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Clinical Investigations: CARDIOLOGY |

Is Telemetry Monitoring Necessary in Low-Risk Suspected Acute Chest Pain Syndromes?* FREE TO VIEW

Adam Snider, DO; Marco Papaleo, MD; Stuart Beldner, MD; Chong Park, MD; Dennis Katechis, DO; David Galinkin, DO; Alan Fein, MD, FCCP
Author and Funding Information

*From the Center for Pulmonary and Critical Care Medicine, North Shore University Hospital, Manhasset, NY.

Correspondence to: Alan M. Fein, MD, FCCP, North Shore University Hospital, 300 Community Dr, Manhasset, NY 11030; e-mail: afein@nshs.edu



Chest. 2002;122(2):517-523. doi:10.1378/chest.122.2.517
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Published online

Background: Non-ICU telemetry monitoring has proven to be a valuable resource for patients suspected of having an acute myocardial infarction. While a significant number of patients are admitted to these units, the actual incidence of events or interventions is low.

Objective: To identify a subset of patients in whom telemetry monitoring does not alter management.

Design: Prospective observational study.

Setting: Large tertiary care facility.

Patients: A total of 414 patients consecutively admitted from the emergency department for suspected acute coronary syndromes were studied. Patients were excluded if they presented with ST-segment elevations, were revascularized on hospital admission, were admitted to a surgical service, were transferred from another floor or unit, or remained in the emergency department for the course of the stay.

Outcomes: Events were defined as development of myocardial infarction, episodes of chest pain, new or rapid atrial arrhythmias, ventricular arrhythmias, any form of AV nodal block, and asystole. Intervention or change in management was any increase, decrease, or change in medication, cardioversion, electrophysiology study, or transfer to the ICU.

Results: Patients who had atypical chest pain and normal ECG findings were significantly less likely to have both intervention and events (4 interventions vs 23 interventions [p < 0.0001], 12 events vs 45 events [p < 0.0001]), compared to those with typical chest pain and abnormal ECG findings. When normal laboratory values were added, only four telemetry events were observed.

Conclusion: Patients with atypical chest pain and normal ECG findings represent a subset of patients with low risk for life-threatening arrhythmia. Use of telemetry monitoring in this subset of patients should be reevaluated.

Figures in this Article

Triage of patients admitted with suspected acute coronary syndromes has undergone significant change over the last 30 years from home-based monitoring,1to ICU monitoring,2and most recently to non-ICU telemetry monitoring.3 In the 1960s, coronary care units (CCUs) were initially employed for cardiac monitoring. Substantial evidence supported the efficacy of these highly specialized units in preventing and treating complications. Mortality was reduced in the first 6 to 12 h following an acute myocardial infarction (AMI).34

Recently, it was found to be more cost-effective,5as well as medically appropriate,68 to place a patient with low risk of AMI in a non-ICU monitored setting. This has led to a larger proportion of chest pain admissions to these non-ICU telemetry beds and a significant expansion of this capability. In fact, our hospital has increased the number of these beds twofold over the past year.

The decision by physicians to admit their patients to this unit is often guided by previously published guidelines by the American College of Cardiology in 1991.9According to these guidelines, a patient suspected of having an AMI should be monitored until infarction can be excluded. However, Estrada et al1011 reported that telemetry identified an arrhythmia that resulted in a transfer to the ICU in only 0.8% of all admissions. This low incidence of significant events for all patients admitted for chest pain prompted us to conduct a prospective observational study to evaluate characteristics of low-risk patients with an uneventful telemetry stay. We evaluated both cardiac events and medical interventions.

The purpose of our study was to identify a subset of patients in whom telemetry monitoring does not alter management. Accordingly, this expensive and limited resource could be allocated more efficiently.

Practice Setting

North Shore University Hospital is a 755-bed facility. It is a major cardiac referral center in the New York City metropolitan area. Cardiac monitoring occurs in all ICUs as well as two telemetry units (63 beds). Patients monitored on telemetry may be admitted through the emergency department, transferred from ICUs, as well as from general medical floors.

