Nitinol Stents in the Femoropopliteal Arterial Segment

One center’s experience with the Cordis SMART stent suggests the device should play a larger role in treating this vessel.

By Mark W. Mewissen, MD

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In the femoropopliteal (FP) arterial segment, the technical success and durability of balloon PTA strongly correlate with lesion morphology.1-5 In general, the results obtained after treating longer stenoses and/or occlusions have not been encouraging. For instance, a 5-year cumulative patency rate of 75% can be expected for short focal stenoses, but the 1-year cumulative patency rate for occlusions longer than 3 cm is significantly lower.2 Similarly, reported 6-month cumulative patency rates have been 86.8% for stenoses shorter than 7 cm and 23.1% for those longer than 7 cm.3 In general, balloon PTA of lesions shorter than 5 cm is more durable than PTA of lesions longer than 10 cm.4

The TransAtlantic Inter-Society Consensus (TASC) Docu-ment was recently published to propose treatment strategies and recommendations for the management of peripheral arterial disease.5 For instance, in the FP segment, each type of vascular lesion can be assigned a lesion grade based on morphology and variables known to affect the success and patency rates of PTA (Table 1). Per recommendation, TASC A lesions are most suitable for endovascular procedures, whereas surgery is recommended for TASC D lesions. The TASC document clearly states that more evidence is needed to make firm recommendations about the role of balloon PTA for TASC B and C lesions. Although such lesions are amenable to balloon PTA, a lower technical success rate and poorer long-term patency are expected.

Intravascular metallic stents have been used in the FP segment, but to a lesser extent than in the iliac arteries. Early metallic stents (Palmaz, Cordis Corporation, a Johnson & Johnson company, Miami, FL; and Wallstent, Boston Scientific Corporation, Natick, MA) provided excellent early technical results, particularly in the role of “bailing out” a failed balloon PTA due to extensive dissection, recoil, or acute thrombosis.5,6 However, their usefulness in preventing intimal hyperplasia and preventing long-term restenosis has been very limited in the infrainguinal region. In fact, TASC Recommendation 36 states that FP stenting as a primary approach to the interventional treatment of intermittent claudication or chronic limb ischemia is not indicated. Stents may, however, have a limited role in salvaging acute PTA failures or complications.5 This recommendation is based on earlier experience with the balloon-expandable Palmaz stent and the self-expandable Wallstent.6 To date, there are few data with newer metallic stents, such as the self-expandable nitinol SMART stent (Cordis Corporation).

Our objectives were to determine the safety of primary stenting with the self-expanding nitinol SMART stent in patients with chronic limb ischemia and complex FP arterial lesions, and, furthermore, to define the natural history of a deployed SMART stent in the FP segment, objectively observed at regular intervals with color duplex scanning, a direct noninvasive imaging technique with accuracy comparable with that of angiography.7,8

Between January 1999 and November 2003, 137 lower limbs in 122 patients with chronic limb ischemia and TASC A (n=12) and B or C (n=125) lesions of the FP artery were treated with Cordis SMART self-expanding stents. The treatment group was composed of 86 men and 34 women, with a mean age of 70.1 years.

Whenever accessible, the contralateral common femoral artery is punctured in a retrograde fashion to place a 7F sheath over the aortic bifurcation (Figure 1). Conventional catheter and guidewire techniques are used to cross the FP lesion. Balloon predilatation is not generally performed. All stents are therefore deployed primarily with the guidance of a 0.035’’ guidewire. Typically, the stent length is selected to ascertain that its proximal and distal edges flare out into a relatively disease-free segment, avoiding overlap at bifurcation points, such as the profunda femoralis.

When multiple stents are necessary to cover the entire lesion length, slight stent overlap is important. The most common stent diameter used is 6 mm. In-stent dilatation is then performed, typically with a 5-mm or 6-mm balloon catheter, avoiding stent edge dilatation.

Patients typically receive 5,000 units of heparin and 300 mg of Plavix (Bristol Myers Squibb, New York, NY) immediately before stent deployment. The administration of Plavix is continued for 30 days.

Definitions of Outcome
Technical success was defined as a patent vessel with &Mac178;30% residual stenosis after the procedure. Patients were evaluated by duplex ultrasound and Doppler-derived pressure measurements at 30 days and 3 months, and at 6-month intervals thereafter. Hemodynamic stent failure occurred with the presence of a > 50% stenosis, measured with color duplex scanning and peak systolic velocity criteria. All data were maintained in a database and analyzed with True Epistat (True Epistat, Richardson, TX). The hemodynamic primary stent patency rate was calculated by the life-table methods from the time of intervention, uninterrupted by hemodynamic stent failure.

One hundred thirty-seven FP lesions, including 20 occlusions, were treated with 246 SMART stents, with a mean of 1.8 stents per limb. The mean lesion length was 12.2 cm (range, 4-28 cm). Fifty-nine lesions (43%) measured less than 10 cm, and 78 lesions (57%) measured greater than 10 cm in length.
The technical success rate was 98%. In two patients, the stent delivery catheter could not be advanced through the lesion. Two patients suffered a major complication, requiring emergent repair of a femoral artery at the catheter entry site in one patient and catheter-directed lytic therapy to treat a distal embolus in the other. There were no procedure-related deaths.

The mean follow-up was 302 days (range, 1 day to 41 months). Within the follow-up period, 24 limbs were diagnosed with a >50% in-stent stenosis. The mean time to hemodynamic stent failure was 290 days, ranging from 14 days to 24 months.

The hemodynamic stent patency rates were 92%, 76%, 66%, and 60% at 6, 12, 18, and 24 months, respectively (Figure 2).

Primary stenting of complex FP lesions is a safe and highly technically successful percutaneous intervention. In our experience, the technical success rate was 98%, irrespective of lesion grade. Acute hemodynamic stent failure (<30 days) was rare, as evidenced by the fact that it occurred in only one patient at 14 days after intervention. Hemodynamic nitinol stent failure continues to be observed, although the 76% 1-year patency is historically improved compared to previously reported data with other metallic stents.5,6 The characteristics intrinsic to the SMART nitinol stent that may be potentially responsible for superior durability are not completely understood. Factors such as radial strength, metal used, cell size, and weaving characteristics may play a role.

The relatively long time before the occurrence of hemodynamic stent failure has had a large impact on the percutaneous treatment of FP disease in our practice. Instantaneous and relatively prolonged improved perfusion to an ischemic ulcer is a prerequisite to wound healing. Select patients with critical limb ischemia and nonhealing ulcers are ideal candidates who are most likely to benefit from FP stenting. Even in patients with multilevel disease and TASC B or C lesions, the recannalized FP segment can serve as a conduit to access tibial lesions, amenable to percutaneous intervention in selected instances. Also, FP stenting can effectively provide inflow for a popliteal-tibial vein bypass graft, particularly in patients whose saphenous veins have previously been harvested.

In the near future, coated stents designed specifically for the treatment of FP disease will further impact the management of the diseased femoropopliteal artery. In the meantime, may I suggest that TASC Recommendation 36 be revised?

In conclusion, our data and increasing patient referral clearly indicate that there is a role for femoropopliteal stenting as a primary approach to the interventional treatment of critical ischemia. As clinical experience with each new device grows, the spectrum of lesions for which it is appropriate should become better defined.

Mark W. Mewissen, MD, is Director of Peripheral Vascular Services, Wisconsin Heart and Vascular Clinics, St. Lukes Medical Center, Milwaukee, Wisconsin. He has no financial interest in any product or manufacturer mentioned herein. Dr. Mewissen may be reached at (414) 649-3580;

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