Aspirin in the primary prevention of cardiovascular disease in the Women's Health Study: effect of noncompliance

Aspirin in Primary Prevention: Looking for Those Who Enjoy It

Based on a wealth of evidence, aspirin is one of the cornerstones of secondary prevention of cardiovascular disease. However, despite several studies showing efficacy also in primary prevention, an unopposed excess risk of bleeding leading to a very thin safety margin is evident in subjects without a clear acute cardiovascular event. Overall, the variability in recommendations from different scientific societies for aspirin use in primary prevention is a classic example of failure of simple risk stratification models based on competing risks (atherothrombosis vs. bleeding), perceived to be opposed but intertwined at the pathophysiological level. Notably, cardiovascular risk is dynamic in nature and cannot be accurately captured by scores, which do not always consider risk enhancers. Furthermore, the widespread use of other potent medications in primary prevention, such as lipid-lowering and anti-hypertensive drugs, might be reducing the benefit of aspirin in recent trials. Some authors, drawing from specific pathophysiological data, have suggested that specific subgroups might benefit more from aspirin. This includes patients with diabetes and those with obesity; sex-based differences are considered as well. Moreover, molecular analysis of platelet reactivity has been proposed. A beneficial effect of aspirin has also been demonstrated for the prevention of cancer, especially colorectal. This review explores evidence and controversies concerning the use of aspirin in primary prevention, considering new perspectives in order to provide a comprehensive individualized approach.

Compliance-Adjusted Estimates of Aspirin Effects Among Older Persons in the ASPREE Randomized Trial

The Aspirin in Reducing Events in the Elderly (ASPREE) Trial recruited 19,114 participants across Australia and the United States during 2010-2014. Participants were randomized to receive either 100 mg of aspirin daily or matching placebo, with disability-free survival as the primary outcome. During a median 4.7 years of follow-up, 37% of participants in the aspirin group permanently ceased taking their study medication and 10% commenced open-label aspirin use. In the placebo group, 35% and 11% ceased using study medication and commenced open-label aspirin use, respectively. In order to estimate compliance-adjusted effects of aspirin, we applied rank-preserving structural failure time models. The results for disability-free survival and most secondary endpoints were similar in intention-to-treat and compliance-adjusted analyses. For major hemorrhage, cancer mortality, and all-cause mortality, compliance-adjusted effects of aspirin indicated greater risks than were seen in intention-to-treat analyses. These findings were robust in a range of sensitivity analyses. In accordance with the original trial analyses, compliance-adjusted results showed an absence of benefit with aspirin for primary prevention in older people, along with an elevated risk of clinically significant bleeding.

Evidence of the Different Associations of Prognostic Factors With Censoring Across Treatment Groups and Impact on Censoring Weight Model Specification: The Example of Anticoagulation in Atrial Fibrillation

Inverse probability of censoring weights (IPCWs) may reduce selection bias due to informative censoring in longitudinal studies. However, in studies with an active comparator, the associations between predictors and censoring may differ across treatment groups. We used the clinical example of anticoagulation treatment with warfarin or a direct oral anticoagulant (DOAC) in atrial fibrillation to illustrate this. The cohort of individuals initiating an oral anticoagulant during 2010-2016 was identified from the Régie de l'assurance maladie du Québec (RAMQ) databases. The parameter of interest was the hazard ratio (HR) of the composite of stroke, major bleeding, myocardial infarction, or death associated with continuous use of warfarin versus DOACs. Two strategies for the specification of the model for estimation of censoring weights were explored: exposure-unstratified and exposure-stratified. The HR associated with continuous treatment with warfarin versus DOACs adjusted with exposure-stratified IPCWs was 1.26 (95% confidence interval: 1.20, 1.33). Using exposure-unstratified IPCWs, the HR differed by 15% in favor of DOACs (1.41, 95% confidence interval: 1.34, 1.48). Not accounting for the different associations between the predictors and informative censoring across exposure groups may lead to misspecification of censoring weights and biased estimate on comparative effectiveness and safety.

Marginal structural models and other analyses allow multiple estimates of treatment effects in randomized clinical trials: Meta-epidemiological analysis

OBJECTIVES

To determine how marginal structural models (MSMs), which are increasingly used to estimate causal effects, are used in randomized clinical trials (RCTs) and compare their results with those from intention-to-treat (ITT) or other analyses.

STUDY DESIGN AND SETTING

We searched PubMed, Scopus, citations of key references, and Clinicaltrials.gov. Eligible RCTs reported clinical effects based on MSMs and at least one other analysis.