Heart rate and rhythm are transmitted continuously by two leads (aVL and V1) fashion. Technicians trained to recognize rhythm disturbances continuously monitor the cardiac rhythm, and report to the nursing and medical staff.

Patient Populations

This study was prospective and observational and conducted over 3 months. Four hundred fourteen patients consecutively admitted from the emergency department to telemetry for suspected acute coronary syndromes were studied. Patients were excluded if they presented with ST-segment elevations, were revascularized on admission, were admitted to a surgical service, were transferred from another floor or unit, or remained in the emergency department for the course of the stay.

One of the investigators obtained clinical information, including previous history (coronary artery disease, congestive heart failure, or arrhythmia), and cardiac risk factors (hypertension, diabetes mellitus, hypercholesterolemia, or family history or smoking history) from the medical records of the study patients. This information was obtained concurrently at admission and recorded on data sheets for standardization and further analysis.

Chest pain, including rest pain, was further classified as typical or atypical based on previously published criteria.7 Typical chest pain was defined as pressure-like retrosternal pain being exacerbated by exercise and relieved at rest or with administration of nitroglycerin. Additionally, if the pain radiated to the neck or left shoulder or arm, it was classified as typical. Atypical chest pain was defined as pain reproducible by palpation, radiating to the back, abdomen, or legs, or was “stabbing” in nature. Chest pain associated with symptoms of palpitations, shortness of breath, and syncope on hospital admission was also noted.

ECGs, electrolytes, cardiac enzymes, and chest radiographs were recorded12 and interpreted by the patients’ attending physicians. Patients with infarction or injury pattern defined as significant Q waves or ST-segment elevations were excluded from our study. Ischemia was defined as any horizontal or downsloping ST-segment depression > 0.1 millivolts (0.2 millivolts in leads V1 through V3) measured 80 ms from the J point, or inverted T waves > 0.3 millivolts. Upsloping ST-segment depressions were included if they were > 2 mm or were dynamic in nature. Atrial arrhythmia was considered any supranodal rhythm other than sinus. Conduction abnormality was considered a right or left bundle-branch block and/or any degree of AV block. Sinus bradycardia (heart rate < 60 beats/min) and sinus tachycardia (heart rate > 100 beats/min) were also recorded.

Outcomes

Events were defined as the development of myocardial infarction (MI), episodes of chest pain, new or rapid atrial arrhythmias, ventricular arrhythmias including nonsustained or sustained ventricular arrhythmia, any form of AV nodal block, and asystole. MI was defined by elevated creatinine kinase (CK) levels (> 200 U), with total myocardial bands (> 10 U) or percentage of myocardial bands > 5%. An intervention or change in management was defined as any increase, decrease, or change in medication, cardioversion, electrophysiology study, or transfer to the ICU.

Statistics

Data were collected by the investigators and analyzed with the North Shore University Hospital biostatistics department. Using software (Filemaker Pro; Filemaker; Santa Clara, CA), a database was created. Data were then analyzed using Microsoft Excel (Microsoft; Redmond, WA) and SAS (SAS Institute; Cary, NC). Most of the results are expressed as percentages, and χ2 or the Fisher exact test (as appropriate) were used to compare percentages between different groups of patients. Statistical results were considered significant if the two-tailed p value was < 0.05.

Demographics

A total of 414 consecutive patients were evaluated during the course of the study (Table 1 ). The average (± SD) age was 67.8 ± 28.7 years. Of these, 191 patients (46.1%) were female and 223 patients (53.9%) were male. Two hundred ninety-four patients (71%) were white, and 39 patients (9.4%) were African American.

Cardiac History and Risk Factors

More than one third of patients had a history of coronary artery disease (n = 152, 36.7%): MI angiographically (n = 79) or on myocardial perfusion imaging (n = 56), or history of coronary artery bypass surgery (n = 23). Fifty-three patients had a history of congestive heart failure, and 64 patients had a history of arrhythmia with or without a history of coronary artery disease (Table 1).

