Claudication as an 'orphan disease': rationale and goals of drug therapy for peripheral arterial disease

The potential role of angiotensin-converting enzyme inhibition in peripheral arterial disease

Peripheral arterial disease (PAD) is associated with significant morbidity and mortality, and yet remains under-recognized and under-treated. Atherosclerosis is the most common cause of lower extremity PAD and pharmacological interventions that alter this central pathogenic role of atherosclerosis may alter the natural history of PAD. There is growing evidence that the renin-angiotensin system (RAS) is a significant mediator of this disease process and that treatment with angiotensin-converting enzyme (ACE) inhibitors is associated with vasculoprotective effects that are independent of the antihypertensive properties of these agents. Numerous lines of evidence suggest that ACE inhibitors directly inhibit the atherosclerotic process and improve vascular endothelial function. In patients with PAD, ACE inhibitors have been shown to improve peripheral circulation as measured by peripheral arterial blood pressure and by increases in peripheral blood flow. Preliminary evidence suggests that ACE inhibitors might improve clinical symptoms in patients with PAD. Recent evidence has confirmed that ACE inhibition is associated with a decrease in morbidity and mortality in patients with arterial disease without left ventricular dysfunction; this benefit was at least as great for the subset of patients with PAD. Overall, these data support a significant role for the RAS in the pathogenesis of all atherosclerotic diseases (including PAD) and suggest that the benefit is independent of the blood pressure lowering properties of these agents. These studies suggest that ACE inhibitor therapy should be considered in the routine management of individuals with PAD, regardless of whether they have hypertension or left ventricular dysfunction.

Propionyl-L-carnitine in Leriche-Fontaine stage II peripheral arterial obstructive disease

Peripheral arterial obstructive disease (PAOD) of the lower limbs affects 5% of the adult population. Uncontrolled arteriopathy is established due to a microcirculatory deficit, which may be present despite a good Winsor index and which leads to exhaustion of the functional microcirculatory reserve. The target of this study was to examine possible improvements in microvascular and tissue homeostasis by the administration of propionyl-L-carnitine (PLC). A total of 26 patients were enrolled in this study, aged 65 +/- 15 years; two males were diagnosed at stage IIA and 17 males and seven females at stage IIB PAOD. The main criterion of inclusion was the worsening of walking distance during the last month. In this study the duration of therapy was 33 days. PLC was administered in three flasks, each containing 300 mg in 250 cc saline by continuous infusion. The following parameters were measured before and after treatment: pain-free and maximum walking distance (measured on a treadmill at 3.2 km/hr with a gradient of 12%), recovery time from pain after maximum walking distance, ankle-brachial index by means of the Doppler apparatus, and evaluation of the microcirculation using capillaroscopy. The results showed that therapy with PLC was effective at restoring activity of skeletal muscle in ischemic conditions. In particular, capillaroscopy showed improvement in the angioarchitecture in the microcirculation fields, expressed as increased numbers of visible capillaries and diminution in the time of loss of sodium fluorescein marker. The clinical data showed increased walking distance and diminished time to recover from pain, and the clinical improvement correlated with improved microcirculatory function. From these preliminary data has emerged an indication of therapy with PLC for chronic obstructive arteriopathy of the lower limbs at stage II. Further studies with higher numbers of patients and more controlled variables are planned.

Lipid-lowering therapy in patients with peripheral arterial disease

Peripheral arterial disease (PAD) is a prevalent, chronic, and progressive atherosclerotic disease process involving the conduit vessels of the extremities. Most patients who present with objective signs of PAD are asymptomatic. These patients are at an increased risk of dying from cardiovascular events. Lipid management is the mainstay of risk-factor modification for patients with cardiovascular disease. Some evidence suggests that hypocholesterolemic drugs may halt the progression of atherosclerotic peripheral vascular disease. More recently, treatment with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) inhibitors have demonstrated improved function in patients with symptomatic peripheral vascular disease. This paper reviews the role of lipid therapy in patients with peripheral arterial disease with focus on functional improvement and symptomatic relief based on the available data.

