Mital Desai

AAA Stent–Grafts: Past Problems and Future Prospects

Endovascular aneurysm repair (EVAR) has quickly gained popularity for infrarenal abdominal aortic aneurysm repair during the last two decades. The improvement of available EVAR devices is critical for the advancement of patient care in vascular surgery. Problems are still associated with the grafts, many of which can necessitate the conversion of the patient to open repair, or even result in rupture of the aneurysm. This review attempts to address these problems, by highlighting why they occur and what the failings of the currently available stent grafts are, respectively. In addition, the review gives critical appraisal as to the novel methods required for dealing with these problems and identifies the new generation of stent grafts that are being or need to be designed and constructed in order to overcome the issues that are associated with the existing first- and second-generation devices.

Inhibition of neointimal formation and hyperplasia in vein grafts by external stent/sheath

Synthetic and to a lesser extent vein graft failure is still a major problem in the treatment of peripheral arterial disease, with neointimal hyperplasia being the main cause for graft occlusion in the medium and long term. This review aims to establish the current status of external stents or sheaths in the prevention of intimal hyperplasia in small diameter (< 6 mm) vein grafts.

A Sutureless Aortic Stent-Graft Based on a Nitinol Scaffold Bonded to a Compliant Nanocomposite Polymer Is Durable for 10 Years in a Simulated In Vitro Model

Purpose To physiologically test the durability of a sutureless aortic stent-graft based on nitinol bonded to polyhedral oligomeric silsesquioxane (POSS) and poly(carbonate-urea) urethane (PCU) for 10 years according to Food and Drug Administration guidelines. Methods Aortic stent-grafts (n = 4) were tested in 37°C distilled water using simulated in vivo hydrodynamic pulse loading. After 400 million cycles, surface topography was assessed by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Dynamic compliance was measured using a pulsatile flow phantom. Mechanical and elastic properties were determined by stress-strain studies and elastic deformation tests. Dynamic scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to assess thermal resistance. Comparison was made with a zero-cycled control. Results All stent-grafts successfully completed accelerated pulsatile fatigue at 94±14-mmHg pulse pressure. SEM images confirmed uniform surface topography without any fractures. FTIR showed increased intensity of -NHCO- bonds, but there was no significant sign of biodegradation. Tensile stress of fatigue-tested polymer compared favorably with the zero-cycled control at 50% to 500% strain (p = 0.69). At a mean pressure range of 60 to 120 mmHg, overall compliance of the fatigue-tested grafts was 3.48±1.27%mmHg−1×10−2 with no significant difference compared to control (3.26±0.65%mmHg−1×10−2; p = 0.47). DSC and TMA showed comparable thermotropic transition. Conclusion Simulated physiological in vivo hydrodynamic loading has no significant degradative effect on an innovative sutureless stent-graft made from POSS-PCU nanocomposite polymer. Sutureless technology incorporating nitinol stents proved to be robust, with no separation over an accelerated 10-year cycle, which may allow development of durable stent-grafts with better compliance.

Isolated endarterectomy of femoral bifurcation in critical limb ischemia: is restoration of inline flow essential?

This retrospective study reviews clinical outcomes of isolated common femoral endarterectomy (CFE) for critical limb ischemia (CLI), in particular whether poor runoff and inability to restore inline flow has negative impact. In 30 patients, runoff was assessed on preoperative angiograms and categorized into groups based on Society of Vascular Surgery criteria. Data were evaluated using Cox Regression survival analysis. Freedom from secondary revascularization was not affected by runoff score (hazard ratio for compromised and poor groups being 1.8 (95% CI 0.16 to 20.8) and 1.47 (95% CI 0.09 to 24.3), respectively; P = .894). Distal inline flow was not achieved in 25 (83%) patients, but this was not associated with significantly worse outcome (P = .295, log-rank test). In conclusion, CFE can be performed in CLI with high technical success and there is no significant effect of runoff score on recurrence of symptoms. Limb salvage can be achieved even if options to restore inline flow are limited.

An Aortic Model for the Physiological Assessment of Endovascular Stent-Grafts

BACKGROUND The aim of this study was to manufacture a new aortic model with physiological properties, which could be used for long-term durability testing of endovascular stent-grafts, as per the recommendations of the Food and Drug Administration. METHODS Porcine abdominal aortas were acquired to establish values for compliance. The aortic model was manufactured using a nanocomposite polymer. Latex mock aorta was used for comparison. A pulsatile flow phantom perfused the aortas and synthetic tubes at physiological pulse pressure and flow. Diametrical compliance and stiffness index were calculated over mean pressures from 30 to 120 mm Hg. Data were analyzed using one-way analysis of variance and Bonferronis test. RESULTS Flow circuit hemodynamic values were similar for porcine aorta and synthetic tubes. Compliance of aorta ranged from 2.97 ± 0.72 (mean ± SD) to 1.42 ± 0.37%/mm Hg × 10⁻². The polymer model showed significantly better compliance (range, 3.66 ± 1.05-2.72 ± 0.28%/mm Hg × 10⁻²; p < 0.05), with no significant difference in elastic stiffness index (range, 101.6 ± 28.9-51.3 ± 10.7 for aorta and 39.8 ± 8.5-34.2 ± 3.8 for polymer model; p > 0.05). It also showed anisotropic behavior similar to the aorta. Latex tubes showed compliance that was lower than that in aorta (range, 0.87 ± 0.24-0.86 ± 0.2%/mm Hg × 10⁻²) and failed by a significant distension on increase in pressure from mean of 90 mm Hg. CONCLUSIONS We have developed physiologically relevant aortic model showing compatible anatomy, compliance, and viscoelasticity, which could be used for long-term fatigue analysis of vascular stents and grafts. The latex mock aortas can fail at physiological pressures.