated stent-grafts. The differences in displacement forces between standard and fenestrated stent-grafts were significant for both phases (p<0.001) at all oversizing levels. CONCLUSION: Improvement in fixation strength was noted with increasing stent-graft oversizing of up to 20%. Fenestrated stent-grafts offer higher ultimate fixation compared to standard devices. However, the ultimate fixation strength was not recruited until an initial phase of short migration occurred as the barbs engaged. While this movement is inconsequential with standard stent-grafts, it has the potential to crush the stents placed into aortic side branches with fenestrated endografts.
Asunto(s)
Aneurisma de la Aorta Abdominal/cirugía , Implantación de Prótesis Vascular/métodos , Prótesis Vascular , Migración de Cuerpo Extraño/prevención & control , Stents , Animales , Fenómenos Biomecánicos , Implantación de Prótesis Vascular/efectos adversos , Bovinos , Migración de Cuerpo Extraño/etiología , Técnicas In Vitro , Presión , Diseño de Prótesis , Proyectos de InvestigaciónRESUMEN
PURPOSE: To measure the tensile strength of the aneurysm wall and the matrix metalloproteinase (MMP) activity in similar samples of aortic tissue. METHODS: Detailed mechanical testing was conducted on 124 standardized specimens of aneurysm wall harvested from 24 patients undergoing elective aneurysm repair. The intrasac pressure required to cause aneurysm rupture was calculated based upon the Law of Laplace. In addition, MMP-2 and 9 were assayed from these specimens. Sixty specimens of nonaneurysmal aorta from 6 cadaveric organ donors served as controls. Intrasubject and intersubject variations were analyzed. RESULTS: In the aneurysm specimens, the Young's modulus was 1.80x10(6) N/m(2), the load at break was 6.36 N, the strain at break was 0.30, the ultimate strength was 0.53x10(6) N/ m(2), and the MMP activity was 312 for MMP-2 and 460 for MMP-9. In the controls, the circumferential measurements were a Young's modulus of 1.82x10(6) N/m(2), a load at break of 5.43 N, strain at break of 0.29, ultimate strength of 0.61x10(6) N/m(2), and MMP activity of 395 for MMP-2 and 2019 for MMP-9. Longitudinal measurements in controls were a Young's modulus of 1.38x10(6) N/m(2), a load at break of 11.39 N, a strain at break of 0.33, and ultimate strength of 1.30x10(6) N/m(2). Intra and intersubject variation of all parameters was very high. Based upon the lowest measured tensile strength for each aneurysm, the intrasac pressure required to cause rupture varied from 142 to 982 mmHg. CONCLUSIONS: Localized "hot spots" of MMP hyperactivity could lead to focal weakening of the aneurysm wall and rupture at relatively low levels of intraluminal pressure. These data suggest that tensile strength of the sac is just as important as intrasac tension in determining the risk of rupture. Moreover, these observations may explain why some small aneurysms rupture and larger aneurysms do not. Assessment of rupture risk based on computation or measurement of wall stress may be subject to error and inaccuracy due to variations in wall tensile strength.
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Aorta Abdominal/fisiopatología , Aneurisma de la Aorta Abdominal/enzimología , Aneurisma de la Aorta Abdominal/fisiopatología , Metaloproteinasa 2 de la Matriz/metabolismo , Metaloproteinasa 9 de la Matriz/metabolismo , Resistencia a la Tracción , Aorta Abdominal/enzimología , Rotura de la Aorta/etiología , Estudios de Casos y Controles , Humanos , Factores de Riesgo , Estrés MecánicoRESUMEN
PURPOSE: To demonstrate the influence of radiographic positioning on the assessment of stent-graft migration using plain radiographs following endovascular abdominal aortic aneurysm repair. METHODS: Equations were derived to correct for artifactual stent-graft migration introduced by geometric distortion due to variations in positioning between radiographs acquired at different times. A phantom system was used to validate the equations. RESULTS: Errors in stent position increase with (1) the distance of the aortic stent-graft from the midline and (2) differences in radiographic centering points in the craniocaudal direction; other variables have little effect. For typical stent positions, errors are small if the centering changes by <8 cm. Consistent radiographic positioning to within 4 cm on successive imaging studies limits errors to 1.5 mm. Even if artifactual migration is large, the true migration can be reliably calculated to within 2 mm. CONCLUSIONS: Artifactual migration due to variation in radiographic centering is not usually clinically significant if care is taken to center radiographs consistently. Radiographs in which artifactual migration may be important are readily identified, and mathematical correction is straightforward.
