What’s the Passcode to Long-Term SFA Patency?
Unlike coronary occlusions that are short and small in diameter, occlusions of the superficial femoral arteries (SFAs) tend to be long and large. Nevertheless, recanalizing these occlusions can be a daunting task, and if left untreated, can lead to serious problems for the patient.
According to a paper published in the Journal of Catheterization and Cardiovascular Interventions, “total occlusions of the femoropopliteal arteries are frequently found in patients with severe claudication or CLI [critical limb ischemia].”
By definition, SFA occlusions have, no matter the length, historically been referred to surgery. This is because the TransAtlantic Inter-Society Consensus (TASC) lesion guidelines, those that are used to manage patients with peripheral arterial disease (PAD), classify SFA occlusions as TASC C and TASC D: The former (TASC C) include single occlusions >5 cm in length and the latter (TASC D) are complete SFA occlusions. Surgery helps salvage limbs which otherwise might be amputated.
The fact is, although endovascular approaches do not guarantee long-term and full recovery from CLI, many patients are poor candidates for surgery. Also, less-invasive solutions such as angioplasty should be considered first, in many cases, particularly because new options for treating these types of lesions are on the horizon.
Why, then, does surgery remain the approach of choice, particularly for hard to treat lengthy SFA occlusions? In many cases, this is the only approach that can successfully restore blood flow to the distal bed. The problem is that surgery for SFA occlusions can usually only be performed on patients “healthy enough” to undergo the procedure.
“Bypass grafting [of the SFA] is associated with a considerable procedure-related morbidity and mortality, [therefore] surgical intervention [is] usually reserved for patients with ischemic rest pain or advanced claudication,” indicates a paper published in the Journal of Endovascular Therapy. So patients who are not healthy enough to undergo surgery and must be treated endovascularly have remained untreated or have been treated medically.
Are We Making Progress?
When angioplasty is compared to surgery, which has been the gold standard for the treatment of SFA occlusions for at least 20 years, patency rates after five years remain around 70 to 80 percent for surgery, versus angioplasty patency rates hovering in the 50 percent range.
So what progress has been made to (1.) improve recanalization of obstructed SFAs via angioplasty and (2.) keep these vessels patent once they have been recanalized using endovascular methods?
Technological advancements have been made in the last decade. Stenting has definitely improved the short-term patency rates following angioplasty; however, long-term outcomes fall short. According to a lecture by Andre Nevelsteen, M.D., of the University of Ziekenhuizen (Leuven, Belgium), three- and five-year primary patency rates following the recanalization and stenting of SFA occlusions fall below 50 percent.
The problem remains long-term patency. Because SFA disease is more diffuse than focal, more occlusive than stenotic, this is likely the reason long-term patency issues exist in this subset of lesions (long SFA occlusions). These vessels are harder to treat, resulting in increased vessel injury and, thus, are prone to higher rates of restenosis.
Crossing Occluded SFAs
Before a stent can be placed, the lesion must be crossed.
SFAs are the arteries that are the most prone to peripheral occlusive atherosclerotic disease, reports Dr. Nevelsteen in the Japanese Journal of Vascular Surgery.
SFA occlusive lesions are also more likely to be long and straight. Japanese interventionalists, recognized leaders in crossing complex arterial lesions, have employed a strategy of using 1.5 mm hydrophilic “J-tip” 0.035-inch guide wires with an over-the-wire balloon catheter under ultrasound guidance. And while it is effective — with a success rate of 97 percent — it is also likely to require several attempts to cross the occluded segment, which can take hours and in some cases, multiple trips to the cath lab. It is unrealistic to believe that U.S. interventionalists will spend hours or multiple attempts to recanalize obstructed SFAs this way. It is simply not profitable.
Although treating long SFA occlusions percutaneously is feasible, long-term patency rates are less favorable than those of short SFA occlusions. In February 2004, Wissgott and colleagues published the results of a study that evaluated long-term hemodynamic effects following laser angioplasty (LA). For this study, 452 patients were enrolled and lesions ranged from 16 cm to 38 cm with the average SFA occlusion being 25.5 cm. There was an 85.5 percent recanalization rate.
The main reason for failure to cross in this case was highly calcified lesions. Patency rates at the four-year follow-up revealed an overall patency of 43.2 percent, significantly less than a short SFA occlusion study conducted by Steinkamp and colleagues in 2002. Dr. Wissgott concluded that even though there was a high crossing success rate using LA, long-term patency rates were poor (<50 percent after four years) even when additional interventions were performed.
Improving Lasing Technology
Spectranetics Corp.’s (Colorado Springs, CO) CLIRpath line of excimer-laser catheters is one technology that has frequently been evaluated in clinical studies to cross occlusions in the SFA. In August 2004, Spectranetics announced that it had received FDA clearance for a new Turbo Catheter for the treatment of long occlusions in the SFA. The Turbo Catheter offers some new features that predicate Spectranetics laser catheters did not, such as increased laser fibers that create 30 percent more energy, which provide faster penetration and more efficient ablation. This results in larger lumens.
The new Turbo Catheters also offer “continuous lasing,” as opposed to the catheter needing to power-down for five seconds after 10 seconds of use. A company press release states: “The continuous ‘on’ feature [enables] shorter procedure times and reduces radiation exposure.”
Another modification to the predicate is a hydrophilic coating feature that allows for easier advancement through tight lesions.
