Systematic review
The updated draft recommendations are based on a new systematic review commissioned by the USPSTF on the effectiveness of aspirin to reduce the risk of CVD events (myocardial infarction and stroke), cardiovascular mortality, and all-cause mortality in persons without a history of CVD.
The systematic review also investigated the effect of aspirin use on CRC incidence and mortality in primary CVD prevention populations, as well as the harms, particularly bleeding harms, associated with aspirin use.
In addition to the systematic evidence review, the USPSTF commissioned a microsimulation modeling study to assess the net balance of benefits and harms from aspirin use for primary prevention of CVD and CRC, stratified by age, sex, and CVD risk level. Modeling study parameter inputs were informed by the results of the systematic review, and the primary outcomes were net benefits expressed as quality-adjusted life-years and life-years.
The USPSTF found 13 randomized clinical trials (RCTs) that reported on the benefits of aspirin use for the primary prevention of cardiovascular morbidity and mortality. The total number of participants was 161,680, and most trials used low-dose aspirin of 100 mg/d or less or aspirin every other day. The 13 primary prevention trials included a balanced number of male and female participants and included a broad distribution of ages, with mean age ranging from 53 years in the Physicians’ Health Study to 74 years in the ASPREE trial.
This body of evidence shows that aspirin use for primary prevention of CVD is associated with a decreased risk of myocardial infarction and stroke but not cardiovascular mortality or all-cause mortality. Results are quite similar when including studies using all doses of aspirin compared with studies using low-dose aspirin.
The USPSTF reviewed 14 RCTs in CVD primary prevention populations that reported on the bleeding harms of aspirin.
When looking at studies reporting on the harms of low-dose aspirin use (≤100 mg/d), which is most relevant to current practice, a pooled analysis of 10 trials showed that aspirin use was associated with a 58% increase in major gastrointestinal bleeding, and a pooled analysis of 11 trials showed a 31% increase in intracranial bleeds in the aspirin group compared with the control group. Low-dose aspirin use was not associated with a statistically significant increase in risk of fatal hemorrhagic stroke.
Data suggested that the increased risk of bleeding associated with aspirin use occurs relatively quickly after initiating aspirin, and data do not suggest that aspirin has a differential relative bleeding risk based on age, sex, presence of diabetes, level of CVD risk, or race or ethnicity. Although the increase in relative risk does not appear to differ based on age, the absolute risk of bleeding, and thus the magnitude of bleeding harm, does increase with age, and more so in adults age 60 years or older, they note.
The microsimulation model to estimate the magnitude of net benefit of low-dose aspirin use incorporated findings from the systematic review.
Modeling data demonstrated that aspirin use in both men and women ages 40-59 years with 10% or greater 10-year CVD risk generally provides a modest net benefit in both quality-adjusted life-years and life-years gained. Initiation of aspirin use in persons aged 60-69 years results in quality-adjusted life-years gained that range from slightly negative to slightly positive depending on CVD risk level, and life-years gained are generally negative.
In persons aged 70-79 years, initiation of aspirin use results in a loss of both quality-adjusted life-years and life-years at essentially all CVD risk levels modeled (ie, up to 20% 10-year CVD risk).
The USPSTF thus determined that aspirin use has a small net benefit in persons aged 40-59 years with 10% or greater 10-year CVD risk, and initiation of aspirin use has no net benefit in persons age 60 years or older.
When looking at net lifetime benefit of continuous aspirin use until stopping at age 65, 70, 75, 80, or 85 years, modeling data suggest that there is generally little incremental lifetime net benefit in continuing aspirin use beyond the age of 75-80 years.
The task force points out that the net benefit of continuing aspirin use by a person in their 60s or 70s is not the same as the net benefit of initiating aspirin use by a person in their 60s or 70s. This is because, in part, of the fact that CVD risk is heavily influenced by age. Persons who meet the eligibility criteria for aspirin use at a younger age (ie, ≥10% 10-year CVD risk in their 40s or 50s) typically have even higher CVD risk by their 60s or 70s compared with persons who first reach a 10% or greater 10-year CVD risk in their 60s or 70s, and may gain more benefit by continuing aspirin use than a person at lower risk might gain by initiating aspirin use, the USPSTF explains.
A version of this article first appeared on Medscape.com.