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Gerry Fowkes: Incidence of cardiovascular
events the same in aspirin and placebo groups
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ABI - the ratio of ankle to arm systolic pressure - is currently used as a simple noninvasive test in clinical practice to indicate leg atherosclerosis. A high index is associated with an increased risk of future cardiovascular events. While the benefits of antiplatelet therapies such as aspirin are well established in prevention of cardiovascular events in the secondary setting, there are still questions in primary prevention. The AAA trial set out to investigate whether lowdose aspirin (100 mg) produced primary prevention benefits in those found at high risk of a future event following ABI screening.
Results showed that aspirin produced no reduction in the number of cardiovascular and cerebrovascular events (HR 1.03, 95% CI 0.84- 1.27). There was, however, an increase in major haemorrhages and gastrointestinal ulcers in the aspirin patients - 2% taking aspirin and 1.2% taking placebo had major haemorrhages; 0.8 % on aspirin and 0.5% on placebo had gastrointestinal ulcers.
The trial, which was conducted in Scotland, sent invitations for screening to 165,795 men and women aged 50 to 75 years, of whom 28,980 not identified with vascular disease proved eligible. Of those screened, 3350 were found with a low ABI and were randomised to aspirin (n=1675) or placebo (n=1675). Follow-up was for 8.2 years.
Principal investigator Professor Gerry Fowkes from the Wolfson Unit for Prevention of Peripheral Vascular Diseases in Edinburgh emphasised that only 60% of those assigned to aspirin continued for the duration of the trial.
“This is the typical level of compliance you find in the primary prevention setting," he said. "Whether aspirin might be more beneficial for fully compliant patients with a low ABI is unknown from this study. He added that the trial was powered to detect no less than a 25% relative risk reduction.
“Our results suggest that using ABI as a tool to screen for cardiovascular disease in the community is unlikely to beneficial if aspirin is the intervention used for those found at higher risk," said Fowkes.