Chest pain risk Stratification...A Clinical Prediction Rule

[Ace844]

Study objective

Current risk stratification tools do not identify very-low-risk patients who can be safely discharged without prolonged emergency department (ED) observation, expensive rule-out protocols, or provocative testing. We seek to develop a clinical prediction rule applicable within 2 hours of ED arrival that would miss fewer than 2% of acute coronary syndrome patients and allow discharge within 2 to 3 hours for at least 30% of patients without acute coronary syndrome.

Methods

This prospective, cohort study enrolled consenting eligible subjects at least 25 years old at a single site. At 30 days, investigators assigned a diagnosis of acute coronary syndrome or no acute coronary syndrome according to predefined explicit definitions. A recursive partitioning model included risk factors, pain characteristics, physical and ECG findings, and cardiac marker results.

Results

Of 769 patients studied, 77 (10.0%) had acute myocardial infarction and 88 (11.4%) definite unstable angina. We derived a clinical prediction rule that was 98.8% sensitive and 32.5% specific. Patients have very low risk of acute coronary syndrome if they have a normal initial ECG, no previous ischemic chest pain, and age younger than 40 years. In addition, patients at least 40 years old and with a normal ECG result, no previous ischemic chest pain, and low-risk pain characteristics have very low risk if they have an initial creatine kinase-MB (CK-MB) less than 3.0 μg/L or an initial CK-MB greater than or equal to 3.0 μg/L but no ECG or serum-marker increase at 2 hours.

Conclusion

The Vancouver Chest Pain Rule for early discharge defines a group of patients who can be safely discharged after a brief evaluation in the ED. Prospective validation is needed.

Editor's Capsule Summary

What is already known on this topic

Although several algorithms and computer programs have been developed for emergency department (ED) patients with potential acute coronary syndrome, none has achieved sufficient accuracy to allow safe and rapid discharge of ED chest pain patients.

What question this study addressed

This study developed a clinical decision rule to identify low-risk ED chest pain patients who can be safely discharged within 2 hours of presentation. This study did not prospectively evaluate this rule.

What this study adds to our knowledge

Not surprisingly, this study found that patients younger than 40 years and with normal initial ECG results and no previous ischemic chest pain were at very low risk of acute coronary syndrome. Additionally, patients older than 40 years had low-risk if they had a normal ECG result, no previous ischemic chest pain, low risk chest pain characteristics, and an initial creatine kinase-MB (CK-MB) less than 3.0 ug/L or an initial CK-MB greater than 3.0 ug/L but without an increase or ECG changes within 2 hours.

How this might change clinical practice

This derivation study should not change clinical practice because it has not yet been validated. It does, however, provide support for the general belief that young patients with a normal ECG result and no cardiac risk factors are at very low risk of an adverse cardiovascular event.

Introduction

Background

Approximately 15% to 25% of patients who present to emergency departments (EDs) with undifferentiated chest pain prove to have acute coronary syndrome within 30 days. US data suggest that 2.1% of patients with acute myocardial infarction and 2.3% of patients with unstable angina are initially misdiagnosed,1 whereas a recent Canadian study identified 11 of 241 (4.6%) missed cases of acute myocardial infarction and 10 of 157 (6.4%) cases of missed unstable angina.2 Chest pain units reduce the rate of missed myocardial infarction but do so in part by including very-low-risk patients in extensive rule-out myocardial infarction protocols.3-5

Many investigators have developed chest pain risk stratification tools. Goldman et al6 developed a clinical/ECG algorithm that identified patients with less than 7% risk of acute myocardial infarction. Limkakeng et al7 subsequently found that 4.9% of patients who had low-risk Goldman criteria and a negative initial troponin I assay result experienced death, acute myocardial infarction, or revascularization within 30 days. Pozen et al8,9 developed a 7-item predictive equation that reduced coronary care unit admissions but not inappropriate discharges. Selker et al10-12 modified this to create the acute cardiac ischemia time-insensitive predictive instrument (ACI-TIPI), which defined low risk as less than 10% chance of acute coronary syndrome. The Erlanger protocol13 is an intense 2-hour assessment that includes serial ECGs and creatine kinase-MB (CK-MB) and troponin measurements, but it does not define a subset of patients who can forgo nuclear stress testing. The American Heart Association/Agency for Health Care Policy and Research guidelines suggest early discharge only for patients with “evidence†of an alternate diagnosis.14 Unfortunately, few patients clearly fall into this category. Our own study of patients with chest pain at 2 Vancouver hospitals identified that 5.4% of patients with acute coronary syndrome were discharged from the ED without a diagnosis or planned investigations and only 30% of those without acute coronary syndrome were discharged less than three hours after ED admission.2

Importance

Clinical prediction rules are decisionmaking tools for clinicians that contain elements of the medical history, physical examination, and simple diagnostic tests.15 An objective clinical prediction rule to identify very-low-risk patients with chest pain who can be safely discharged without prolonged ED observation, expensive rule-out protocols, or provocative testing is needed. Such a rule would help reduce emergency crowding, minimize patient inconvenience, and improve cost-effectiveness of acute coronary syndrome diagnostic testing.

