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People who quit taking aspirin have an increased risk for a cardiovascular event, a large national registry has shown.
The use of aspirin for has fallen from favor in recent years but aspirin for secondary prevention is still broadly popular and supported by guidelines.
Many people who take aspirin, whether for primary or secondary prevention, discontinue treatment over time. Previous studies have suggested that these people are at higher risk for a new cardiovascular event, but these studies typically relied on self-reported data and may suffer from other methodological limitations.
To overcome some of these limitations, Swedish researchers used a comprehensive national registry to analyze the association between discontinuation of long-term aspirin treatment and subsequent cardiovascular events. In a paper published in Circulation, Johan Sundström (Uppsala, Sweden) and colleagues analyzed data from more than 600,000 people in Sweden who were prescribed low-dose aspirin. After 3 years, 15% of long-term, low-dose aspirin users were no longer taking aspirin.
Discontinuation of aspirin therapy was associated with a 37% greater risk of cardiovascular events. The increase occurred almost immediately after discontinuing therapy, supporting the idea that aspirin discontinuation produces a rebound effect. The early increase in risk did not appear to diminish over time, the authors reported.
The findings correspond to an absolute increase of 13.5 events per 1,000 person-years, or one additional CV event in 1 year for every 74 patients who discontinued aspirin.
Of the study population, 54% took aspirin for secondary prevention and 46% for primary prevention. The risk reduction was much bigger in the secondary prevention population -- a 46% increase in risk versus a 28% increase in the primary prevention population. This translated into one additional CV event in 1 year for every 36 patients in the secondary prevention population compared with every 146 patients in the primary prevention population.
"Low-dose aspirin therapy is a simple and inexpensive treatment," said Sundström, in a press release. "As long as there's no bleeding or any major surgery scheduled, our research shows the significant public health benefits that can be gained when patients stay on aspirin therapy."
But the bleeding issue remains problematic. Responding to an email question, Sundström acknowledged that the investigators did not report the change in bleeding complications after people stopped taking aspirin. Thus, the risks versus benefits of discontinuing aspirin cannot be fully assessed based on the data in this paper.
"CVD prevention guidelines unequivocally recommend aspirin anyway in high-risk patients," Sundström said.
For the lower-risk primary prevention population, however, the risk to benefit equation is much more difficult to assess and requires a careful consideration of bleeding complications. Sundström said that "the lack of such information is a limitation of the paper."