Key points

Introduction

The evaluation of ACS in EDs remains diagnostically challenging. On a yearly basis it is estimated that more than 6 million people visit an ED for the evaluation of chest pain or other symptoms that are concerning for myocardial ischemia. The differential diagnosis of chest pain is broad and includes many organ systems. In addition to ACS, there are other immediately life-threatening diseases, such as pulmonary embolism, tension pneumothorax, cardiac tamponade, and aortic dissection, that also need to be considered. In several cases, a diagnosis can be made quickly based on initial screening ECG with detection of ST-segment elevation myocardial infarction (STEMI). Patients who present de novo to an ED with STEMI, however, are by far the minority compared with all-comers with a chief complaint of chest pain. Clinical decision rules and accelerated diagnostic protocols help with timely and accurate risk assessment but do not allow for immediate discharge of a majority of patients.

Apprehension about preventable sudden death drives most physicians to err conservatively on the side of admission. The cost of these admissions, however, remains high. As early as 1997 in the United States, hospitalization for more than 3 million patients cost approximately $3 billion to 4 billion annually for those who ultimately are determined disease-free. Furthermore, despite diagnostic advances in recent years, missed acute myocardial infarction (AMI) and ACS remain problematic, with estimates ranging between 2% and 10%. Missed AMI remains one of the leading causes of malpractice suits against emergency physicians.

These factors combined to produce the development of a safe, effective, and efficient manner of assessing risk of ACS in ED patients. The use of observation units dates back to the late 1980s as EDs began to struggle with growing waiting room numbers, hospital crowding, and overall lack of available inpatient beds. The popularity of ED-based observation units (EDOUs) has increased in recent years and is likely to continue, given policy pressures to reduce hospitalizations, in particular short-terms hospitalizations. EDOUs afford institutions the ability to perform serial cardiac biomarker testing and a wide array of stress testing modalities to identify those patients who would benefit from timely intervention to reduce their risk of a major adverse cardiac event (MACE). EDOUs have been associated with significant reductions in patient-related costs. Furthermore, this model has been shown safe and cost-effective and has a high sensitivity for diagnosis of ACS.

There are many methods for identifying appropriate EDOU patients. Typically, patients who are selected for observation for this indication receive serial cardiac biomarkers, telemetry monitoring, and some form of objective cardiac testing, such as stress testing. Some units variably incorporate other elements of patient cardiac risk reduction education (smoking cessation, for example) or other further risk stratification care, such as measuring of serum lipids. This article reviews tenets of observation medicine for ED patients with symptoms suggestive of ACS.

Introduction

The evaluation of ACS in EDs remains diagnostically challenging. On a yearly basis it is estimated that more than 6 million people visit an ED for the evaluation of chest pain or other symptoms that are concerning for myocardial ischemia. The differential diagnosis of chest pain is broad and includes many organ systems. In addition to ACS, there are other immediately life-threatening diseases, such as pulmonary embolism, tension pneumothorax, cardiac tamponade, and aortic dissection, that also need to be considered. In several cases, a diagnosis can be made quickly based on initial screening ECG with detection of ST-segment elevation myocardial infarction (STEMI). Patients who present de novo to an ED with STEMI, however, are by far the minority compared with all-comers with a chief complaint of chest pain. Clinical decision rules and accelerated diagnostic protocols help with timely and accurate risk assessment but do not allow for immediate discharge of a majority of patients.

Apprehension about preventable sudden death drives most physicians to err conservatively on the side of admission. The cost of these admissions, however, remains high. As early as 1997 in the United States, hospitalization for more than 3 million patients cost approximately $3 billion to 4 billion annually for those who ultimately are determined disease-free. Furthermore, despite diagnostic advances in recent years, missed acute myocardial infarction (AMI) and ACS remain problematic, with estimates ranging between 2% and 10%. Missed AMI remains one of the leading causes of malpractice suits against emergency physicians.

