S. Rao Vallabhaneni

Lessons learnt from the EUROSTAR registry on endovascular repair of abdominal aortic aneurysm repair

OBJECTIVE The EUROSTAR project is a multicentred database of the outcome of endovascular repair of infra-renal aortic aneurysms. To date 92 European centres of vascular surgery have contributed. The purpose of the article here is to review the medium term (up to 4 years) results of endovascular aneurysm repair as reported to Eurostar. PATIENTS AND METHODS Patients intended for endovascular aneurysm repair were notified to the EUROSTAR Data Registry Centre before treatment in order to eliminate bias due to selective reporting. The following data was collected on all patients: (1) their demographic details and the anatomical characteristics of their aneurysms, (2) details of the endovascular device used, (3) procedural complications and the immediate outcome, (4) results of contrast enhanced CT imaging at 3, 6, 12 and 18 months after operation and at yearly intervals thereafter, (5) all adverse events. Life table analysis was performed to determine the cumulative rates of: (1) death from all causes, (2) secondary intervention. Risk factors for rupture and late conversion were identified by regression analysis. RESULTS By July 2000, 2862 patients had been registered and their median duration of follow-up was 12 mo (range 0-72). Successful deployment was achieved in 2812 patients with a perioperative (30 day) mortality of 2.9%. In 2464 patients enrolled by March 2000 late rupture of the aneurysm occurred in 14 patients for an annual cumulative rate of 1%. The significant factors were proximal type I endoleak (P=0.001), midgraft (type III) endoleak (P=0.001), graft migration (P=0.001) and post-operative kinking of the endograft (P=0.001). Forty-one patients had late conversion to open repair for an annual cumulative rate (risk) of approximately 2.1%. Risk factors (indications) for late conversion were: proximal type I endoleak (P=0.001), midgraft (type III) endoleak (P=0.001), type II endoleak (P=0.003), graft migration (P=0.001), graft kinking (P=0.001) and distal type I endoleak (P=0.001). CONCLUSIONS Endovascular repair of infra-renal aortic aneurysms using the first and second-generation devices that predominated in this study was associated with a risk of late failure of 3% per year, based upon an analysis of observed primary endpoints of rupture and conversion. Eurostar continues to provide responsible evaluation of the technique for the benefit of both physicians and the industry.

Late Rupture of Abdominal Aortic Aneurysm After Previous Endovascular Repair: A Systematic Review and Meta-analysis.

Purpose: To report a systematic literature review of late rupture of abdominal aortic aneurysm (AAA) after endovascular aneurysm repair (EVAR) and the results of a pooled analysis of causes, treatment, and outcomes. Methods: Electronic information sources and bibliographic reference lists were interrogated using a combination of free text and controlled vocabulary searches; 11 articles were ultimately identified that fulfilled the inclusion criteria. The articles reported a total of 190 patients who were included in the qualitative and quantitative synthesis. Mortality within 30 days or during the admission with aneurysm rupture was a primary endpoint; major perioperative morbidity was a secondary endpoint. A meta-analysis was performed for 30-day/in-hospital mortality using the random effects model. Results: A total of 152 ruptures occurred after 16,974 EVAR procedures reported by 8 of the case series, giving an incidence of 0.9% [95% confidence interval (CI) 0.77 to 1.05]. The mean time to rupture was 37 months. Twenty-nine percent (95% CI 20 to 39) of the patients had at least one previous secondary endovascular intervention following the initial EVAR, and 37% (95% CI 30 to 45) were not compliant with surveillance. Type I and III endoleaks were the predominant causes of rupture. Open surgical treatment was undertaken in 61% (95% CI 53 to 68) of the patients who underwent treatment. The pooled estimate for perioperative mortality was 32% (95% CI 24 to 41). A significantly lower mortality was found with endovascular treatment than open surgical management (p=0.027). Conclusion: Graft-related endoleaks appear to be the predominant causes of late aneurysm rupture. Quality of and compliance with post-EVAR surveillance are important factors in late rupture; a large proportion of late ruptures are amenable to endovascular treatment.