Goals of This Investigation

Our specific objective was to develop a clinical prediction rule that would improve on current practice by identifying patients with chest pain who are safe for discharge after 2 hours of ED evaluation. The rule will miss fewer than 2% of acute coronary syndrome patients and allow discharge within 2 to 3 hours of at least 30% of patients without acute coronary syndrome.

Materials and Methods

Study Design

Using established methodology for clinical prediction rules,15-17 this prospective cohort study was conducted in 2 separate periods between June 29, 2000, and January 24, 2003, when research assistants were funded.

Setting and Selection of Participants

Patients presenting to St. Paul's Hospital, an urban tertiary care ED, with a primary complaint of anterior or lateral chest pain were eligible for the study. Research assistants obtained informed consent and enrolled eligible patients between 7 am and 10 pm 7 days per week. Patients were excluded if they were younger than 25 years, had a clear traumatic or radiologically evident cause, were enrolled in the study in the previous 30 days, had a terminal noncardiac illness, had severe communication problems, were without a fixed address in the province of British Columbia, or were without available telephone contact. The Providence Health Care Research Ethics Board approved the study protocol.

Data Collection and Processing

This report conforms to the published standard reporting guidelines for studies evaluating risk stratification of ED patients with potential acute coronary syndromes,18 although they were developed before this publication. A total of 123 potential predictor variables were screened (Figure 1). During the first 2 hours of the index visit, research assistants documented vital signs every 30 minutes, initiated ST-segment monitoring, and ensured that serial ECGs (0, 1, and 2 hours) were performed. Cardiac markers at 0 and 2 hours were evaluated on several platforms: creatine phosphokinase (Access, Beckman Coulter, Mississauga, Ontario, Canada), troponin I (Access and Biosite Triage, San Diego, CA), troponin T (Roche Elecsys, Hoffman LaRoche, LaValle, Quebec, Canada), myoglobin (Biosite Triage), and CK-MB (Biosite Triage). Serum markers ordered by research protocol but not for clinical purposes were unavailable to clinicians. They acquired chest pain characteristics, patient risk factors, and medical history independently of clinicians and recorded physical findings determined by emergency physicians, provisional emergency diagnosis, admission and discharge times, consultations, cardiac medications administered, other cardiac investigations, hospital discharge diagnoses, and predefined adverse events.

Figure 1

List of all predictors collected for possible inclusion in the prediction rule. Those meeting criteria for inclusion in the model are identified with an asterisk.

AMI, Acute myocardial infarction; Hx, history; MI, myocardial infarction; PCI, percutaneous coronary intervention; CABG, coronary artery bypass graft; CVA, cerebrovascular accident; TIA, transient ischemic attack; ASA, acetyl salicylic acid; ACE, angiotensin-converting enzyme.

Pain and Associated Symptom Characteristics

Age

Sex

Chest pain present on arrival?

Chest pain continue at rest?

Number of episodes in previous 24 hours

Number of episodes in previous week

Maximum duration of previous episode

Diaphoresis

Weakness

Shortness of breath

Nausea

Vomiting

Palpitations

Syncope

Dizziness/lightheadedness

Radiation to left arm/shoulder

Radiation to right arm/shoulder

Radiation to back

Radiation to neck

Radiation to jaw

Radiation to abdomen

Radiation to lower limb

Pain center of chest

Pain in left lateral chest

Pain in right anterior chest

Pain in right lateral chest

Most prominent character of pain

Heavy chest discomfort

Maximum discomfort level

Pain diagnosed in past as AMI

Pain diagnosed in past as angina

Pain diagnosed in past as either AMI or angina

Pain worse with deep breaths

Pain worse with movement

Pain worse in different positions

Did pain improve within 5 minutes of nitroglycerin?

Did pain improve within 5 minutes of oxygen?

Did pain improve within 5 minutes of liquid antacid?

During 2 hours, did pain relieve and not return?

During 2 hours, did pain continue?

During 2 hours, did pain come and go?

