Care of the patient presenting to an emergency department (ED) with chest pain remains a common yet challenging aspect of emergency medicine. Acute coronary syndrome presents in nonspecific fashion. The development and evolution of the ED-based observation unit has helped to safely assess and diagnose those most at risk for an adverse cardiac event. Furthermore, there are several provocative testing modalities to help assess for coronary artery disease. This article serves to describe and discuss the modern ED-based observation unit approach to patients with chest pain and/or angina equivalents presenting to an ED.
Key points
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Increases in emergency department (ED) use by patients presenting with chest pain has led to the development of short-term observation units to facilitate an expedited and accurate assessment of their symptoms.
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Clinical decision rules have evolved to help clinicians assess risk of acute coronary syndrome (ACS) in patients presenting with chest pain and play an integral role in determining whether a patient should be a candidate for placement in an observation unit.
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Several provocative testing modalities are available to clinicians to help determine the extent, if any, of symptomatic coronary artery disease.
Lucy Epstein is a 63-year-old woman with a history of hypothyroidism, hypertension and breast cancer (now in remission after treatment). Over the past 3 weeks, she has noticed increased dyspnea on exertion. This morning she felt a 4/10 substernal chest pressure in the shower. The pain did not radiate; it was nonpleuritic and spontaneously resolved after approximately 20 minutes. She denies diaphoresis or nausea. Two hours after the chest pain episode, she arrives in an ED where she has an ECG that shows normal sinus rhythm with no new T-wave inversions or ST-segment depressions or elevations. Her physical examination, a chest radiograph and an initial troponin assay are normal. She is placed in an observation unit and repeat ECG and troponin at 6 hours are unchanged; the next day she receives a stress echo that is reassuring and is discharged home with instructions to follow-up with her primary care doctor within the next week.
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.
HEART Risk Score
The HEART risk score was developed specifically for patients presenting to an ED with undifferentiated chest pain. This score is composed of 5 parameters: history, ECG, age, risk factors, and troponin. The provider attributes a score (0–2) within each category to calculate a total of 0 to 10 ( Table 1 ). The risk of MACE in patients with a HEART score less than or equal to 3 is 0.9%, 12% in patients with HEART score 4 to 6, and 65% in patients with HEART score greater than or equal to 7. The HEART score was consecutively validated in a single-center retrospective study in 122 patients and a multicenter retrospective investigation in 880 patients. Mahler and colleagues conducted a randomized trial of implementing a pathway incorporating the HEART score, finding a 12.1% reduction in objective testing and a 21.3% increase in early discharges without any MACE in discharged patients. The lead author’s institution (JBB, Duke University Medical Center) currently advises routine cardiology admission for patients with HEART scores greater than 7.
| HEART score for Chest Pain Patients | ||
|---|---|---|
| History | Highly suspicious | 2 |
| Moderately suspicious | 1 | |
| Slightly suspicious | 0 | |
| ECG | Significant ST depression | 2 |
| Nonspecific repolarization disturbance | 1 | |
| Normal | 0 | |
| Age | ≥65 y | 2 |
| 45–65 | 1 | |
| ≤45 y | 0 | |
| Risk factors | ≥3 risk factors of history of atherosclerotic disease | 2 |
| 1 or 2 risk factors | 1 | |
| No risk factors known | 0 | |
| Troponins | ≥3× normal limit | 2 |
| 1–3× normal limit | 1 | |
| ≤ normal limit | 0 | |
Thrombolysis in Myocardial Infarction
The Thrombolysis in Myocardial Infarction (TIMI) investigators, led by Antman and colleagues, developed and validated a 7-point risk score ( Table 2 ) to predict the risk of an adverse cardiac outcome (death, [re]infarction, or recurrent severe ischemia requiring revascularization) within 14 days of presentation for patients with unstable angina or non-STEMI.
| Historical | |
| Age ≥65 y | 0 |
| 1 | |
| ≥3 risk factors for coronary artery disease | 0 |
| 1 | |
| Known coronary artery disease (stenosis ≥50%) | 0 |
| 1 | |
| Acetylsalicylic acid use in the past 7 d | 0 |
| 1 | |
| Presentation | |
| Recent (≤24 h) severe angina | 0 |
| 1 | |
| Positive cardiac biomarkers | 0 |
| 1 | |
| ST deviation ≥0.5 mm | 0 |
| 1 | |
The TIMI risk score is derived from the TIMI 11B trial, a multinational, randomized clinical trial, comparing unfractionated heparin to enoxaparin, which included all patients with confirmed ACS. Pollack and colleagues tested the score in an undifferentiated ED population and showed that the risk of 30-day adverse events ranged from 2.1% for patients with TIMI score of 0 or 1 to 45% to 100% for patients with a TIMI score of 6 or 7. Furthermore, the utility of this score was confirmed specifically in an EDOU population.
ADAPT Study
In 2012, Than and colleagues published a new accelerated diagnostic protocol (ADAPT) to identify low-risk ED chest pain patients suitable for early discharge. With the use of this ADP, a large group of patients (20%) presenting with possible ACS was identified as suitable for outpatient care. The ADAPT study team later validated this tool and demonstrated the ability to discharge patients safely with short ED stays. This group also derived and validated a second tool called the Emergency Department Assessment of Chest Pain Score accelerated diagnostic pathway that identified half of a large validation cohort as low risk, with 100% sensitivity. An external validation of this rule failed, however, to identify 2 of 17 patients with 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.
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.
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