Chest pain evaluation units

Chest pain is a common cause of emergency department (ED) presentation. In the United States, it accounts for 5% to 6% of new ED attendances.^1,2 The principal challenge in these patients is to identify those with an acute coronary syndrome. Early diagnosis allows effective treatment, and premature discharge may have disastrous consequences for patient and doctor: in the United States, between 2% and 5% of patients with acute myocardial infarctions are discharged from the ED, and 20% of malpractice claims against emergency physicians relate to the management of acute coronary syndrome.³

The problem with the emergency assessment of these patients lies in the limitations of diagnostic tests for acute coronary ischemia—electrocardiography (ECG) is diagnostic of acute myocardial infarction in only 40% to 65% of patients and is even less useful in those with unstable angina.⁴ Despite recent advances, serum markers for myocardial necrosis detect, at best, 66% of patients with acute myocardial infarction on arrival.⁵ Faced with these diagnostic difficulties and the consequences of misdiagnosis, ED physicians have a low threshold for admitting patients with chest pain in whom the diagnosis is not immediately clear. Some 60% to 65% of these patients have an eventual diagnosis of noncardiac chest pain,³ and although serious disease is diagnosed in a few, this traditional approach to chest pain is both time-consuming and expensive.

It is against this background that the concept of ED-based chest pain evaluation units emerged, with the aim to provide medically equivalent care at a lower cost for patients presenting to an ED with chest pain with a probability for acute coronary syndrome that is low, but not sufficiently low to allow discharge. The concept originated in, and has been almost exclusively confined to, the United States. The first chest pain evaluation unit was set up in 1981 and, by 1997, 15% of EDs in the United States had followed suit.⁶ In this article, I review the literature on chest pain evaluation units to answer the following questions:

• How are patients managed on chest pain evaluation units?

• Is there evidence for their clinical effectiveness?

• Are they cost-effective?

• Is there evidence of patient satisfaction?

SEARCH METHODS

A literature search was carried out to identify research articles and those whose principal focus was chest pain evaluation units run by EDs for the assessment of chest pain of possible cardiac origin. The following databases were searched: MEDLINE, EMBASE, the Cochrane Library, and the Database of Abstracts of Reviews for Effectiveness. The following search terms were used: “emergency service, hospital,” “myocardial infarction/diagnosis,” “myocardial ischemia/diagnosis,” “angina pectoris/diagnosis,” “chest pain/diagnosis,” “chest pain/therapy,” “cost-benefit analysis,” and “randomized controlled trials.” In addition, the reference lists of retrieved articles were searched for those not identified in the computerized search. Journals were not hand-searched, and authors were not contacted for unpublished work. Articles were selected if they described patient management or presented evidence for clinical efficacy, cost-effectiveness, or patient satisfaction. Where appropriate, articles were critically appraised along standard guidelines.^7,8 Conference abstracts were not selected because the brevity of information hinders meaningful critical appraisal.

RESULTS

Patient management

Eight articles were identified that described the management process in 6 chest pain evaluation units. These are summarized in table 1.^{9,10,11,12,13,14} Despite differences in the detail, the overall approach to patient management is similar in the different centers. All are described as being located in, or adjacent to, the ED. All centers include patients with nontraumatic chest pain deemed to be at low risk for acute myocardial infarction. In 4 centers, the ascription of risk is at the discretion of the treating physician, according to local guidelines. In the other 2 units, risk is determined according to the Goldman algorithm, a validated tool that divides patients with chest pain into groups with differing probabilities of acute myocardial infarction, based on history, examination, and ECG findings.¹⁵ Patients are eligible for these chest pain evaluation units if they have a probability of acute myocardial infarction that is calculated to be less than 7%.

Table 1.

Management protocols in 6 chest pain evaluation units

Study, year	Duration of protocol, hr	ECG	Biochemical markers	Additional testing
Zalenski et al,9 1997	12	0, 6, and 12 hr	CK-MB at 0, 4, 8, and 12 hr	Exercise tolerance testing (ETT)
Gibler et al,10 1995	9	Continuous ST segment monitor	CK-MB at 0, 3, 6, and 9 hr	2-dimensional echo, ETT
Hoekstra et al,11 1994	9	Continuous ST segment monitor	CK-MB at 0, 3, 6, and 9 hr	Thallium ETT
Doherty et al,12 1994	9	0, 3, 6, and 9 hr	CK-MB at 0, 3, 6, and 9 hr	Cardiology consultation, ETT, thallium ETT, MUGA scan
Mikhail et al,13 1997	8	Continuous ST segment monitor	Total CK at 0 hours; with or without CK-MB at 0, 4, and 8 hr; with or without myoglobin at 0 and 4 hr	ETT, stress echo, dobutamine echo, thallium ETT
Gomez et al,14 1996	9	Continuous ST segment monitor	Total CK and CK-MB at 0, 3, 6, and 9 hr	ETT, dobutamine echo
ECG = electrocardiography; CK-MB = creatine kinase—muscle-brain isoenzymes; echo = echocardiography; MUGA = multigated angiocardiography.

