BACKGROUND: Cardiac rehabilitation (CR) is effective in prolonging survival and reducing disability in patients with coronary heart disease. However, national use patterns and predictors of CR use have not been evaluated thoroughly. METHODS AND RESULTS: Using Medicare claims, we analyzed outpatient (phase II) CR use after hospitalizations for acute myocardial infarctions or coronary artery bypass graft surgery in 267,427 fee-for-service beneficiaries aged > or = 65 years who survived for at least 30 days after hospital discharge. We used multivariable analyses to identify predictors of CR use and to quantify geographic variations in its use. We obtained unadjusted, adjusted-smoothed, and standardized rates of CR use by state. Overall, CR was used in 13.9% of patients hospitalized for acute myocardial infarction and 31.0% of patients who underwent coronary artery bypass graft surgery. Older individuals, women, nonwhites, and patients with comorbidities (including congestive heart failure, previous stroke, diabetes mellitus, or cancer) were significantly less likely to receive CR. Coronary artery bypass graft surgery during the index hospitalization, higher median household income, higher level of education, and shorter distance to the nearest CR facility were important predictors of higher CR use. Adjusted CR use varied 9-fold among states, ranging from 6.6% in Idaho to 53.5% in Nebraska. The highest CR use rates were clustered in the north central states of the United States. CONCLUSIONS: CR use is relatively low among Medicare beneficiaries despite convincing evidence of its benefits and recommendations for its use by professional organizations. Use is higher after coronary artery bypass graft surgery than with acute myocardial infarctions not treated with revascularization procedures and varies dramatically by state and region of the United States.

BACKGROUND: A model using administrative claims data that is suitable for profiling hospital performance for heart failure would be useful in quality assessment and improvement efforts. METHODS AND RESULTS: We developed a hierarchical regression model using Medicare claims data from 1998 that produces hospital risk-standardized 30-day mortality rates. We validated the model by comparing state-level standardized estimates with state-level standardized estimates calculated from a medical record model. To determine the stability of the model over time, we used annual Medicare cohorts discharged in 1999-2001. The final model included 24 variables and had an area under the receiver operating characteristic curve of 0.70. In the derivation set from 1998, the 25th and 75th percentiles of the risk-standardized mortality rates across hospitals were 11.6% and 12.8%, respectively. The 95th percentile was 14.2%, and the 5th percentile was 10.5%. In the validation samples, the 5th and 95th percentiles of risk-standardized mortality rates across states were 9.9% and 13.9%, respectively. Correlation between risk-standardized state mortality rates from claims data and rates derived from medical record data was 0.95 (SE=0.015). The slope of the weighted regression line from the 2 data sources was 0.76 (SE=0.04) with intercept of 0.03 (SE=0.004). The median difference between the claims-based state risk-standardized estimates and the chart-based rates was <0.001 (25th percentile=-0.003; 75th percentile=0.002). The performance of the model was stable over time. CONCLUSIONS: This administrative claims-based model produces estimates of risk-standardized state mortality that are very good surrogates for estimates derived from a medical record model.

BACKGROUND: A model using administrative claims data that is suitable for profiling hospital performance for acute myocardial infarction would be useful in quality assessment and improvement efforts. We sought to develop a hierarchical regression model using Medicare claims data that produces hospital risk-standardized 30-day mortality rates and to validate the hospital estimates against those derived from a medical record model. METHODS AND RESULTS: For hospital estimates derived from claims data, we developed a derivation model using 140,120 cases discharged from 4664 hospitals in 1998. For the comparison of models from claims data and medical record data, we used the Cooperative Cardiovascular Project database. To determine the stability of the model over time, we used annual Medicare cohorts discharged in 1995, 1997, and 1999-2001. The final model included 27 variables and had an area under the receiver operating characteristic curve of 0.71. In a comparison of the risk-standardized hospital mortality rates from the claims model with those of the medical record model, the correlation coefficient was 0.90 (SE=0.003). The slope of the weighted regression line was 0.95 (SE=0.007), and the intercept was 0.008 (SE=0.001), both indicating strong agreement of the hospital estimates between the 2 data sources. The median difference between the claims-based hospital risk-standardized mortality rates and the chart-based rates was <0.001 (25th and 75th percentiles, -0.003 and 0.003). The performance of the model was stable over time. CONCLUSIONS: This administrative claims-based model for profiling hospitals performs consistently over several years and produces estimates of risk-standardized mortality that are good surrogates for estimates from a medical record model.