Hypertension was the most common risk factor for coronary artery disease (n = 225, 54%). About one fourth of patients had a history of hypercholesterolemia (n = 118). Diabetes mellitus was a risk factor in 89 patients, smoking was a risk factor in 86 patients, and a family history significant for coronary artery disease was a risk factor in 36 patients.

Presentation

The majority of patients presented with atypical chest pain (n = 248, 60.%; Table 2 ). One hundred sixty-six patients presented with typical chest pain (40%). There were no associated symptoms of dyspnea, palpitations, or syncope in most patients (n = 254, 61%), with the remaining 160 patients (39%) having one or more of these symptoms. Specifically, 106 patients presented with associated dyspnea, 63 patients presented with associated palpitations, and 19 patients presented with syncope. Two hundred sixty-five patients (64%) had one or more laboratory abnormalities, including WBC count elevation (n = 81), electrolyte abnormalities (n = 46), elevated CK levels (n = 54), and congestive heart failure by chest radiograph (n = 31).

ECG findings were normal in approximately one half of patients (n = 210, 51%), with 204 patients having one or more abnormalities (including nonspecific ST/T wave changes) on ECG. Ninety-nine patients presented with ischemic changes on their ECG. Fifty patients had an atrial arrhythmia, 42 patients had conduction abnormalities, 18 patients had a paced rhythm, and 22 patients had sinus bradycardia or tachycardia. No patients in the study presented with ventricular arrhythmia.

Outcomes

After hospital admission, 107 patients (28.5%) had one or more events while on telemetry (Tables 3, 4 ). The majority of these were atrial arrhythmias or ectopy (n = 46, 11%) and ventricular arrhythmias or ectopy (n = 45, 11%). Sinus bradycardia or tachycardia was noted in 36 patients. Additionally, among 12 different patients, there were three deaths, 6 patients with episodes of asystole, and 3 patients with complete heart block.

Only 47 of these 107 patients (11%) had a change in their management while on the telemetry monitor. The most common intervention was the initiation of a new antiarrhythmic agent. Only eight patients (2%) were transferred to an ICU. Eight patients underwent an electrophysiology study. Eight patients (2%) had an increase in the dose of an admission medication, four patients (1%) had a decrease in the dose of an admission medication, two patients (0.5%) were started on a new medication other than an antiarrhythmic, and one patient (0.24%) underwent direct current cardioversion.

Of the 248 patients (Fig 1 ) who presented with atypical chest pain, 47 patients (19%) had events, compared to 60 patients of the 166 patients (36%) presenting with typical chest pain (p < 0.0001). Among those patients with events, 40% of patients (19 of 47 patients) with atypical chest pain had a change in management, compared to 47% of those with typical chest pain (28 of 60 patients; p < 0.005). Of the patients with typical chest pain, 22 patients had an MI, compared to only 6 patients with atypical chest pain. Patients with atypical chest pain and events had a lower rate of intervention.

Patients with chest pain (typical or atypical) without other associated symptoms had only 40 events while on telemetry service, representing 16% of this subgroup. In comparison, patients having one or more associated symptoms commonly did have events (40 patients vs 67 patients; p < 0.0001). Thirteen patients who lacked associated symptoms had a change in management, compared to 34 of the patients with one or more associated symptoms (p < 0.0001).

Normal ECG findings also correlated well with an uneventful hospital course. With normal ECG findings (Fig 2 ), 27 patients (13%) had an event, compared to almost 39% of patients with abnormal admission ECG findings (p < 0.0001). Interventions were also more uncommon in patients with normal ECG findings on presentation (9 patients vs 38 patients, p < 0.0001). Among patients with abnormal admission ECG findings, there were 21 MIs, compared to 7 MIs in the group with normal ECG findings.

