Impact of underuse, overuse, and discretionary use on geographic variation in the use of coronary angiography after acute myocardial infarction

BACKGROUND. Geographic variation in the use of medical procedures has been well documented. However, it is not known whether this variation is due to differences in use when procedures are indicated, discretionary, or contraindicated. OBJECTIVES, TO examine whether use of coronary angiography after acute myocardial infarction (AMI) according to appropriateness criteria varied across geographic regions and whether underuse, overuse, or discretionary use accounted for variation in overall use, DESIGN. Retrospective cohort study using data from the Cooperative Cardiovascular Project. SETTING, Ninety-five hospital referral regions. PATIENTS. There were 44,294 Medicare patients hospitalized with AMI during 1994 or 1995, classified according to appropriateness for angiography, MAIN OUTCOME MEASURE. Variation in use of angiography, as measured by the difference between high and low rates of use across regions. RESULTS. Across regions, variation in the use of angiography was similar for indications judged necessary; appropriate, but not necessary; or uncertain. Variation was lowest for indications judged unsuitable (difference between high rate and low rate across regions = 16.3%; 95% CI = 12.6%; 20.6%), The primary cause of variation in the overall rate of angiography was due to use for indications judged appropriate, but not necessary or uncertain, When variation associated with these indications was accounted for, the difference between the resulting high and low overall rates was 10.8% (9.4%, 12.4%). In contrast, variation in the overall rate remained high when underuse in necessary situations or overuse in unsuitable situations was accounted for. CONCLUSIONS. Across regions, practice was more similar for patients categorized unsuitable for angiography than for patients with other indications. Variation in overall use of angiography appeared to be driven by utilization for discretionary indications rather than by underuse or overuse. If equivalent rates across geographic areas are judged desirable, then greater effort must be directed toward defining care for patients with discretionary indications.