Assessing Vascular Surgery Options In Patients With PAD
Peripheral arterial disease (PAD) is a very common condition that affects 20 to 30 percent of patients over 50 years of age, equating to an estimated 10 million Americans. As the population ages, the incidence of PAD will likely increase dramatically.1
Intermittent claudication is a symptom among patients with PAD and one can use the presence of these symptoms as a diagnostic tool.2 True claudication is an aching or cramping within the muscles in the involved extremity that is exertion-related, relieved by rest and occurs at a relatively constant walking distance.3 As the disease progresses, symptoms may occur at rest, involve the toes and become worse at night.
Other signs and symptoms of PAD include numbness or weakness of the lower extremity, cold legs and feet, hair loss or changes in skin color, ischemic foot ulcers and erectile dysfunction, which happens to be one of the initial indications of PAD.4
A 2001 study discussed the implications of asymptomatic PAD. The study included findings from a national survey that involved nearly 7,000 patients over the age of 70 and patients over the age of 50 who had a history of smoking or diabetes. Researchers screened patients’ ankle-brachial indices (ABIs) and diagnosed peripheral vascular disease (PVD) in 29 percent of all patients. Forty-four percent of patients with PVD had PVD alone. In addition, PVD was also previously undiagnosed and physicians uncovered it only through use of the ABI, despite no symptoms. Clinicians who rely on the classic symptom (claudication) for diagnosing PAD are likely to miss 85 to 90 percent of the cases.5
Why is this important? In the Coronary Artery Surgery Study (CASS) involving patients with known coronary artery disease (CAD), the presence of PAD increased cardiovascular mortality by 25 percent during a 10-year follow-up.6 Peripheral arterial disease, symptomatic or asymptomatic, is a powerful independent predictor of CAD and coronary vascular disease (CVD).7
Pertinent Diagnostic Pointers
When it comes to the diagnosis of PAD, there are a number of components, beginning with an in-depth history and physical examination. It has been noted that practitioners often miss the diagnosis of PAD during a routine physical exam. Ninety-two percent of the time, physicians perform cardiovascular histories during exams but only 37 percent of internists address questions and history regarding PAD.8 During the history portion of the exam, it is important to ask if the patient has any other medical problems or conditions, such as Leriche syndrome, which can have some of the same signs and symptoms of PAD.
Internists also only calculate an ABI or palpate a dorsalis pedis pulse 60 percent of the time in comparison to the heart and lung exam, which patients undergo 92 percent of the time. During the history and physical, one should emphasize the peripheral vasculature, take blood pressure, palpate pulses (taking into account the quality of the pulse), and perform auscultation of pulses and bruits in addition to noninvasive and, if necessary, invasive diagnostic testing.8 Noninvasive testing includes ABI, segmental pulse pressures, exercise testing and ultrasonic duplex scanning.
Ankle-brachial indices have become a mainstay in the initial evaluation of patients suspected to have PAD. They are simple to perform as they only require the use of an ordinary blood pressure cuff and a Doppler ultrasound. A reduced ABI in patients with claudication symptoms confirms the presence of an occlusive disease between the heart and the ankle. An ABI reading of <0.90 is the cutoff point for the diagnosis of PAD.3 The lower the ABI, the more severe the occlusive disease.
Measurement of segmental pressures and pulse volume recordings can localize occlusions of different limb segments. One would compare systolic blood pressures and pulse volumes to segments both distal and proximal to the occlusion.
If the area of the occlusion needs to be localized further than the arterial segments, a duplex ultrasound is a good diagnostic measure.4 One can use a duplex ultrasound to obtain information on artery wall thickness, the degree of flow turbulence, changes in blood flow velocity in areas of stenosis and vessel morphologic characteristics.8 Since the duplex ultrasound is costly in comparison to other noninvasive tests, physicians should reserve it for patients who need more detailed information on flow characteristics and vessel morphology. An arteriogram is a roadmap for treatment only and cannot qualify the quantity of flow.9
Without effective intervention, PAD can lead to chronic limb ischemia, a condition characterized by intermittent claudication, poor healing capability in the presence of a wound and eventual amputation.10 Traditionally, vascular surgeons have treated PAD with techniques such as open surgical bypass, surgical endarterectomy, balloon angioplasty and stent placement. While each of these procedures has its advantages in a given patient population, each also has a fair share of shortcomings that warrant the use of a better approach in the management of PAD.