Features on hospital admission that identified low-risk patients were specifically examined. Patients who had atypical chest pain and normal ECG findings were significantly less likely to have both intervention and events (4 patients vs 23 patients [p < 0.0001], and 12 patients vs 45 patients [p < 0.0001], respectively), compared to patients with typical chest pain and abnormal ECG findings (Fig 3 ). When normal laboratory values at presentation were added to atypical chest pain and normal ECG findings, only four telemetry events were observed.

In our series, 37% of patients had atypical chest pain and normal ECG findings. Events on telemetry (sinus bradycardia, sinus tachycardia, and nonsustained ventricular tachycardia) were observed in only 8% of this subgroup. None of these patients displayed supraventricular tachycardia, sustained ventricular arrhythmia, heart block, or asystole. There were only four patients who had events that led to an intervention. There were no transfers to critical care units or deaths. We found three cases of MI in this group, and none of these patients had a cardiac history. Two patients had hypertension, and the other patient had a history of smoking.

Based on initial ECG findings and history of presenting illness in patients suspected of acute coronary syndromes, it is possible to identify low-risk patients in whom telemetry monitoring does not appear to alter management. Its role should be reevaluated in these patients.

CCUs were introduced in the United States in the early 1960s in an attempt to lower the high mortality rate among hospitalized patients with AMI.2 Since then, it has been the standard of care in the United States to admit all patients with suspected MI into CCUs equipped to respond to life-threatening arrhythmias. Ninety percent of patients with AMI have cardiac rhythm abnormality, and 25% have a conduction disturbance. In addition, the incidence of serious arrhythmias, such as ventricular fibrillation, is greatest within the first hour of AMI.4However, most patients admitted to the CCU with suspected AMI do not, in fact, prove to have this diagnosis.5 In contrast to this approach, a chest pain observational unit has been developed. Units like this have already been adopted by many hospitals in the United States. These institutions provide extended care in the emergency department to avoid admission of patients with low risk of acute coronary syndrome.

This led to cost-effective analyses5and predictive instruments68 to identify low-risk patients who may be initially admitted to an intermediate care unit.1315 Analysis examining the clinical and economic consequences of alternatives to CCU care have demonstrated that patients at low risk of AMI can be managed in an intermediate care unit, with telemetry monitoring.3 Studies1619 have supported the safety and efficacy of telemetry monitoring in those patients with suspected AMI who have “ruled in.”

The value of telemetry monitoring in the non-CCU setting for low-risk acute coronary syndromes has been questioned. Estrada et al10 observed 2,240 patients admitted to telemetry for various indications, including chest pain, syncope, congestive heart failure, and arrhythmias, and noted that the role of telemetry monitoring may be overestimated by physicians. These authors reported that telemetry monitoring rarely led to management changes and cardiologists perceived telemetry as a useful adjunct to care in only 12.6% of cases. In addition, < 1% of all patients admitted to telemetry had arrhythmias detected by telemetry that led to a transfer to a CCU.10

If a subset of patients in whom telemetry monitoring would not alter management could be identified on presentation to the emergency department, it may be possible to allocate available telemetry monitoring more efficiently. Clinical practice guidelines10 published in 1994 recommend that patients with unstable angina who present to the emergency department judged to be at high risk be admitted to the CCU. Those at intermediate risk can be admitted to telemetry units, and those at low risk can be further evaluated and even managed as outpatients.20However, studies2122 have described the outcome of missed MIs in patients sent home from the emergency department. Physicians are therefore reluctant to send patients home who present with low-risk suspected acute coronary syndromes. One hundred one patients (25%) of the total presenting with atypical chest pain, no associated symptoms, normal ECG findings, and normal laboratory values were admitted to telemetry in our study (Fig 3). Of these, no patients had MI by serial cardiac enzymes. Of the four patients who had arrhythmias (sinus bradycardias and tachycardias), there were no interventions. These low-risk patients, according to the 1994 guidelines and based on our results, could have been managed as outpatients. Patients with atypical chest pain and normal ECG findings (153 of 414 patients, 37%) appear to be the group that warrants hospital admission but does not gain benefit from telemetry monitoring. In this group, there were 3 of 153 patients (2%) who ruled-in by serial cardiac enzymes, which would have been missed if these patients were not admitted to the hospital. It should be noted that telemetry monitoring neither led to the diagnosis nor revealed events necessitating intervention in this subset of patients.

