Lower Extremity Peripheral Artery Disease

Introduction

Lower extremity peripheral arterial disease refers to the presence of plaque accumulation in the blood vessels that deliver blood to the feet. These blood vessels may include the distal abdominal aorta, iliac arteries, common femoral arteries, superficial femoral arteries, popliteal arteries, and/or infrapopliteal arteries. The plaque accumulation in these blood vessels is due to a disease called atherosclerosis. Atherosclerosis is also the disease that causes heart attacks when the plaque accumulates in the blood vessels that feed the heart. Atherosclerosis causes strokes if the plaque accumulates in the blood vessels that feed the brain.

Prevalence

Lower extremity peripheral arterial disease is very common. The disease is present in 25-30% of people over age 70. The disease is also present in 25-30% of high risk individuals over age 50. Individuals who have a history of diabetes or tobacco use are considered to be at high risk for developing lower extremity peripheral arterial disease.

Symptoms

The classic symptom of lower extremity peripheral artery disease is called intermittent claudication. Intermittent claudication is described as a tightness that occurs in the thighs or calves with ambulation. Interestingly, intermittent claudication only occurs in 10% of patients who have lower extremity peripheral arterial disease. Atypical leg symptoms refer to any other type of leg discomfort that occurs in patients with lower extremity peripheral arterial disease. Atypical leg symptoms occur in 30% of patients with lower extremity peripheral arterial disease. Sixty percent of patients with lower extremity peripheral arterial disease are asymptomatic. Despite the fact that the majority of patients with lower extremity peripheral arterial disease are asymptomatic, it is very important to diagnose the disease in these asymptomatic individuals.

Mortality

Mortality rates are four times greater amongst individuals with lower extremity peripheral arterial disease compared to individuals without the disease. The increased risk of death is equally present in lower extremity peripheral arterial disease patients with or without symptoms. The five-year mortality rate for patients with lower extremity peripheral arterial disease is 25% (one of four patients with the disease are dead in 5 years if not treated). Seventy-five percent of the deaths that occur in patients with lower extremity peripheral arterial disease are cardiovascular deaths (predominantly heart attack and stroke). Patients with lower extremity peripheral arterial disease are at high risk for heart attack and stroke because individuals with plaque accumulation in the lower extremity arteries are very likely to have plaque accumulation the arteries that feed the heart and brain. Atherosclerosis is a systemic disease.

Risk Factors

The risk factors for lower extremity peripheral arterial disease are similar to the risk factors for heart attack and stroke. The risk factors include: tobacco use, diabetes, high blood pressure, high cholesterol, family history of atherosclerosis, and advanced age. For unclear reasons, tobacco use and diabetes carry a much higher risk for lower extremity peripheral arterial disease than the other risk factors. The risk of developing lower extremity peripheral arterial disease is equal amongst men and women. Certain races are at higher risk for developing lower extremity peripheral arterial disease such as African Americans.

Diagnosis

The diagnosis of lower extremity peripheral arterial disease is readily established with the use of the Ankle-Brachial Index (ABI). The ABI is the perfect screening test because it is safe, cheap, accurate and readily available. The ABI can be measured with the use of a simple hand-held Doppler by obtaining the systolic blood pressure in the ankle and brachial arteries. The calculation and interpretation of the ABI are demonstrated in figures 2 and 3. In my opinion, the ABI is the ideal test to establish the diagnosis of atherosclerosis, in asymptomatic individuals. Experts suggest performing a screening ABI on all individuals over age 70, and high risk individuals over age 50. Screening ABI’s facilitate the early diagnosis of systemic atherosclerosis in asymptomatic individuals.

When patients have symptoms that are concerning for lower extremity peripheral arterial disease, more sophisticated diagnostic tests may be required to diagnose and treat the patient’s symptoms. These diagnostic tests include duplex ultrasound, magnetic resonance angiography, CT angiography, and invasive angiography.

