The routine use of Acetylsalicylic acid ( Aspirin ) for the primary prevention of vascular events in people with asymptomatic disease cannot be supported, according to results from the Aspirin for Asymptomatic Atherosclerosis ( AAA ) study. The study is the first placebo-controlled randomised trial designed to determine the effect of Acetylsalicylic acid in asymptomatic atherosclerosis as reflected by a low ankle brachial index ( ABI ). Results found no statistically significant difference in primary endpoint events between those subjects allocated to Acetylsalicylic acid or placebo ( HR=1.03 ).

The benefits of antiplatelet therapy in the prevention of future cardio- and cerebrovascular events is well established in patients with a clinical history of arterial vascular disease ( secondary prevention ); however, evidence in primary prevention is limited, with studies suggesting that any benefit of Acetylsalicylic acid must be weighed against the risk of bleeding. The aim of the AAA trial was to determine the effectiveness of Acetylsalicylic acid in preventing events in people with asymptomatic atherosclerosis detected by ABI screening.

The study recruited 28,980 men and women aged 50 to 75 years who were free of clinically evident cardiovascular disease in central Scotland; all were given an ABI screening test. Those with a low ABI ( 3350 subjects, less than or equal to 0.95 ABI ) were entered into the trial and randomised to once daily 100 mg Acetylsalicylic acid or placebo. Participants were followed up for a mean of 8.2 years and outcomes ascertained by annual contact, general practitioner records, linkage to discharges from Scottish hospitals, and death notification. The primary endpoint was a composite of initial fatal or non-fatal coronary event or stroke, or revascularisation. There were two secondary endpoints: all initial vascular events defined as a composite of a primary endpoint event or angina, intermittent claudication or transient ischaemic attack; and all-cause mortality.

Results showed that 357 participants had a primary endpoint event ( 13.5 per 1000 person years ), 181 in the Acetylsalicylic acid group and 176 in the placebo group. A vascular event comprising the secondary endpoint occurred in 578 participants, but again no statistically significant difference was found between the aspirin and placebo groups ( 288 vs 290 events ). All-cause mortality was similar in both groups ( 176 v 186 deaths ). An initial event of major bleeding requiring admission to hospital occurred in 34 (2%) of subjects in the Acetylsalicylic acid group and 20 ( 1.2% ) in the placebo group.

Source: European Society of Cardiology, 2009

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