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Aneurisma de la Aorta Abdominal/diagnóstico por imagen , Aneurisma de la Aorta Abdominal/cirugía , Aortografía/métodos , Artefactos , Errores Diagnósticos , Migración de Cuerpo Extraño/diagnóstico por imagen , Estudios de Seguimiento , HumanosRESUMEN
PURPOSE: To investigate the effect on intrasac pressure of stent-graft deployment within a life-size silicone rubber model of an abdominal aortic aneurysm (AAA) maintained under physiological conditions of pressure and flow. METHODS: A commercial bifurcated device with the polyester fabric preclotted with gelatin was deployed in the AAA model. A pump system generated physiological flow. Mean and pulse aortic and intrasac pressures were measured simultaneously using pressure transducers. To simulate a type I endoleak, plastic tubing was placed between the aortic wall and the stent-graft at the proximal anchoring site. Type II endoleak was simulated by means of side branches with set inflow and outflow pressures and perfusion rates. Type IV endoleak was replicated by removal of gelatin from the graft fabric. RESULTS: With no endoleak, the coated graft reduced the mean and pulse sac pressures to negligible values. When a type I endoleak was present, mean sac pressure reached a value similar to mean aortic pressure. When net flow through the sac due to a type II endoleak was present, mean sac pressure was a function of the inlet pressure, while pulse pressure in the sac was dependent on both inlet and outlet pressures. As perfusion rates increased, both mean and pulse sac pressures decreased. When there was no outflow, mean sac pressure was similar to mean aortic pressure. In the presence of both type I and type II endoleaks, mean sac pressure reached mean aortic pressure when the net perfusion rate was low. CONCLUSIONS: In vitro studies are useful in gaining an understanding of the impact of different types of endoleaks, in isolation and in combination, on intrasac pressure after aortic stent-graft deployment.
Asunto(s)
Angioplastia , Aneurisma de la Aorta Abdominal/cirugía , Modelos Cardiovasculares , Complicaciones Posoperatorias/etiología , Stents , Angioplastia/métodos , PresiónRESUMEN
PURPOSE: To determine if pressure measured at a single location within aneurysm sac thrombus accurately reflects the force applied to the aneurysm wall and the risk of rupture by examining (1) if pressure is distributed uniformly within aneurysm thrombus, (2) the pressure transmission through aneurysm thrombus, and (3) the microstructural basis for pressure transmission. METHODS: Pressure within aneurysm thrombus was measured by direct puncture through the aneurysm wall at 121 sites in 26 patients during open abdominal aortic aneurysm repair. Measurements were taken prior to cross clamping and compared with intrasac pressure measured at 30 sites in 6 patients without aneurysm thrombus (controls). Transmission of pressure through aneurysm thrombus was further examined ex vivo by subjecting fresh thrombus to a pressure gradient in a custom-made pressure cell. Pressure transmission was correlated with matrix density as determined by light microscopy and image analysis. RESULTS: Mean pressure within aneurysm thrombus was higher than mean systemic pressure in 11 patients, lower in 1, and identical in 9. In 5 patients, the pressure was greater than systemic in some areas of the thrombus but less in others. Sac pressure was identical to systemic pressure at all sites in the controls. In 12 thrombus specimens (6 patients) examined in the pressure cell, pressure transmission varied significantly between specimens, correlating directly with matrix density (R(2)=0.747, p=0.001). CONCLUSIONS: Pressure transmission through aneurysm thrombus is variable and depends upon the microstructure of the thrombus. Pressure measured at a single location may not, therefore, accurately reflect the pressure acting on the aneurysm wall.
