Do CK-MB results affect chest pain decision making in the emergency department?

To analyze the effect of creatine kinase isoenzyme (CK-MB) results on decision making in the evaluation of emergency department patients with chest pain.

Prospective, controlled observational study of clinical decision making.

EDs of two teaching hospitals, a Veterans Affairs medical center, and a medical school university hospital.

Patients more than 30 years old complaining of chest discomfort warranting an ECG. Excluded were hemodynamically unstable patients and patients with ECG evidence of an acute myocardial infarction (AMI).

After the initial assessment including ECG but not CK-MB data, physicians answered questions regarding estimated probability of AMI and disposition plans. CK-MB levels were drawn every hour for as long as three hours (from one to four CK-MBs) with results readily available. Physicians could admit their patients into the hospital at any time. At disposition after reviewing a second ECG and all available CK-MB data, the physicians answered the same questions and rank ordered the contribution to disposition of the following six factors: initial and serial clinical evaluations, initial and serial ECGs, and initial and serial CK-MB enzymes, respectively. The absolute log likelihood ratio test measured the contribution of CK-MB to decision certainty.

Three hundred seventy-six patients were studied: 29 (7.7%) with AMI and 347 without AMI (nonAMI). Physicians indicated that CK-MB levels were useful for more than one third of study patients. When considered useful, CK-MB results strengthened the impression of AMI in AMI patients and decreased the impression of AMI for nonAMI patients; CK-MB also correlated with the perceived need for cardiac care unit admission in AMI patients and with a reduced need to admit nonAMI patients. The use of CK-MB results did not significantly increase ED release rates.

The rapid availability of serial CK-MB results appears to affect decision making in one third of ED patients with chest pain and nondiagnostic ECGs. CK-MB levels appear to complement clinical evaluation of the ED chest pain patient in a manner analogous to the ECG.