Physical Examination

Chest clear

Crackles at bases

Crackles to scapulae

Wheezes

Heart sounds normal

Systolic murmur

Diastolic murmur

S3

S4

Carotid pulses equal with no bruit

Radial pulses equal

Chest tenderness reproducing pain

Right arm systolic pressure, left arm systolic pressure

Systolic pressure <90 mm Hg in 2 hours

Bradycardia <50 beats/min in 2 hours

Tachycardia >100 beats/min in 2 hours

Jugular venous pressure

Risk Factors

Regular smoker

Hx diabetes

Hx hypertension

Hx hyperlipidemia

Parent or sibling with heart attack <65 years

Ratio of weight (kg) over height (cm)

Recreational substance use

Alcohol use in past 24 hours

Cocaine use in 48 hours

ECG Findings

First ECG result normal

First ECG with only T-wave flattening

Aggregate of ECGs no ischemic changes

2-h ST segment monitoring (any ST elevation or ST depression)

Laboratory Markers

0-h CPK (Standard)

2-h CPK (Standard)

Difference in CPK (2 h–0 h) (Standard)

0-h Tn I or T (Standard)

2-h Tn I or T (Standard)

Difference in Tn I or T (2 h–0 h) (Standard)

0-h CRP

0-h CK-MB (Biosite)

2-h CK-MB

Difference in CK-MB (2 h–0 hour) (Biosite)

0-h TnI (Biosite)

2-h TnI (Biosite)

Difference in TnI (2 h–0 h) (Biosite)

0-h Myoglobin (Biosite)

2-h Myoglobin (Biosite)

Difference in myoglobin (2 h–0 h) (Biosite)

Cardiovascular History

Previous angina

Previous MI

Previous cardiac arrest

Previous angiogram yes and previous lesion >50%

Previous angiogram and no lesion >50%

Previous PCI

Previous peripheral vascular surgery

Previous CABG

Previous CVA

Previous TIA

Previous ventricular arrhythmia

Previous atrial arrhythmia

Previous unknown arrhythmia

Medications

Previous ASA

Previous other antiplatelets

Previous calcium-channel blockers

Previous ACE inhibitor

Previous digitalis

Previous β-blocker

Previous Coumadin

Previous low-molecular-weight heparin

Previous nitrates

Previous lipid-lowering agents

Previous antiarrhythmics

Previous diuretics

Previous antihypertensives

Adverse events included death, tachycardia requiring intervention, bradycardia requiring intervention, assisted ventilations, proven pulmonary thromboembolism, proven aortic aneurysm or dissection, new congestive heart failure requiring intravenous therapy, hypotension requiring intervention, chest compressions, percutaneous intervention, and coronary artery bypass grafting.

Interobserver reliability was estimated by having a second emergency physician blindly evaluate 95 patients.

At 30 days, research staff telephoned patients to review current medications, physician visits, and hospital visits. Reports of all diagnostic tests performed during the 30 days in any setting were obtained, and relevant physicians were contacted for confirmation of any new diagnoses. In cases in which patient contact was lost, other city hospital records were reviewed to identify hospital visits, procedures, and new diagnoses, and the study list was cross-referenced against the British Columbia Death Registry.

Outcome Measures

Investigators used predefined explicit criteria to assign a 30-day outcome diagnosis of acute myocardial infarction, definite unstable angina, possible unstable angina, or no acute coronary syndrome. The primary outcome was definite acute coronary syndrome (acute myocardial infarction or definite unstable angina). The diagnosis of acute myocardial infarction required any one of the following: (1) a CK-MB increase definite for acute myocardial infarction based on the specific hospital criteria or troponin I level greater than or equal to1.0 μg/L; (2) a troponin I increase (>0.1 μg/L but <1.0 μg/L) with dynamic ECG changes consistent with ischemia, a coronary angiogram with greater than 70% lesion, a positive stress test result (radionuclide scan, echocardiogram, or ECG), or urgent revascularization; (3) ECG evolution consistent with acute myocardial infarction; (4) fibrinolytic therapy or primary angioplasty and a clinical diagnosis of acute myocardial infarction; or (5) death with no other definite cause found in pre- or postmorbid investigation. The diagnosis of definite unstable angina required rest pain greater than or equal to 20 minutes and at least 1 of the following related to the presenting symptoms: (1) troponin increase 0.1 to 0.99 μg/L but no other acute myocardial infarction criteria, (2) dynamic ECG changes consistent with ischemia in 2 contiguous leads (dynamic ST depression >0.5 mm or dynamic deep T-wave inversion) but no persistent ST elevation, (3) a coronary angiogram with greater than 70% lesion plus hospital admission for acute coronary syndrome, or (4) a positive stress test result (radionuclide scan, echo, or ECG stress test) plus admission for acute coronary syndrome.

