Preliminary Experience With DESs in Tibial Arteries
Sirolimus-eluting stents appear to be safe and effective in treating focal infrapopliteal obstructions.
Arterial revascularization with restoration of straight-line, pulsatile arterial blood flow is the major therapeutic goal in patients with advanced peripheral arterial disease and chronic critical limb ischemia (CLI), thereby achieving relief of pain or facilitating wound healing.1
THE USE OF STENTS
Recent advances in endovascular techniques and materials have extended the applicability of interventional treatment options for patients with advanced peripheral arterial occlusive disease due to obstructions of the crural arteries.2-5 The use of endovascular stents in below-the-knee arteries has been limited by the fact that no dedicated devices for this indication are available. Nevertheless, the results achieved with the use of balloon-expandable coronary stents are encouraging and may be superior to PTA alone.6,7 Unfortunately, due to the relatively small caliber of the vessels and the diffuse nature of the disease, reobstructions are a relatively frequent finding.6 According to systematic angiographic follow-up investigations performed in our institution in patients undergoing tibial stenting, the reobstruction rate after 6 months exceeds 50%.
In the coronary circulation, the use of drug-eluting stents has led to a significant improvement of the follow-up results after stenting procedures. Between several available pharmacological concepts, the application of sirolimus-eluting stents has been associated with consistently reduced binary restenosis rates and minimal late lumen loss as assessed during follow-up angiography.8,9 Moreover, positive results have been reported for nondiabetic and diabetic patients.10,11
Based on these clinical experiences in the coronary arteries, a pilot study was carried out at our institution assessing the safety and efficacy of sirolimus-eluting balloon-expandable coronary stents for treatment of focal infrapopliteal lesions (Figure 1).12
A total of 60 consecutive patients with infrapopliteal arterial obstructions were treated by elective stent implantation into the tibial and peroneal arteries, and the data were entered into a prospective registry. Only patients with focal lesions treatable with a single balloon-expandable coronary stent with a stent length of 33 mm and a nominal diameter of 3.5 mm were eligible for enrollment. Thirty patients (56.7% male; mean age, 71.4 years; 83.3% diabetics) received a sirolimus-eluting balloon-expandable stent (Cypher Select). Thirty patients (63.3% male; mean age, 73.0 years; 76.6% diabetics) were treated with uncoated bare-metal stents (Sonic, Cordis Corporation).
Angiographic follow-up, performed after a mean of 6.5 months, revealed a significantly reduced in-stent reobstruction rate in the sirolimus group: stent occlusions 0% versus 17.4% (P=.032), restenosis (>50%) 0% versus 39.1% (P=.0007), demonstrating that neointimal proliferation could be effectively prevented by the polymer-based sirolimus coating (Figure 2).
Despite the small sample size, the use of sirolimus-eluting stents also resulted in a significant reduction of the major adverse event rate. During follow-up, there were seven unrelated deaths (sirolimus, n=3; bare metal, n=4). The rates of major amputation, bypass surgery, or target lesion revascularization (TLR) were all 0% for the sirolimus group compared with 10%, 0%, and 23.3% in the control group.
Very similar results were obtained in a study published by Siablis et al13 who reported 6-month angiographic results of a single-center study investigating the efficacy of sirolimus-eluting stents used for bailout after infrapopliteal revascularization of patients with CLI. Twenty-nine patients (65 lesions in 40 arteries) were treated with bare-metal stents, whereas another 29 patients (66 lesions in 41 arteries) received sirolimus-eluting stents (Cypher). The binary in-stent restenosis rate was 55.3% for bare stents versus 4% for sirolimus-eluting stents (P<.001). The TLR rate, as well as the minor amputation rate, could be significantly reduced by the use of sirolimus-eluting stents (TLR, 17% vs 4%; P=.02; minor amputation, 17.2% vs 3.4%; P=.04).
Stenting of infrapopliteal arteries for treatment of CLI has the potential to improve both the acute procedural success as well as the long-term clinical outcome. In fact, 1-year clinical data are promising; nevertheless, the angiographic restenosis rate is considerably high and exceeds 50%. Although this finding may not automatically translate into a recurrence of CLI,2,14-16 deterioration of clinical improvement and prolonged or stagnating wound healing are frequently explained by the presence of reobstructions. The long-term results may be less favorable, particularly in diabetic patients. From that perspective, the clinical evaluation of drug-eluting stents for the indication of CLI seems to be very important. In fact, in both studies mentioned, the primary use of sirolimus-eluting stents not only resulted in a significant reduction of the reobstruction rate but also led to a significant reduction of clinical events, including the need for TLR or amputation. This demonstrates that the clinical application of sirolimus-eluting stents could have a major impact on the treatment results of patients with CLI secondary to infrapopliteal obstructions. Furthermore, given more favorable long-term results after implantation of drug-eluting stents, this technique could also be considered for treatment of patients with claudication due to primarily infrapopliteal disease.
A major area of concern related to stent treatment in peripheral arteries is the potential of stent compression or strut fracture.17,18 Therefore, in our investigation, the angiographic follow-ups were analyzed together with the corresponding plain x-ray images demonstrating the absence of any stent compression or destruction in both study groups.12 Based on these findings, the utilization of sirolimus-eluting, balloon-expandable coronary stents as a platform for an antiproliferative drug coating appears to be safe and feasible.
Nevertheless, currently there is no clear answer whether a balloon-expandable or a self-expanding stent platform is more appropriate for infrapopliteal application. So far, due to the limited availability of self-expanding stents with an appropriate dimension, mainly balloon-expandable coronary stents have been studied in this vessel area. Because the course of the tibial and peroneal arteries is relatively protected, balloon-expandable coronary stents are generally considered to be applicable in these arteries, and the results obtained with these stents are appropriate. In fact, no stent fractures or stent compressions have been seen during systematic angiographic follow-up after tibial stenting performed in our institution. Nevertheless, the major limitation remains to be the limited length of the available devices, which restricts the application of stents to relatively focal disease. The higher flexibility of self-expanding stents would help to overcome this problem, allowing for the opportunity to produce longer stents. Furthermore, the use of self-expanding stents is essential when the stented segment has to be extended into the distal popliteal segment. In this vessel segment, the possibility of external compression during flexion of the leg is a relevant concern.
According to the available preliminary data, sirolimus-eluting stents appear to be a safe and effective treatment option for focal infrapopliteal obstructions, allowing a significant improvement of the angiographic patency rate and a significant reduction of clinical events, including the need for TLR or amputation. These encouraging results should be investigated further in randomized, multicentric trials. To extend these promising treatment options to more complex lesion morphologies, there is a demand for dedicated drug-eluting tibial stents with low-profile characteristics and longer stent length.
Dierk Scheinert, MD, is Head of the Departments of Angiology at the Heart Center-University of Leipzig and the Park Hospital, Leipzig, Germany. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Scheinert may be reached at firstname.lastname@example.org.
Giancarlo Biamino, MD, is Director of the Department of Clinical and Interventional Angiology at the Heart Center-University of Leipzig, Germany. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Biamino may be reached at +49 341 865 1478; email@example.com.
Andrej Schmidt, MD, is from the Departments of Angiology at the Heart Center-University of Leipzig and the Park Hospital, Leipzig, Germany. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Schmidt may be reached at firstname.lastname@example.org.