Open surgical bypass produces quite favorable long-term clinical results for the treatment of lower limb PAD.11 However, one must consider the invasiveness of such a procedure in the face of the comorbidities that often affect patients with PAD. Complications encountered in open bypass include a prolonged hospital stay, the need for rehabilitation, increased wound complications (ischemic or infectious wounds and surgical dehiscence), prolonged healing time (> three months) and a delayed return to normal activity.12
Even though the mortality rate associated with the bypass procedure itself is not very high, the morbidity linked to bypass often disqualifies certain high-risk patients (those patients with multiple comorbidities) from undergoing the procedure. Goshima, Mills and Hughes reported a revisionary procedure rate of 49.3 percent (112 out of 318 patients) within six months of patients undergoing a bypass.12
Endarterectomy, the surgical removal of plaque from a narrowed artery, is an effective method for the removal of well-defined atheromatous plaque from the vessel lumen. Although this is less invasive than open surgical bypass, the procedure does not lend itself well to the type of ill defined, dispersive lesions frequently encountered in the lower extremity.13 Endarterectomy does remain a viable option for occlusion of upper extremity vessels, such as the carotid artery. While balloon angioplasty has long been the mainstay in minimally invasive treatment of PAD, it is plagued by poor long-term patency rates and an up to 60 percent rate of vessel dissection, requiring stent placement.14 The primary reason for the failure of angioplasty is restenosis (defined as a 50 percent or greater lumen loss at a two-year follow-up), which is caused by intimal barotraumas, hyperplasia and plaque recoil.13,15 Certain modifications to angioplasty have produced procedures such as brachytherapy, cryoplasty and cutting balloons to minimize restenosis rates. These procedures have yet to show significant improvements on the traditional angioplasty in order for them gain widespread clinical use.16
The efficacy of stent placement is limited due to plaque mobilization or shifting, which can lead to restenosis in another location. This is especially a problem in ostial areas and areas of vessel bifurcation.17 A 2005 study of stent fractures after stenting in the femoropopliteal area showed a fracture rate of 37.2 percent, leading to restenosis in 32.8 percent and total reocclusion in 34.4 percent of these cases.18
A Closer Look At The SilverHawk Plaque Excision System
Over 100,000 cases of lower extremity amputation performed annually in the U.S. are attributed to PAD. Lower extremity interventions for PAD are limited by their invasiveness and a large restenosis rate, necessitating a therapy that is less invasive and exhibits clinical success in long-term outcome studies.19
The SilverHawk Plaque Excision System (ev3) was approved by the U.S. Food and Drug Administration in 2003 and is an improvement on earlier percutaneous plaque excision devices such as the Simpson atherectomy catheter (Guidant Corp.), the Bard Rotary Atherectomy System (CR Bard), the Rotoblator (Boston Scientific), and the Xtrak device (Xtrak Medical, Inc.).13
The main advantages the SilverHawk has over these older devices is its smaller size (sized more to the target vessel lumen) and the fact that it does not include a balloon as one of its components. The lack of a balloon prevents barotraumas.13 Other changes include its faster speed (2,000 to 8,000 revolutions per minute), a carbide (as opposed to steel in the older devices) cutting blade, and a low-profile monorail design to better facilitate device delivery and catheter exchanges.13,17,20
The SilverHawk is a battery-powered catheter with a 135 cm flexible shaft ending in a cutting apparatus, consisting of a blade and a nosecone designed to collect the long strips of atherosclerotic plaque.15 The blade can also be rotated in 10-degree increments using a dial at the base of the catheter. One typically has to empty the collected plaque from the nosecone after two to six passes, depending on the length of the vessel.20 Physicians can empty the nosecone via vigorous saline flushing or mechanically using specially designed adaptors.15
The original SilverHawk comes in four sizes that correspond to femoral, popliteal and tibial vessels. There are two modifications available in the original device: the flush version and two with greater capacity nosecones.15 Newer innovations to the original device include the development of smaller sizes and the newest device, the DS, for use in vessels as small as 1.5 to 2 mm. There are also larger sizes for the treatment of PAD above the knee.
Micro Efficient Compression (MEC) technology refers to laser-drilled vent holes in the tip of the catheter. These vent holes release fluid pressure and allow more space for the collection of tissue in the tip. This has the potential to reduce procedure time by allowing the physician to collect more tissue and empty the nosecone less frequently.
A Pertinent Review Of The Current Literature
Clinical results using the SilverHawk have been encouraging but information regarding post-op outcomes of more than two years is scarce.
