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Peripheral Artery Disease

By Harvey B. Simon, M.D.
Content provided by the Faculty of the Harvard Medical School

Arteries are the vital channels that carry oxygen-rich blood from the heart to all the body's tissues. When blockages develop, blood flow slows and tissues suffer. That's when heart attacks and strokes occur. But peripheral artery disease (PAD), which gets less attention, is a major problem, too.

What is Peripheral Artery Disease?

PAD is a form of atherosclerosis, the same disease that causes most strokes and nearly all heart attacks. It most commonly affects the legs, but it can affect arteries anywhere in the body, including the heart and brain. That's why people with PAD have an increased risk of heart attack and stroke and are two to four-times more likely to die from cardiovascular disease than people without PAD.

The disease begins when LDL ("bad") cholesterol passes from the blood into the walls of an artery. Arteries damaged by high blood pressure, diabetes, or smoking are particularly at risk for PAD and cholesterol build-up. As the cholesterol builds up, it triggers inflammation, which adds to the damage.

Unless treatment halts the process, the cholesterol deposit builds up into a plaque or blockage that narrows the artery. Mild narrowing may not produce any symptoms, but moderate narrowing may prevent muscles from getting the extra blood they need during exercise. When blockages are severe, the tissues suffer even during rest. Blood clots can add to the problem.

Who Gets PAD?

Only about 3% of Americans below age 50 have the problem, but about 20% of people above age 75 have PAD, which is more common in men. In all, about 8 million Americans have PAD.

Because PAD is a form of atherosclerosis, most major heart disease risk factors — smoking, diabetes, abnormal cholesterol levels, high blood pressure and advancing age — also increase the chances of developing PAD. (One exception: ethnicity and chronic kidney disease appear to have a greater influence in PAD than heart disease.) Other risk factors for PAD include:

  • Abdominal obesity

  • African American heritage

  • Chronic kidney disease

  • Tendency to form blood clots

  • Increased levels of homocysteine, an amino acid in the blood.

Symptoms

The earliest and most common symptom is called intermittent claudication, which causes cramp-like muscle pain. Claudication occurs when muscles are not getting enough oxygen. The discomfort can occur in the foot, calf, thigh, or buttock, depending on the site of the blockage. Men can also develop erectile dysfunction if PAD strikes in the aorta or iliac arteries because they supply blood to the penis.

PAD can also produce numbness, tingling, weakness or fatigue. Because muscles need more oxygen when they're working, claudication begins during exercise and resolves with a few minutes of rest. People with mild blockages can walk substantial distances before the symptoms set in, but patients with severe PAD may experience distress in just a few yards.

A more serious symptom is rest pain. It occurs when muscles can't get enough oxygen — even at rest — due to severe blockages. It's most common in the foot. At first, the pain is most troublesome when the leg is elevated, particularly in bed at night. But if the disease progresses, the pain can become constant. Even sitting or standing won't relieve it. Patients with moderate to severe PAD can also develop ulcers or other skin problems in their feet and legs. Rest pain usually requires surgery.

The most dangerous symptom is known as critical limb ischemia. Ischemia means tissue damage caused by lack of blood and oxygen. It's triggered by a blood clot that blocks a narrowed artery. Critical limb ischemia requires emergency treatment to prevent amputation, gangrene, or death.

Diagnosing PAD

If you have any of these symptoms, early diagnosis and treatment is critical because lifestyle treatment and medications can be very effective. Many patients with PAD don't have any symptoms but are diagnosed during an doctor's exam or screening test, such as the ankle-brachial index described below. But diagnosis and treatment is important for them, too.

1. Office evaluation

Your doctor will ask about your risk factors for PAD and your symptoms. It's important to rule out other causes of exercise-induced leg pain, especially arthritis of the lower spine (called spinal stenosis).

Your doctor will do a physical exam. This includes checking your blood pressure and the pulses on the top of your feet, at your ankle, behind your knee, and in your groin. It's important for the doctor to check your pulses in both legs and examine your skin. In PAD, the skin may not get enough oxygen-rich blood. Over time, it becomes cool, thin, and shiny, and hair growth is diminished.

Your doctor will also want to check your cholesterol, blood sugar, and kidney function with a blood test.

2. The Ankle-Brachial Index (ABI)

The ABI is a safe, non-invasive test that can detect PAD and estimate its severity. It can be performed in some doctors' offices or in vascular labs. A technician will use a Doppler probe and a blood pressure cuff to measure the systolic blood pressures in your ankles and arms (the brachial artery). To understand how it works, just step on a garden hose. The blockage produced by your foot will reduce water pressure at the nozzle. Similarly, a blockage in a leg artery will lower blood pressure at the ankle.

3. Doppler duplex ultrasound test

This test uses ultrasound to measure blood flow in the legs. It can be done at rest and after exercise. It's a non-invasive, risk-free way to identify the site of a blockage and to determine how narrow the artery is. In general, a narrowing of more than 50% is likely to produce symptoms.

Patients who are candidates for revascularization (see Treatment) procedures require detailed images produced by angiography. Until recently, that meant an invasive test that required puncturing an artery and injecting a dye to allow blockages to show up on x-rays.

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