It is perceived that telemetry provides a higher level of care than can be provided on a general ward. However, this level of care is maintained by an increased cost of nursing, telemetry technicians, and equipment. Thus, unnecessary admissions to telemetry translate into unnecessary added costs.

A major limitation of this study is that it is an observational study. Furthermore, the study is limited by the small sample size (153 patients with atypical chest pain and normal ECG findings).

Additionally our findings do not apply to other indications for telemetry, including patients admitted through the emergency department for evaluation of syncope, new-onset arrhythmia, coronary artery disease awaiting revascularization, or those transferred from the catheterization laboratory, general medical floor, or ICU.

Although an ICU/CCU or telemetry unit is likely to provide better treatment for most patients, these beds represent a limited resource. Patients with atypical chest pain and normal ECG findings are a subset of patients in whom telemetry monitoring does not generally affect hospital course. Previous hospital admission guidelines suggested that these patients could be managed as outpatients. In fact, some of these patients do indeed prove to have MI. Thus, admission to the hospital and serial cardiac enzymes is warranted, even if telemetry is not.

Patients that present to the hospital with atypical chest pain and normal ECG findings are at low risk for life-threatening arrhythmias. In those who present without associated symptoms and with normal laboratory values, outpatient management can be considered an appropriate alternative to hospitalization.

Abbreviations: AMI = acute myocardial infarction; CCU = coronary care unit; CK = creatinine kinase; MI = myocardial infarction

Table Graphic Jump Location
Table 1. Patient Characteristics*
* 

Data are presented as No. (% of the study population) unless otherwise indicated.

Table Graphic Jump Location
Table 2. Presentation
Table Graphic Jump Location
Table 3. Events
Table Graphic Jump Location
Table 4. Interventions
Figure Jump LinkFigure 1. Rates of events and interventions according to chest pain.Grahic Jump Location
Figure Jump LinkFigure 2. Rates of events and interventions according to ECG abnormalities.Grahic Jump Location
Figure Jump LinkFigure 3. Events and interventions for selected presentations.Grahic Jump Location
Hill, J, Hampton, JR, Mitchell, JR (1978) A randomized trial of home-versus-hospital management for patients with suspected myocardial infarction.Lancet1,837-841. [PubMed]
 
Goldman, L Coronary care units: a prospective on their epidemiologic impact.Int J Cardiol1982;2,284-287. [PubMed] [CrossRef]
 
Fineberg, H, Scadden, D, Goldman, L, et al Care of patients with a low probability of acute myocardial infarction.N Engl J Med1984;310,1301-1306. [PubMed]
 
Grijseels, EW, Deckers, JW, Hoes, AW, et al Optimal use of coronary care units: a review.Prog Cardiovasc Dis1995;6,415-421
 
Tosteson, AN, Goldman, L, Udvarhelyi, IS, et al Cost-effectiveness of a coronary care unit versus an intermediate care unit for emergency department patients with chest pain.Circulation1996;94,143-150. [PubMed]
 
Pozen, MW, D’Agostino, RB, Mitchell, JB, et al The usefulness of a predictive instrument to reduce inappropriate admissions to the coronary care unit.Ann Intern Med1980;92,238-242. [PubMed]
 
Goldman, L, Weinberg, M, Weisberg, M, et al A computer-derived protocol to aid in the diagnosis of emergency room patients with chest pain.N Engl J Med1982;307,588-596. [PubMed]
 
Goldman, L, Cook, EF, Brand, DA, et al A computer protocol to predict myocardial infarction in the emergency department with chest pain.N Engl J Med1988;318,797-803. [PubMed]
 