Pragmatic Minimum Reporting Standards for Endovascular Abdominal Aortic Aneurysm Repair

Jonathan R. Boyle, MD, FRCS1; Matt M. Thompson, MD, FRCS2; S. Rao Vallabhaneni, MD, FRCS, EBSQ-Vasc3; Rachael E. Bell, MS, FRCS4; John A. Brennan, MD, FRCS3; Tom F. Browne, FRCS5; Nicholas J. Cheshire, MD, FRCS6; Robert J. Hinchliffe, MD, FRCS2; Michael P. Jenkins, MS, FRCS, FEBVS6; Ian M. Loftus, MD, FRCS2; Sumaira Macdonald, FRCP, FRCR, PhD7; Mark J. McCarthy, PhD, FRCS8; Richard G. McWilliams, FRCR3; Robert A. Morgan, FRCR2; Olufemi A. Oshin, BEng, MRCS3; R. Mark Pemberton, MS, FRCS9; Woolagasen R. Pillay, FCS(SA), MMEDSc10; and Robert D. Sayers, MD, FRCS8 for the British Society of Endovascular Therapy

Adjunctive Iliac Stents Reduce the Risk of Stent-Graft Limb Occlusion following Endovascular Aneurysm Repair with the Zenith Stent-Graft:

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 units 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.

Guidewire stiffness: what's in a name?

Purpose To measure the stiffness of commonly used “stiff” guidewires in terms of their flexural modulus, an engineering parameter related to bending stiffness. Methods Eleven different intact stiff guidewires were selected to undergo a 3-point bending test performed using a tensile testing machine. Testing was performed on 3 new and intact specimens of each guidewire at 10 locations along the wires length, excluding the floppy tip. The flexural modulus (in gigapascals, GPa) was calculated from the results of the bending test. Results The flexural modulus of the plain Amplatz wire was 9.5 GPa compared to 11.4 to 14.5 GPa for the “heavy duty” wires. Within the Amplatz family of guidewires, the flexural modulus was 17 GPa for the “stiff,” 29.2 GPa for the “extra stiff,” 60.3 GPa for the “super stiff,” and 65.4 GPa for the “ultra stiff.” The Backup Meier measured 139.6 GPa and the Lunderquist Extra Stiff 158.4 GPa. Conclusion The Instructions for Use of some endovascular devices specify a wire type selected from a range of undefined “stiffness” descriptors. These descriptors have little correlation with the measured flexural modulus. Two guidewires with the description “extra stiff” can have a 5-fold difference in flexural modulus. We recommend that guidewire catalogues and packaging include the flexural modulus and that device manufacturers amend their Instructions for Use accordingly.

Comparison of the fixation strength of standard and fenestrated stent-grafts for endovascular abdominal aortic aneurysm repair.

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.

Closure technique after carotid endarterectomy influences local hemodynamics

BACKGROUND Meta-analysis supports patch angioplasty after carotid endarterectomy (CEA); however, studies indicate considerable variation in practice. The hemodynamic effect of a patch is unclear and this study attempted to elucidate this and guide patch width selection. METHODS Four groups were selected: healthy volunteers and patients undergoing CEA with primary closure, trimmed patch (5 mm), or 8-mm patch angioplasty. Computer-generated three-dimensional models of carotid bifurcations were produced from transverse ultrasound images recorded at 1-mm intervals. Rapid prototyping generated models for flow visualization studies. Computational fluid dynamic studies were performed for each model and validated by flow visualization. Mean wall shear stress (WSS) and oscillatory shear index (OSI) maps were created for each model using pulsatile inflow at 300 mL/min. WSS of <0.4 Pa and OSI >0.3 were considered pathological, predisposing to accretion of intimal hyperplasia. The resultant WSS and OSI maps were compared. RESULTS The four groups comprised 8 normal carotid arteries, 6 primary closures, 6 trimmed patches, and seven 8-mm patches. Flow visualization identified flow separation and recirculation at the bifurcation increased with a patch and was related to the patch width. Computational fluid dynamic identified that primary closure had the fewest areas of low WSS or elevated OSI but did have mild common carotid artery stenoses at the proximal arteriotomy that caused turbulence. Trimmed patches had more regions of abnormal WSS and OSI at the bifurcation, but 8-mm patches had the largest areas of deleteriously low WSS and high OSI. Qualitative comparison among the four groups confirmed that incorporation of a patch increased areas of low WSS and high OSI at the bifurcation and that this was related to patch width. CONCLUSIONS Closure technique after CEA influences the hemodynamic profile. Patching does not appear to generate favorable flow dynamics. However, a trimmed 5-mm patch may offer hemodynamic benefits over an 8-mm patch and may be the preferred option.

