Coronary Artery Disease vs. Peripheral Artery Disease

CAD versus PAD

This article reviews the main concepts of coronary artery disease (CAD) and peripheral artery disease (PAD). The similarities and differences will be examined, along with treatment options. 

What is Coronary Artery Disease?

CAD is a progressive narrowing of the coronary arteries caused by atherosclerosis. To be considered CAD, the coronary arteries must be at least 70% occluded.

Coronary artery disease is the build-up of plaque in the coronary arteries.

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Pathophysiology of CAD

When discussing the pathophysiology of CAD, it is important to look at both the risk factors and etiologies. 

The risk factors of CAD include:

• Smoking. Smoking causes repeated inflammation that damages the lining of vessels.
• Hypertension. High blood pressure will damage the vessels over time.
• Diabetes. Diabetes will damage the vessels over time.
• Age. The risk of developing CAD increases with age. Men over the age of 45 and women over the age of 55 are at higher risk.
• High cholesterol. High cholesterol contributes to the formation of plaques, especially with a high low-density lipoprotein (LDL) cholesterol level. High cholesterol is also known as hyperlipidemia or dyslipidemia.
• Family history. A family history of heart disease is a risk factor for CAD.

The pathophysiology of CAD involves an inflammatory response in the lining of the coronary arteries. Any or a combination of the risk factors can set off the inflammatory response. Inflammation is intended to heal and repair when there is exposure to something that should not be there. When the inflammatory responses are set off abnormally, it is harmful to the arteries. 

These etiologies, or risk factors, set off the inflammatory cascade. Normally when that happens, cytokines are released. The cytokines attract macrophages to stick to that site, and they release LDL cholesterol. That LDL cholesterol is bad for the blood vessels. It is sticky, which eventually leads to the formation of fatty streaks within the inner lining of the vessels.

Those fatty streaks become fibrotic plaques when “stuff” keeps building up. Eventually, the plaque ruptures and sets off the coagulation cascade, which causes the production of thrombin. When this happens, fibrinogen is converted to fibrin and platelets are attracted to the site, causing a thrombus in a coronary artery.

Over time, injury to the arteries can lead to the development of plaques, or atherosclerosis.

The process where plaques build up in the arteries is called atherosclerosis.

Medications can help prevent the development or worsening of atherosclerosis. The most common medications are antiplatelets and aspirin. Clopidogrel (Plavix^®) is an antiplatelet that prevents platelet aggregation.

The concern in CAD is if the fibrotic plaque ruptures and triggers the coagulation cascade. This causes a thrombus in the coronary arteries. The thrombus can potentially lead to partial or complete occlusion of the coronary artery, causing infarction, which is known as acute coronary syndrome or myocardial infarction.

Treatments for CAD

The keystone of treatment for CAD is lifestyle changes, especially if it has not yet developed into a myocardial infarction. Interventions are aimed at preventative measures. Medication and procedures are also used if needed.

Some of the recommended lifestyle interventions include:

• Eating a heart-healthy diet that is low in cholesterol, sodium, and fat.
• Exercising for at least 30 minutes three times per week.
• Losing weight, if the patient is obese.
• Quitting smoking.
• Managing chronic conditions, such as hypertension and diabetes. 

Medications used in the treatment of CAD include lipid-lowering agents and other cardiac drugs.

• Statins. The most widely used class of cholesterol-lowering medications are the statins. They are first-line for treatment of high cholesterol. Statins work well to lower the cholesterol, but they negatively affect the liver.
• Aspirin. Aspirin works as an antiplatelet and helps prevent clots. It is used to prevent myocardial infarction. It is also used following a myocardial infarction.
• Antiplatelets. Clopidogrel (Plavix^®) and ticagrelor  (Brilinta^®) are also antiplatelet drugs, but they work differently than aspirin. These antiplatelets are used when a patient cannot tolerate or take aspirin. If the patient hasn’t had a recent myocardial infarction, they should take either aspirin or an antiplatelet for CAD, but not both.
• Bile acid resins (also called bile acid sequestrants). Cholestyramine is an example of a bile acid resin. Bile acid resins lower cholesterol by attaching to the bile inside the intestines and preventing the body from absorbing fats. Essentially, they make the patient pass fat through the stool.
  