BACKGROUND: One approach to improving quality of care is to encourage physicians to follow evidence-based practice guidelines. Examples of evidence-based guidelines are the PORT recommendations for the treatment of schizophrenia. However, few studies have examined the relationship between adherence to guidelines and patient outcomes in clinical settings. OBJECTIVE: The purpose of this article is to report the relationship between guideline adherence to antipsychotic medication dose and self-reported health status, side effects, and perceptions of care. RESEARCH DESIGN: This report is based on a subsample of patients from a larger prospective observational study of disabled Massachusetts Medicaid beneficiaries treated for schizophrenia. SUBJECTS: Participants were 329 acutely ill, vulnerable, high-risk Medicaid adult beneficiaries enrolled after visiting any 1 of 8 psychiatric emergency screening teams for hospital admission evaluation. MEASURES: Dose levels, symptoms, and functioning from medical records; self-reports as data collected from BASIS-32, SF-12, and CABHS; and paid health benefit claims for psychiatric treatment were measured. RESULTS: Approximately 40% of the patients in this study had daily antipsychotic doses well above the recommended range, but there was no evidence that their health status was better than those on doses below 1000 CPZ units recommended for acute episodes. High-dose levels had no relationship to baseline symptom profile or referral source. CONCLUSIONS: There was no evidence that health status was better on higher-than-recommended doses, but we cannot conclude that lower doses for some would have led to poorer outcomes. Physicians who believe that higher doses are more therapeutic for patients need to demand rigorous effectiveness research that tests whether there are benefits of higher doses and determine the ratio of those benefits to the clinical costs, including the risk of side effects.

BACKGROUND: To improve insurance coverage of mental health and substance-abuse services, the Federal Employees Health Benefits (FEHB) Program offered mental health and substance-abuse benefits on a par with general medical benefits beginning in January 2001. The plans were encouraged to manage care. METHODS: We compared seven FEHB plans from 1999 through 2002 with a matched set of health plans that did not have benefits on a par with mental health and substance-abuse benefits (parity of mental health and substance-abuse benefits). Using a difference-in-differences analysis, we compared the claims patterns of matched pairs of FEHB and control plans by examining the rate of use, total spending, and out-of-pocket spending among users of mental health and substance-abuse services. RESULTS: The difference-in-differences analysis indicated that the observed increase in the rate of use of mental health and substance-abuse services after the implementation of the parity policy was due almost entirely to a general trend in increased use that was observed in comparison health plans as well as FEHB plans. The implementation of parity was associated with a statistically significant increase in use in one plan (+0.78 percent, P<0.05) a significant decrease in use in one plan (-0.96 percent, P<0.05), and no significant difference in use in the other five plans (range, -0.38 percent to +0.23 percent; P>0.05 for each comparison). For beneficiaries who used mental health and substance-abuse services, spending attributable to the implementation of parity decreased significantly for three plans (range, -201.99 dollars to -68.97 dollars; P<0.05 for each comparison) and did not change significantly for four plans (range, -42.13 dollars to +27.11 dollars; P>0.05 for each comparison). The implementation of parity was associated with significant reductions in out-of-pocket spending in five of seven plans. CONCLUSIONS: When coupled with management of care, implementation of parity in insurance benefits for behavioral health care can improve insurance protection without increasing total costs.

This study compared the self-report Behavior and Symptom Identification Scale (BASIS-32) and clinician-rated Global Assessment of Functioning (GAF) in their ability to predict a measure of psychiatric outcome, 1-year psychiatric hospital readmission. BASIS-32 and GAF were completed at admission for 1034 patients in an inpatient psychiatric facility. Multiple informants analysis was used to determine the difference between the two in predicting readmission within 1 year. We also examined sensitivity, specificity, and predictive value positive of the two measures, and whether self-report added information above clinician rating in predicting outcome. While the odds of 1-year readmission decreased with increasing BASIS-32 score, there was no association between change in GAF score and 1-year readmission. Although neither measure used alone demonstrated high predictive value, using both scores improved predictive ability over using clinician rating alone. In this setting, self-report was better than clinician rating in predicting psychiatric outcome. Differences between the two in relation to other outcomes need to be examined.