Recommended guidelines for in-hospital cardiac monitoring of adults for detection of arrhythmia: Emergency Cardiac Care Committee members.J Am Coll Cardiol1991;18,1431-1433. [PubMed]
 
Estrada, CA, Prasad, NK, Rosman, HS, et al Outcomes of patients hospitalized to a telemetry unit.Am J Cardiol1994;74,357-362. [PubMed]
 
Estrada, CA, Prasad, NK, Rosman, HS, et al Role of telemetry monitoring in the non-intensive care unit.Am J Cardiol1995;76,960-965. [PubMed]
 
Slater, DK, Hlatky, MA, Mark, DB, et al Outcome in suspected acute myocardial infarction with normal or minimally abnormal admission electrocardiographic findings.Am J Cardiol1987;60,766-770. [PubMed]
 
Fuchs, R, Scheidt, S Improved criteria for admissions to coronary care units.JAMA1981;246,2037-2041. [PubMed]
 
Stark, ME, Vacek, JL The initial electrocardiogram during admission for myocardial infarction.Arch Intern Med1987;147,843-846. [PubMed]
 
Lloyd-Jones, DM, Camargo, CA, Lapuerta, P, et al Electrocardiographic and clinical predictors of acute myocardial infarction in patients with unstable angina pectoris.Am J Cardiol1998;81,1182-1186. [PubMed]
 
Fiebach, NH, Cook, EF, Lee, TH, et al Outcomes in patients with myocardial infarctions who are initially admitted to stepdown units: data from the Multicenter Chest Pain Study.Am J Med1990;89,15-20. [PubMed]
 
Gaspoz, JM, Lee, TH, Weisberg, MC, et al Outcome of patients who were admitted to a new short-stay unit to “rule-out” myocardial infarction.Am J Cardiol1991;68,145-149. [PubMed]
 
Sivaram, CA, Summers, JH, Ahmed, N Telemetry outside critical care units: patterns of utilization and influence on management decisions.Clin Cardiol1998;21,503-505. [PubMed]
 
Aufderheide, TP Arrhythmias associated with acute myocardial infarction and thrombolysis.Emerg Med Clin North Am1998;16,583-600. [PubMed]
 
Braunwald, E, Mark, DB, Jones, RH, et al. Unstable angina: diagnosis and management clinical practice guideline number 10 (amended). May 1, 1994; Agency for Health Care Policy and Research, National Heart, Lung, and Blood Institute, US Department of Health and Human Services. Rockville, MD: publication No. 94–0602.
 
McCarthy, BD, Beshansky, LR, D’Agostino, RB, et al Missed diagnoses of acute myocardial infarction in the emergency department: results from a multicenter study.Ann Emerg Med1993;22,579-582. [PubMed]
 
Kannel, WB, Abbot, RD Incidence and prognosis of unrecognized myocardial infarction.N Engl J Med1984;311,1144-1147. [PubMed]
 

Figures

Figure Jump LinkFigure 1. Rates of events and interventions according to chest pain.Grahic Jump Location
Figure Jump LinkFigure 2. Rates of events and interventions according to ECG abnormalities.Grahic Jump Location
Figure Jump LinkFigure 3. Events and interventions for selected presentations.Grahic Jump Location

Tables

Table Graphic Jump Location
Table 1. Patient Characteristics*
* 

Data are presented as No. (% of the study population) unless otherwise indicated.

Table Graphic Jump Location
Table 2. Presentation
Table Graphic Jump Location
Table 3. Events
Table Graphic Jump Location
Table 4. Interventions

References

Hill, J, Hampton, JR, Mitchell, JR (1978) A randomized trial of home-versus-hospital management for patients with suspected myocardial infarction.Lancet1,837-841. [PubMed]
 
Goldman, L Coronary care units: a prospective on their epidemiologic impact.Int J Cardiol1982;2,284-287. [PubMed] [CrossRef]
 
Fineberg, H, Scadden, D, Goldman, L, et al Care of patients with a low probability of acute myocardial infarction.N Engl J Med1984;310,1301-1306. [PubMed]
 