RESULTS

We included 12 RCTs reporting 138 analyses for 24 clinical questions. In 19/24 (79%), MSM-based and other effect estimates were all in the same direction, 22/22 had overlapping 95% confidence intervals (CIs), and in 19/22 (86%), the MSM effect estimate lay within all 95% CIs of all other effects (in two cases no CIs were reported). For the same clinical question, the largest effect estimate from any analysis was 1.19-fold (median; interquartile range 1.13-1.34) larger than the smallest. All MSM and ITT effect estimates were in the same direction and had overlapping 95% CIs. In 71% (12/17), they also agreed on the presence of statistical significance. MSM-based effect estimates deviated more from the null than those based on ITT (P = 0.18). The effect estimates of both approaches differed 1.12-fold (median; interquartile range 1.02-1.22).

CONCLUSIONS

MSMs provided largely similar effect estimates as other available analyses. Nevertheless, some of the differences in effect estimates or statistical significance may become important in clinical decision-making, and the multiple estimates require utmost attention of possible selective reporting bias.

Intramuscular 17-hydroxyprogesterone caproate to prevent preterm birth among HIV-infected women in Zambia: study protocol of the IPOP randomized trial

BACKGROUND

Each year, an estimated 15 million babies are born preterm, a global burden borne disproportionately by families in lower-income countries. Maternal HIV infection increases a woman's risk of delivering prematurely, and antiretroviral therapy (ART) may compound this risk. While prenatal progesterone prophylaxis prevents preterm birth among some high-risk women, it is unknown whether HIV-infected women could benefit from this therapy. We are studying the efficacy of progesterone supplementation to reduce the risk of preterm birth among pregnant women with HIV in Lusaka, Zambia.

METHODS

The Improving Pregnancy Outcomes with Progesterone (IPOP) study is a Phase III double-masked, placebo-controlled, randomized trial of intramuscular 17-alpha hydroxprogesterone caproate (17P) to prevent preterm birth in HIV-infected women. A total of 800 women will be recruited prior to 24 weeks of gestation and randomly allocated to 17P or placebo administered by weekly intramuscular injection. The primary outcome will be a composite of live birth prior to 37 completed gestational weeks or stillbirth at any gestational age. Secondary outcomes will include very preterm birth (< 34 weeks), extreme preterm birth (< 28 weeks), small for gestational age (<10th centile), low birth weight (< 2500 g), and neonatal outcomes. In secondary analysis, we will assess whether specific HIV-related covariates, including the timing of maternal ART initiation relative to conception, is associated with progesterone's prophylactic efficacy, if any.

DISCUSSION

We hypothesize that weekly prenatal 17P will reduce the risk of HIV-related preterm birth. An inexpensive intervention to prevent preterm birth among pregnant women with HIV could have substantial global public health impact.

TRIAL REGISTRATION

NCT03297216 ; September 29, 2017.

Aspirin Use and Mortality in Two Contemporary US Cohorts

BACKGROUND

Daily aspirin use has been recommended for secondary prevention of cardiovascular disease, but its use for primary prevention remains controversial.

METHODS

We followed 440,277 men and women from the NIH-AARP Diet and Health Study (ages 50-71) and the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (ages 55-74) for mortality for 13 years on average. Frequency of aspirin use was ascertained through self-report, and cause of death by death certificates. We calculated multivariate hazard ratios (HRs) and 95% confidence intervals (CIs) for mortality using Cox proportional hazards models for each cohort and combined by meta-analysis.

RESULTS

We found a consistent U-shaped relationship between aspirin use and mortality in both studies, with differential risk patterns for cardiovascular mortality by disease history. Among individuals with a history of cardiovascular disease, daily aspirin use was associated with reduced cardiovascular mortality [HR = 0.78 (95% CI, 0.74, 0.82)]. However, among those without a previous history, we observed no protection for daily aspirin users [HR = 1.06 (1.02, 1.11)], and elevated risk of cardiovascular mortality for those taking aspirin twice daily or more [HR = 1.29 (1.19, 1.39)]. Elevated risk persisted even among participants who lived beyond 5 years of follow-up and used aspirin without other nonsteroidal antiinflammatory drugs [HR = 1.31 (1.17, 1.47)].

CONCLUSIONS

Results from these 2 large population-based US cohorts confirm the utility of daily aspirin use for secondary prevention of cardiovascular mortality; however, our data suggest that caution should be exercised in more frequent use, particularly among individuals without a history of cardiovascular disease.

The Choice of Analytical Strategies in Inverse-Probability-of-Treatment-Weighted Analysis: A Simulation Study

We sought to explore the impact of intention to treat and complex treatment use assumptions made during weight construction on the validity and precision of estimates derived from inverse-probability-of-treatment-weighted analysis. We simulated data assuming a nonexperimental design that attempted to quantify the effect of statin on lowering low-density lipoprotein cholesterol. We created 324 scenarios by varying parameter values (effect size, sample size, adherence level, probability of treatment initiation, associations between low-density lipoprotein cholesterol and treatment initiation and continuation). Four analytical approaches were used: 1) assuming intention to treat; 2) assuming complex mechanisms of treatment use; 3) assuming a simple mechanism of treatment use; and 4) assuming invariant confounders. With a continuous outcome, estimates assuming intention to treat were biased toward the null when there were nonnull treatment effect and nonadherence after treatment initiation. For each 1% decrease in the proportion of patients staying on treatment after initiation, the bias in estimated average treatment effect increased by 1%. Inverse-probability-of-treatment-weighted analyses that took into account the complex mechanisms of treatment use generated approximately unbiased estimates. Studies estimating the actual effect of a time-varying treatment need to consider the complex mechanisms of treatment use during weight construction.

