Stenting for peripheral artery disease of the lower extremities: an evidence-based analysis.
BACKGROUND



OBJECTIVE
In January 2010, the Medical Advisory Secretariat received an application from University Health Network to provide an evidentiary platform on stenting as a treatment management for peripheral artery disease. The purpose of this health technology assessment is to examine the effectiveness of primary stenting as a treatment management for peripheral artery disease of the lower extremities.


OBJECTIVE
CONDITION AND TARGET POPULATION Peripheral artery disease (PAD) is a progressive disease occurring as a result of plaque accumulation (atherosclerosis) in the arterial system that carries blood to the extremities (arms and legs) as well as vital organs. The vessels that are most affected by PAD are the arteries of the lower extremities, the aorta, the visceral arterial branches, the carotid arteries and the arteries of the upper limbs. In the lower extremities, PAD affects three major arterial segments i) aortic-iliac, ii) femoro-popliteal (FP) and iii) infra-popliteal (primarily tibial) arteries. The disease is commonly classified clinically as asymptomatic claudication, rest pain and critical ischemia. Although the prevalence of PAD in Canada is not known, it is estimated that 800,000 Canadians have PAD. The 2007 Trans Atlantic Intersociety Consensus (TASC) II Working Group for the Management of Peripheral Disease estimated that the prevalence of PAD in Europe and North America to be 27 million, of whom 88,000 are hospitalizations involving lower extremities. A higher prevalence of PAD among elderly individuals has been reported to range from 12% to 29%. The National Health and Nutrition Examination Survey (NHANES) estimated that the prevalence of PAD is 14.5% among individuals 70 years of age and over. Modifiable and non-modifiable risk factors associated with PAD include advanced age, male gender, family history, smoking, diabetes, hypertension and hyperlipidemia. PAD is a strong predictor of myocardial infarction (MI), stroke and cardiovascular death. Annually, approximately 10% of ischemic cardiovascular and cerebrovascular events can be attributed to the progression of PAD. Compared with patients without PAD, the 10-year risk of all-cause mortality is 3-fold higher in patients with PAD with 4-5 times greater risk of dying from cardiovascular event. The risk of coronary heart disease is 6 times greater and increases 15-fold in patients with advanced or severe PAD. Among subjects with diabetes, the risk of PAD is often severe and associated with extensive arterial calcification. In these patients the risk of PAD increases two to four fold. The results of the Canadian public survey of knowledge of PAD demonstrated that Canadians are unaware of the morbidity and mortality associated with PAD. Despite its prevalence and cardiovascular risk implications, only 25% of PAD patients are undergoing treatment. The diagnosis of PAD is difficult as most patients remain asymptomatic for many years. Symptoms do not present until there is at least 50% narrowing of an artery. In the general population, only 10% of persons with PAD have classic symptoms of claudication, 40% do not complain of leg pain, while the remaining 50% have a variety of leg symptoms different from classic claudication. The severity of symptoms depends on the degree of stenosis. The need to intervene is more urgent in patients with limb threatening ischemia as manifested by night pain, rest pain, ischemic ulcers or gangrene. Without successful revascularization those with critical ischemia have a limb loss (amputation) rate of 80-90% in one year. Diagnosis of PAD is generally non-invasive and can be performed in the physician offices or on an outpatient basis in a hospital. Most common diagnostic procedure include: 1) Ankle Brachial Index (ABI), a ratio of the blood pressure readings between the highest ankle pressure and the highest brachial (arm) pressure; and 2) Doppler ultrasonography, a diagnostic imaging procedure that uses a combination of ultrasound and wave form recordings to evaluate arterial flow in blood vessels. The value of the ABI can provide an assessment of the severity of the disease. Other non invasive imaging techniques include: Computed Tomography (CT) and Magnetic Resonance Angiography (MRA). Definitive diagnosis of PAD can be made by an invasive catheter based angiography procedure which shows the roadmap of the arteries, depicting the exact location and length of the stenosis / occlusion. Angiography is the standard method against which all other imaging procedures are compared for accuracy. More than 70% of the patients diagnosed with PAD remain stable or improve with conservative management of pharmacologic agents and life style modifications. Significant PAD symptoms are well known to negatively influence an individual quality of life. For those who do not improve, revascularization methods either invasive or non-invasive can be used to restore peripheral circulation.  TECHNOLOGY UNDER REVIEW: A Stent is a wire mesh "scaffold" that is permanently implanted in the artery to keep the artery open and can be combined with angioplasty to treat PAD. There are two types of stents: i) balloon-expandable and ii) self expandable stents and are available in varying length. The former uses an angioplasty balloon to expand and set the stent within the arterial segment. Recently, drug-eluting stents have been developed and these types of stents release small amounts of medication intended to reduce neointimal hyperplasia, which can cause re-stenosis at the stent site. Endovascular stenting avoids the problem of early elastic recoil, residual stenosis and flow limiting dissection after balloon angioplasty.