  This class of medications should be taken with food. Importantly, bile acid resins interfere with the absorption of other drugs. Patients need to be educated to take bile acid resins one hour before or four hours after taking other drugs.
• Ezetimibe (Zetia^®). Ezetimibe is also a cholesterol-lowering medication. Ezetimibe is not used first-line but can be used alone or in addition to statins to help lower cholesterol.
• Niacin (B-vitamin, or nicotinic acid). Niacin also lowers cholesterol, but it is not a first-line option. Niacin can cause facial flushing and warmth because it is a vasodilator.
• Beta-blockers. Beta-blockers are first-line antihypertensive agents in CAD because they have been shown to decrease mortality. Beta-blockers help the heart fill during diastole, which decreases cardiac contractility and the myocardial demand.

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What is Peripheral Arterial Disease?

Peripheral arterial disease (PAD) is a circulatory problem caused by narrowed arteries in the extremities, particularly the legs. The extremities do not receive enough blood flow to keep up with the demand due to the narrowed arteries.

Pathophysiology of PAD

The pathophysiology of PAD is the same process as CAD. Both conditions are caused by atherosclerosis, the process that leads to narrowing of the arteries. The difference between PAD and CAD is which blood vessels are affected. In CAD, the coronary arteries are affected. In PAD, the arteries that feed the lower legs and feet are impacted.

There are two classifications of PAD:

• Functional PAD. Functional PAD is characterized by intermittent claudication, the classic sign of PAD. The blood flow is good at rest, but ischemia occurs with exercise. Functional PAD is otherwise known as Stage II disease.
• Critical PAD. Critical PAD is characterized by pain at rest (Stage III disease). The final stage of PAD (Stage IV disease) is characterized by trophic skin changes, such as dryness, scaling, and lack of hair growth.

When a patient’s foot does not have adequate blood flow for a long period, the foot will not be healthy. It will lack hair, the skin will look flaky, and the toenails will dry and scale off.

Peripheral arterial disease is caused by atherosclerosis in the peripheral arteries.

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Clarifying the Difference between PAD and Peripheral Venous Insufficiency

What is the difference between PAD and peripheral venous insufficiency? PAD is a blood flow issue, while peripheral venous insufficiency is a blood return issue.

In PAD, the body does not have adequate blood flow to the extremities. The classic signs and symptoms are paresthesia, neuropathic pain, and tingling. The skin is cool to the touch and pallor. There is low hair growth.

Another sign is pulselessness. It is usually difficult to find the pedal pulse and may require use of a Doppler. If a patient has an ulcer, the ulcer will have a “punched out” appearance with clean and clear borders, usually presents on the outside of the ankle without swelling.

Ulcers are common on the outside of the foot in peripheral arterial disease.

With peripheral venous insufficiency, blood is getting to the limbs but not returning properly. The most common cause of venous insufficiency is varicose veins. Another cause is incompetent valves. 

Signs and symptoms of peripheral venous insufficiency include edema, pain that improves when the legs are raised, a “messy” ulcer, and swelling. The ulcer may be brown in color with drainage. The ulcer will typically be located at the medial malleolus or the inside of the ankle.

Varicose veins are the most common cause of peripheral venous insufficiency.

Nursing Care for PAD

Since PAD is a blood flow issue, the nursing care involves:

• Keeping the legs below the level of the heart to make sure they are perfused. Raising the legs might reduce the blood flow even more.
• Keeping the extremities warm with socks or gloves. A heating pad should not be used because patients, especially those with advanced peripheral neuropathy, may not be able to feel the heat to indicate if it is too hot.

Treatments for PAD

Treatment for PAD consists of lifestyle interventions, medications, and potentially surgery. Lifestyle interventions for PAD are similar to those for CAD.

Lifestyle interventions that help manage and reduce the progression of PAD are:

• Quitting smoking
• Exercising
• Eating a healthy diet

Some medications used in the treatment of PAD include:

• Pentoxifylline (Trental^®). Pentoxifylline helps to reduce blood viscosity. It helps the blood flow more easily through narrowed arteries.
• Cilostazol (Pletal^®). Cilostazol is an antiplatelet drug and a vasodilator. It increases blood flow to the extremities. When a patient is prescribed cilostazol, it is important to know if they are taking other vasodilators, such as nitroglycerin or sildenafil (Viagra^®).

Pentoxifylline and cilostazol help to reduce the pain of intermittent claudication. They are used for symptom management but do not cure PAD.

CAD is a progressive narrowing of the coronary arteries caused by atherosclerosis. PAD is a circulatory problem caused by narrowed arteries in the extremities, particularly the legs. Both conditions result in decreased blood flow, and it is important to understand the pathophysiology of these diseases and the ways they are treated to provide guidance and treatment.