CONTEXT: The Centers for Medicare & Medicaid Services (CMS) and the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) measure and report quality process measures for acute myocardial infarction (AMI), but little is known about how these measures are correlated with each other and the degree to which inferences about a hospital's outcomes can be made from its performance on publicly reported processes. OBJECTIVE: To determine correlations among AMI core process measures and the degree to which they explain the variation in hospital-specific, risk-standardized, 30-day mortality rates. DESIGN, SETTING, AND PARTICIPANTS: We assessed hospital performance in the CMS/JCAHO AMI core process measures using 2002-2003 data from 962 hospitals participating in the National Registry of Myocardial Infarction (NRMI) and correlated these measures with each other and with hospital-level, risk-standardized, 30-day mortality rates derived from Medicare claims data. MAIN OUTCOME MEASURES: Hospital performance on AMI core measures; hospital-specific, risk-standardized, 30-day mortality rates for AMI patients aged 66 years or older. RESULTS: We found moderately strong correlations (correlation coefficients > or =0.40; P values <.001) for all pairwise comparisons between beta-blocker use at admission and discharge, aspirin use at admission and discharge, and angiotensin-converting enzyme inhibitor use, and weaker, but statistically significant, correlations between these medication measures and smoking cessation counseling and time to reperfusion therapy measures (correlation coefficients <0.40; P values <.001). Some process measures were significantly correlated with risk-standardized, 30-day mortality rates (P values <.001) but together explained only 6.0% of hospital-level variation in risk-standardized, 30-day mortality rates for patients with AMI. CONCLUSIONS: The publicly reported AMI process measures capture a small proportion of the variation in hospitals' risk-standardized short-term mortality rates. Multiple measures that reflect a variety of processes and also outcomes, such as risk-standardized mortality rates, are needed to more fully characterize hospital performance.

OBJECTIVES: To quantify the influence of physicians' experiences of adverse events in patients with atrial fibrillation who were taking warfarin. DESIGN: Population based, matched pair before and after analysis. SETTING: Database study in Ontario, Canada. PARTICIPANTS: The physicians of patients with atrial fibrillation admitted to hospital for adverse events (major haemorrhage while taking warfarin and thromboembolic strokes while not taking warfarin). Pairs of other patients with atrial fibrillation treated by the same physicians were selected. MAIN OUTCOME MEASURES: Odds of receiving warfarin by matched pairs of a given physician's patients (one treated after and one treated before the event) were compared, with adjustment for stroke and bleeding risk factors that might also influence warfarin use. The odds of prescriptions for angiotensin converting enzyme (ACE) inhibitor before and after the event was assessed as a neutral control. RESULTS: For the 530 physicians who had a patient with an adverse bleeding event (exposure) and who treated other patients with atrial fibrillation during the 90 days before and the 90 days after the exposure, the odds of prescribing warfarin was 21% lower for patients after the exposure (adjusted odds ratio 0.79, 95% confidence interval 0.62 to 1.00). Greater reductions in warfarin prescribing were found in analyses with patients for whom more time had elapsed between the physician's exposure and the patient's treatment. There were no significant changes in warfarin prescribing after a physician had a patient who had a stroke while not on warfarin or in the prescribing of ACE inhibitors by physicians who had patients with either bleeding events or strokes. CONCLUSIONS: A physician's experience with bleeding events associated with warfarin can influence prescribing warfarin. Adverse events that are possibly associated with underuse of warfarin may not affect subsequent prescribing.

BACKGROUND: Since the 1990s, parity laws have been implemented to reduce inequities in mental health coverage compared with that for general medical conditions. It is unclear if parity under managed care is associated with improvements in mental health treatment quality. Major depressive disorder (MDD) is a prevalent but often undetected and undertreated and thus could potentially benefit from parity implementation. OBJECTIVE: The objective of this study was to examine the association between parity implementation and changes in MDD treatment quality in the Federal Employees' Health Benefits (FEHB) Program. METHODS: We conducted retrospective analyses of insurance claims data. Logistic regression models estimated quality changes for MDD-diagnosed enrollees from pre- to postparity. SUBJECTS: Subjects included MDD-diagnosed FEHB insured enrollees, aged 18-64, across multiple states and 6 FEHB plans before (1999-2000) and after (2001-2002) parity implementation. MEASURES: Measures included receipt of any antidepressant or psychotherapy within a given calendar year of diagnosis; receipt of appropriate psychotherapy frequency/intensity and duration; and pharmacotherapy duration during acute-phase treatment episodes. RESULTS: Postparity, several plans improved significantly in the likelihood of receiving antidepressant medication. In the acute-phase episodes, the greatest improvement was seen in the likelihood of follow up >or=4 months. Few or no other changes were observed in the acute-phase treatment intensity or duration quality measures. CONCLUSIONS: Parity under managed care was associated with modest improvements. The observed improvements were consistent with secular trends in MDD treatment. Whereas mental health parity is an important policy goal, these results highlight its limitations: improving the financing of care may not be sufficient to improve quality.