If a diagnosis could not be assigned or if an investigator assigned a diagnosis of “no acute coronary syndrome†despite objective criteria (eg, positive troponin assay result), or if an investigator assigned a diagnosis of “definite unstable angina†based only on a positive troponin assay result, 2 cardiologist coinvestigators independently reviewed all clinical data and assigned an adjudicated outcome diagnosis. If necessary, final diagnosis was based on agreement of any 2 adjudicators and the principal investigator. If all 3 disagreed, the final outcome was the most significant diagnosis.

Investigators reviewed all ECGs in a structured format to identify T-wave flattening, T-inversion in 2 contiguous leads, ST depression (≥0.05 mV) in 2 contiguous leads, ST-elevation (≥0.1 mV in limb leads or ≥0.2 mV in precordial leads), and the presence of left bundle-branch block, paced rhythm, or left ventricular hypertrophy. In addition, investigators blinded to final outcome reviewed all ECGs for each patient and recorded their impression of the likelihood of ischemia. Evaluation of all available ECGs was used for outcome determination. Evaluation of ECGs up to 2 hours was used as predictors in the rule.

Primary Data Analysis

Data were collected on specific study data forms and entered into an Oracle database (Oracle Corporation, Redwood City, CA, USA). Proportions, medians, means, and SDs were calculated and multiple clinical prediction rules were derived using the S-Plus (Insightful Corp., Seattle, WA) “rpart†recursive partitioning module. The algorithm was run using all of the default options except that a 10:1 loss was specified for missed acute coronary syndrome patients versus missed non-acute coronary syndrome patients. This higher penalty on missed acute coronary syndrome patients encouraged the algorithm to choose splits that maximized sensitivity and so reduce the complexity of the model. Cut points for continuous predictors were chosen initially by the algorithm and then rounded to convenient values by the investigators, and the patients were reclassified based on rounded values. Predictor variables were allowed in the model if they were univariately associated with the primary outcome (P<.2). In addition, variables subjected to interpretation (medical history and physical examination findings) were included if they were reliable (lower bound of confidence [95%] was at least 0.4 for the reliability measure; prevalence and bias adjusted κ coefficient for dichotomous variables and intraclass correlation coefficient for continuous variables).

Investigators reviewed each derived rule for clinical relevance. Nodes with small numbers of patients were reaggregated and recursive partitioning was reinstituted to simplify the branch points. This modification, although not previously described, makes clinical sense and reduces the chance of selecting a nonoptimal splitting variable when partitioning groups with smaller sample sizes. The simplest, most specific prediction rule that met the goal of sensitivity greater than 98% was chosen.

We do not report confidence intervals (CI) around the sensitivity and specificity values, because these values arise as a consequence of the rule development process, not as an evaluation of a fixed rule. Specifically, the sampling variability in the estimated sensitivity cannot be assessed because different samples lead to different rules (all of which are forced to satisfy the “at least 98% sensitive†criterion). Meaningful CIs will be obtained in the validation phase.

The sample size of 800 patients was chosen so that equal numbers would be used in rule development and in subsequent rule validation. In the validation phase, the aim is to confirm that the sensitivity of the rule exceeds current practice (ie, to obtain a lower bound on the 95% CI for sensitivity of acute coronary syndrome detection that is no less than 0.95). Assuming that the true sensitivity is of the rule is 0.98, roughly 187 positive cases (800 patients in total) are needed to achieve this lower bound with 90% probability.

Results

We enrolled 819 patients and subsequently excluded 50 patients from analysis, 31 who met exclusion criteria and 19 who were lost to follow-up. Of the 19 lost to follow-up, 14 were known to be alive at subsequent hospital visits, and the other 5 did not appear in the provincial death registry. Table 1 summarizes baseline characteristics and outcomes for the 769 patients analyzed showing 30-day diagnosis was acute myocardial infarction in 77 (10.0%) and definite unstable angina in 88 (11.4%). Documented adverse events related or unrelated to acute coronary syndrome included tachycardia (35), bradycardia (14), assisted ventilations (4), proven pulmonary thromboembolism (5), proven thoracic aortic aneurysm or dissection (0), new congestive heart failure requiring intravenous therapy (12), hypotension requiring intervention (9), and chest compressions (2). Eighty-three patients had percutaneous intervention and 31 had coronary artery bypass grafting within 30 days.

Table 1. Baseline characteristics and outcomes of patient cohort (n=769).

