How To Detect Peripheral Arterial Disease
Peripheral arterial disease (PAD) affects 12 million people in the United States.1 More than half of the patients with PAD are asymptomatic or have atypical symptoms.2 PAD is a narrowing of blood vessels characterized by atherosclerotic occlusive disease of the lower extremities, restricting blood flow. There are many causes of PAD. In addition to a major risk factor like smoking, diseases such as diabetes, Buerger’s disease, hypertension and Raynaud’s disease predispose patients to developing PAD. Inadequate perfusion to the lower extremity will always result in a non-healing wound, which often leads to infection, tissue loss and amputation. Tissue loss in the lower extremity can be due to PAD, which reduces the supply of oxygen, nutrients and soluble mediators involved in the tissue repair and maintenance process. A lack of tissue perfusion decreases tissue resilience, leads to rapid death of tissue and impedes wound healing.3 Podiatric physicians play a pivotal role in assessing the disease and can often be the first to recognize and diagnose either the onset or advanced stages of PAD. What You Should Know About The Common Symptoms In order to identify risk factors for PAD, one must obtain a thorough patient history and perform a complete physical examination. These patients may experience pain in the lower extremity musculature due to inadequate perfusion. Early symptoms include an achy, tired sensation of affected muscles, usually in the legs. Intermittent claudication is the most common and classic symptom of PAD. Patients will describe it as pain, cramping or aching in the calves, thighs or buttocks that occurs when walking and is relieved by rest.1 Complaints of pain may be acute or chronic in onset. The sudden onset of extremity pain may be associated with coolness and/or numbness resulting from acute thrombosis of distal vasculature. Patients presenting with chronic pain may relate symptoms of burning pain that are relieved by elevation and aggravated by dependency. These patients are deemed to have rest pain. Critical limb ischemia, which involves the development of tissue loss or gangrene in the lower extremity, is a more critical manifestation of PAD.1 Obtaining a thorough history will influence the decision process when treating patients who have PAD. Past medical, past surgical, social, ambulatory status and nutritional histories all play an important role in arriving at an appropriate course of treatment for the patient. Essential Keys To The Vascular Examination The vascular examination begins with the two most important components, visual inspection and palpation of lower extremity pulses. One should note and evaluate the color and integrity of the skin. When patients have a pallor upon elevation and rubor upon dependency, this is often the first indicator of vascular insufficiency. After elevation of the extremity, keep in mind that it normally takes less than 20 seconds for the return of blood to the dependent extremity. This is a useful marker in evaluating the severity of the vascular deficit. One should also inspect the skin for trophic changes. When patients have PAD, the integument becomes dry, shiny, fissured and hairless. You may also note brittle and dystrophic nails. Also be sure to inspect the interdigital spaces for maceration and ulcerations. Proceed to assess the skin temperature of the affected limb and compare it to the contralateral limb, noting any coolness. Temperature is a good indicator of blood flow in the dermal vessels.3 One should palpate the femoral, popliteal and pedal pulses routinely in every physical examination. However, keep in mind that palpable pulses do not preclude the presence of limb threatening ischemia.4 Also be aware that the dorsalis pedis has been reported to be absent in 8.1 percent of healthy individuals and the posterior tibial pulse is absent in 2.0 percent of the population as a whole.1 Therefore, there is a high false positive and false negative rate when it comes to evaluating pulses by palpation.1 If the pulses are nonpalpable, proceed to assess the pulses with a hand-held Doppler. A Guide To Noninvasive Vascular Evaluations The vascular evaluation can include both physiologic testing and anatomic imaging. The physiologic testing includes invasive and noninvasive testing while the anatomic imaging includes invasive arteriography, less invasive digital subtraction angiography and noninvasive anatomic imaging, which includes magnetic resonance angiography, CT angiography and duplex imaging.3 Noninvasive vascular evaluations provide an objective diagnostic tool for evaluating PAD. The noninvasive vascular evaluation includes ankle brachial index and ankle pressures, toe pressures, segmental pressure measurements, plethysmographic waveform analysis, skin perfusion pressure