OBJECTIVE: The aims of this study were to examine labor supply effects of interventions for major depressive disorder and to compare these effects with a summary measure of clinical effectiveness. METHODS: Research articles published in English-language journals from 1980 through May 2004 were searched by using five research databases. Only randomized trials that included a placebo group or a usual care group were eligible for the study, regardless of the specific type of intervention. Valid trials were those that enrolled adult patients with major depressive disorder and assessed changes in labor output by using a measure of time worked or labor market participation. From a total of 706 trials uncovered from the database searches, only four met all inclusion criteria. Trial outcomes were transformed into standardized effect sizes on the basis of Cohen's d. Hierarchical linear models were used to separately pool work outcomes and clinical outcomes. RESULTS: An improvement of .34 standard deviation was found in the size of the clinical effect of interventions compared with placebo or usual care among 1,261 unique patients with depression. An improvement of .12 standard deviation was found in the size of the effect on labor supply among 1,848 unique patients. CONCLUSIONS: Although the interventions studied were associated with reduced symptoms of depression and increased labor output, the labor benefits were small according to standard benchmarks used in interpreting the substantive significance of values of Cohen's d. The difference in effects may have been due to different underlying efficacies, brief durations of follow-up, or extrinsic factors that affect labor supply.

PURPOSE: Despite dramatic changes in heart failure management during the 1990s, little is known about the national heart failure mortality trends during this time period, particularly among the elderly. The purpose of this study was to determine temporal trends in outcomes of elderly patients with heart failure between 1992 and 1999. SUBJECTS AND METHODS: We analyzed a national sample of 3,957,520 Medicare beneficiaries aged 65 years or more who were hospitalized with heart failure between 1992 and 1999, assessing temporal trends in 30-day and 1-year all-cause mortality and 30-day and 6-month all-cause hospital readmission. In risk-adjusted analyses, mortality and readmission for each year between 1994 and 1999 were compared with the referent year of 1993. RESULTS: Crude 30-day and 1-year mortality decreased slightly (range for 1992-1999: 11.0%-10.3% and 32.5%-31.7%, respectively), whereas 30-day and 6-month readmission increased (10.2%-13.8% and 35.4%-40.3%, respectively). After risk adjustment, there was no change in 30-day mortality between 1993 and 1999 (eg, for 1999 vs 1993, odds ratio [OR] 1.01, 95% confidence interval [CI], 1.00-1.02). One-year mortality was lower in 1994 compared with 1993 (OR 0.91, 95% CI, 0.90-0.92), but data from subsequent years suggested no continuous improvement after 1994 (1999 vs 1993: OR 0.93, 95% CI, 0.92-0.94). Thirty-day readmission increased (1999 vs 1993: OR 1.09, 95% CI, 1.07-1.10), but there was no change in 6-month readmission (1999 vs 1993: OR 1.00, 95% CI, 0.99-1.01). CONCLUSION: We found no substantial improvement in mortality and hospital readmission during the 1990s among elderly patients hospitalized with heart failure. These findings suggest that recent innovations in heart failure management have not yet translated into better outcomes in this population.

BACKGROUND: Pay for performance has increasingly become the subject of intense interest and debate, both of which have been heightened as the Centers for Medicare and Medicaid Services moves closer to adopting this approach for Medicare. Although many claims have been made for the effectiveness of this approach, the extent of its national penetration remains unknown. METHODS: We surveyed a sample of 252 health maintenance organizations (HMOs) (response rate, 96%) drawn from 41 metropolitan areas across the nation about use of pay for performance. We determined the prevalence of pay-for-performance programs, detailed the features of such programs, and examined the adoption of pay for performance as a function of the characteristics of both the health plans and markets. RESULTS: More than half the HMOs, representing more than 80% of persons enrolled, use pay for performance in their provider contracts. Of the 126 health plans with pay-for-performance programs, nearly 90% had programs for physicians and 38% had programs for hospitals. Use of pay for performance was statistically associated with geographic region, use of primary care providers (PCPs) as gatekeepers, use of capitation to pay PCPs, and whether the plans themselves received bonuses or penalties according to performance. CONCLUSIONS: Pay for performance is now commonly used by HMOs, especially those that are situated to assign responsibility for a particular patient to a PCP or medical group. As the design of Medicare with pay for performance moves forward, it will be important to leverage the early experience of pay for performance in the commercial market.

