Robert Staffa

Importance of material model in wall stress prediction in abdominal aortic aneurysms

BACKGROUND Results of biomechanical simulation of the abdominal aortic aneurysm (AAA) depend on the constitutive description of the wall. Based on in vitro and in vivo experimental data several constitutive models for the AAA wall have been proposed in the literature. Those models differ strongly from each other and their impact on the computed stress in biomechanical simulation is not clearly understood. METHODS Finite element (FE) models of AAAs from 7 patients who underwent elective surgical repair were used to compute wall stresses. AAA geometry was reconstructed from CT angiography (CT-A) data and patient-specific (PS) constitutive descriptions of the wall were derived from planar biaxial testing of anterior wall tissue samples. In total 28 FE models were used, where the wall was described by either patient-specific or previously reported study-average properties. This data was derived from either uniaxial or biaxial in vitro testing. Computed wall stress fields were compared on node-by-node basis. RESULTS Different constitutive models for the AAA wall cause significantly different predictions of wall stress. While study-average data from biaxial testing gives globally the same stress field as the patient-specific wall properties, the material model based on uniaxial test data overestimates the wall stress on average by 30 kPa or about 67% of the mean stress. A quasi-linear description based on the in vivo measured distensibility of the AAA wall leads to a completely altered stress field and overestimates the wall stress by about 75 kPa or about 167% of the mean stress. CONCLUSION The present study demonstrated that the constitutive description of the wall is crucial for AAA wall stress prediction. Consequently, results obtained using different models should not be mutually compared unless different stress gradients across the wall are not taken into account. Highly nonlinear material models should be preferred when the response of AAA to increased blood pressure is investigated, while the quasi-linear model with high initial stiffness produces negligible stress gradients across the wall and thus, it is more appropriate when response to mean blood pressure is calculated.

Safety of early endarterectomy in patients with symptomatic carotid artery stenosis: an international multicenter study

Although the latest recommendations suggest that carotid endarterectomy (CEA) should be performed in symptomatic carotid artery stenosis (sCAS) patients within 2 weeks of the index event, only a minority of patients undergo surgery within the recommended time‐frame. The aim of this international multicenter study was to prospectively evaluate the safety of early CEA in patients with sCAS in everyday clinical practice settings.

Automatic identification and validation of planar collagen organization in the aorta wall with application to abdominal aortic aneurysm.

Arterial physiology relies on a delicate three-dimensional (3D) organization of cells and extracellular matrix, which is remarkably altered by vascular diseases like abdominal aortic aneurysms (AAA). The ability to explore the micro-histology of the aorta wall is important in the study of vascular pathologies and in the development of vascular constitutive models, i.e., mathematical descriptions of biomechanical properties of the wall. The present study reports and validates a fast image processing sequence capable of quantifying collagen fiber organization from histological stains. Powering and re-normalizing the histogram of the classical fast Fourier transformation (FFT) is a key step in the proposed analysis sequence. This modification introduces a powering parameter w, which was calibrated to best fit the reference data obtained using classical FFT and polarized light microscopy (PLM) of stained histological slices of AAA wall samples. The values of w = 3 and 7 give the best correlation (Pearsons correlation coefficient larger than 0.7, R 2 about 0.7) with the classical FFT approach and PLM measurements. A fast and operator independent method to identify collagen organization in the arterial wall was developed and validated. This overcomes severe limitations of currently applied methods like PLM to identify collagen organization in the arterial wall.

Randomized controlled trial comparing the safety and efficacy between the FUSION BIOLINE heparin-coated vascular graft and the standard expanded polytetrafluoroethylene graft for femoropopliteal bypass

OBJECTIVE Despite improvements in endovascular therapy for lower extremity arterial disease, open surgical revascularization is still required when the disease is extensive. Although autogenous vein is the conduit of choice for open femoropopliteal bypass, prosthetic grafts can be an acceptable alternative when adequate vein is not available. The FUSION BIOLINE heparin-coated vascular graft (Maquet Endovascular, Wayne, NJ) was developed to improve the patency rate associated with standard prosthetic grafts. The current study, the FINEST Trial (Comparison of Safety and Primary Patency Between the FUSION BIOLINE Heparin-Coated Vascular Graft and EXXCEL Soft ePTFE), was designed to assess the clinical outcome of heparin-coated and standard vascular grafts in a prospective, randomized, controlled, multicenter trial. METHODS During a 25-month period ending in June 2012, 209 eligible patients scheduled to undergo elective prosthetic femoral to above-knee or below-knee popliteal bypass were randomized to receive a standard expanded polytetrafluoroethylene (ePTFE) graft or the heparin-coated FUSION BIOLINE vascular graft. Among 203 patients in the efficacy analysis, claudication was the presenting symptom in 147 (72.4%), and the site of the distal anastomosis was at the above-knee level in 174 (85.7%). Grafts were assessed by duplex ultrasound imaging and ankle-brachial indices performed postoperatively at discharge and at 30 days, 6 months, and 12 months. The primary efficacy end point was primary patency of the study graft. The primary safety end point was the composite of major adverse events and periprocedural death. Secondary end points included the time to hemostasis of bleeding at the anastomotic suture hole and primary assisted and secondary patency. RESULTS The primary patency rates at 6 months were 86.4% for the FUSION BIOLINE heparin-coated vascular graft group compared with 70.0% for the standard ePTFE group, a difference of 16.4% (95% confidence interval, 2.7%-29.9%; P = .006), and the respective rates at 12 months were 76.5% and 67.0% (95% confidence interval, -4.8% to 23.0%; P = .05). The mean time to hemostasis of bleeding at the suture hole was 3.5 minutes in the FUSION BIOLINE group and 11.0 minutes in the standard ePTFE group (P < .0001). Major adverse events were significantly lower in the FUSION BIOLINE group, occurring in 17.1%, compared with 30.7% in the standard ePTFE group (P = .033), principally a result of a lower rate of major graft reinterventions through 12 months in the FUSION BIOLINE group (16.2% vs 30.7%). CONCLUSIONS Data from this randomized multicenter study demonstrated improved midterm patency, less bleeding at the suture hole, and lower major adverse events with the FUSION BIOLINE heparin-coated vascular graft compared with standard ePTFE grafts. Although the ultimate long-term benefit of the graft cannot be ascertained with the data currently available, the utility of the FUSION BIOLINE vascular graft appears promising.

