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Monday, September 26, 2011
Advances Fall 2011
A 74-year-old man with advanced peripheral artery disease and critical limb ischemia.
Although peripheral artery disease (PAD) is widely prevalent in the United States, afflicting 8 to 12 million individuals, or more than 20 percent of the population older than age 65, the disease is often unrecognized by patients and physicians alike. Since atherosclerosis in the leg arteries often accompanies disease in the coronary and cerebral vessels, patients with PAD are at elevated risk for heart attack, stroke, and death from cardiovascular causes. Moreover, the greater the severity of PAD, the higher the risk of adverse cardiovascular events. As a result, prompt diagnosis of patients with PAD is critical to promote prompt therapy for the modification of cardiovascular risk factors, and in select patients, to allow revascularization for the alleviation of symptoms.
Whereas bypass surgery has historically been considered the gold standard for revascularization of patients with severe PAD, the evolution of catheter-based endovascular techniques now offers minimally invasive alternatives that rival surgical intervention. Although some endovascular treatments may require repeating more frequently than bypass, these interventional measures are proving effective in preventing limb loss, while allowing quicker recovery and lower procedure-associated morbidity.
Mass General physicians routinely use sophisticated therapies to treat patients who once may have required bypass, or those who are not candidates for bypass because of advanced age or comorbidities. Many such patients suffer from critical limb ischemia, with disabling leg pain at rest, nonhealing ulcers, and gangrene, which—if left untreated—may ultimately require amputation.
Sophisticated Approaches to Lower Limb Endovascular Therapy
Physicians at the Mass General Vascular Center have distinguished themselves as early adopters and pioneers in novel endovascular techniques. Among the most challenging interventions they perform are those that involve the smallest, most distal arteries of the leg—the infrapopliteal vessels. Treatment of these vessels requires the use of very low-profile catheter systems that physicians use with great finesse and perseverance to open even the most severely narrowed vessels leading to the foot. In 2010, Vascular Center physicians performed approximately 175 endovascular procedures involving the infrapopliteal arteries.
A major technical challenge in endovascular procedures is the treatment of blood vessels that are 100 percent blocked with atherosclerotic plaque. Traditional endovascular intervention—for vessels that are not entirely occluded—involves the careful advancement of a flexible guide wire through a channel that remains in the middle of the plaque-laden segment of a blood vessel; in turn, the wire serves as a rail over which an angioplasty balloon (and/or a stent) may subsequently be advanced to treat the blockage. In cases in which the cholesterol obstruction occupies 100 percent of the vessel’s lumen, the operator must pierce and penetrate the plaque itself with the guide wire. The wire is then very carefully directed back into the lumen of the vessel downstream from the plaque. This technique is often accomplished with sharper and stiffer wires than would ordinarily be employed for partially obstructive lesions.
For very long, totally occluded arterial segments, it may not always be possible to pass a wire through the full length of the plaque throughout its entire length. In such cases, Vascular Center physicians may use the subintimal technique in which a wire is passed between the layers of the arterial wall, skipping over the segment of cholesterol occlusion, and then re-entering the lumen downstream by penetrating back through the layers of the vessel wall. The re-entry technique may sometimes be facilitated by the use of novel catheters that allow precise steering and placement of the wire to accomplish this goal.
Angiography of a 91-year-old woman presented with two months of right foot pain and clinical evidence of critical limb ischemia, with digital ulceration revealing total occlusion of the distal right superficial femoral artery and popliteal artery (left) and single-vessel runoff via the right peroneal artery (right), which itself is totally occluded in the mid-portion and is accompanied by diffuse total occlusion of the anterior tibial and posterior tibial arteries (not visualized).
In some cases in which all conventional endovascular techniques have failed, Vascular Center physicians have used the retrograde approach to cross the length of the plaque blockage. Physicians insert a very narrow guiding wire and catheter directly into the small blood vessels of the foot, directing them in a retrograde direction (upward, toward the heart) through the recalcitrant blockages of the leg. This aggressive and relatively unconventional approach treats some of the most extreme lesions and provides hope for patients in whom all other treatment strategies have failed.
At the Vascular Center, physicians are adapting the latest trends in coronary interventional techniques to provide novel care for patients with PAD. Over the past several years, the use of the radial artery for arterial access, or the transradial approach, has gained widespread approval in the world of coronary intervention. This is because the rates of post-procedural bleeding and vascular complications are lower than with traditional transfemoral access. Also, patients often prefer this approach for the fact that it is dramatically more comfortable during the point at which the interventional equipment is removed and the procedure ends. In peripheral intervention, Mass General physicians are adopting transradial access for the treatment of lesions in the upper extremity, the renal arteries, and the iliac and proximal femoral arteries with excellent results and patient satisfaction.
Patient’s two regions of total occlusion were treated with angioplasty and stenting (right superficial artery and popliteal artery, not shown) and angioplasty alone (peroneal artery) with excellent angiographic result, and restoration of pulsatile, “straight-line” flow to the right foot.
Stents That Resist Compression
The appropriate use of stents is also important in managing patients with PAD. Douglas Drachman, MD, director of the Cardiology Fellowship Program and associate director of the Interventional Cardiology Fellowship Program at Mass General, is the site principal investigator for the SUPERB trial (Comparison of the Supera Peripheral System to a Performance Goal Derived from Balloon Angioplasty Clinical Trials in the Superficial Femoral Artery). The SUPERB trial, whose national principal investigator is Kenneth Rosenfield, MD, section head of vascular medicine at Mass General, examines the safety and efficacy of the iDEV Supera stent in the treatment of symptomatic stenosis of the superficial femoral artery. The study is currently enrolling PAD patients to receive stents made of braided wire (nitinol), which resists compression but remains flexible. Such a design may be particularly valuable for use in the superficial femoral artery because it is subject to the rigors of the knee and leg’s repetitive movement. In exposed vascular segments of the femoral artery, the currently available stents may more likely become pinched, compressed, or distorted during leg movement, and they may be less likely to retain a large, circular lumen in the vessel. Candidates for the SUPERB trial include those with symptomatic narrowings of the superficial femoral artery of more than 60 percent and between 4.0 and 14.0 centimeters in length.