The Turbo Catheter press release quotes professor Giancarlo Biamino (Heart Centre Leipzig, Leipzig, Germany) stating that the Turbo Catheter produced larger channels/lumens and that the “Turbo will be useful to atherectomize tissue in larger vessels such as…distal superficial femoral arteries,” however no mention was made regarding the device’s longer-term efficacy. The only statement from Biamino on this point is that the use of the Turbo Catheter may “reduce the need for stenting.”
Whether or not this is an indication of long-term patency is yet to be determined.
Another approach to treating occlusions in the SFA is endovascular remote endarterectomy (or EndoRE). This technique combines open surgical and endovascular techniques. It is a minimally invasive procedure that is performed in the cath lab with instruments that look more like something a surgeon would use then an interventionalist.
According to the Vascular Architect (formerly of San Jose, CA) Web site, the company that sells the instruments for EndoRE procedures, EndoRE is the new front-line therapy for revascularizing occluded SFAs. One EndoRE specialist is John Martin, M.D. (Vascular Institute Anne Arundel Medical Center, Annapolis, MD). According to Vascular Architect, Dr. Martin has performed over 140 EndoRE procedures in the past three years.
This hybrid approach requires the interventionalist to make an incision in the groin and to deliver the tools to a predesignated reconstitution point that has been determined using an arteriogram. Then a proximal dissection, under fluoroscopic guidance, is made using the Martin Dissector, an instrument that separates the plaque from the vessel wall. Along with the Martin Dissector, an appropriately sized dissector ring is also used.
Once the predesignated endpoint is reached, a cutting instrument — the MollRing Cutter — is moved across the plaque core over the same dissection plane to the predetermined endpoint.
Then, according to Dr. Martin in an article he wrote for Endovascular Today, “the plaque is remotely transected and the entire athromatous core is removed.” The excised plaque core is removed through the incision in the groin which, in most cases, is at least 20 cm in length and can weigh anywhere from 4 g to 17 g. Once the plaque core is excised and a channel is opened, the dissection is secured. This is followed by a predilatation using an angioplasty balloon, and then a stent is placed.
Procedural success is achieved in 90 percent of cases, according to Dr. Martin. Primary patency rates in 40 patients that underwent EndoRE with stenting for occlusions in the SFA between 2000 and 2003 was nearly 70 percent after 18 months. Those who needed repeat interventions saw improvement in patency of nearly 90 percent after 15 months. The problem, again, is that no longer-term patency rates (>3 years) were reported — at least not in the Endovascular Today article.
Can Stenting Solve the Problem?
Stents will likely play a significant role in combating restenosis and keeping SFA occlusions patent following peripheral angioplasty. Debulking of the lesion will be needed to prep the SFA segment for stenting. Early stent studies show very little patency differences between angioplasty and angioplasty with stent placement.
A study published in the Journal of Invasive Cardiology in 2003 by Dr. Cho and colleagues explains that poor patency results in cases when stents were placed in highly stenosed SFAs could potentially be the result of using of stainless steel stents. In many cases, stainless steel stents deployed in the lower limbs lack the strength and flexibility needed to match the force, the pressure and stress exerted from this part of the body. It is not unusual for stainless steel stents to fracture and/or deform under pressure in the SFA.
Dr. Cho’s group evaluated the use of nitinol (nickel-titanium) stents and compared these to balloon angioplasty (POBA). Nitinol is a memory metal — it is strong material that can be preshaped and is very flexible.
Forty patients were selected who had previously undergone peripheral angioplasty for occluded SFAs. Patients were assigned at the discretion of the physicians to POBA or received a Cordis Corp. (Miami Lakes, FL) SMART nitinol slotted tube stent — 16 patients received the SMART stent. The mean SFA occlusion length was 71 mm. Although none of the 40 patients underwent repeat angiography, Dr. Cho’s group observed a statistically significant decrease in gradient pressure in the stent group (32 mmHg vs. 72 mmHg with a p-value of 0.02).
Dr. Cho concluded that the patients in the stented group had high rates of clinical patency at six months compared to the angioplasty group.
“[The stented group] had a greater reduction in post-procedure translesion gradient and [needed less] adjunctive medical treatment,” their report stated. Again, only short-term (six months) results were presented with no angiographic follow-up.
According to ClinicalTrials.gov, Cordis Corp. initiated The Super Study for the purpose of evaluating the performance of the Cordis SMART nitinol self-expanding stent for the treatment of SFA occlusions. The study’s anticipated start-date was March 2005 with completion expected in May 2009. Patients enrolled in The Super Study will be randomized (1:1) to either stenting or angioplasty — expected enrollment is 150 patients with SFA occlusions ranging in length from 5 cm to 14.5 cm and a diameter of 4 cm to 6 cm. Patients would be subjected to three phone follow-ups at three, six and nine months, in addition to a 12-month Duplex Ultrasound assessment.
Although nitinol stents are a step in the right direction, they are not enough to achieve the patency rates observed with bypass surgery. Most physicians will agree that bypass surgery has better long-term results than peripheral angioplasty with or without stenting.
Weighing the Cost
Which treatment is more cost effective? According to Drs. Virginia Oliva and Ross Milner of Emory University School of Medicine in Atlanta, GA, the average cost for an SFA angioplasty procedure with stent placement, including an overnight hospital stay without in-hospital complications, is in the ballpark of $16,000. This is compared to the $31,000 it costs to have bypass surgery.
“However, in cases of therapeutic failure, continuing to perform angioplasties diminishes the cost advantages,” they state in their October 2004 Endovascular Today article. According to the doctors, if a patient undergoes three repeat procedures the cost of the angioplasty triples. This results in no savings.