A systematic review of aspirin in primary prevention: is it time for a new approach?

Background and Objectives

While evidence in support of aspirin use in secondary prevention is well documented, the role of aspirin in primary prevention remains unclear. We conducted a systematic literature review to evaluate aspirin use in cardiovascular disease (CVD) and cancer primary prevention, and consider whether aspirin’s role is set to become more clearly defined based on past and prospective studies.

Data Sources

Utilizing PubMed, the reviewers identified appropriate Medical Subject Headings (MeSH) terms to establish CVD-based studies, cancer-based studies, and studies on adherence.

Study Eligibility Criteria

Date restrictions of May 31, 2008 to May 31, 2013 were applied to capture the most robust meta-analyses and randomized controlled trials. Websites of relevant EU and US scientific societies were used to identify the key guidelines for aspirin use in primary prevention of CVD, and ClinicalTrials.gov was used to establish future or ongoing trials.

Results

Evidence in support of aspirin prophylaxis is conflicting, though some meta-analyses have underlined potential benefit in reducing cardiovascular events. Despite this apparent benefit, bleeding risk with aspirin is consistently higher versus control, and remains a concern. A reduction of cancer incidence and mortality after a least 3 and 5 years treatment, respectively, is also apparent with aspirin.

Conclusion

Available data on aspirin in primary prevention suggest a modest benefit for patients at high risk of CVD, and a promising benefit for those at risk of cancer. Future studies should help to elucidate whether the benefit of aspirin outweighs risk in appropriate patient groups.

The Generation R Study: Biobank update 2015

The Generation R Study is a population-based prospective cohort study from fetal life until adulthood. The study is designed to identify early environmental and genetic causes and causal pathways leading to normal and abnormal growth, development and health from fetal life, childhood and young adulthood. In total, 9,778 mothers were enrolled in the study. Data collection in children and their parents include questionnaires, interviews, detailed physical and ultrasound examinations, behavioural observations, Magnetic Resonance Imaging and biological samples. Efforts have been conducted for collecting biological samples including blood, hair, faeces, nasal swabs, saliva and urine samples and generating genomics data on DNA, RNA and microbiome. In this paper, we give an update of the collection, processing and storage of these biological samples and available measures. Together with detailed phenotype measurements, these biological samples provide a unique resource for epidemiological studies focused on environmental exposures, genetic and genomic determinants and their interactions in relation to growth, health and development from fetal life onwards.

Application of marginal structural models in pharmacoepidemiologic studies: a systematic review

PURPOSE

We systematically reviewed pharmacoepidemiologic studies published in 2012 that used inverse probability weighted (IPW) estimation of marginal structural models (MSM) to estimate the effect from a time-varying treatment.

METHODS

Potential studies were retrieved through a citation search within Web of Science and a keyword search within PubMed. Eligibility of retrieved studies was independently assessed by at least two reviewers. One reviewer performed data extraction, and a senior epidemiologist confirmed the extracted information for all eligible studies.

RESULTS

Twenty pharmacoepidemiologic studies were eligible for data extraction. The majority of reviewed studies did not report whether the positivity assumption was checked. Six studies performed intention-to-treat analyses, but none of them reported adherence levels after treatment initiation. Eight studies chose an as-treated analytic strategy, but only one of them reported modeling the multiphase of treatment use. Almost all studies performing as-treated analyses chose the most recent treatment status as the functional form of exposure in the outcome model. Nearly half of the studies reported that the IPW estimate was substantially different from the estimate derived from a standard regression model.

CONCLUSIONS

The use of IPW method to control for time-varying confounding is increasing in medical literature. However, reporting of the application of the technique is variable and suboptimal. It may be prudent to develop best practices in reporting complex methods in epidemiologic research.

The Rotterdam Study: 2014 objectives and design update

The Rotterdam Study is a prospective cohort study ongoing since 1990 in the city of Rotterdam in The Netherlands. The study targets cardiovascular, endocrine, hepatic, neurological, ophthalmic, psychiatric, dermatological, oncological, and respiratory diseases. As of 2008, 14,926 subjects aged 45 years or over comprise the Rotterdam Study cohort. The findings of the Rotterdam Study have been presented in over a 1,000 research articles and reports (see www.erasmus-epidemiology.nl/rotterdamstudy ). This article gives the rationale of the study and its design. It also presents a summary of the major findings and an update of the objectives and methods.