Key Clinical Questions
How is the diagnosis of lower-extremity peripheral arterial disease established?
When is lower-extremity ischemia an emergency?
When should vascular surgery consultation be obtained?
What are the essential nonsurgical elements of managing lower-extremity ischemia?
While specific estimates vary, it is clear that lower-extremity peripheral arterial disease (PAD) affects a substantial fraction of the US population. For example, a 1999 analysis of the National Health and Nutrition Examination Survey results demonstrated that 4.3% of Americans over the age of 40 years had PAD, defined as an ankle-brachial index (ABI) of less than 0.90, corresponding to over 5 million people. The PAD Awareness, Risk, and Treatment: New Resources for Survival (PARTNERS) program, a multicenter, cross-sectional US study, showed that 29% of its cohort of nearly 7000 patients at least 50 years old had PAD based on a history of revascularization or an identical ABI criterion.
Clearly, recognition of PAD is important to guide appropriate limb-based therapy. However, given its close association with coronary and cerebrovascular arterial disease, it is perhaps more critical as a reason to motivate aggressive management of cardiovascular risk, which is discussed below.
Nonmodifiable risk factors for PAD include increasing age and nonblack Hispanic race. Gender is controversial. Some studies have shown a male predominance with less severe disease and an equal gender ratio in more advanced disease while others have ranged from no difference at any severity to a female predominance.
Irrespective of the particular risk factors in any given patient an obstructive arterial lesion with diminished distal flow is the final common pathway of PAD. Typically, this is atherosclerotic disease in chronic ischemia but there is a large array of rare causes that require investigation when clinically appropriate (Table 256-1). Degree of obstruction, however, is not the sole determinant of patient symptomatology. Indeed, around 15% of asymptomatic men were found to have 50% stenosis in at least one leg artery at autopsy. In addition to severity, symptoms depend on the timescale of disease development. Rapid narrowing of a vessel produces more profound distal ischemia because of inadequate time for the development of collateral vessels. As such acute arterial occlusion, for example from cardioembolism, often leads to extreme ischemia requiring surgical intervention while slowly developing atherosclerosis may be asymptomatic even if extensive (Figure 256-1). Finally, symptoms will also depend upon the demands of the affected vascular bed. Lesions that are hemodynamically significant at rest may not be clinically apparent until exertion. For example, patients’ reports of cramping leg pain with walking that abates with rest—the so-called intermittent claudication—is described well by this mechanism. Once blood flow drops below a minimal threshold continuous ischemia will present as rest pain, ulceration, or gangrene.
TABLE 256-1Selected Causes of Chronic Limb Ischemia