The Unnatural History of Peripheral Artery Disease
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Peripheral artery disease (PAD) is widely viewed as either a risk factor for cardiovascular events or a coronary artery disease (CAD) risk equivalent. Both constructs represent a failure to understand atherosclerosis as a unified disease, which has worked to the detriment of patients with PAD by denying them diagnostic and treatment options available to patients who present with atherosclerosis in other vascular beds.
Pad as a Risk Factor
From a pathophysiologic perspective, PAD has long been coupled with the development of lower extremity symptoms resulting from arterial occlusive disease; through this prism, the rationale for diagnosing PAD has been to determine the cause underlying a patient’s symptoms. This pioneer linking of leg symptoms to occlusive disease predates the recognition that atherosclerosis is systemic. As evidence, in 1996, when the US Preventive Services Task Force, a government agency tasked with determining appropriateness of screening tests, evaluated the utility of the ankle brachial index (ABI) in patients asymptomatic for leg complaints, it did so as a means to avoid leg events. Later, once the atherosclerotic link between PAD and CAD became solidified, the Task Force redefined PAD as a risk factor for CAD akin to other cardiovascular risk factors. Ultimately, in its 2013 report, the Task Force evaluated the ABI as a “predictor for other cardiovascular disease (eg, CAD and cerebrovascular disease) and atherothrombotic events such as myocardial infarction (MI), stroke, and death.”1
Although well intentioned, and well within their mandate, US Preventive Services Task Force recommendations on screening for PAD diminished the perceived importance of PAD. Currently, the use of the ABI in screening asymptomatic patients is conflated with its diagnostic use in patients with an abnormal physical examination. The relationship between the severity of ABI reduction and cardiovascular events is strong, whereas the link between leg symptoms and cardiovascular events is not. If the perceived threshold for ordering an ABI is leg pain, the majority of those with this condition will not be diagnosed. We do not begrudge the Task Force’s role in determining the value of the ABI as a screening test. However, misinterpretation of their message has limited the clinician’s ability to diagnose atherosclerosis among those with lower extremity manifestations. Screening a population to avoid cardiovascular events is quite different from pursuing an abnormal symptom (leg pain) or sign (absent pulses or bruit).
Pad as a Disease
The community of specialty physicians who care for patients with atherosclerosis consider PAD to be a unique disease, like CAD, and cerebrovascular disease. Indeed, in most domains of the medical world, PAD is considered a separate and specific illness with a broad-based coalition of physicians providing care. This view is evident in specific guidelines for PAD separate from other manifestations of atherosclerosis; separate Food and Drug Administration drug approval for CAD, stroke, and PAD; and distinct medical subspecialties organized to provide care for patients with 2 of the 3 diseases. We think that the lack an American Board of Internal Medicine–certified specialty focused on patients with PAD has undermined their medical care. For example, noninvasive diagnostics are reimbursed for patients with CAD and cerebrovascular disease based on signs or symptoms, but, for those with PAD, only for symptoms. Similarly, rehabilitation is provided for patients with symptomatic CAD and stroke, but not for those with symptomatic PAD.
The aggregation of these factors (a target organ focus, no solely responsible medical specialty, characterization by the US Preventive Services Task Force and primary care community as a risk factor, and others) has created an environment in which PAD is de-emphasized, infrequently sought, and the recipient of significantly less diagnostic and therapeutic coverage than other manifestations of atherosclerosis. Thus, it should come as no surprise that more than half of patients with PAD remain undiscovered in the United States, most who are diagnosed remain undertreated, and these patients experience high rates of death and disability as a result.2
We think that the proper taxonomy of PAD is as a subsidiary of atherosclerosis, which may have a variety of target organ complications including critical limb ischemia, non-ST–segment myocardial infarction, or transient ischemic attack. Just as metastatic lung cancer to the brain is not referred to as “brain met disease,” atherosclerosis with a clinical manifestation in the lower extremities should not be viewed as a separate disease. The underlying medical regimen for atherosclerosis (antiplatelet agents, statins, and angiotensin-converting enzyme inhibition) is identical in guidelines for PAD, CAD, and extracranial carotid and vertebral artery disease. Other treatment differences hinge on the particular presentation, not the underlying disease.
Equalizing the Care of Patients with Pad
To improve the care of patients with PAD, we submit that 3 changes must occur: the ABI must be viewed as a diagnostic test rather than a screening test when ordered during a clinical encounter, evidence-based care must be reimbursed, and efforts to improve quality of life among symptomatic patients must be prioritized.
Perhaps the greatest barrier to helping these patients is the economic disincentive against finding them. Conflating the screening and diagnostic purposes of the ABI removes the clinician from the care of these patients and ignores the Centers for Medicare and Medicaid Services definition of diagnostic testing: A service is “ ‘diagnostic’ if it is an examination or procedure to which the patient is subjected, or which is performed on materials derived from a hospital outpatient, to obtain information to aid in the assessment of a medical condition or the identification of a disease.”3 By this definition, the ABI is a diagnostic test. Currently, Centers for Medicare and Medicaid Services does not cover an ABI in a patient without pedal pulses unless symptoms are present. This needs to be remedied because Centers for Medicare and Medicaid Services coverage is tantamount to a stated endorsement for a particular physician behavior.
Once diagnosed, patients with symptomatic limb atherosclerosis do not receive the same Centers for Medicare and Medicaid Services coverage as those with symptomatic atherosclerosis in other beds. The clearest example is supervised exercise rehabilitation. There are now numerous controlled studies that show that supervised exercise rehabilitation increases walking distance in comparison with the recommendation of exercise. Despite this evidence base, supervised exercise rehabilitation remains covered for patients who have had coronary artery bypass grafting, percutaneous coronary intervention, myocardial infarction, heart failure, or angina, yet not for patients with intermittent claudication. The lack of coverage for this outpatient treatment is irrational and results in a care disparity.
Finally, treatment goals of atherosclerotic symptoms should be similar across all affected beds. Although the goal for patients with stroke is recovery of function and the goal for patients with angina is symptom eradication, the treatment of claudication is beset by competition over treatment modality rather than restoration of ambulation.4 We need a construct that does not minimize the impact of limb dysfunction and applies all proven therapies to improve the functional impairments as aggressively as we do in other patients with symptomatic atherosclerosis.
The historic accident of compartmentalizing atherosclerosis into separate diseases by target organ manifestation hinders our rational approach to patients with PAD. PAD patients, in particular, have suffered because of misunderstood US Preventive Services Task Force recommendations and absent Centers for Medicare and Medicaid Services coverage, both of which have relegated PAD to a status inferior to CAD and cerebrovascular disease. Systemic atherosclerosis should be recognized as a unified disease, like lung cancer or diabetes mellitus, with varying clinical presentations, that merits a unified approach to treatment with management of target organ complications as they arise.
Dr Aronow is the Chair of the Peripheral Vascular Disease Section of the American College of Cardiology (ACC). Dr. Beckman is the Chair of the Peripheral Vascular Disease Council of the American Heart Association (AHA). Neither the ACC nor the AHA has reviewed or endorsed this perspective piece.
Dr Beckman reports consulting for Merck, Astra Zeneca, and Bristol Myers Squibb; research for Bristol Myers Squibb; and ownership in EMX and Janacare. Dr Aronow has no disclosures to report.
The opinions expressed in this article are not necessarily those of the editors or of the American Heart Association.
Circulation is available at http://circ.ahajournals.org.
- © 2016 American Heart Association, Inc.
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