Exclusion criteria are described for 5 of the centers. Common exclusion criteria are ECG evidence of acute myocardial ischemia or the presence of complications of cardiac ischemia (for example, arrhythmia, hypotension, congestive cardiac failure, and prehospital cardiac arrest). The identification of a noncardiac diagnosis is stated as an exclusion criterion in 4 of the 5 centers. Two units exclude patients with a history of coronary artery disease, and 1 specifically includes these patients. The inability to perform an exercise test excludes patients in 1 center.

Once admitted to the units, patients receive serial clinical, ECG, and biochemical assessment at specified intervals. If evidence of acute myocardial infarction or unstable angina emerges, the patient is transferred to a critical care unit. Patients with normal results at the end of the testing period undergo exercise stress testing or an equivalent in those physically unfit for the treadmill. If these tests are positive, the patient is admitted for further evaluation. If negative, the patient is discharged home. Follow-up is arranged with a cardiologist or family physician.

Clinical efficacy

An effective chest pain evaluation unit should have a diagnostic protocol that performs as well as standard management. The gold standard for evaluating a new diagnostic test (chest pain evaluation unit) entails its independent, blind comparison with a reference standard of diagnosis (standard inpatient management), the reference being applied irrespective of the new test result.¹⁶ Five published studies have assessed the diagnostic utility of their chest pain evaluation unit's protocol, but only 1 meets the above criterion. Zalenski et al⁹ studied 317 patients, all of whom were initially admitted to a chest pain evaluation unit. At the end of the testing protocol, all patients were admitted to the hospital for the establishment of reference diagnoses according to the standard inpatient examination. Final reference diagnoses were assigned by a physician blinded to the results of the chest pain evaluation unit outcomes. The sensitivity and specificity of the protocol for acute coronary insufficiency were 90.0% (95% confidence interval [CI], 73.4%-97.9%) and 50.5% (95% CI, 44.6%-56.4%), respectively. Negative and positive predictive values were 98.0% (95% CI, 94.2%-99.6%) and 16.0%, respectively. The authors assume a sensitivity of 100% for the inpatient protocol.

Four other articles used the incidence of adverse outcomes over a period of follow-up as a measure of the diagnostic accuracy of their protocol. Table 2^10,12,13,14 summarizes the results.

Table 2.

Outcomes of patients discharged from 4 chest pain evaluation units

Study, year	No. of patients*	Period of follow-up	Adverse outcomes
Doherty et al,12 1994	176	9 mo	None
Mikhail et al,13 1997	410	5 mo	1 acute MI at 6 days
Gibler et al,10 1995	829	1 mo	1 acute MI at 3 days; 4 noncardiac deaths at 1 mo
Gomez et al,14 1996	46	30 days	None
MI = myocardial infarction.

^*Number of patients discharged after negative evaluation in chest pain unit.

The proportion of patients discharged home after the protocol, the duration of stay, and the frequency with which ischemic heart disease is diagnosed in all chest pain unit patients and in those admitted with positive results all relate to the effectiveness of the unit.

Cost comparisons

Four articles report comparative studies, with cost as a primary outcome. Roberts et al¹⁸ randomly allocated 166 patients eligible for the chest pain evaluation unit to either the chest pain unit (intervention) or standard inpatient treatment (control). The mean total cost per chest pain unit patient was $1,528 compared with $2,095 for controls (P<0.01). Mean costs for patients admitted after chest pain unit evaluation were $2,410, higher than the cost for patients discharged after chest pain unit evaluation ($803, P<0.001) and for controls ($2,095, P<0.13). This study was well designed with robust randomization, clearly stated sample size calculations, intention-to-treat analysis, and rigorous cost analysis. Blinding was not possible because patients were managed in different areas.

In a second randomized controlled trial, Gomez et al¹⁴ reported mean hospital charges of $1,297 in the chest pain unit group versus $5,719 in the routine care (control) group (P<0.001). Figures are not presented for the cost differences between those admitted from the chest pain unit and those discharged.

Mikhail et al¹³ report a comparative study using retrospective controls. The mean total cost per case for patients discharged from the chest pain unit was $894. The corresponding figure for controls was $2,364.

In another nonrandomized trial, Hoekstra et al¹¹ report a cost analysis for chest pain units in 2 centers. Patients admitted to the hospital when the chest pain units were full were used as controls. In both centers, mean charges were significantly less for chest pain unit patients than for controls (center 1: $2,797 vs $3,957 [P<0.01]; center 2: $1,931 vs $3,961 [P<0.01]). This article also reports higher mean charges in patients admitted following chest pain unit evaluation than in controls, although these differences were not statistically significant.

Patient satisfaction

Rydman at al¹⁹ report a randomized controlled trial comparing patient satisfaction between those admitted to a chest pain observation unit and controls admitted for routine care, using patient interviews to score a number of satisfaction markers from 1 (most dissatisfied) to 4 (most satisfied). The chest pain unit scored higher than inpatient management on all 7 satisfaction indices, with the attainment of a statistically significant difference in 4 of these scores.

