Abstract
Objective: To examine the efficacy and durability of an interwoven self-expanding nitinol stent for the treatment of superficial femoral and popliteal arteries.
Method: Consecutive patients with severely diseased superficial femoral and popliteal arteries who received SUPERA stents were retrospectively identified.
The patients were followed for 12 months by Doppler ultrasound examinations, stent roentgenograms, and estimation of Rutherford–Becker class and ankle-brachial index.
Results: From July 2012 to May 2014, 42 limbs in 36 patients (mean age, 61.5 7.5 years; 75% male) were treated with angioplasty and primary stenting. Total occlusions were present in 14 limbs, and 63.8% had either moderate or severe calcification. The mean ( SD) lesion length was 105 mm ( 28). Primary patency was 91.4% at 6 months and 85.7% at 12 months. The ankle brachial index increased from 0.57 0.19 preoperative to 0.91 0.12 postoperative. There was no procedural or device-related morbidity or mortality after revascularization and only one major amputation was observed on follow-up.
Conclusions: Our experience shows that, Supera stents are safe and effective in our cohort of patients, with acceptable patency rates. There were no stent fractures so far even with stenting of the femoropopliteal segments. Stent design provides a viable option for high-grade obstructive disease in the femoropopliteal artery.
Keywords
Superficial femoral artery, peripheral artery disease, occlusion, angioplasty, nitinol stent, stent fracture
Introduction
Percutaneous interventions for peripheral arterial dis-ease (PAD) in the superficial femoral artery (SFA) and the femoropopliteal artery have been associated with high restenosis rates and poor long-term patency with balloon angioplasty alone.1 Treatment strategies in the SFA and femoropopliteal artery are potentially com-promised by the high calcium content within the plaque and vessel wall, long length of lesions, and unique dynamic forces found within these arteries.2
Multiple clinical trials with laser-cut nitinol stents in primary stent placement have demonstrated improved patency rates compared with either percutaneous trans-luminal angioplasty with provisional stent placement or a predefined percutaneous transluminal angioplasty performance goal.3–5 However, with 12-month patency rates in these trials ranging from 53% to 83% after nitinol stent implantation, restenosis rates are still greater than desirable, especially in difficult lesion seg-ments. Another potential risk factor for reocclusion stems from stent fractures, which range from 0.4% to 8.1% at 12 months.6,7 Since then, significant improvements in the design of laser-cut nitinol stents have been made, which have increased the axial flexi-bility of the implants.6 While the rates of fractures reported with this second generation of nitinol stents tend to be lower, data on stented segments >15 cm are missing, and major stent fractures continue to occur after the treatment of shorter segments. In the recently reported DURABILITY study, a clear correlation was observed between major stent fractures and restenosis and target lesion revascularization.6
The objective of this analysis was to evaluate the performance and durability of a novel stent system designed to withstand the compression, torsion, bend-ing, lengthening, shortening, and pulsations found within the SFA. We report our single-center experience in patients with PAD who received interwoven nitinol stents in the femoropopliteal arteries.
Methods
Patients
All patients who received Supera interwoven nitinol stents (IDEV Technologies, Webster, TX, USA) in the femoropopliteal artery segment at our hospital were retrospectively identified. Patients underwent baseline physical examinations with a focus on lower limb ischemia, categorized according to the Rutherford–Becker classification (RBC). Ankle bra-chial index (ABI) measurements and duplex ultrasound studies were performed, followed by selective angiog-raphy of the femoropopliteal segment to outline the anatomy of the vessels and define the lesion characteristics.
Treatment and follow-up were according to the standard procedures implemented in our institution. All patients gave written informed consent before undergoing the procedure. To collect scientifically and clinically meaningful information, the study intention-ally included patients presenting with a wide variety of complex lesions in the femoropopliteal arteries, includ-ing heavy calcifications and total occlusions, without prespecified inclusion and exclusion criteria. The sys-tematic follow-up focused on the incidence of stent fractures and restenosis. Patients with lower limb femoropopliteal arterial stenosis or occlusions, as shown on preoperative duplex ultrasound assessment, were included in this study. Patients with acute throm-bus or aneurysm in the index vessel, unsalvageable limb, poor inflow or total absence of runoff vessels, lesions unsuitable for angioplasty, very limited life expectancy, or doubts in the willingness or capability to allow follow-up examination were excluded.
Patients with renal impairment who were deemed very high risk of developing contrast nephropathy would be optimized as much as possible and those who could not tolerate the intervention or subsequent follow-up were excluded.
