Aspirin for primary prevention of CVD: Are the right people using it?

DISCUSSION

Aspirin was generally underutilized in the group with significant CVD risk (n=268) in our study, with slightly less than a third of participants for whom aspirin therapy was indicated taking it most days of the week. Despite trends of increased aspirin use among US adults in recent years,¹⁵ aspirin therapy in the 2008-2010 SHOW sample was lower than in 2005 to 2008. It was also lower than national estimates of aspirin use for primary CVD prevention^15,22—but about 20% higher than estimates of overall aspirin use in Wisconsin 20 years ago.²³ Consistent with previous research, the final adjusted model and sensitivity analysis indicated that older individuals were more likely to take aspirin regularly.

Contrary to the findings in some previous studies,^15-17 however, our analysis suggested that women had a higher adjusted odds of regular aspirin use compared with men. This result should be interpreted with extreme caution, however, because so few females (9 of 464 [3%]) met the current USPSTF criteria for aspirin therapy for primary CVD prevention. The previous USPSTF guidelines^24,25 were less conservative, with a lower minimum age and threshold for CVD risk for women. The revision is the likely result of recent primary prevention trials¹⁰ that found regular aspirin use provided less cardioprotection for younger women.

The sample without an aspirin indication—roughly twice the size of the group with an aspirin indication (563 vs 268), which is reflective of the general population of Wisconsin—was useful in highlighting inappropriate use. There were clear indications of aspirin overuse in this group, with 18% of the sample reporting that they took aspirin regularly. The finding that inappropriate aspirin use was more likely in non-Hispanic whites vs minorities is similar to the result of an earlier study in which blacks, Hispanics, and Chinese Americans with low CVD risk were much less likely to report regular aspirin use compared with whites at low risk.¹⁵

The main concern with regular aspirin use in those for whom it is not indicated for primary CVD prevention is the risk of upper gastrointestinal bleeding and, less commonly, hemorrhagic stroke.²⁶ To illustrate this point, consider the following: About 10% of SHOW participants ages 35 to 74 years had no history of CVD and no indication for aspirin therapy based on the latest USPSTF guidelines, but took aspirin regularly nonetheless. Extrapolating those numbers to the entire state of Wisconsin would suggest that approximately 270,000 state residents have a similar profile. Assuming an extra 1.3 major bleeding events per 1000 person-years of regular aspirin use (as a meta-analysis of studies of adverse events associated with antiplatelet therapy found),²⁷ that would translate into an estimated 350 major bleeding events per year in Wisconsin that are attributable to aspirin overuse.

In view of the current USPSTF recommendations,¹⁰ aspirin is not optimally utilized by Wisconsin residents for the primary prevention of CVD. Aspirin therapy is not used enough by those with a high CVD risk, who could derive substantial vascular disease protection from it. Conversely, aspirin therapy is overused by those with a low CVD risk, for whom the risk of major bleeding is significantly higher than the potential for vascular disease protection. Furthermore, younger individuals at high CVD risk appear to be least likely to take aspirin regularly.

Recommendations

The strongest modifiable predictor of regular aspirin use is a recommendation from a clinician.¹³ Therefore, we recommend stronger primary care initiatives to ensure that patients are screened for aspirin use more frequently, particularly middle-aged men at high CVD risk. This clinic-based initiative could reach a larger proportion of the general population when combined with broader, community-oriented CVD preventive services.²⁸

More precise marketing and education are also needed. Because aspirin is a low-cost over-the-counter product that leads the consumer market for analgesics,²⁹ the general public (and older, non-Hispanic whites, in particular) needs to be better informed about the risks of medically inappropriate aspirin use for primary CVD prevention.