Undertreatment of dyslipidemia in peripheral arterial disease and other high-risk populations: an opportunity for cardiovascular disease reduction

Atherosclerosis is a form of arterial disease that manifests in the coronary circulation as coronary artery disease (CAD), in the carotid arteries as cerebrovascular disease, and in the aorta and lower extremity arteries as peripheral arterial disease (PAD). The systemic nature of the disease is reflected in the fact that individuals with PAD or carotid artery disease are more likely to have CAD than those without. Since individuals with PAD are at markedly increased risk of cardiovascular ischemic events, early identification of this population and more aggressive medical interventions could substantially improve both morbidity and survival. The incidence of PAD in the general population is high, and currently affects 8-10 million Americans. The risk of developing PAD is predicted by both age and common atherosclerosis risk factors (e.g., smoking and diabetes). Efficient office-based PAD detection depends on the application of objective techniques to establish this diagnosis. Objective noninvasive tests, such as measurement of the ankle-brachial index (ABI), are known to be more sensitive than traditional clinical assessments. Since the major threat to patients with PAD is from secondary cardiovascular ischemic events, a primary therapeutic goal is to modify atherosclerotic risk factors. While national recommendations mandate aggressive lowering of serum low-density lipoprotein cholesterol (LDL-C) levels as a primary treatment goal in all patients with overt atherosclerosis, as 'coronary heart disease risk equivalent' syndromes, individuals with PAD are less intensively treated than those with CAD. Statins are the most effective of current treatments in lowering LDL-C, and have proven efficacy in secondary prevention among patients with established CAD. The use of statin medications in high-risk groups such as PAD patients could prove particularly beneficial in reducing cardiovascular morbidity and mortality and therefore merits prospective clinical investigation.

Progression of atherosclerosis in patients with peripheral arterial disease as a function of angiotensin-converting enzyme gene insertion/deletion polymorphism

Angiotensin-converting enzyme insertion/deletion (I/D) gene polymorphism plays a role in determining the inter-individual variability of circulating angiotensin-converting enzyme activity and intracellular angiotensin-converting enzyme levels. Angiotensin-converting enzyme, as a key enzyme in the renin-angiotensin system, catalyzes the activation of the vasoconstricting and proliferation-stimulating angiotensin II and breaks down the vasodilatory peptide bradykinin. It is assumed that the excess supply of angiotensin II (due to the deletion polymorphism of the angiotensin-converting enzyme gene) contributes to endothelial dysfunction and in this way promotes the onset and progression of atherosclerosis. The aim of this study was to test whether the presence of the deletion allele of the angiotensin-converting enzyme gene predisposes a more rapid systemic progression of a preexisting peripheral arterial disease. To this end, the course of disease was surveyed for an average of 5 years in 97 patients who were angiotensin-converting enzyme gene-typed and suffered from a stable stage II peripheral arterial disease according to Fontaine. These patients did not suffer from an additional coronary artery disease, a cerebrovascular disease, or other serious illness. A local progression in the periphery or a systemic progression in the coronary or cerebrovascular areas was regarded as study endpoints. Of the patients, 49.5% showed an atherosclerosis progression during the surveillance period. With II-carriers, a progression was registered in 42.1% and with DD carriers, progression was seen in 59.4%. D/I allele frequencies were seen in patients with progression at a level of 0.60/0.40 vs 0.55/0.45 for patients without progression. The average duration of disease in stable stage II (before progression appeared) amounted to 108 +/- 14 months for II carriers, 88 +/- 8 months for ID carriers, and 92 +/- 11 months for DD carriers (p = 0.21). Based on these findings, the deletion polymorphism of the angiotensin-converting enzyme gene is not an independent risk factor for progression of atherosclerosis in patients with peripheral arterial disease.