Stent procedure and medical regimens
All patients had initial diagnostic angiography of the lower limb with standard contrast intra-arterial digital subtraction angiogram to outline the vascular anatomy and define the lesion characteristics and to confirm their candidacy for the study. The endovascular procedures were performed by experienced vascular specialists in a hybrid endovascular suite (Siemens Artis Zeego Multipurpose System; Siemens, Munich, Germany). The procedures were performed under monitored anes-thetic care or under local anesthesia, with ipsilateral or contralateral common femoral artery and retrograde popliteal artery accessed with a 6 F sheath for the diag-nostic angiogram. All the patients received intra-arter-ial heparin through the sheath. From the intraoperative angiogram, it was possible to calculate and document the diameter of the target vessel, the minimal luminal diameter, minimal luminal area, and the length of sten-osis–occlusion. Patients with chronic SFA occlusion underwent percutaneous recanalization from a retro-grade popliteal access. The popliteal artery was punc-tured using an 18-G needle under ultrasound guidance. After insertion of a 5–6 F introducer sheath, and per-formance of diagnostic angiogram, intravenous heparin (100 U/kg) was administered. For crossing the stenosis or occlusion, 0.035 road runner guidewire was used through the right judkins 5-6 guiding catheter. The ini-tial passage of the occlusion was carried out; the wire was exchanged for a 0.018-in. or 0.020-in. wire. The Rotarex device was introduced for chronic total occlu-sions and slowly moved forward with a to-and-fro motion at a speed of about 1–2 cm/s until the distal end of the occlusion was reached. A control angiogram was performed after the first passage and, if necessary, additional runs were performed until all thrombotic material was removed. After the first or second passage of the occlusion, the flow was checked by dye injection while the catheter was still in position distal to the occlusion. If flow was restored, the wire was pulled back into the catheter lumen, and the device was slowly retracted while rotating the slightly bent tip of the catheter. This allowed clearing thrombi from a larger area of the vessel. After recanalization of the SFA and proximal popliteal artery with balloon angio-plasty and Rotarex catheter system, Supera interwoven nitinol stents were deployed to cover the needed parts of the lesion (Figure 2). The interwoven nitinol Supera stent is constructed from six pairs of nitinol wires woven together to create a helical pattern. The wires form closed loops at both ends of the stent. The stent is premounted and delivered via a 6-F or 7-F catheter-based delivery system over a 0.014-in. or 0.018-in. wire. All lesions were routinely dilated before stent placement using a balloon 0.5–1.0 mm larger than the reference vessel diameter to allow adequate expansion of the stent. Stent length was selected so as to cover the lesion and at least 5 mm of lesion-free proximal and distal vessel. When more than one stent was needed, stents were over lapped for at least 10 mm. Dilation with a noncompliant balloon was performed after stent placement if the operator recognized that some segments of stent were underexpanded. A control angiogram was done to visualize the flow within the SFA and PA and to exclude the presence of thrombo-embolic material distally.
The antithrombotic regimen was administered per usual institutional practices, including periprocedural anticoagulation with weight-based heparin to maintain activated clotting time >250 s. Dual antiplatelet ther-apy with aspirin and clopidogrel was prescribed after the procedure for at least 30 days unless a contraindi-cation existed; this was followed by aspirin alone indefinitely.
Follow-up and study end points
All patients were evaluated before discharge from the hospital and were scheduled to return for ambulatory follow-up visits at 1, 6, 12, and 24 months after the procedure. At these visits, physical examinations, cat-egorization of the RBC, ABI measurements, and duplex ultrasound studies for the detection of restenosis were performed; the duplex ultrasound recordings were analyzed by an independent investigator. To confirm the integrity of the stent, and in compliance with the institution’s practices, plain roentgenograms of the stented segment were obtained between 12 and 24 months after the index procedure in two oblique views with the leg extended and with the knee bent.
The primary efficacy end point of this analysis was stent patency, defined as absence of binary restenosis (>50% decrease in vessel diameter) on duplex ultra-sound examination as represented by a peak systolic velocity ratio > 2.4.8 The secondary end points included (1) procedural success, defined as a, 30% residual vessel stenosis; (2) clinical status according to the RBC; (3) ABI measurements; (4) incidence of stent fractures on radiographic screening; and (5) the rate of target lesion revascularization.