BACKGROUND: The Joint Commission on Accreditation of Healthcare Organizations and the Centers for Medicare and Medicaid Services recently began reporting on quality of care for acute myocardial infarction, congestive heart failure, and pneumonia. METHODS: We linked performance data submitted for the first half of 2004 to American Hospital Association data on hospital characteristics. We created composite scales for each disease and used factor analysis to identify 2 additional composites based on underlying domains of quality. We estimated logistic regression models to examine the relationship between hospital characteristics and quality. RESULTS: Overall, 75.9% of patients hospitalized with these conditions received recommended care. The mean composite scores and their associated interquartile ranges were 0.85 (0.81-0.95), 0.64 (0.52-0.78), and 0.88 (0.80-0.97) for acute myocardial infarction, congestive heart failure, and pneumonia, respectively. After adjustment, for-profit hospitals consistently underperformed not-for-profit hospitals for each condition, with odds ratios (ORs) ranging from 0.79 (95% confidence interval [CI], 0.78-0.80) for the congestive heart failure composite measure to 0.90 (95% CI, 0.89-0.91) for the pneumonia composite. Major teaching hospitals had better performance on the treatment and diagnosis composite (OR, 1.37; 95% CI, 1.34-1.39) but worse performance on the counseling and prevention composite (OR, 0.83; 95% CI, 0.82-0.84). Hospitals with more technology available, higher registered nurse staffing, and federal/military designation had higher performance. CONCLUSIONS: Patients are more likely to receive high-quality care in not-for-profit hospitals and in hospitals with high registered nurse staffing ratios and more investment in technology. Because payments and sources of payments affect some of these factors (eg, investments in technology and staffing ratios), policy makers should evaluate the effect of alternative payment approaches on quality.

A majority of employees can choose among health insurance plans of varying generosity. They may switch plans if prices, information, or their health status change. This paper analyzes switching behavior presumptively caused by changes in health status. We show that people who move to a less generous plan have lower medical spending prior to the switch than the average for the generous plan in which they started, while those who move to a more generous plan appear to anticipate higher spending, which they delay until after the switch. This transfer of costs from a less to a more generous plan increases the burden of adverse selection. Our data suggest that switching may be more important to the level of premiums than previously documented.

With the proliferation of efforts to report publicly the outcomes of healthcare providers and institutions, there is a growing need to define standards for the methods that are being employed. An interdisciplinary writing group identified 7 preferred attributes of statistical models used for publicly reported outcomes. These attributes include (1) clear and explicit definition of an appropriate patient sample, (2) clinical coherence of model variables, (3) sufficiently high-quality and timely data, (4) designation of an appropriate reference time before which covariates are derived and after which outcomes are measured, (5) use of an appropriate outcome and a standardized period of outcome assessment, (6) application of an analytical approach that takes into account the multilevel organization of data, and (7) disclosure of the methods used to compare outcomes, including disclosure of performance of risk-adjustment methodology in derivation and validation samples.

PURPOSE: The study investigated the determinants of warfarin use in patients with atrial fibrillation (AF). METHODS: We assembled a retrospective cohort of community-dwelling elderly patients (aged > or = 66 years) with AF using linked administrative databases. We identified the physicians responsible for the ambulatory care of these patients using physician service claims and compared patients who did and did not have an identifiable provider. For those patients with an identifiable provider, we assessed the association between patient, physician, and hospital factors and warfarin use. RESULTS: Our cohort consisted of 140,185 patients, of whom 116,200 (83%) had an identifiable cardiac provider. Patients without a provider were significantly more likely to have comorbid conditions that increase their risk of warfarin-associated bleeding. After adjustment for clinical factors, patients without a provider were significantly less likely to receive warfarin (odds ratio 0.37, 95% confidence interval: 0.36-0.38). Of patients with providers, 50,551 patients (43.5%) received warfarin within 180 days after hospital discharge. Warfarin use was positively associated with AF-associated stroke risk factors (eg, prior stroke, congestive heart failure) and negatively associated with warfarin-associated bleeding risk factors (eg, history of intracerebral hemorrhage). After controlling for patient and hospital factors, patients cared for by noncardiologist physicians with cardiology consultation were more likely to receive warfarin then patients treated in noncollaborative environments. CONCLUSIONS: Warfarin continues to be substantially underprescribed to patients who are at high risk for AF-associated cardioembolic stroke. Our findings highlight the need for targeted quality improvement interventions and suggest preferred models of AF care involving routine collaboration between cardiologists and other physicians.