Asunto(s)
Angioplastia , Aneurisma de la Aorta Abdominal/cirugía , Aneurisma de la Aorta Abdominal/fisiopatología , Humanos , Monitoreo Fisiológico , Valor Predictivo de las Pruebas , Presión , Insuficiencia del TratamientoRESUMEN
PURPOSE: To determine aneurysm neck diameter change after endovascular repair (EVR) of abdominal aortic aneurysm (AAA) and its relationship to stent-graft diameter. MATERIALS AND METHODS: The cases of 73 patients with AAAs who underwent EVR were reviewed retrospectively: 68 had preoperative imaging available. Neck diameter was reviewed by a single observer (M.F.B.) on preoperative, immediate postoperative, annual, and most recent contrast-enhanced computed tomographic scans. Baseline and follow-up neck diameters were compared with the manufacturers' values for unconstrained stent-graft diameters. RESULTS: Intraobserver error was 2 mm. Aneurysm neck diameter increased from 21.8 mm (range, 17-28 mm) at baseline to 22.8 mm (range, 19-30 mm) postoperatively and 25.8 mm (range, 19-31 mm; P <.001) at a mean follow-up of 25.5 months (range, 6.2-60.8 mo). Neck diameter increase was more than 2 mm in 24 patients (33%). Mean change in the first, second, third, and fourth years was +1.63 mm, +0.52 mm, +0.25 mm, and +0.33 mm, respectively. Baseline mean stent-graft oversizing was 2.9 mm (13.7%; range, -1 to +8 mm), which decreased to 0.7 mm (range, -4 to +6 mm) at latest follow-up. Neck diameter exceeded stent-graft diameter (mean, 1.8 mm; range, 1-4 mm) in 21 cases (28%) and by more than 2 mm in five cases (6.8%). When neck diameter change was correlated with change in sac diameter, it was found to be insignificant (P =.24); however, it was significantly correlated with baseline oversizing (P =.01). CONCLUSIONS: After EVR, the aneurysm neck dilates, mostly in the first 2 years, by greater than 2 mm in one third of patients. This is possibly related to the presence of the endograft. The associated reduction of stent-graft oversizing warrants continued vigilance for proximal endoleak.
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Aneurisma de la Aorta Abdominal/patología , Aneurisma de la Aorta Abdominal/cirugía , Implantación de Prótesis Vascular , Anciano , Anciano de 80 o más Años , Aneurisma de la Aorta Abdominal/diagnóstico por imagen , Estudios de Cohortes , Dilatación Patológica , Femenino , Humanos , Masculino , Persona de Mediana Edad , Variaciones Dependientes del Observador , Radiografía , Stents , Factores de TiempoRESUMEN
PURPOSE: To compare unenhanced and enhanced ultrasound imaging to biphasic computed tomography (CT) in the detection of endoleak after endovascular abdominal aortic aneurysm (AAA) repair. METHODS: Fifty-three patients (44 men; mean age 70 years) were examined during 96 follow-up visits after endovascular AAA repair. All patients had color Doppler and power Doppler ultrasound studies performed before and after the administration of an ultrasound contrast agent. Biphasic (arterial and delayed) CT was performed on the same day, and the ultrasound and CT studies were independently scored to record the presence or absence of endoleak and the level of confidence in the observation. RESULTS: The sensitivity of the ultrasound techniques to detect endoleak improved with the use of ultrasound contrast media, ranging from a low of 12% with unenhanced color Doppler to 50% with enhanced power Doppler. However, the enhanced power Doppler failed to detect 9 type II endoleaks identified by CT (86% negative predictive value for endoleak). There were only 2 graft-related endoleaks in the study; one was diagnosed from the ultrasound image, but the other had nondiagnostic ultrasound scans because of poor views. CONCLUSIONS: Ultrasound scanning with or without contrast enhancement was not as reliable as CT in diagnosing type II endoleak. CT imaging remains our surveillance modality of choice.