These factors combined to produce the development of a safe, effective, and efficient manner of assessing risk of ACS in ED patients. The use of observation units dates back to the late 1980s as EDs began to struggle with growing waiting room numbers, hospital crowding, and overall lack of available inpatient beds. The popularity of ED-based observation units (EDOUs) has increased in recent years and is likely to continue, given policy pressures to reduce hospitalizations, in particular short-terms hospitalizations. EDOUs afford institutions the ability to perform serial cardiac biomarker testing and a wide array of stress testing modalities to identify those patients who would benefit from timely intervention to reduce their risk of a major adverse cardiac event (MACE). EDOUs have been associated with significant reductions in patient-related costs. Furthermore, this model has been shown safe and cost-effective and has a high sensitivity for diagnosis of ACS.

There are many methods for identifying appropriate EDOU patients. Typically, patients who are selected for observation for this indication receive serial cardiac biomarkers, telemetry monitoring, and some form of objective cardiac testing, such as stress testing. Some units variably incorporate other elements of patient cardiac risk reduction education (smoking cessation, for example) or other further risk stratification care, such as measuring of serum lipids. This article reviews tenets of observation medicine for ED patients with symptoms suggestive of ACS.

Patient selection

In patients with ACS presenting with significant ECG changes, such as STEMI and/or increased levels of cardiac biomarkers, the disposition is often straightforward. Absence of such abnormalities, however, does not exclude ACS. Several clinical risk scores have been proposed and validated in ED patients with symptoms suggestive of ACS.

Vancouver Chest Pain Rule

Like the risk stratification scores discussed previously, the Vancouver Chest Pain Rule sought to identify patients with chest pain who are safe for discharge after 2 hours of ED evaluation. The rule missed fewer than 2% of ACS patients and allowed for discharge within 2 to 3 hours of at least 30% of patients without ACS.

Using this decision-making tree ( Fig. 1 ), the Vancouver Chest Pain Rule was 98% sensitive and 32.5% specific for prediction of adverse cardiac events within 30 days of presentation. Jalili and colleagues later validated this decision rule in a prospective cohort study.

Vancouver Chest Pain Rule algorithm for early discharge of very-low-risk patients with chest pain. CK-MB, creatine kinase–myocardial band isoenzyme. Note: patients with suspicion of other causes for chest pain (eg, pulmonary embolus, aortic dissection) should be investigated independent of this clinical prediction rule. ^a T-wave flattening is the only acceptable ST-T abnormality. ^b Prior ischemic chest pain is defined as a past known diagnosis of MI or angina, previously prescribed nicroglycerin or a clear history of effort-related angina. ^c Low-risk Pain Characteristics is defined as pain not radiating (arm/neck/jaw) OR increasing with a deep breath OR increasing with palpation. MI, myocardial infarction; Tn, troponin.

( From Christenson J, Innes G, McKnight D, et al. A clinical prediction rule for early discharge of patients with chest pain. Ann Emerg Med 2006;47(1):6; with permission from Elsevier.)

In summary, numerous risk stratification tools exist to screen patients who have too low a risk for observation unit care. These seem to improve on clinician gestalt in identifying patients who require further care. A further advance has been the development of shared decision-making tools for ACS work-up. These tools have been shown to decrease testing without any increase in adverse cardiac events.

Cardiac biomarkers

Concurrent with the evolution of EDOUs has been the adoption of cardiac troponin assays. In 2000, the American College of Cardiology (ACC), American Heart Association (AHA), and European Society of Cardiology officially advanced the definition of an AMI to the troponin standard. This move was made in recognition of troponin’s prognostic value and impact on therapeutic decision making, which was demonstrated in numerous studies. A major limitation of cardiac troponin assays is the delay between onset of symptoms and elevation of serum levels. As such, the diagnosis of AMI may require prolonged monitoring and serial blood sampling over a period of up to 3 hours to 12 hours.

An important consideration is that performing a rule out with only cardiac markers is often insufficient. There remains a subset of patients with serial negative troponin assays who remain at short-term risk for MACE. Limkakeng and colleagues evaluated the use of a single cardiac troponin I value in conjunction with a Goldman risk score of less than or equal to 4%, with the hope of identifying patients at low enough risk to immediately be discharged from EDs. The results indicated that even with the combination of a low clinical risk and a negative initial troponin I, the risk for AMI was still present (2.3% at 30 days). The risk stratification tools, discussed previously, have reduced the need for provocative testing and some investigators postulate other technological advances may obviate it (discussed later). For the near future, however, there remains a population of patients who benefit from further objective cardiac testing beyond serial cardiac markers.