OBJECTIVE To determine whether a new protocol, using a rapid and sensitive CK-MB_mass assay and serial sampling, can rule out myocardial infarction in patients with chest pain and decrease their length of stay in the cardiac emergency room without increasing risk.

DESIGN The combined incidence of cardiac death and acute myocardial infarction at 30 days, six months, and 24 months of follow up were compared between patients discharged home from the cardiac emergency room after ruling out myocardial infarction with a CK-MB_activity assay in 1994 and those discharged home after a rapid CK-MB_mass assay in 1996.

SETTING Cardiac emergency room of a large university hospital.

PATIENTS In 1994 and 1996, 230 and 423 chest pain patients, respectively, were discharged home from the cardiac emergency room with a normal CK-MB and an uneventful observation period.

RESULTS The median length of stay in the cardiac emergency room was significantly reduced, from 16.0 hours in 1994 to 9.0 hours in 1996 (p < 0.0001). Mean event rates in patients from the 1994 and 1996 cohorts, respectively, were 0.9% (95% confidence interval (CI) −0.3% to 2.1%)v 0.7% (95% CI −0.1% to 1.5%) at 30 days, 3.0% (95% CI 0.8% to 5.2%) v 2.8% (95% CI 1.2% to 4.4%) at six months, and 7.0% (95% CI 3.7% to 10.3%) v 5.7% (95% CI 3.5% to 7.9%) at 24 months. Kaplan–Meier survival analysis showed no difference in mean event-free survival at 30 days, six months, and 24 months of follow up.

CONCLUSIONS Using a rule-out myocardial infarction protocol with a rapid and sensitive CK-MB_mass assay and serial sampling, the length of stay of patients with chest pain in the cardiac emergency room can be reduced without compromising safety.