Grijseels, EW, Deckers, JW, Hoes, AW, et al Optimal use of coronary care units: a review.Prog Cardiovasc Dis1995;6,415-421
 
Tosteson, AN, Goldman, L, Udvarhelyi, IS, et al Cost-effectiveness of a coronary care unit versus an intermediate care unit for emergency department patients with chest pain.Circulation1996;94,143-150. [PubMed]
 
Pozen, MW, D’Agostino, RB, Mitchell, JB, et al The usefulness of a predictive instrument to reduce inappropriate admissions to the coronary care unit.Ann Intern Med1980;92,238-242. [PubMed]
 
Goldman, L, Weinberg, M, Weisberg, M, et al A computer-derived protocol to aid in the diagnosis of emergency room patients with chest pain.N Engl J Med1982;307,588-596. [PubMed]
 
Goldman, L, Cook, EF, Brand, DA, et al A computer protocol to predict myocardial infarction in the emergency department with chest pain.N Engl J Med1988;318,797-803. [PubMed]
 
Recommended guidelines for in-hospital cardiac monitoring of adults for detection of arrhythmia: Emergency Cardiac Care Committee members.J Am Coll Cardiol1991;18,1431-1433. [PubMed]
 
Estrada, CA, Prasad, NK, Rosman, HS, et al Outcomes of patients hospitalized to a telemetry unit.Am J Cardiol1994;74,357-362. [PubMed]
 
Estrada, CA, Prasad, NK, Rosman, HS, et al Role of telemetry monitoring in the non-intensive care unit.Am J Cardiol1995;76,960-965. [PubMed]
 
Slater, DK, Hlatky, MA, Mark, DB, et al Outcome in suspected acute myocardial infarction with normal or minimally abnormal admission electrocardiographic findings.Am J Cardiol1987;60,766-770. [PubMed]
 
Fuchs, R, Scheidt, S Improved criteria for admissions to coronary care units.JAMA1981;246,2037-2041. [PubMed]
 
Stark, ME, Vacek, JL The initial electrocardiogram during admission for myocardial infarction.Arch Intern Med1987;147,843-846. [PubMed]
 
Lloyd-Jones, DM, Camargo, CA, Lapuerta, P, et al Electrocardiographic and clinical predictors of acute myocardial infarction in patients with unstable angina pectoris.Am J Cardiol1998;81,1182-1186. [PubMed]
 
Fiebach, NH, Cook, EF, Lee, TH, et al Outcomes in patients with myocardial infarctions who are initially admitted to stepdown units: data from the Multicenter Chest Pain Study.Am J Med1990;89,15-20. [PubMed]
 
Gaspoz, JM, Lee, TH, Weisberg, MC, et al Outcome of patients who were admitted to a new short-stay unit to “rule-out” myocardial infarction.Am J Cardiol1991;68,145-149. [PubMed]
 
Sivaram, CA, Summers, JH, Ahmed, N Telemetry outside critical care units: patterns of utilization and influence on management decisions.Clin Cardiol1998;21,503-505. [PubMed]
 
Aufderheide, TP Arrhythmias associated with acute myocardial infarction and thrombolysis.Emerg Med Clin North Am1998;16,583-600. [PubMed]
 
Braunwald, E, Mark, DB, Jones, RH, et al. Unstable angina: diagnosis and management clinical practice guideline number 10 (amended). May 1, 1994; Agency for Health Care Policy and Research, National Heart, Lung, and Blood Institute, US Department of Health and Human Services. Rockville, MD: publication No. 94–0602.
 
McCarthy, BD, Beshansky, LR, D’Agostino, RB, et al Missed diagnoses of acute myocardial infarction in the emergency department: results from a multicenter study.Ann Emerg Med1993;22,579-582. [PubMed]
 
Kannel, WB, Abbot, RD Incidence and prognosis of unrecognized myocardial infarction.N Engl J Med1984;311,1144-1147. [PubMed]
 
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