and laser Doppler pressure, color duplex imaging and ultrasonography, transcutaneous oxygen content, cutaneous oximetry and treadmill exercise testing. Assessing The ABI The ankle brachial index (ABI) is a reproducible and fairly accurate measurement of the ankle and brachial systolic pressures. It is 95 percent sensitive and 100 percent specific for peripheral arterial disease.5 One would use a standard blood pressure cuff to take the systolic blood pressure at the dorsalis pedis and posterior tibial arteries, as well as both brachial arteries. The ankle brachial index is calculated by dividing the highest systolic ankle pressure by the higher of the two systolic brachial pressures. • A normal ABI range is >=0.9. • Mild claudication or obstruction occurs with an ABI <0.9-0.75. • Moderate to severe claudication occurs with an ABI <0.75-0.4. • Ischemic rest pain and severe disease is present with an ABI <0.4. • Tissue loss will occur with an ABI <0.5. • A threatened limb will have an ABI <0.15. • Irreversible ischemia is present with an ABI <0.15. Overall, the ABI is a simple test to perform, is noninvasive and provides a quantitative measurement of the patency of the lower extremity arterial system. One pitfall of the ABI is that it yields abnormally high values with medial calcification of arteries, which one commonly sees in the diabetic population. Medial calcification will lead to an ABI range of >1.3 due to poorly compressible arteries at the ankle level. Understanding The Benefits Of Segmental Pressures, Toe Pressures And Pulse Volume Recordings When one has confirmed the PAD diagnosis, you can obtain segmental pressures when trying to assess the location and severity of the disease. Place four standard-sized blood pressure cuffs at the high thigh, above-knee, below-knee and ankle positions. Obtaining pressures at these successive levels allows you to ascertain the localized level of the disease. A 20-mmHg pressure gradient between successive levels on the same extremity is considered a significant pressure drop and correlates with flow limiting vascular lesions. Systolic pressures should not vary more than 20 mmHg at the same level in both legs. One should consider segmental pressures for patients with poorly compressible vessels (medial calcinosis) or those with a normal ABI whom you have a high suspicion of PAD.1 For toe pressures, place a pneumatic cuff on the digit and a photoelectrode on the tip of the digit to obtain photoplethysmographic arterial waveform. The plethysmographic sensor measures the quantity of red blood cells in the cutaneous circulation via an infrared light that is transmitted into the superficial layers of the skin. Obtaining toe pressures are useful in that a toe pressure of greater than 30 mmHg gives a favorable estimation of healing potential. Pulse volume recordings are a qualitative assessment of blood flow. Pulse volume recordings are similar to segmental pressures because they are useful for patients with suspected PAD when it is important to know the location and severity of the disease. One can obtain this waveform analysis by using sequential blood pressure cuffs with an air plethysmographic technique. The blood volume in the tissue beneath the cuff is indirectly measured throughout the cardiac cycle to produce a waveform. Pulse volume recordings are a measurement of capillary bed volume. Normal pulse volume recordings have a sharp upstroke and peak with a reflected wave before returning to the baseline. The waveform becomes irregular with low amplitudes proportionate to the obstructive disease. In a mild obstruction, the reflected wave is lost, the upstroke is delayed and the peak is blunted. Moderate to severe obstruction illustrates a bowing of the down stroke away from the baseline. A flat pulse volume recording has an irregular low amplitude indicative of severe obstruction. Weighing The Merits Of Other Diagnostic Modalities Transcutaneous oxygen (TcPO2) is a measurement of oxygen tension in the tissue. Modified Clark-platinum electrodes are used to assess the PO2 of the skin surface during heat induced local vasodilation. A normal TcPO2 value in the foot is 60 mmHg. An oxygen tension >40 mmHg is likely to heal. TcPO2 values between 30 to 40 mmHg have a moderate probability of healing while those between 20 to 30 mmHg have a medium probability of healing. A TcPO2 <20 mmHg has a low likelihood of healing. Be aware that the accuracy of oxygen tension can be limited by local edema, inflammation, infection, skin temperature and pharmacologic agents. Treadmill exercise testing is useful and may help in diagnosing patients with atypical symptoms or patients with a normal ankle brachial index and classic claudication symptoms. When it comes to patients with claudication, one will typically see a drop of >20 mmHg in ankle pressure after