Self-expanding stents and aortoiliac occlusive disease: a review of the literature

The treatment of symptomatic aortoiliac occlusive disease has shifted from open to endovascular repair. Both short- and long-term outcomes after percutaneous angioplasty and stenting rival those after open repair and justify an endovascular-first approach.
In this article, we review the current endovascular treatment strategies in patients with aortoiliac occlusive disease, indications for primary and selective stenting in the iliac artery, and physical properties and future perspectives of self-expanding stents.

Introduction
The prevalence of peripheral arterial disease (PAD) in the US is more than 4% among adults aged 40 years and over. PAD increases dramatically with age and the prevalence exceeds 14% among those aged 70 years or over.
One subset of PAD is aortoiliac occlusive disease (AIOD), defined as any stenosis or occlusion from the distal aorta to the common femoral artery (CFA). [/color
]Conventional surgical revascularization of AIOD is associated with excellent long-term patency rates.However, open repair is also associated with a significantly longer hospital stay and higher complication rates and inpatient costs, compared with endovascular treatment.
The TransAtlantic Intersociety Consensus (TASC) II, published in 2007, recommends endovascular therapy for straightforward AIOD (TASC A lesions) and surgery for complex AIOD (TASC D lesions).
However, due to the rapid development of endovascular techniques and improved competence, experienced centers advocate an “endovascular first” approach. In recent years, endovascular treatment has become widespread and is the preferred method of treatment nowadays for lower extremity arterial obstructions.

Endovascular treatment of AIOD consists of percutaneous transluminal angioplasty (PTA) with or without stenting. In a meta-analysis of six PTA studies (1,300 patients) and eight PTA and stent studies (816 patients), additional stenting was associated with an increased technical success rate and improved long-term patency. The results of endovascular treatment of AIOD have been described in multiple publications.
Technical success and both short- and long-term patency rates have been satisfactory, even in challenging lesions.
These results justify an endovascular-first approach for symptomatic AIOD treatment.

Primary versus selective stenting
The Dutch Iliac Stent Trial enrolled 279 patients with intermittent claudication on the basis of iliac artery stenosis of >50%. The study randomly assigned 143 patients to direct stent placement (group I) and 136 to primary angioplasty, with selective stent placement in case of a residual mean pressure gradient >10 mmHg across the treated lesion (group II).

Clinical success, cumulative patency, and reintervention rates at 2 years were similar between the groups.
Long-term results (after 5–8 years) showed a better clinical outcome in patients with PTA and selective stenting in the iliac artery. Iliac patency, ankle–brachial index, and quality of life did not support a difference between groups.

More recent studies showed that primary stenting has significant benefits over angioplasty alone in TASC C and D aortoiliac lesions.
In a nonrandomized series of 151 patients with iliac stenosis, a total of 110 consecutive patients (149 lesions) underwent primary stenting. The results were compared with 41 patients (41 lesions) who had PTA followed by selective stenting for suboptimal PTA.
The overall early clinical success rate was superior for the primary stent group .For TASC A and B lesions, the initial and late clinical success rates were comparable but were inferior in selective stenting for TASC C and D lesions.12

A recent meta-analysis of 16 reports including 958 patients with endovascular treatment of TASC C and D aortoiliac arterial lesions found better patency rates for primary stenting than for selective stenting.

The Stents Versus Angioplasty for the Treatment of Iliac Artery Occlusions (STAG) trial randomly assigned 112 patients with an iliac occlusion to PTA or primary stent placement. PTA was performed in 55 patients and primary stenting in 57.
Technical success in the primary stenting group was higher (98% vs 84%) and major complications (predominantly distal embolization) occurred less frequently (5% vs 20%) compared with PTA. Patency rates did not differ after 1 and 2 years.

Predictors of success or failure

Independent predictors of iliac endovascular intervention success or failure have been described in multiple publications.
The presence of two-vessel femoral runoff or at least two patent below-the-knee vessels, or both, is associated with improved iliac artery primary patency.
Poor outflow requiring a bypass is associated with decreased iliac artery primary patency rates.
In another study, iliac PTA and stenting, combined with an untreated superficial femoral artery stenosis >50% resulted in a decreased primary patency rate.

The presence of an iliac artery occlusion is considered an independent risk factor for patency loss.
However, similar results after treatment of iliac stenoses and occlusions have been published. In a series of 73 patients including 76 occluded iliac arteries (33 common, 34 external, and nine both) the primary patency was 79% at 1 year and 69% at 3 years.
In a prospective series of 223 patients with AIOD, endovascular treatment was performed for iliac occlusion in 109 patients and for iliac stenosis in 114 patients. No differences were observed in the complication rate or in short- and long-term patency rates.

Other predictors for decreased primary patency include diabetes mellitus,age <50 years, TASC C and D lesions,hypertension,hypercholesterolemia,chronic renal insufficiency,external iliac artery (EIA) disease, female sex, and smoking history.

Conclusion
PTA and stenting is the preferred treatment modality in patients with AIOD and has been associated with satisfactory long-term results, even in challenging lesions.
Primary stenting is indicated in iliac artery occlusions, while in iliac artery stenoses, selective stenting is preferred.
Unfortunately, detailed information about the performance of different stent types in clearly defined iliac artery segments is limited.
The unique properties of self-expanding stents make them particularly suitable for the treatment of long, tortuous, and mobile arteries, like the EIA.
The most important limitation is in-stent restenosis resulting from neointimal hyperplasia. Use of covered or DESs seems promising, but more evidence is needed to finally prove these concepts .

G Mohan.