Fatigue Behavior of Peripheral STENt of the Superficial Femoral Artery

Atherosclerotic Pathology of the Superficial Femoral Arteries: Study and Patient-specific Prediction of the Fatigue Behavior of Peripheral STENt in Nitinol Via Mathematical Modeling. Prospective Enrollment

Endovascular treatment of superficial femoral artery stenosis/obstruction is still the subject of debate in the scientific literature.

Previous clinical studies have in fact reported conflicting data regarding the benefits of implanting self-expanding Nitinol stents in the superficial femoral artery district compared to simple percutaneous transluminal angioplasty. Invariably, patient comorbidities and anatomic characteristics of the lesions appear to be important factors influencing procedural success and one-year patency rates. Additionally, there are concerns regarding the potential clinical impact of stent fractures, reported at rates ranging from 12% to 37.2% at one year.

Despite the improved outcomes seen with newer Nitinol stent designs, the primary limitations of stenting in the superficial femoral artery are the use of multiple overlapping stents or long stents and the associated potential rate of stent fracture resulting reocclusion of the treated superficial femoral artery and clinical worsening of patients who in most cases are initially treated for disabling claudication.

Being able to preoperatively determine in which patients there are risk factors prognostically associated with a higher rate of fracture/reocclusion could represent a help for the operator in choosing the best therapeutic strategy.

The study involves the prospective collection of the following data:

• Preoperative: vessel diameters, plaque length, plaque type, percentage of stenosis, position of the stenosis. These data will be collected from the analysis of CT images, magnetic resonance imaging, color Doppler ultrasound or angiographies performed by patients in the diagnostic phase;
• Intraoperative: number and model (brand and size) of stent implanted, position of the stent. The stents used are those foreseen by the usual clinical practice of each center. In particular, the behavior of the following stents will be analysed:

or Absolute Pro® Vascular Self-Expanding Stent System - ABBOTT VASCULAR or S.M.A.R.T.® Flex Vascular Self-Expanding Stent - CORDIS or LifeStent® - BARD PV or Zilver® - COOK MEDICAL

- Follow-up: restenosis event, stent fracture event. In particular, the restenosis event will be defined by the presence of a reduction in the caliber of the vessel morphologically greater than 30% or with PVR (Peak Velocity Ratio = peak systolic velocity in correspondence with the stenosis/peak systolic velocity upstream in a non-stenotic tract ) recorded on color Doppler ultrasound > 2.4. The stent fracture event will be defined by the presence of discontinuity images in the stent structure itself. These data will be collected from the analysis of arterial color-Doppler ultrasound images of the lower limbs (reference investigation foreseen by the study) or other investigations (CT, magnetic resonance imaging, angiographies) performed by patients in the follow-up phase.

The mathematical model:

The computational analysis involves a reproduction via 3D model of the morphology of the pathological superficial femoral artery specific to the diagnostic data of the patients and the peripheral Nitinol stents used.

The recanalization/dilation and stenting treatment is simulated using a finite element model, taking into account the phases of the clinical procedure and the consequent cyclic stress conditions to which the device is subjected in vivo.

The results of the computational model are analyzed in order to obtain the state of stress acting on the device and evaluate its risk of breakage.

In particular, the models created to reproduce the cases of the study will be developed using a commercial software in which the collected pre- and intraoperative parameters are entered, and from which the prediction values of whether or not the superficial femoral stent will break will be extracted.

The prediction given by the mathematical model will be compared with the data actually observed during the 3-year follow-up.

The collected data will then be entered into a database and analyzed using the JMP 5.1.2 statistical software (S.A.S. Institute).

Inclusion Criteria:

• adult patients (≥ 18 years) hospitalized in the Operating Units participating in the study and subjected to a recanalization/dilation and stenting procedure of the superficial femoral artery due to stenosis or obstruction of the same conditioning disabling claudication or critical ischemia of the lower limb (class 3-4-5-6 according to Rutherford).

Exclusion Criteria:

• minor patients (age <18 years);
• patients who have not given their consent to participate in the study;
• Pregnant women.