Treatment

The treatment of patients with lower extremity peripheral arterial disease is best summarized with the Lower Extremity PAD Treatment Triangle which is demonstrated in figure 8. The most important priority in the care of patients with lower extremity peripheral arterial disease involves addressing the high risk of cardiovascular mortality. This priority is emphasized on the Lower Extremity PAD Treatment Triangle by the placement of this priority at the top of the triangle. Strategies used to address the high risk of cardiovascular mortality in patients with lower extremity peripheral arterial disease include:

• Smoking cessation

• Antiplatelet therapy (aspirin or clopidogrel)

• Cholesterol control (target LDL < 70)

• Hypertension control (ACE inhibitors are the preferred agent)

• Diabetes control (target Hgb A1C < 7.0)

• Therapeutic Lifestyle Changes (heart healthy diet, routine exercise, weight loss)

• Flu shot annually

The next priority to be addressed in patients with lower extremity peripheral arterial disease is protecting the feet from amputation. This priority is demonstrated on the Lower Extremity PAD Treatment Triangle located at the left lower corner of the triangle. This priority is addressed by referring patients with lower extremity peripheral arterial disease to a podiatrist for annual foot exams and patient education for diligent foot care. Additionally, physicians caring for patients with lower extremity peripheral arterial disease need to be able to diagnose critical limb ischemia and acute limb ischemia to protect their patients’ feet from amputation.

Critical limb ischemia is defined as limb pain occurring at rest or impending limb loss that is caused by severe compromise of blood flow to the affected extremity. Patients with critical limb ischemia have objectively proven arterial occlusive disease as well as chronic ischemic rest pain, ulcers, or gangrene. Patients suffering with critical limb ischemia require elective but prompt referral to a vascular specialist. They will require more sophisticated diagnostic testing to establish a treatment strategy.

Acute limb ischemia refers to a rapid or sudden decrease in limb perfusion that threatens limb viability. Acute limb ischemia is associated with the six P’s:

– Pain

– Paralysis

– Paresthesia

– Pulselessness

– Pallor

– Polar

Patients with acute limb ischemia need to be admitted to the hospital and will require urgent consultation with a vascular specialist to promptly determine whether they are a candidate for urgent revascularization. Invasive angiography is likely to be required to guide treatment options.

The final priority to be addressed in patients with lower extremity peripheral arterial disease is the treatment of leg pain that may be due to intermittent claudication. This priority is demonstrated on the Lower Extremity PAD Treatment Triangle located at the right lower corner of the triangle. Claudication symptoms can be treated with exercise rehabilitation, pharmacologic therapy, and/or revascularization.

Formalized exercise rehabilitation programs lasting 3 to 6 months have been proven to increase patient walking distances 100-150%. Rehabilitation sessions typically last 35 to 60 minutes. Patients are instructed to walk at an intensity that causes pain in 3 to 5 minutes, followed by rest until pain resolution, followed by walking again.

Pharmacologic therapy for claudication involves the prescription of cilostazol at a dose of 100 mg twice daily. Cilostazol has been proven to increase patient walking distances by 50%. Cilostazol has limited use with many lower extremity peripheral arterial disease patients because of common side effects that include headache, diarrhea, dizziness, and palpitations. Also noteworthy is that cilostazol has a black box warning contraindicating its use in patients with a history of congestive heart failure.

Finally, revascularization may be required in patients with lower extremity peripheral arterial disease who do not achieve adequate symptom relief with exercise rehabilitation or pharmacologic therapy. Revascularization strategies include endovascular techniques (balloon angioplasty, stents, atherectomy, or laser) and surgical techniques (bypass surgery).

Conclusions

Lower extremity peripheral arterial disease is a disease with a high prevalence. Most patients with lower extremity peripheral arterial disease are asymptomatic or have atypical symptoms. Patients with lower extremity peripheral arterial disease have significantly higher mortality rates (25% five year mortality) compared to the general population. Patients with lower extremity peripheral arterial disease die of cardiovascular diseases such as heart attack and stroke. Lower extremity peripheral arterial disease can easily be diagnosed in most patients with a cheap, safe, and simple screening test in the office (ABI). Treatment of all patients with lower extremity peripheral arterial disease should primarily focus on lowering their risk of cardiovascular death. Patients with lower extremity peripheral arterial disease require routine foot exams and diligent footcare. Some patients with lower extremity peripheral arterial disease will require treatment to improve claudication symptoms (exercise, pharmacologic, and/or revascularization). A smaller minority of patients will require revascularization to treat critical limb ischemia or acute limb ischemia.