Despite improvements in the treatment of cardiovascular disease, peripheral arterial disease (PAD) continues to be a significant health problem. PAD affects more than 15% of the population over the age of 70 and is associated with significant morbidity and mortality. The Framingham study has shown that claudication symptoms of PAD are associated with a greater than two-fold increase in the frequency of coronary events and significantly higher mortality. The natural history of PAD is highly variable, with up to 70% of PAD patients remaining stable or improving over time and up to 30% progressing to severe or critical limb ischemia. This built-in uncertainty about the prognosis of PAD has made establishing appropriate treatment strategies for patients with PAD difficult. However, significant progress has been made in the past 10 years in understanding effective treatment strategies for claudication and critical limb ischemia due to PAD. PAD is now understood to be a systemic atherosclerotic process, and patients with PAD are at high risk for cardiovascular events. These patients are best managed with aggressive global risk reduction of their atherosclerosis. This concept has led to the development of writing groups and guidelines from vascular medicine societies and building an evidence base for effective medical therapy of PAD. Due to the complex multifaceted nature of PAD and the disparate treatment strategies that have been proposed, a multidisciplinary approach to the care of PAD patients has been advocated. The remainder of this chapter and this text will outline an approach to multidisciplinary care of PAD based on disease severity with detailed discussions of specific treatment modalities.
Diagnosis and Assessment
In patients considered for revascularization therapy and in those with low ABI values or atypical leg symptoms, additional noninvasive testing and anatomic imaging may be warranted. High quality magnetic resonance angiography (MRA) and computed tomographic angiography (CTA) are noninvasive tests that can provide detailed anatomic information, allowing for adequate planning of surgical or endovascular revascularization. However, given the risks of contrast agents and the expense of MRA and CTA, the use of these imaging modalities should be reserved for specific indications.
In recent years, the use of vascular ultrasound has become more popular as a noninvasive means for assessing atherosclerotic lesions. While standardized protocols for ultrasound evaluation of PAD have not been firmly established, it is a useful tool for assessing disease severity and progression and has been shown to have a sensitivity and specificity equivalent to that of ABI.
As a comparison with arteriography, measurement of ABI has a sensitivity of 90%, a specificity of 98%, a positive predictive value of 47%, and a negative predictive value of 99%. While the gold standard for diagnosing PAD is arteriography, it is an impractical and costly method to employ for routine screening of all patients at risk for PAD due to its invasive nature.
Ankle-brachial index (ABI), a simple noninvasive physiologic study, has been endorsed by the American Heart Association as a useful test for the diagnosis and assessment of PAD. Recommending ABI measurements on a routine basis for patients at risk for PAD is a simple and cost-effective way to diagnose PAD. An ABI value ≤0.90 is sensitive and specific for the diagnosis of PAD. However, it is important for clinicians to be aware of the limitations of ABI.
A patient who presents with leg symptoms suggestive of muscle ischemia or with an asymmetric decrease in blood pressure between the upper extremities and lower extremities, particularly those over the age of 50 or with a history of diabetes or smoking, should be considered for PAD. It is worth noting that the leg symptoms of some patients with PAD, especially those with diabetes, may be atypical. In such individuals, leg symptoms (e.g., claudication) may be diminished given underlying neuropathy and the resultant lack of pain sensation.
Treatment and Management
A consistent treatment of PAD should be aimed at minimizing blockage while maximizing blood flow to the legs and feet. There are both invasive (procedures) and non-invasive methods for achieving this goal. Of the non-invasive methods, aggressive lipid lowering with diet, exercise, and medications are the cornerstone for improving cardiovascular health. A stepwise approach to relieving claudication symptoms should be taken starting with walking programs and medications. All patients with claudication should undergo an aggressive program of cardiovascular risk reduction. These measures include: smoking cessation, regular exercise, and treatment for elevated blood pressure, high cholesterol, and diabetes. For the majority of patients with intermittent claudication, revascularization of the affected limb is not effective when compared to medical therapy. However, some patients with disabling claudication and those with critical limb ischemia may benefit from either an endovascular or surgical revascularization. Measures for improving blood flow in critical limb ischemia are highly variable and range from oral medications and angioplasty to major vascular surgery and major amputation. The risks and benefits of these therapeutic methods are highly variable depending on specific patient factors and the anatomy of the affected limb. Cost and probable outcome should also be weighed by the patient. Finally, the relief of PAD symptoms by revascularization may lead to improved mobility, but this does not necessarily lead to improvement in overall quality of life. An intense treatment of limb-threatening ischemia is aimed at relief of rest pain and healing of ischemic ulcers and/or preventing limb loss. This is regarded as a medical emergency, and revascularization is generally recommended. High morbidity and mortality rates in these patients are largely related to associated cardiovascular disease, and therefore these patients should undergo an aggressive program of cardiovascular risk reduction.
Future Directions
In the future, the early detection and aggressive treatment of PAD may eventually decrease the number of patients that have critical limb ischemia. These preventive measures will also decrease the numbers of lower extremity amputations that are the result of PAD. One study suggests that a national campaign to increase public and physician awareness of PAD could improve the preventative care of this disease and decrease its prevalence. Since the burden of PAD is likely to increase substantially in the next few decades, vascular medicine has to build a workforce at several levels starting with general awareness raising and screening of high-risk groups, progression to prevention and implementation of best medical therapies, and effecting of programs to increase revascularization for advanced PAD. New initiatives to train PCPs in the diagnosis and treatment of PAD are also vital. With the growing American elderly population, more geriatricians should be trained about PAD. Models foresee progressively increased healthcare costs in relation to the care of PAD patients. Since prevention and management of atherosclerotic risk factors has been shown to diminish cardiovascular disease mortality rates, the burden of PAD can only be substantially decreased by the prevention of its at-risk population from developing symptomatic PAD. High-risk groups include diabetics, smokers, and people older than 50, but most people with PAD are asymptomatic. These patients can be identified early with an ankle brachial index and aggressive treatment of atherosclerotic risk factors maintaining this group in a state of asymptomatic PAD should decrease morbidity rates of PAD and its end-stage limb diseases. This would represent a healthy investment because by subverting disease progression there would be less future healthcare costs compared to treating manifestations of PAD.
