Optimal Timing of Intervention in Non–ST-Segment Elevation Acute Coronary Syndromes

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Abstract
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 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.

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