Preventing atherothrombotic events in peripheral arterial disease: the use of antiplatelet therapy

Patients with peripheral arterial disease (PAD) are at increased risk of generalized atherothrombotic events. Epidemiologic data shows a high rate of co-prevalence of PAD and atherosclerosis in other vascular beds. Aggressive risk-factor modification and antiplatelet therapy has become the cornerstone of treatment to prevent ischaemic events associated with PAD. Recent clinical trials have confirmed the clinical benefit of clopidogrel and ticlopidine in patients with PAD, agents that irreversibly inhibit the binding of adenosine diphosphate to its platelet receptor. In the clopidogrel versus aspirin in patients at risk of ischaemic events (CAPRIE) trial, clopidogrel was associated with an overall risk reduction of 8.7% (compared with aspirin, P=0.043) in myocardial infarction (MI), ischaemic stroke and vascular death. These results demonstrated that long-term administration of clopidogrel was effective in preventing ischaemic events in patients with atherosclerotic vascular disease including PAD. Aspirin and/or clopidogrel are the antiplatelet agents of choice for the reduction of atherothrombotic events in patients with PAD.

The Minnesota Regional Peripheral Arterial Disease Screening Program: toward a definition of community standards of care

The Minnesota Regional Peripheral Arterial Disease Screening Program was designed to define the efficacy of community PAD detection efforts, to assess the disease-specific and health-related morbidity, to assess PAD awareness rates, and to determine the magnitude of atherosclerosis disease risk factors and the intensity of their management. The target population was recruited via mass media efforts directed at individuals over 50 years of age and those with leg pain with ambulation. Screening sessions included assessments of the ankle-brachial index, blood pressure, fasting lipid profile, and use of validated tools to detect symptomatic claudication (by the Modified WHO-Edinburgh Claudication Questionnaire), walking impairment (Walking Impairment Questionnaire - WIQ), quality of life (MOS SF-36), PAD awareness, and the intensity of PAD medical therapeutic interventions. PAD was defined as any ankle-brachial index < or =0.85 or a history of lower extremity revascularization. The program evaluated 347 individuals and identified 92 subjects with PAD and 255 subjects without PAD, yielding a detection rate of 26.5%. Individuals with PAD were older, tended to have higher blood pressures, and had a significant walking impairment and an impaired health-related quality of life compared with the non-PAD subjects. Current rates of tobacco use were low. Lipid-lowering, estrogen replacement, anti-platelet, and antihypertensive medications and exercise therapies were underutilized in the PAD cohort. Peripheral arterial disease awareness was low in these community-identified patients. This Program demonstrated that individuals with PAD can be efficiently identified within the community, but that current standards of medical care are low. These data can assist in the future development of PAD awareness, education, and treatment programs.

Randomized reliability study evaluating constant-load and graded-exercise treadmill test for intermittent claudication

The aim of this randomized study was to compare the reliability of the treadmill test at constant-load (C-test, 3 km/hr; fixed grade of 12%) recommended in Germany with that of the graded-exercise test (G-test, 3 km/hr; increase in grade of 3.5% every 3 minutes) propagated in the United States. In 50 patients with an absolute claudication distance (ACD) in the C-test of between 50 and 400 m, the two treadmill tests were carried out in randomized order on one and the same day, and repeated on 3 days within 1 week. For the initial claudication distance (ICD), the intraclass correlation was 0.88 in the C-test and 0.87 in the G-test. For the ACD the coefficients were identical at 0.91. The within-subject variation (CVwithin) in the C-test and G-test was 25% and 27% for the ICD and for the ACD 24% and 21%, respectively. The between-subject variation was very similar with 72% and 73% (ICD) and with 78% and 68% (ACD). However, in ACDs below 100 m and between 100 to 150 m, the C-test showed significantly smaller coefficients of variation than the G-test: 13% vs 81% and 14% vs 50%, respectively. In conclusion, the results showed that both C-test and G-test are equally well reproducible.