April 14, 2008
Peripheral arterial disease (PAD) affects 12% to 20% of Americans over the age of 65. Among the factors that increase the chances of developing the disease are aging, smoking, high blood pressure, diabetes, and obesity. As the population ages and rates of diabetes and obesity rise, the incidence of PAD is also expected to increase.
PAD often occurs in the iliac arteries, which carry blood from the abdominal aorta to the legs and feet. Often the first sign of iliac artery disease is claudication, a cramplike pain in the leg or thigh.
Some people affected by PAD experience pain when walking or exercising, explains Katharine L. Krol, MD, FSIR, FACR, director of interventional radiology at CorVasc MD’s in Indianapolis. “People with mild cases will say, ‘I used to be able to run five miles, and now I can only run two,’” Krol says. “If it is more severe, they might say they can’t make it to their mailbox and back.” In mild cases, the pain goes away during rest, but in more severe cases, it can be more constant.
In its most severe form, PAD can cause painful sores on a patient’s toes and feet. If the circulation does not improve, the ulcers will become dry, gray or black, and eventually gangrenous.
Treatment depends on the location and severity of the blockage, symptoms, and the patient’s overall health. Treatment typically includes lifestyle changes such as losing weight, stopping smoking, and exercising, as well as taking medications that lower cholesterol, blood pressure, and the risk of clots. If the symptoms are severe enough to require intervention, angioplasty and stenting are often the first choice because they are minimally invasive options, according to Krol. Asymptomatic patients are not treated with stents.
Old Treatment, New Stents
Treating PAD with stents is not new. “We’ve been doing it 17, 18 years now,” Krol says, but new stents have been developed. Krol was the lead author of a study published in the January issue of the Journal of Vascular and Interventional Radiology about the clinical evaluation of the self-expanding Zilver vascular stent for symptomatic iliac artery disease.
The study, which involved 151 patients at 24 investigative sites in the United States, concluded that the Zilver vascular stent, which is made by Cook Group Inc. in Bloomington, Ind., is safe and effective as an adjunct to percutaneous transluminal angioplasty for treating symptomatic disease of the iliac arteries.
Krol says the study was significant because “there has been a lot of talk lately from the [FDA] and others about the off-label use of stents in blood vessels. So this trial was very timely and excellent [because] now these stents have FDA indication for use in arteries.”
Richard Saxon, MD, FSIR, of the San Diego Cardiac & Vascular Institute, who was also involved in the study, says the Zilver stent is one of several stents approved by the FDA for iliac arteries.
Smaller Stents and Catheters
The first stent for PAD was approved in 1988, according to Barry T. Katzen, MD, FACR, FACC, founder and medical director of Baptist Cardiac & Vascular Institute in Miami and another physician who participated in the study. Earlier generations of stents required bigger catheters, he says.
“One of the things that has happened over time is that the results have improved with each iteration of stent and each clinical trial,” Katzen says. “Part of that is the result of the technology itself, and part of it is related to the improved skill of the operators.”
Before stenting, patients who required intervention for iliac artery issues would have to undergo surgery for bypass grafts. “Because the abdominal aorta splits into the two iliac arteries just beneath the belly button, the surgery would involve a large abdominal incision for the most part,” Krol says.
Balloon angiography to open the clogged arteries was a great boon to many patients, especially those who couldn’t undergo surgery. “When stents came along, it was the icing on the cake,” Krol says. “It took us from [a] 75% to 80% primary success rate to now almost a 100% primary success rate getting that vessel open and getting flow restored.”
Katzen believes that stenting for iliac artery disease is an exciting area for vascular therapy, though some types of blockages, such as those that involve very large segments or those affecting the aorta, may still require open surgery. “But probably 90% of all patients with PAD can be treated without open surgery,” he says.
