Emergency physicians see more than 8 million patients a year with a chief complaint of chest pain. Of those, more than half are admitted for further evaluation. A quarter of admitted patients are discharged with alternative diagnoses, resulting in more than $6 billion of additional cost. On the other hand, missed acute coronary syndrome is one of the top five reasons emergency physicians are sued for malpractice, accounting for 20% of malpractice costs.

On a daily basis, emergency physicians face this dichotomy of the expensive, low-prevalence, but high-risk clinical syndrome known as acute coronary syndrome (ACS), and in particular for non-ST-elevation myocardial infarction (NSTEMI).

Cardiac markers are often a key component in the evaluation of chest pain. Numerous studies, guidelines, and vendors propose a variety of approaches based on markers and clinical presentation. Options such as point of care testing exist that could theoretically speed throughput, although recent studies have shown no improvement.

Four markers are frequently referenced in the evaluation of patients to identify the presence and severity of acute myocardial infarction: troponin, CK-MB, myoglobin, and BNP. Choice of marker depends on time of onset of symptoms and desired clinical information. The American College of Emergency Physicians’ 2006 Clinical Policy “Critical Issues in the Evaluation and Management of Adult Patients with Non-ST Segment Elevation Acute Coronary Syndromes” provides an in-depth analysis and review of these markers (see summary below).

To obtain a sense of how emergency physicians are actually using these recommendations, the authors surveyed 98 emergency department physician leaders in 21 academic and 77 community emergency departments to ascertain which markers are commonly used and their current practice regarding bedside cardiac marker testing.

The first question of our survey asked which marker combination physicians utilized of the three markers ACEP recommends (troponin, CK-MB, and myoglobin) as a routine or by protocol in the emergency department. Results shown in Table 1 show the vast majority of respondents choose the combination of troponin and CK-MB. The next popular combination was troponin, CK-MB and myoglobin, with troponin alone following as a close third. Of note, academicians preferred the troponin-only model in a 7:1 ratio, compared with the all-three-marker combination. The least popular combination was troponin and myoglobin, although academicians once again preferred this over the three-marker combination.

The authors asked respondents if they routinely performed serial cardiac markers in the emergency department. As Table 2 shows, the majority of our respondents did not perform serial markers. Some of the “no” respondents commented that the patient went to an ED observation/clinical decision unit for serial testing, or that serial markers were done when patients were held in the emergency department awaiting an inpatient bed. For those who answered yes to serial markers, some respondents commented that it was done only for low-risk patients, with the intent to discharge for outpatient evaluation, and others commented that serial markers were performed only if the patient was admitted to the hospital.

The survey also questioned the clinical use of the B-type natriuretic peptide (BNP) as a cardiac marker, or if this marker was being used for the differential diagnosis of dyspnea patients and congestive heart failure management only. ACEP’s clinical policy briefly comments on the prognostic, not diagnostic, role of BNP in AMI, stating that elevated BNP has been shown to predict higher rates of morbidity and mortality in patients with acute myocardial infarction. Table 3 demonstrates an overwhelming majority of respondents do not use BNP as a cardiac marker, using it for dyspnea and CHF patients only. Of note, none of the academicians used BNP as a cardiac marker in the emergency department.

Finally, the survey asked whether respondents had bedside cardiac markers available in their institution; if yes, which one; and if not, why not. As demonstrated in Table 4, less than a third of respondents have bedside cardiac marker testing. For those who did not, as shown in Table 5, the most common reason was that lab turnaround time was just as fast. Other comments included expense and lab politics. Of interest, three respondents who answered “no” had cardiac marker bedside testing but abandoned it because of QC problems and expense, because rapid cardiac markers made no difference in clinical decisionmaking, and because of a high false-negative rate.

This study suggests that a combination of troponin and CKMB may be the most popular protocol to rule out AMI in patients in the emergency department. BNP is rarely if ever used as an AMI marker and is primarily used for the differential diagnosis of dyspnea and management of congestive heart failure. Both of these practices are consistent with the ACEP 2006 clinical policy recommendations for cardiac marker use based on clinical presentation. The survey also suggests that bedside cardiac marker testing requires many resources, does not necessarily improve throughput, and may be a potentially expensive and unnecessary alternative for emergency departments that have well functioning hospital laboratory services. Nonetheless, having some cardiac marker strategy as a part of the evaluation of possible AMI is a part of the evaluation of chest pain in all emergency departments surveyed.

References

• Ann. Emerg. Med. 2006;48:270-301.
• Ann. Emerg. Med. 2009;53:321-8.

Dr. Parker is a regional medical director for EmCare Central Region and clinical assistant professor of emergency medicine at Texas Tech University Health Sciences Center, El Paso. Dr. Suter is a past president of the American College of Emergency Physicians and the International Federation for Emergency Medicine.