BACKGROUND: Choice of statistical methodology may significantly impact the results of provider profiling, including cardiac surgery report cards. Because of sample size and clustering issues, logistic regression may overestimate systematic interprovider variability, leading to false outlier classification. Theoretically, the use of hierarchical models should result in more accurate representation of provider performance. METHODS: Extensively validated and audited data were available for all 4,603 isolated coronary artery bypass grafting procedures performed at 13 Massachusetts hospitals during 2002. To produce the official Massachusetts cardiac surgery report card, a 19-variable predictor set and a hierarchical generalized linear model were employed. For the current study, this same analysis was repeated with the 14 predictors used in the New York Cardiac Surgery Reporting System. Two additional analyses were conducted using each set of predictor variables and applying standard logistic regression. For each of the four combinations of predictors and models, the point estimates of risk-adjusted 30-day mortality, 95% confidence or probability intervals, and outlier status were determined for each hospital. RESULTS: Overall unadjusted mortality for coronary bypass operations was 2.19%. For most hospitals, there was wide variability in the point estimates and confidence or probability intervals of risk-adjusted mortality depending on statistical model, but little variability relative to the choice of predictors. There were no hospital outliers using hierarchical models, but there was one outlier using logistic regression with either predictor set. CONCLUSIONS: When used to compare provider performance, logistic regression increases the possibility of false outlier classification. The use of hierarchical models is recommended.

BACKGROUND: Recent studies indicate that a routine invasive approach for patients with unstable angina (UA) and non-ST-segment elevation myocardial infarction (NSTEMI) yields improved outcomes compared with a conservative approach, but the optimal timing of this approach remains open to debate. METHODS AND RESULTS: We used day of hospital presentation as an instrumental variable to study the impact of timing of cardiac catheterization and revascularization therapy on acute outcomes (death, reinfarction, stroke, cardiogenic shock, or congestive heart failure) among patients with UA and NSTEMI. Between January 2001 and September 2003, 56,352 patients with UA or NSTEMI were treated at 310 US hospitals participating in the CRUSADE national quality improvement initiative. Weekend patients were defined as those who presented to the hospital between 5 PM on Friday and 7 AM on Sunday. All other patients were classified as weekday. Weekday patients were similar to weekend patients in terms of demographics, clinical characteristics, and the use of medical therapies in the first 24 hours. Although overall rates of cardiac catheterization and revascularization were similar for the 2 groups, median time to catheterization was significantly longer for weekend than for weekday patients (46.3 versus 23.4 hours, P<0.0001). This delay was not associated with increased in-hospital adverse events, including death (weekend 4.4% versus weekday 4.1%, P=0.23), recurrent MI (2.9% versus 3.0%, P=0.36), or their combination (6.6% versus 6.6%, P=0.86). These findings were not affected by risk adjustment or use of alternative definitions of weekend versus weekday presentation. When weekend presentation was used as the basis for an instrumental variable analysis, we found that catheterization within the first 12 hours of presentation was associated with a nonsignificant trend toward reduced in-hospital mortality (absolute risk reduction 1.9%; 95% CI 6.7% lower to 2.9% higher; P=0.43) that decreased with longer treatment delays. CONCLUSIONS: Although weekend presentation is associated with a delay in invasive management among patients with UA and NSTEMI, in the context of contemporary medical therapy, this does not increase adverse events. Weekend presentation appears to fulfill accepted criteria as an instrumental variable for studying the optimal timing of invasive management for acute coronary syndrome patients. Using weekend status as an instrumental variable, we found no significant benefit to early catheterization, although we could not exclude an important risk reduction, particularly for catheterization within 12 hours of presentation.