Most practices have gone from using balloon-expandable to self-expanding stents, Krol says. Self-expanding stents such as the Zilver are flexible and can meander around the curves normally found in the iliac arteries, she explains. “There really isn’t any difference in the success rate or long-term patency, but when we moved from technology where you could accurately measure the vessel to digital subtraction imaging and trying to measure vessels that way, self-expanding [stents] are a little more forgiving as to not having to have it exactly right on the millimeter.”
Stents are also a benefit to patients with multilevel disease, Krol says. In some patients, opening the iliac will not be enough to restore blood flow; they will also need bypass surgery. “But whenever you have to go with the bypass from the aorta in the belly all the way down, below the knee or wherever you have to go with the bypass, stenting the iliac makes the bypass shorter and typically not involving an incision outside the abdomen. This is one stage in fixing the overall problem that is much less invasive and that makes the invasive surgery easier,” she says.
Only those patients who have symptoms will undergo stenting. “Generally, you need a narrowing that is greater than 70% for it to be significant,” Katzen says. Most people, Krol adds, feel better immediately after the artery is opened.
The procedure, which takes roughly 60 to 90 minutes and is performed with local anesthesia, is fairly simple and similar to placing stents in clogged arteries in other parts of the body, according to Katzen. “It depends on how extensive the blockage is and also whether you’re doing the diagnostic studies at the same time,” Krol says.
At Krol’s and Katzen’s practices, patients usually undergo angioplasty and stenting, if they are found to be necessary, at the same time. “We do mostly catheter-directed angiography so that when a patient comes in for the angiogram and we are in the artery, we go ahead and do the iliac stent at the same time, and they go home the same day,” Krol says. “At our practice, we tend to do it all at once so that the patient doesn’t have to go through a similar procedure twice.”
Occasionally, the diagnostic and treatment procedures are separated. If, for example, the patient has renal insufficiency “and you want to limit the dye load or you may look at the anatomy and say, ‘This isn’t ideal for a stent.’ Then you might want to stop to talk to a surgeon to see if there is a better option for the patient,” Krol says.
Sometimes, however, the reverse is true, she adds. A patient is not an ideal candidate for open surgery and “so you really want to try stenting.”
Up and About
Most patients are ambulated roughly two to six hours after the stenting procedure. “Depending on your institution and what environment your patients are in, they can generally go immediately back to normal activities,” Katzen says. “Compared to open surgery, it’s a pretty dramatic difference.”
“Our primary success rate is almost 100%,” Krol says. “We can almost always get that vessel open. I can’t remember the last time we couldn’t get one open.”
The secondary patency rate varies, she adds. A lesion that is very short and has good inflow and outflow will do well and have a high long-term patency rate. Those where the iliac artery is tiny and diffusely diseased “and everything above and below it is diseased won’t do as well long term. They have more of a chance that they will become blocked again.”
The good news is that if the artery gets blocked again, the procedure can be repeated. “Even people that come in with the stent occluded, a lot of times, we will be able to open that back up,” Krol says.
In the Zilver trial, the acute procedure success rate and 30-day clinical success rate were 98% and 94%, respectively. The nine-month patency rate, measured with duplex ultrasonography, was 92.9%. Significant improvement was seen in the ankle brachial index, which compares blood pressure in the ankle to the arm, and walking distance and walking speed scores relative to preprocedural values at one month and nine months follow-up.
Katzen says the success rate at his institution is also roughly 98% to 99%. With a 100% blockage, the success rate is roughly 93%, he says.
One problem with PAD is that it is often misdiagnosed. “People are told they have arthritis or back disease when what they really have is PAD,” Krol says.
PAD is diagnosed by taking a patient history and doing a physical exam. “When patients are telling you their story, you have to recognize the symptoms and say, ‘Ah ha! I wonder if they have good circulation,’” Krol says. “You have to do a physical exam and feel pulses, look at the foot and the skin color, temperature, and capillary refill.”
“Once we suspect iliac artery disease, it can be detected with computed tomography angiography or magnetic resonance angiography,” Katzen says. “That’s generally the next thing we do.”
— Beth W. Orenstein is a freelance medical writer in Northampton, Pa.