The learning curve of robot-assisted laparoscopic aortofemoral bypass grafting for aortoiliac occlusive disease

BACKGROUND Since the end of the 20th century, robot-assisted surgery has been finding its role among other minimally invasive methods. Vascular surgery seems to be another specialty in which the benefits of this technology can be expected. Our objective was to assess the learning curve of robot-assisted laparoscopic aortofemoral bypass grafting for aortoiliac occlusive disease in a group of 40 patients. METHODS Between May 2006 and January 2010, 40 patients (32 men, 8 women), who were a median age of 58 years (range, 48-75 years), underwent 40 robot-assisted laparoscopic aortofemoral reconstructions. Learning curve estimations were used for anastomosis, clamping, and operative time assessment. For conversion rate evaluation, the cumulative summation (CUSUM) technique was used. Statistical analysis comparing the first and second half of our group, and unilateral-to-bilateral reconstructions were performed. RESULTS We created 21 aortofemoral and 19 aortobifemoral bypasses. The median proximal anastomosis time was 23 minutes (range, 18-50 minutes), median clamping time was 60 minutes (range, 40-95 minutes), and median operative time was 295 minutes (range, 180-475 minutes). The 30-day mortality rate was 0%, and no graft or wound infection or cardiopulmonary or hepatorenal complications were observed. During the median 18-month follow-up (range, 2-48 months), three early graft occlusions occurred (7%). After reoperations, the secondary patency of reconstructions was 100%. Data showed a typical short learning curve for robotic proximal anastomosis creation with anastomosis and clamping time reduction. The operative time learning curve was flat, confirming the procedures complexity. There were two conversions to open surgery. CUSUM analysis confirmed that an acceptable conversion rate set at 5% was achieved. Comparing the first and second half of our group, all recorded times showed statistically significant improvements. Differences between unilateral and bilateral reconstructions were not statistically significant. CONCLUSIONS Our results show that the success rate of robot-assisted laparoscopic aortofemoral bypass grafting is high and the complication rate is low. Anastomosis creation, one of the main difficulties of laparoscopic bypass grafting, has been overcome using the robotic operating system and its learning curve is short. However, the endoscopic dissection of the aortoiliac segment remains the most difficult part of the operation and should be addressed in further development of the method to reduce the operative times. Long-term results and potential benefits of this minimally invasive method have to be verified by randomized controlled clinical trials.

Pedal bypass for limb salvage

Abstract Background: Pedal bypass grafting is often the only method of limb salvage in patients with chronic critical lower limb ischemia due to atherosclerotic obliteration of the crural arteries, including patients with diabetic foot gangrene. It involves arterial reconstruction with distal anastomosis to one of the pedal arteries. Material and Methods: Between January 2000 and June 2004, 54 pedal bypasses were performed in 53 patients with chronic critical lower limb ischemia. Forty-seven (87%) patients had gangrene or ischemic ulcer, 36 (68%) had diabetes. In some of the patients (16.7%), previous percutaneous transluminal angioplasty (PTA) of the crural arteries had failed. Preoperative angiographic findings were unsatisfactory in the majority of the patients; the plantar arch was not visualized in 36 (66.7%) limbs. Results: In the period investigated (54 months) 11 grafts (20.4%) failed. Early thrombectomy resulting in long-term graft patency salvaged five limbs. One limb with graft occlusion occurring after foot ulcer healing was also salvaged. However, one amputation had to be performed despite a patent graft. The perioperative mortality rate was 3.8%. Cumulative primary and secondary graft patency rates and limb-salvage rates at 54 months were 76%, 78% and 81%, respectively. Conclusion: Pedal bypass grafting is a safe method with very good long-term outcomes. The absence of the pedal arteries or plantar arch on preoperative angiograms need not be taken as a contraindication to pedal vascular reconstruction. In discussions on the plantar arch it is recommended to discriminate between its actual absence and a mere “angiographic” absence.