OBJECTIVE
In individuals with PAD of the lower extremities (superficial femoral artery, infra-popliteal, crural and iliac artery stenosis or occlusion), is primary stenting more effective than percutaneous transluminal angioplasty (PTA) in improving patency?In individuals with PAD of the lower extremities (superficial femoral artery, infra-popliteal, crural and iliac artery stenosis or occlusion), does primary stenting provide immediate success compared to PTA?In individuals with PAD of the lower extremities (superficial femoral artery, infra-popliteal, crural and iliac artery stenosis or occlusion), is primary stenting associated with less complications compared to PTA?In individuals with PAD of the lower extremities (superficial femoral artery, infra-popliteal, crural and iliac artery stenosis or occlusion), does primary stenting compared to PTA reduce the rate of re-intervention?In individuals with PAD of the lower extremities (superficial femoral artery, infra-popliteal, crural and iliac artery stenosis or occlusion) is primary stenting more effective than PTA in improving clinical and hemodynamic success?Are drug eluting stents more effective than bare stents in improving patency, reducing rates of re-interventions or complications?


METHODS



METHODS
A literature search was performed on February 2, 2010 using OVID MEDLINE, MEDLINE In-Process and Other Non-Indexed Citations, OVID EMBASE, the Cochrane Library, and the International Agency for Health Technology Assessment (INAHTA). Abstracts were reviewed by a single reviewer and, for those studies meeting the eligibility criteria, full-text articles were obtained. Reference lists were also examined for any additional relevant studies not identified through the search. The quality of evidence was assessed as high, moderate, low or very low according to GRADE methodology.


METHODS
English language full-reports from 1950 to January Week 3, 2010Comparative randomized controlled trials (RCTs), systematic reviews and meta-analyses of RCTsProven diagnosis of PAD of the lower extremities in all patients.Adult patients at least 18 years of age.Stent as at least one treatment arm.Patency, re-stenosis, re-intervention, technical success, hemodynamic (ABI) and clinical improvement and complications as at least an outcome.


METHODS
Non-randomized studiesObservational studies (cohort or retrospective studies) and case reportFeasibility studiesStudies that have evaluated stent but not as a primary intervention


METHODS
The primary outcome measure was patency. Secondary measures included technical success, re-intervention, complications, hemodynamic (ankle brachial pressure index, treadmill walking distance) and clinical success or improvement according to Rutherford scale. It was anticipated, a priori, that there would be substantial differences among trials regarding the method of examination and definitions of patency or re-stenosis. Where studies reported only re-stenosis rates, patency rates were calculated as 1 minus re-stenosis rates.


METHODS
Odds ratios (for binary outcomes) or mean difference (for continuous outcomes) with 95% confidence intervals (CI) were calculated for each endpoint. An intention to treat principle (ITT) was used, with the total number of patients randomized to each study arm as the denominator for each proportion. Sensitivity analysis was performed using per protocol approach. A pooled odds ratio (POR) or mean difference for each endpoint was then calculated for all trials reporting that endpoint using a fixed effects model. PORs were calculated for comparisons of primary stenting versus PTA or other alternative procedures. Level of significance was set at alpha=0.05. Homogeneity was assessed using the chi-square test, I(2) and by visual inspection of forest plots. If heterogeneity was encountered within groups (P < 0.10), a random effects model was used. All statistical analyses were performed using RevMan 5. Where sufficient data were available, these analyses were repeated within subgroups of patients defined by time of outcome assessment to evaluate sustainability of treatment benefit. (ABSTRACT TRUNCATED)