In a 2004 study, vascular surgeons used a stainless steel cutting blade and an 8 Fr vascular sheath to remove atherosclerotic plaque from porcine and human cases. The study reported a decrease in pretreatment diameter stenosis from 75 percent to 23.7 percent in patients.21
Zeller, et al., reported that six months after atherectomy, more than 80 percent of all patients were symptom free or had no lifestyle limiting claudication, and patients’ ABIs were significantly improved in primary lesions from an average of 0.57 to 0.72.22 Another study by Zeller reported a six-month restenosis rate of 22 percent and a six-month patency rate of 94.1 percent.23
A 2006 study by Kandzari, et al., focused on patients with critical limb ischemia and cases in which amputation had been the planned procedure. These authors found that using the SilverHawk prevented more extensive amputation or avoided it altogether in 82 percent of limbs at six-month follow-up.24
Yancy, et al., assessed the use of the SilverHawk system for limb salvage in patients with TASC C lesions (defined as a single stenosis or occlusion of > 5 cm or multiple stenoses or occlusions, each 3 to 5 cm with or without heavy calcification) and critical limb ischemia. Although the early data was promising, the study authors noted that ABIs at the six-month follow-up had returned to baseline levels. At the 12-month follow-up, only 22 percent of patients remained free of restenosis.25
The authors attribute the high incidence of recurrent symptoms and restenosis to the fact that their particular subset of patients had multilevel occlusive inflow or runoff disease that resulted in true critical limb ischemia.25
The largest study to date was with the Fox Hollow Corporation’s TALON registry, an observational, consecutive, non-randomized, multicenter registry.10
Vascular surgeons treated more than 601 patients with 1,258 symptomatic lower extremity lesions with the SilverHawk. Prior to intervention, 14.6 percent of the lesions produced ischemic symptoms that were classified as 5 or greater on the Rutherford scale, 26.8 percent of the lesions were occlusions and the mean percent diameter stenosis was 85.6 percent in patients with stand-alone plaque excision.10
After plaque excision, 97.6 percent of patients had less than 50 percent residual diameter stenosis and the mean percent diameter stenosis decreased to 10.5 percent (from 85.6 percent) for stand-alone plaque excision.10 Plaque excision improved the mean ABI from 0.70 to 0.85 at six months and 0.05 at 12 months. The study authors suggest this supports plaque excision as a primary endovascular therapy for patients undergoing lower extremity arterial revascularization.10
In 2007, Zeller, et al., reported two-year follow-up outcomes in patients who had undergone atherectomy of below-the-knee arterial lesions with the Silverhawk device for critically ischemic limbs that the authors classified as a Rutherford 4 or 5. Treatment decreased the average stenosis from 89 percent to 12 percent and the mean ABI increased from 0.48 to 0.81.26 Restenosis rates after 12 and 24 months were 33 and 40 percent respectively. At long-term follow-up, the mean ABI remained significantly improved at 0.72 after 12 months and 0.86 after 24 months.26
The presence of intermittent claudication is a strong indicator for PAD but physicians should not rely upon this solely for the diagnosis of PAD. Ankle brachial indexes have become a mainstay in the initial evaluation of patients suspected to have PAD. An ABI reading of <0.90 is the cutoff point for the diagnosis of PAD.4 The lower the ABI, the more severe the occlusive disease.
It is the responsibility of every podiatric physician to screen for PAD, recognize its signs and symptoms, educate our patients on the effects of PAD, and refer to our vascular colleagues or primary care doctors when appropriate.
In order to facilitate appropriate referrals, it is also important to stay abreast of the most current information on technological advances that the vascular team can utilize to improve outcomes for patients.
Dr. Fisher has just graduated from the New York College of Podiatric Medicine and will be attending the Jewish Hospital St. Mary’s Healthcare PM&S 36 residency program in Louisville, Ky.
Dr. Sizemore has just graduated from the New York College of Podiatric Medicine and will be attending the Jewish Hospital St. Mary’s Healthcare PM&S 36 residency program in Louisville, Ky.
Dr. Khan is a Clinical Assistant Professor in the Department of Medical Sciences at the New York College of Podiatric Medicine. He is also a Clinical Instructor at the University of Texas Health Science Center at San Antonio.
Dr. Steinberg is an Assistant Professor in the Department of Plastic Surgery at the Georgetown University School of Medicine in Washington, D.C. Dr. Steinberg is a Fellow of the American College of Foot and Ankle Surgeons.
For further reading, see “How To Diagnose Peripheral Arterial Disease” in the April 2007 issue of Podiatry Today. Also check out the archives at www.podiatrytoday.com.
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