Lessons Learned From the COURAGE Trial: Generalizability, Limitations, and Implications

Clinical utility of polygenic risk scores for coronary artery disease

Over the past decade, substantial progress has been made in the discovery of alleles contributing to the risk of coronary artery disease. In addition to providing causal insights into disease, these endeavours have yielded and enabled the refinement of polygenic risk scores. These scores can be used to predict incident coronary artery disease in multiple cohorts and indicate the clinical response to some preventive therapies in post hoc analyses of clinical trials. These observations and the widespread ability to calculate polygenic risk scores from direct-to-consumer and health-care-associated biobanks have raised many questions about responsible clinical adoption. In this Review, we describe technical and downstream considerations for the derivation and validation of polygenic risk scores and current evidence for their efficacy and safety. We discuss the implementation of these scores in clinical medicine for uses including risk prediction and screening algorithms for coronary artery disease, prioritization of patient subgroups that are likely to derive benefit from treatment, and efficient prospective clinical trial designs.

Estimating Decision-Relevant Comparative Effects Using Instrumental Variables

Instrumental variables methods (IV) are widely used in the health economics literature to adjust for hidden selection biases in observational studies when estimating treatment effects. Less attention has been paid in the applied literature to the proper use of IVs if treatment effects are heterogeneous across subjects. Such a heterogeneity in effects becomes an issue for IV estimators when individuals' self-selected choices of treatments are correlated with expected idiosyncratic gains or losses from treatments. We present an overview of the challenges that arise with IV estimators in the presence of effect heterogeneity and self-selection and compare conventional IV analysis with alternative approaches that use IVs to directly address these challenges. Using a Medicare sample of clinically localized breast cancer patients, we study the impact of breast-conserving surgery and radiation with mastectomy on 3-year survival rates. Our results reveal the traditional IV results may have masked important heterogeneity in treatment effects. In the context of these results, we discuss the advantages and limitations of conventional and alternative IV methods in estimating mean treatment-effect parameters, the role of heterogeneity in comparative effectiveness research and the implications for diffusion of technology.

Recent Changes in Practice of Elective Percutaneous Coronary Intervention for Stable Angina

Background—

The COURAGE (Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation) trial was designed to compare optimal medical therapy alone versus optimal medical therapy and percutaneous coronary intervention (PCI) for treatment of patients with stable coronary artery disease and showed equal efficacy for optimal medical therapy with or without PCI. The impact of results from the COURAGE trial on clinical practice is unknown.

Methods and Results—

We analyzed 26 388 consecutive patients from the Northern New England Cardiovascular Disease PCI Registry who underwent PCI between January 2006 and June 2009. We identified a COURAGE-like patient group as patients who were undergoing (1) an elective procedure; (2) for an indication of stable angina; and (3) on the day of admission (ie, the date of admission was the same as the procedure date). All other PCI patients were placed in an “other indications” cohort. We compared temporal trends in overall volume in PCI for stable angina and for other indications, comparing quarterly time periods before and after release of COURAGE in March 2007. Over the study period, there was a statistically significant decrease in total PCI volume from 2064 in Quarter 1 2006 (before COURAGE) to 1708 in Quarter 3 2007 (after COURAGE) ( P <0.01). These trends were sustained through June 2009, with an approximate 16% peak relative reduction in all PCI compared with before COURAGE. As a percentage of all PCI, stable angina reached a high of 20.9% before COURAGE and began to decrease immediately after publication of COURAGE in Quarter 2 2007 to 16.1% ( P <0.01). Among patients undergoing PCI for stable angina, there was a significant 26% peak decrease in post-COURAGE PCI volumes compared with pre-COURAGE Quarter 1 2006 ( P trend, 0.01), which was maintained through the end of the study period.

Conclusions—

Publication of results from the COURAGE trial was temporally associated with a significant and sustained decline in the use of PCI to treat patients with stable angina. The long-term impact of this change in practice on patient outcomes remains to be determined.