Reflex testing II: evaluation of an algorithm for use of cardiac markers in the assessment of emergency department patients with chest pain.
A reflex algorithm was developed and evaluated for the use of serum cardiac markers for the diagnosis and rule out of acute myocardial infarction (AMI), and risk stratification of unstable angina patients for those who present to emergency departments (ED) with chest pain. The process begins with testing of total CK and myoglobin at admission. Based on these results, the algorithm determines the need for subsequent testing for the CK-MB isoenzyme and cardiac troponin I (cTnI). The algorithm also directs the need for further blood collection and cardiac marker testing at 4, 8, and 12 h after presentation. A total of eleven stopping points were identified. For some of these stopping points, the algorithm concluded that further blood collections and testing was unnecessary and redundant. The algorithm was retrospectively evaluated on 101 non-consecutive chest pain patients who presented to the EDs at three hospitals. For the AMI group (n=34), six of nine possible different stopping points were reached: 64.7% of cases were diagnosed with the first sample at admission, an additional 32.3% after 4 h, and 2.9% at 8 h. The 12-h sample was not necessary for any of the AMI patients. For the non-AMI group (n=67), most reached the stopping point of no cardiac injury or risk. There were five unstable angina patients who had minor myocardial damage on the basis of a marginally increased cTnI. Of these, one patient subsequently suffered AMI, and three others required angioplasty or bypass surgery. Compared to performing four tests on all patient samples, the reflex algorithm would have reduced the number of necessary tests from 442 to 130 (71% reduction) for AMI patients, and 871 to 469 (46% reduction) for non-AMI patients, if prospectively implemented.