Statistical analysis
Statistical analysis was performed with Graphpad Instat software (version 3 for Mac; version 11.5, GraphPad Software Inc.). Descriptive statistics were used to present the mean standard deviation or median (range) for continuous variables and the counts (percentages) for categorical variables. Cumulative patency rates with their standard errors were estimated using Kaplan–Meier analysis. Comparisons of mean ABI and RBCs at various time points were made using the Student’s t-test for depend-ent samples. Statistical significance was defined as p < 0.05.
Results
Patient characteristics
From July 2012 to May, 36 consecutive patients (26 males) with symptomatic femoropopliteal lesions were treated with angioplasty and primary stenting using the Supera stent at our institution. Twenty-two were left-sided lesions, 14 were right-sided lesions, and 4 patients have bilateral interventions. Mean ( SD) age was 61.5 ( 7.3) years. (Range, 56–82 years); 26 (72%) patients were male. Demographic data, risk factors, and comor-bidities are summarized in Table 1.
Of the 42 interventions performed, most (64.2%) involved the SFA only, and 14.2% involved the poplit-eal artery only (Table 1). Before the interventions, total occlusions were present in 14 limbs (38.8%), 22% had tissue loss, and 63.8 % of lesions showed moderate or severe calcification on fluoroscopy. Cardiovascular risk factors were prevalent; 80.5% (29 patients) were on antihypertensive medication, 72% (26 patients) were active smokers, 52.7% (19 patients) were diabetic, and 30.5% (11 patients) had proven hyperlipidemia (Table 1). The majority (29, 80.5%) of patients pre-sented with severe claudication (Rutherford–Becker category 3); 7 (19.4%) had critical limb ischemia (Rutherford–Becker category 4–5).
Lesions and procedural characteristics
Lesion characteristics and number of runoff vessels are summarized in Table 2, with 14 (38.8%) cases involving the proximal SFA, 20 (55.5%) cases involving the mid-SFA, 23 (63.8%) cases involving the distal-SFA, 17 (47.2%) cases involving the above-knee popliteal artery, and 10 (27.7%) cases involving the below-knee popliteal artery. The mean lesion length was 105 mm ( 28), and over half (20, 55.5%) of the lesions were moderately to severely calcified.
Technical success (puncture of the popliteal artery or femoral artery with Doppler Ultrasound (DUS) guid-ance and SFA recanalization) was achieved in all patients. Endoluminal recanalization was possible from the popliteal access in most of the patients with chronic total occlusions (n &#188; 13). SFA recanalization in one case was obtained through the subintimal space. We did not use reentry device for crossing chronic total occlusions. Procedure success (visually estimated residual arterial stenosis 10 cm, and primarily severe to critical limb ischemia), a 97.2% technical suc-cess rate was achieved, which resulted in significant clinical improvement. To achieve these excellent implantation results, we had to be more precise during the stent implantation process than would be required with standard laser-cut nitinol stents. First, careful attention was paid to properly match the stent diameter (1:1) to the reference vessel diameter to ensure that the stent could be deployed close to its nominal diameter, where it reaches its highest radial strength. Moreover, to ensure optimal compliance of the vessel during stent deployment, the artery was systematically predilated using a balloon catheter with a diameter that was at least equal to the reference vessel diameter. In selected cases with very rigid, calcified lesions, the artery was dilated with oversized or high-pressure bal-loons before stenting.
Most importantly, in our analysis, the Supera stent was very durable and remained free from fractures at a mean of 13.8 months despite the relatively long length of the stented segment (mean 124 45 mm) and the fact that nearly half of the stents were implanted into the distal SFA partially extending into the proximal popliteal segment. Similarly, the primary patency rates of 94.2% and 85.7% at 6 and 12 months, respect-ively, are very encouraging and compared favorably with the reported literature.
One of the limitations to our study is that it was a single vascular center experience. Our study has a high proportion of patients with critical limb ischemia, and many of the patients are elderly. We regard our initial results as being as accurate as possible, and the primary Supera stenting was encouraging with no clinical limb loss, no device related morbidity–mortality, and no stent fractures. Since there is as yet little long-term experience with this new helical stent worldwide, we recommended continuous surveillance of the treated segment with color-coded Doppler sonography. However, the number of patients studied is relatively small and lacks random-ization. There will inevitably be patient selection bias, which may have influenced the results.
Conclusion
Implantation of a novel self-expanding Supera stent achieved very encouraging acute and follow-up results in a cohort of patients with a wide range of femoropo-pliteal lesions. The interwoven nitinol stent design provides flexibility, and strength translate into high long-term patency and fracture resistance. Although the data are promising, additional multicenter studies are needed.






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