Prevention of Restenosis: Drug-Coated Angioplasty Balloons
No matter how meticulously performed, all endovascular treatments result in injury of the blood vessel wall. In many cases, the healing response to injury may result in the formation of scar tissue in the blood vessel lumen known as restenosis. In certain circumstances, restenosis may be so severe that it renarrows the blood vessel, limits blood flow, and recapitulates the symptoms, causing the original plaque blockage. Although drug-eluting stents have been tremendously successful at limiting restenosis in the coronary circulation, similar breakthroughs have been very slow to develop for the treatment of PAD. One strategy that has shown great promise in early clinical trials is the use of drug-coated angioplasty balloons that apply anti-restenotic medication directly to the peripheral arterial vessel wall at the time of endovascular treatment. The first drug-coated balloon trial to be launched in the United States—the LEVANT-2 trial—will soon begin enrollment for patients with symptomatic PAD. The Mass General Vascular Center will be the only center in greater New England to host this trial, boasting both the trial’s national principal investigator—Dr. Rosenfield—and site-specific principal investigator—Dr. Drachman—among its staff.
Atherectomy: An Option for Certain Patients
Debulking the lesions in the vessel with atherectomy is another approach that may reduce the need for stents. Physicians at the Vascular Center are currently using a minimally invasive revascularization system that restores circulation by removing both hard and soft plaque, calcium, thrombus, and fibrotic lesions. These systems are particularly effective for use in areas that are not amenable to stenting, such as the adductor canal and popliteal area. In 2010, nearly 50 patients had atherectomy through the Vascular Center.
Laser technology is also being used in atherectomy at the Vascular Center. One system uses an excimer laser to ablate blockages in blood vessels and restore blood flow.
New Imaging Techniques Fill Unmet Need
A robust imaging program helps physicians manage patients with all types of PAD. Through the Vascular Center, patients with high levels of calcification benefit from one of the first dual-energy CT scanners, which provides a very clear picture of the lumen.
The scanner, which Mass General acquired in 2010, uses two different energy beams and special software that erases calcium from the scanned image, making it easier for physicians to note the exact size of the lumen, particularly when there is a large calcific plaque.
Patients may also benefit from imaging via a dual-source CT flash scanner, which can provide a fast study of the atherosclerotic disease process throughout the body. This eliminates the need for multiple regional studies involving contrast injections, which can be toxic to kidneys. The scanner employs only a fraction of the radiation other systems use.
In addition, imaging options for PAD patients with kidney dysfunction—which is about 20 percent of the total PAD population—have been limited until now. Sanjeeva Kalva, MD, associate director of clinical affairs for the Division of Vascular Imaging and Intervention, has been working with colleagues to develop noncontrast methods of magnetic resonance angiography for assessing blood vessels in PAD patients with kidney disease. Specifically, his team has designed new software algorithms and pulse sequencing for magnetic resonance angiography in patients who cannot receive contrast material.
Dr. Kalva has also studied a new contrast material that will soon replace gadolinium-DTPA for magnetic resonance angiography. The new contrast agent, gadofosvesettrisodium, binds with albumin in the blood and stays in the circulation for 24 hours, compared with only three minutes for gadolinium-DTPA. This allows physicians to scan multiple regions at high resolution without having to administer more contrast material to patients.
Team Approach to Follow-up
The Mass General Vascular Center brings together several specialties to treat PAD, including vascular medicine and cardiology, vascular and endovascular surgery, vascular imaging and intervention, podiatric medicine, and wound care. Because medical management and lifestyle modifications, such as exercise and smoking cessation, can be so critical to the health of these patients, designing personalized treatment plans is important. The Vascular Center team maintains close follow-up of their interventional patients and works with referring physicians to coordinate therapy. This also involves monitoring the use of statins, which is now the standard of care for PAD patients. The Vascular Center is developing a unique data-collection tool to prospectively evaluate optimal treatment paradigms among patients with PAD, including optimal medical management.
In addition, Mark Conrad, MD, MMSc, director of clinical research and assistant program director of the Division of Vascular and Endovascular Surgery, has maintained a retrospective database of PAD cases since 2002. Outcomes data reveal that while the primary patency of angioplasty of the infrainguinal arteries is not equivalent to that of vein bypass, with multiple, minimally invasive interventions, patients are able to achieve limb-salvage rates comparable to bypass.
Massachusetts General Hospital Vascular Center
Massachusetts General Hospital established the Vascular Center to provide comprehensive care for patients with vascular disease. As a dedicated vascular center with specialists in every area of vascular disease, the Vascular Center offers a uniquely focused, multidisciplinary approach to vascular medicine. Specialists in seven critical disciplines work together. These include cardiac surgery, cardiology/vascular medicine, nephrology, neurology, neurosurgery, vascular and endovascular surgery, and vascular imaging and intervention.
Multispecialty Programs: Aortic Disease Program; Brain Aneurysm and Arteriovenous Malformations Program; Fibromuscular Dysplasia Program; Peripheral Artery Disease Program; Stroke and Carotid Artery Disease Program; Venous Disease Program; Visceral Vascular Disease Program.
For more information about the Vascular Center services or to refer a patient, please call 877-644-8346 or visit the Vascular Center website
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