Causes and Risk Factors
Peripheral arterial disease (P.A.D.) is a very common disorder. The risk of developing P.A.D. increases with age. In the non-Hispanic white population age 70 or older, the risk is 15-20%. P.A.D. is caused by arteriosclerosis, which is the buildup of plaque in the arteries. The buildup of plaque occurs in the same fashion as it does in the heart. Over time, the plaque calcifies and the artery becomes narrow and rigid. Furthermore, there is another condition which can lead to P.A.D. known as aortic-iliac disease. This condition is caused by atherosclerosis in the aorta and presents with symptoms in the legs due to the poor blood flow. Another potential cause of P.A.D. is the rare genetic disorder, homocystinuria. This disorder causes an abnormal buildup of homocysteine in the blood. There have been some tests on animals that suggest an increased risk of developing atherosclerosis and deep vein thrombosis with high levels of homocysteine. Creating a proper experimental model for these studies is very difficult because there are many variables that affect arteriosclerosis and it is impossible to isolate homocysteine’s effects. High levels of serum cholesterol or low-density lipoprotein are additional risk factors; however, they are not as correlated with P.A.D. as are cerebrovascular disease or coronary artery disease. High levels of homocysteine and the presence of cerebral or coronary atherosclerosis may be confounding factors.
Diagnosis and Treatment
There are several ways to manage PAD and the most simplistic is to ameliorate the risk factors. It has been shown that cardiovascular risk reduction with improvement of hypertension, diabetes and lipid control can not only prevent CAD but also improve symptoms of PAD. Cessation of smoking is of utmost importance as it has shown to slow the progression of occlusive disease. A supervised exercise programme has proven to increase pain-free walking distance and time, this in turn will increase functional status and is a treatment for symptomatic PAD. Pharmacotherapy such as cilostazol, pentoxyphylline and Naftidrofuryl have shown to improve symptoms with increase in ability to walk, but the evidence for reduction in cardiovascular events is weak. This has led to a interventional treatment strategy in attempt to improve quality of life along with prevention of limb loss and reduction of cardiovascular events. Revascularization can be both surgical and endovascular dependant on the patient profile and lesion severity. Potential benefits of bypass surgery over endovascular methods are better durability and longer symptom free interval with better long term mortality. However endovascular methods have much lower procedural risk and have the possibility of similar increase in claudication distance and improvement in quality of life. The decision on revascularization must be taken through informed discussion with the patient with analysis of long as well as short term risks and quality of life attained after intervention.
Diagnosis of PAD is characterized by an altered ankle-brachial blood pressure index (ABPI) at resting stage. The utilization of a hand-held Doppler device would profit to compare systolic blood pressure in the limbs to decide existence of abnormal rate of blood flow down the leg and also to detect level and area of occlusive disease. The learning curve for ABPI measurement is steep but it is the most cost-effective and easy to use method for diagnosis of PAD. Doppler ultrasound alone is reliant upon the operator’s skill but is non-invasive and can provide an accurate assessment. Duplex scanning is more detailed and sensitive but is also operator dependent and the limitations are that it cannot evaluate distal vessels well, and is poor in evaluation of calcified vessels. Segmental blood pressure measurements is sensitive in disease detection and monitoring but has poor localization of disease, whereas angiography is time-consuming, expensive, and is invasive with slight possibility of complications, it is still considered the gold standard of diagnostic tools for PAD because it can provide detailed visualization of the location, severity and length of lesion and can also guide revascularization. MRI and CTA have become more popular as they are non-invasive tests and have the possibility to measure for plaque composition and long lesion analysis.
Prevention and Management
Prevention and management of PAD are important even for patients who are asymptomatic because PAD indicates a systemic atherosclerotic process and conveys a higher risk of major cardiovascular events. Only a minority of patients with PAD will present with intermittent claudication or critical limb ischemia. The most common presenting symptoms of PAD are pain at rest or ulceration. These symptoms, skin atrophy or weakness in the limb muscles carry a significantly increased risk of lower limb amputation. Specific strategies to prevent cardiovascular events are discussed in Section 3. In summary, they entail the management of atherothrombotic risk and lifestyle modification. Measures to improve walking distance are reasonably clear in patients with intermittent claudication who are functionally limited and have significant morbidity. However, those with PAD and asymptomatic patients may also benefit from these strategies to improve cardiovascular health. High morbidity of ischemic events suggests that they should be prioritized in many patients with PAD, not just those with intermittent claudication. They involve control of cardiovascular risk factors and global measures for cardiovascular protection.