exercise. Treadmill functional testing can be a useful adjunct in evaluating treatment efficacy as well as assessing physical function.1 Employing color duplex imaging and ultrasonography facilitates vessel identification with anatomical detail of specific vessels. Color Doppler allows you to analyze the direction of blood flow as well as the presence of turbulence. Color-flow scanning adds Doppler information to the conventional duplex scan to survey arteries throughout their course. By employing color duplex imaging, one can identify all lesions and stenoses or occlusions, estimate the percentage diameter reduction, and determine the length of the lesion. Ultrasonography provides a real-time analysis and audible signals that produce images and signals for assessing blood flow.3 Postoperatively, duplex ultrasound is also useful in monitoring patients for graft and stent patency so one can pursue appropriate intervention prior to thrombosis. One can also assess skin perfusion pressure with a laser Doppler, effectively combining laser Doppler principles with air plethysmography. This modality is most often used to diagnose chronic ischemia and assess wound healing potential as well as determining amputation level. What You Should Know About Vascular Imaging Arteriography is an invasive study giving an anatomic assessment of the vasculature commonly obtained in patients whom revascularization is considered. Arteriography is useful when limb pressures are insufficient to clarify the diagnosis of PAD. Intravenous contrast angiography remains the gold standard for imaging blood vessels and is often reserved for anatomical assessment of stenoses or occlusions prior to planned intervention. A small risk of contrast induced nephrotoxicity exists with X-ray angiography. Therefore, this procedure is typically reserved for evaluating patients who may undergo a revascularization procedure. Magnetic resonance angiography is another imaging modality that can be used instead of intravenous contrast angiography. Visualization of vessels with magnetic resonance angiography is solely dependent on the patient’s blood flow alone. Therefore, patients who are unable to tolerate a contrast load are candidates for this imaging modality. Although magnetic resonance angiography is more sensitive than angiography in identifying patent vessels, its limitation lies with the inability to visualize the distal vasculature in patients who have severe inflow disease. In Conclusion All of the symptoms and consequences of PAD are related to restricted blood flow. When one recognizes ischemia via findings of diminished or absent pulses, pallor on elevation, rubor on dependency, delay of capillary refill, and integument changes including thickened nails or absence of hair, quantifying the severity of the condition may be difficult. Palpable pulses do not preclude the possibility of limb-threatening ischemia so you should seek additional noninvasive evaluations for patients you suspect of having PAD.5 If tissue loss ensues and/or if an infected foot requires debridement or open partial foot amputation, one must observe the foot and wound on a daily basis. One should see prompt signs of healing once the infection is eradicated. Wound granulation should be robust and healthy within several days. If you do not see the signs of healing in these wounds, you should pursue an arteriogram. An aggressive multidisciplinary approach is essential in treating patients with peripheral vascular disease. Clearly, the prognosis depends on the underlying disease and the stage at which the disease is diagnosed. However, one can treat PAD successfully when a thorough history and physical examination, noninvasive and invasive testing, and intervention are instituted in a timely and mutually respectful fashion. Dr. Blume is a Clinical Assistant Professor in the Department of Orthopaedics and Rehabilitation at the Yale School of Medicine. He is also a Fellow of the American College of Foot and Ankle Surgeons, and is the Director of Limb Preservation at the Yale New Haven Hospital in New Haven, Conn. Dr. Key is a Chief Resident at Yale/VACT Healthcare Systems. Dr. Sumpio is the Chief of the Section of Vascular Surgery at the Yale University School of Medicine.
References 1. American Diabetes Assoc.: Peripheral arterial disease in people with diabetes. Diabetes Care 26:3333-3341, 2003. 2. Hiatt WR: Medical treatment of peripheral arterial disease and claudication. N Engl J Med 344:1608-1621, 2001. 3. Sumpio, BE, Lee, T, Blume P. Vascular evaluation and arterial reconstruction of the diabetic foot. Clin Podiatr Med Surg; 2003; 20:689-708. 4. Sumpio BE. Foot ulcers. N Engl J Med 2000; 343(11):787-93. 5. Bernstein EF, Fonek A: Current status of non-invasive tests in the diagnosis of peripheral arterial disease. Surg Clin North Am 62:473-487, 1982.