Infrared thermography as option for evaluating the treatment effect of percutaneous transluminal angioplasty by patients with peripheral arterial disease.

Aim of this study was to evaluate the possible use of infrared thermography as a supplementary method to the ankle-brachial index used in assessing the treatment effect of percutaneous transluminal angioplasty. The study included 21 patients, mean age was 60.22 years. Healthy control group included 20 persons, mean age was 55.60 years. Patients with symptomatic peripheral arterial disease (Fontaine stages I–III) were admitted for endovascular treatment by percutaneous transluminal angioplasty. Thermal images and ankle-brachial index values were obtained before and after treatment by percutaneous transluminal angioplasty. Median temperature change in the treated limb was 0.4℃, for non-treated limb was –0.5℃. The median value of ankle-brachial index in the treated limb increased by 0.17 from 0.81 after the procedure. The median value of ankle-brachial index in the non-treated limb decreased by 0.03 from the value of 1.01. Significant difference between treated limb and non-treated limb in change of ankle-brachial index was found with p value = .0035. The surface temperature obtained by the infrared thermography correlates with ankle-brachial index. We present data showing that the increase of ankle-brachial index is associated with increase of skin temperature in the case of limbs treated by percutaneous transluminal angioplasty. Our results also suggest potential of the use of infrared thermography for monitoring foot temperature as a means of early detection of onset of foot ischemic disorders.

Correlation between transversal and orthogonal maximal diameters of abdominal aortic aneurysms and alternative rupture risk predictors

PURPOSE There is no standard for measuring maximal diameter (Dmax) of abdominal aortic aneurysm (AAA) from computer tomography (CT) images although differences between Dmax evaluated from transversal (axialDmax) or orthogonal (orthoDmax) planes can be large especially for angulated AAAs. Therefore we investigated their correlations with alternative rupture risk indicators as peak wall stress (PWS) and peak wall rupture risk (PWRR) to decide which Dmax is more relevant in AAA rupture risk assessment. MATERIAL AND METHODS The Dmax values were measured by a trained radiologist from 70 collected CT scans, and the corresponding PWS and PWRR were evaluated using Finite Element Analysis (FEA). The cohort was ordered according to the difference between axialDmax and orthoDmax (Da-o) quantifying the aneurysm angulation, and Spearmans correlation coefficients between PWS/PWRR - orthoDmax/axialDmax were calculated. RESULTS The calculated correlations PWS/PWRR vs. orthoDmax were substantially higher for angulated AAAs (with Da-o≥3mm). Under this limit, the correlations were almost the same for both Dmax values. Analysis of AAAs divided into two groups of angulated (n=38) and straight (n=32) cases revealed that both groups are similar in all parameters (orthoDmax, PWS, PWRR) with the exception of axialDmax (p=0.024). CONCLUSIONS It was confirmed that orthoDmax is better correlated with the alternative rupture risk predictors PWS and PWRR for angulated AAAs (DA-O≥3mm) while there is no difference between orthoDmax and axialDmax for straight AAAs (DA-O<3mm). As angulated AAAs represent a significant portion of cases it can be recommended to use orthoDmax as the only Dmax parameter for AAA rupture risk assessment.

Organization model for allotransplantations of cryopreserved vascular grafts in Czech Republic

The transplantation of fresh or cryopreserved vascular allografts in patients with a prosthetic graft infection or critical limb ischemia is necessary for their limb salvage and, in many cases, represents a lifesaving procedure. While transplantation of fresh allografts has a long history in the Czech Republic, the standard use of cryopreserved vascular allografts was introduced into the clinical practice in 2011 as a result of the implementation of EU Directive 2004/23/EC into national legislation (Human Cell and Tissue Act No. 296/2008 Coll.). The authors present an organizational model based on cooperation between the majority of Czech Transplant Centers with a tissue establishment licensed by the national competent authority. In various points, we are addressing individual aspects of experimental and clinical studies which affect clinical practice. Based on experimental and clinical work, the first validation of cryopreserved arterial and venous grafts for clinical use was performed between 2011 and 2013. The growing number of centers participating in this programme led to a growing number of patients who underwent transplantation of vascular allografts. In 2015 the numbers of transplanted fresh versus cryopreserved allografts in the Czech Republic were almost equal. Cooperation of the participating centers in the Czech Republic with the licensed Tissue Establishment made it possible to achieve a full compliance with the European Union Directives, and harmonized national legal norms and assured a high quality of cryopreserved vascular allografts.

Treatment of infrapopliteal post‐PTA dissection with tack implants: 12‐month results from the TOBA‐BTK study

The Tack implant is designed for focal, minimal metal management of dissections. This study evaluated Tacks for treating postpercutaneous transluminal angioplasty (PTA) dissection in patients with below‐the‐knee (BTK) arterial occlusive disease.