DISCUSSION

The management strategy used in chest pain evaluation units represents a condensed form of traditional inpatient management. Protocols differ in some of their components, although no study has compared 1 with another. Recent evidence on the performance of troponin T and troponin I assays in patients with chest pain and normal ECGs offers the prospect of even shorter testing periods. In a well-designed validation study, Hamm et al⁵ report that troponin T and troponin I tests were positive in 94% and 100% (respectively) of patients with acute MI within 6 hours of pain onset, although this study was not carried out in the context of a chest pain unit.

All units perform some form of provocative testing before discharge. This practice recognizes the safety of early exercise testing in patients with chest pain who have a low risk of acute coronary syndrome^20,21 and the dangers of omitting such testing—Gaspoz et al²² reported a 1.2% missed MI rate in patients discharged from a cardiology-run chest pain observation unit, only 19% of whom had had an exercise test before discharge.

It is clear that the success of these units stands or falls on rapid and extended access to cardiac enzyme assays and stress testing facilities. Most of the reporting US centers can access blood assays 24 hours a day and exercise testing 7 days a week. Excluding patients unable to perform exercise tests may simplify the logistics by obviating the need for rapid access to more sophisticated provocation tests but would probably limit the usefulness of the unit.

Despite the considerable investment required, chest pain units may have a modest effect on chest pain management in a given department. In a feasibility study, Zalenski et al¹ found that only 28% of patients deemed to be at low risk for myocardial infarction were eligible for the chest pain unit. Characteristics of the study population, protocols used, and chest pain unit exclusion criteria all affect this proportion.

The available evidence suggests that chest pain evaluation units deliver what they promise, providing equivalent clinical outcomes to inpatient management, in a shorter time and for lower cost. Follow-up of discharged patients has demonstrated the safety of the protocols, although given the sensitivity of 90% reported by Zalenski et al,⁹ and with a disease prevalence of 10%, about 1 of 100 tested patients would be wrongly classified as disease free. The specificities of the protocols are moderate, and most patients admitted to the hospital after having had positive findings in the chest pain unit prove ultimately not to have an acute coronary syndrome (table 3). This underscores the limitations of current diagnostic tests.

Table 3.

Outcomes of patients admitted to chest pain evaluation units (CPEUs)

Study, year	No. of patients	Discharged, no. (%)	Duration (control), hr	% Admitted with ACS*	% CPEU patients with ACS†
Gomez et al,14 1996‡	50	46 (92)	15.4 (54.6)	25	2
Doherty et al,12 1994	226	176 (78)	17.4 (52.87)	10	2
Toner,17 1997	1,724	1,233 (72)	6.5	NS	NS
Gibler et al,10 1995	1,010	829 (82)	NS	28	4
Mikhail et al,13 1997	477	410 (86)	NS	66	9
ACS = acute coronary syndrome; NS = not stated.

^*Percentage of patients admitted from the CPEU with an eventual diagnosis of an acute coronary syndrome.

^†Percentage of all patients admitted to the CPEU with a final diagnosis of an acute coronary syndrome.

^‡This study was a randomized controlled trial.

Two well-designed studies have demonstrated the cost benefits of chest pain evaluation units. The important observation is that patients managed on the unit who are subsequently admitted to a hospital cost more than those managed in the routine way. Savings can be made only if most of those managed on the unit are discharged. Most units achieve this (table 3). It is probable that some patients will be admitted to the unit who would otherwise have been discharged after initial evaluation. This is essential to decrease missed MI rates but will affect overall cost-effectiveness.

Table 3^{10,12,13,14,17} summarizes the available evidence on these issues.

There is a potential in chest pain evaluation units to overlook other causes of chest pain, given the overwhelming focus on excluding cardiac disease. Many of these alternative diagnoses are not readily apparent, and some may have serious consequences. In addition, chest pain evaluation units run the risk of downplaying the importance of symptoms other than chest pain in the presentation of myocardial ischemia. These possible pitfalls have received little attention in the literature, although it seems likely that focused education would lessen the risk.

It is estimated that, since 1991, more than 500 chest pain evaluation units have been established in EDs across the United States.²³ There are no published reports of such emergency department-based units from any other country. Retrospective denial of payment for patients admitted with noncardiac chest pain is not an uncommon occurrence in the United States,³ and it is clear from the literature that financial pressures have had an important role in the development of chest pain evaluation units. Of the 3 randomized controlled trials identified, 2 focus on cost. The clinical benefits are largely reported in observational studies. Whatever their origin, the role of chest pain units continues to develop in the United States, with the recent publication of the results of a randomized trial reporting the safe, clinically and cost-effective use of a chest pain observation unit for the treatment of patients with unstable angina deemed to be at intermediate risk for cardiac events.²⁴

CONCLUSION

Experience in the United States has demonstrated that chest pain units manage patients at low risk for myocardial infarction as effectively as inpatient admission and at less cost. They seem like a good idea. However, all available evidence emanates from the United States and may not be generalizable to other countries.

Figure 1.

Dedicated chest pain units aim to detect patients with coronary artery disease, as is the reason for this angiogram

^{© Mehau Kulyk/SPL}