Magnitude of the Forces Acting on Target Vessel Stents as a Result of a Mismatch Between Native Aortic Anatomy and Fenestrated Stent-Grafts

Purpose To quantify the compression force acting on target vessel stents as a consequence of the misalignment between the native aortic anatomy and the fenestrated stent-graft owing to measuring errors during the design of the device. Methods The material properties of a fenestrated Zenith stent-graft were determined using a standardized tensile testing protocol. Aortic anatomy was modeled using fresh porcine aortas that were subjected to tensile testing. The net force acting on a target vessel stent due to incremental discrepancy between the target vessel ostia and the stent-graft fenestrations was calculated as the difference in wall tension between the aorta and the stent-graft in diastole and systole. The change in diameter between diastole and systole was set to 8%. Results Using the diastole model, underestimation of circumferential target vessel position by 15°, 22.5°, and 30° resulted in net forces on the target vessel stent of 0.6, 0.8, and 1.1 N, respectively. Overestimation of target vessel position by the same increments resulted in net forces of 0.3, 0.6, and 0.9 N, respectively. With the systolic model, underestimating target vessel position by 30° resulted in a 2.1-N maximum force on the stent, which potentially threatened the seal. In the longitudinal direction, underestimating target vessel separation by up to 10 mm resulted in a maximal force on the stent of 6.1 N, while overestimating target vessel separation did not result in any additional force on the stent due to fabric infolding. Conclusion The magnitude of the forces generated solely due to mismatch between stent-graft design and native anatomy is modest and is unlikely to cause significant deformation of target vessel stents. Mismatch, however, may cause loss of seal.

Intra- and interobserver variability of target vessel measurement for fenestrated endovascular aneurysm repair.

Purpose: To evaluate intra- and interobserver agreement of target vessel measured from computed tomography (CT) scans with 2 measuring techniques used in planning fenestrated endovascular aneurysm repairs (FEVAR): multiplanar reconstruction (MPR) and semi-automated central lumen line (CLL). Methods: CT datasets from 25 FEVAR patients were independently analyzed by 2 experienced observers according to a standardized protocol using the MPR (Leonardo workstation) and CLL (Aquarius workstation) techniques for each patient. Longitudinal vessel separation and clock-face position of the visceral aortic branches were measured twice. The repeatability coefficient (RC) was calculated using the Bland and Altman method to measure intra- and interobserver variability. Differences between groups were examined by paired t test (continuous data) or chi-squared analysis (categorical). Clock-face discrepancy >30 minutes was considered significant. Results: Intraobserver mean difference was insignificant regardless of the measurement technique: the observer and workstation-specific RCs varied between 3.9 and 4.9 mm. Paired measurements differed by >3 mm in 8%. Interobserver variability was greater: observer and workstation-specific RC varied between 5.6 and 7.4 mm, with a tendency toward consistency using MPR, although the mean difference was insignificant. Paired measurements differed by >3 mm in 18%. There was no significant intraobserver variation in clock-face measurement, while interobserver variation was significant in 12% of measurements using the Aquarius workstation and 6% using the Leonardo workstation (p=0.19). Conclusion: Subjective interpretation of anatomical landmarks is more important than measurement techniques or workstations used in the generation of measurement inconsistencies. Introduction of consensus regarding interpretation of anatomical detail and development of fenestrated stent-grafts tolerant of measurement errors might ameliorate some of the problems encountered in FEVAR.

EVAR in Iliac Occlusion

Purpose: To report the recanalization of an occluded common iliac artery (CIA) to allow endovascular repair of an abdominal aortic aneurysm (AAA) with a bifurcated stent-graft. Case Report: A 76-year-old man with a 75-mm infrarenal AAA and an occluded right CIA was successfully treated with a Zenith bifurcated stent-graft. The right CIA was recanalized allowing access, delivery, and deployment of the stent-graft. Follow-up computed tomography at 9 months showed no evidence of endoleak; maximum aneurysm diameter was reduced to 72 mm, and the iliac vessels were patent. Conclusion: Bifurcated stent-graft repair of an AAA can be performed following recanalization of an occluded CIA. This option may be preferable to an open repair or an aortomonoiliac stent-graft with extra-anatomical bypass in some patients. Long-term surveillance will be necessary to ensure freedom from iliac-related secondary intervention.