Original articleValidating recommendations for coronary angiography following acute myocardial infarction in the elderly: A matched analysis using propensity scores
Introduction
The widespread and increasing use of guidelines and protocols has led researchers to investigate two questions: first, the extent to which current practices are consistent with these guidelines; and second, the extent to which adherence to guidelines leads to better outcomes for patients. Because of the importance of cardiovascular disease in terms of morbidity, mortality, and cost, many investigations have focused on this clinical condition. For example, several researchers have examined coronary angiography and revascularization procedures and demonstrated wide variability in use 1, 2, 3, 4, 5, 6 and some instances of inappropriate use 7, 8, 9, 10, 11. The correlation between adherence to treatment recommendations and outcomes has been studied less often, although one study of HMO enrollees in California [12] suggested improved survival among patients undergoing angiography who were rated necessary for the procedure.
In this study we assessed the link between adherence to recommendations for coronary angiography and survival using observational data from seven US states. Because guidelines increasingly incorporate a continuum of recommendations (e.g., the procedure is necessary, is appropriate but not necessary, is of uncertain benefit, or is inappropriate), we undertook to validate the accuracy of the explicit scale of appropriateness embedded in these guidelines. If there is no clear relationship with outcomes and the appropriateness scale, these scales should be discarded.
To achieve our goals, we studied a large national sample of Medicare beneficiaries treated after an acute myocardial infarction (AMI). We evaluated the appropriateness of coronary angiography more than 12 h after symptom onset but prior to hospital discharge and determined the extent to which use of the procedure in accordance with appropriateness ratings correlated with survival at 3 years from admission. We focused on coronary angiography because of wide variations in its use. Because our study is based on observational data, we adjusted for confounding by creating a matched sample using propensity scores.
Section snippets
Study population
We obtained our sample through the Cooperative Cardiovascular Project (CCP) [13] undertaken by the Health Care Financing Administration (HCFA). The sample included 64,140 fee-for-service Medicare beneficiaries aged 65–89 years who were discharged with a diagnosis of AMI from hospitals located in California, Florida, Massachusetts, New York, Ohio, Pennsylvania, and Texas during the period January 1, 1994 through June 30, 1995. These states were selected because they were known to differ in
Characteristics of the study population
The study cohort consisted of 37,788 patients, the majority of whom were white, slightly less than half were female, and 46% of whom underwent angiography during the initial episode of hospital care (Table 1). Twenty-nine percent, 36%, and 34% of patients were rated as necessary, appropriate but not necessary, or uncertain for angiography, respectively, in the matched cohort. Unadjusted survival at 3 years was 64% in the full cohort and 68% in the matched cohort.
The distribution of patients
Discussion
This study provides data on two important questions related to the management of patients after an AMI. First, we observed a relationship between coronary angiography and improved survival for those patients undergoing catheterization more than 12 h after symptom onset. Second, the strength of this relationship correlated with the continuum of recommendations for this procedure in the expected directions. These results are important because the patient population was a large and generalizable
Acknowledgements
The authors are indebted to Joseph P. Newhouse, Ph.D. for valuable comments; Laurie Silva, Ph.D. for project coordination; and Margaret Volya, M.Sc. and Christina Fu, Ph.D.; for expert programming assistance—all in the Harvard Medical School, Boston, MA; and two anonymous reviewers for their helpful comments. Supported by Grant RO1-HS08071 from the Agency for Health Care Policy and Research, Rockville, MD.
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