Prof. Pavel Poredos,
Antiplatelet therapy reduces the risk of cardiovascular events and progression of local disease in patients with PAD. Low dose aspirin is the first – line antiplatelet drug since it is safe, easily accessible and most cost – effective among antiplatelet agents and clopidogrel is its effective alternative. There is no evidence to support the efficacy of combined antiplatelet treatment. Oral anticoagulation therapy with warfarin alone or in combination with aspirin in not indicated to reduce the risk of cardiovascular events in PAD patients. However oral anticoagulants should be considered in certain patients with thrombembolic state or history of peripheral graft occlusions.
Many studies have suggested that patients with peripheral arterial disease (PAD) manifest platelet hyperaggregability, increased levels of soluble platelet activation markers, enhanced thrombin generation and altered fibrinolytic potential. These data underline the importance of antithrombotic prophylaxis in patients with PAD (1). Therefore, antiplatelet and antithrombotic drugs represent one of the basic options for prevention and treatment of such patients (2). There are no trials including only patients with PAD that would have sufficient power to precisely estimate the preventive effect of these drugs.
The effect of antiplatelet therapy on cardiovascular events has been systematically reviewed by the Antithrombotic Trialists' Collaboration (3). A meta-analysis comprising 287 studies compared the efficacy of antiplatelet therapy in approximately 135.000 high-risk patients with vascular diseases including lower extremity peripheral arterial disease.
Among those patients with PAD treated with antiplatelet therapy, there was a 22 % odds reduction for adverse cardiovascular events, including MI, stroke, or vascular death.
Similar benefit was observed in patients with intermittent claudication, those having peripheral angioplasty, and those having peripheral bypass graft procedures. The most frequently used drug was aspirin and some trials included ticlopidine.
Low dose aspirin (75 - 325 mg daily) is as effective as higher doses, but it already comes at the price ofincreased risk of gastrointestinal bleeding – odds ratio 1.7 (95 % confidence interval, 0.8-3.3) for a major extracranial bleeding.
However there was a significantly smaller (13 %) reduction in cardiovascular events in patients being treated with less than 75 mg of aspirin per day.
Clopidogrel is thesecond most frequently used drug after aspirin for prevention of cardiovascular events in PAD patients.
Although clopidogrel is generally recognised as slightly more effective than aspirin in preventing major atherothrombotic events in high risk patients, the magnitude of this benefit is statistically uncertain and, mainly due to its much higher cost, clopidogrel has not been accepted as superior by regulatory authorities. Aspirin thus remains the first-line antiplatelet drug and clopidogrel as its effective alternative (5).
The question arises regarding whether a combination of 2 or more antiplatelet drugs is more effective than a single one. The combination of clopidogrel plus aspirin versus aspirin alone has been examined in patients who had presented with acute coronary syndrome.
In patients with acute coronary syndrome :
In patients with vascular disease, high risk or low extremity PAD :
Another important, but less well-documented issue is whether antiplatelet treatment prevents worsening of lower limb ischemia in patients with PAD. Several studies have suggested that antiplatelet therapy may reduce the risk of progression to arterial occlusion in patients with lower extremity PAD.
The efficacy of oral anticoagulants with coumarin derivates such as warfarin, in reducing adverse cardiovascular events was confirmed primarily in studies of patients with coronary artery disease. Meta-analyses comprising 37 trials of anticoagulant therapy (OAC) in more than 20.000 patients with coronary artery disease evaluated the efficacy and safety of oral anticoagulation (warfarin) alone versus the control (12).
In patients with CAD
Three major trials have shown, that oral anticoagulation (target International Normalised Ratio - INR 2-3) on top of aspirin is effective in reducing cardiovascular death, reinfarction and stroke after myocardial infarction in comparison to aspirin alone (13). Thus, among patients with coronary artery disease, moderate and high-intensity oral anticoagulation with coumarin derivatives reduces the risk of MI and death but increases the rate of bleeding.
There are only a few studies evaluating the effect of oral anticoagulation to aspirin in PAD patients.
In the WAVE trial over 2.100 patients with peripheral vascular disease were randomised to the combination of oral anticoagulation (target INR 2-3, achieved INR 2.2) plus aspirin, or to aspirin alone and followed for nearly 3 years (15).
Anand et al recently reported a meta-analysis of nine randomised trials of oral anticoagulants compared with control (no treatment) involving 4889(16). They found that
The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.
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16. Anand S. Warfarin Antiplatelet Vascular Evaluation: a randomized controlled trial testing moderate intensity oral anticoagulation and antiplatelet therapy vs. antiplatelet therapy alone in patients with peripheral arterial disease. World Congress of Cardiology. Hotline Session II, Barcelona, Spain 2006 (WAVE), (WAVE).
Prof. P. Poredos, Dr. M. Ježovnik Department for Vascular Diseases, University Medical Centre Ljubljana, Slovenia
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