Characteristic Value

Mean age (y±SD) 58±14

Age range, y 25–93

% Male 62.0

% With diabetes 16.6

% Smokers 30.4

% With hypertension 38.2

% With hyperlipidemia 36.2

Median time from symptom onset to arrival in minutes (quartiles) 104 (52.5, 262)

Mean systolic BP on arrival (mm Hg±SD) 142±27

Mean pulse rate on arrival (beats/min±SD) 81±20

Mean respiratory rate on arrival (breaths/min±SD) 19±3

% With past MI 24.2

% With past angina 35.9

% With abnormal initial ECG result 30.1

% With pain similar to past MI or angina 27.0

% With pain radiating to left arm, jaw, or neck 59.0

% With pain increasing with a deep breath 32.8

% With chest pressure reproducing pain 16.6

% with CK-MB <3.0 μg/L on arrival 63.5

% With any increase in Tn during 2 hours 19.5

% With any increase in CK-MB during 2 hours 41.8

30-Day outcomes (%)

Definite AMI 77 (10.0)

Definite unstable angina 88 (11.4)

Possible unstable angina 29 (3.7)

AE but no acute coronary syndrome 32 (4.2)

No acute coronary syndrome or adverse event 543 (70.6)

Overall 30-day mortality 9 (1.2)

Mortality with AMI (%) 5 (6.5)

Mortality with definite unstable angina (%) 1 (1.0)

Mortality with possible unstable angina (%) 0

Mortality with no acute coronary syndrome but an adverse event (%) 2 (6.3)

Mortality with no acute coronary syndrome and no adverse event (%) 1 (0.2)

Of the 123 possible predictor variables screened, 48 were retained for entry into the recursive partitioning algorithm. Table 2 lists the variables selected for the rule by diagnostic groups with respective univariate statistics and P values. These variables include a normal ECG result (which could include T-wave flattening but no ST deviation or T-wave inversion), age, previous ischemic pain, 3 pain descriptors, 1 physical finding, and both CK-MB and troponin results. Reliability measures (95% CI) for clinical subjective variables were pain radiates to neck, 0.68 (95% CI 0.54 to 0.83); pain radiates to jaw, 0.81 (95% CI 0.69 to 0.93); pain radiates to left arm, 0.79 (95% CI 0.67 to 0.91); and chest tenderness reproduces pain, 0.63 (95% CI 0.45 to 0.80).

Table 2. Univariate predictive statistics for predictors used in the rule.

Predictor Acute Coronary Syndrome No Acute Coronary Syndrome Odds Ratio 95% CI for Odds Ratio

N (all patients) 165 604

First ECG result not normal† 57.6 % 22.6% 4.65 3.2–6.7

Age ≥40 y 99.4% 87.9% 22.55 3.8–908.0

Previous MI 35.8% 21.0% 2.09 1.4–3.1

Previous angina 53.9% 31.0% 2.61 1.8–3.8

Previous nitrate use 48.5% 23.8% 3.01 2.1–4.4

Previous angina, MI, or nitrate use 66.7% 40.6% 2.93 2.0–4.3

Pain radiates to neck 35.2% 24.3% 1.69 1.1–2.5

Pain radiates to jaw 24.9 % 12.3 % 2.37 1.5–3.7

Pain radiates to left arm 57.0% 43.4% 1.73 1.2–2.5

Pain does not increases with deep breath 78.2% 64.2% 1.99 1.3–3.1

Chest tenderness does not reproduce pain 94.3% 80.5% 4.04 2.0–9.3

Pain radiates to neck, jaw, or left arm AND pain does not increase with deep breath or palpation 48.4% 25.6% 2.73 1.9–4.0

0-h CK-MB ≥3.0 μg/L 56.3% 31.2% 2.84 2.0–4.1

CK-MB increase during 2 h 46.7% 40.4% 1.29 0.89–1.9

Tn increase during 2 h 35.5% 15.1% 3.10 2.0–4.7

CK-MB or Tn increase during 2 h 60.5% 48.2% 1.65 1.1–2.4

Possible ischemic changes in ECGs during 2 h in all patients 68.9% 33.5% 1.22 0.44–2.9

ST-T changes in 1- or 2-h ECG in patients with initial normal ECG (n=539) 42.9% 20.7% 2.87 1.7–4.8

Predictors with an odds ratio >1 indicate that the predictor is associated with an increased risk of acute coronary syndrome.

†

“ECG normal†is defined as no ST-segment deviation and no T-wave inversion regardless of conditions such as left ventricular hypertrophy or left bundle-branch block. T-wave flattening was not defined as abnormal.

Figure 2 outlines the classification tree, and Figure 3 is a simplified clinical algorithm of the chest pain prediction rule. In this development cohort, the rule is 98.8% sensitive, identifying all but 2 patients with unstable angina, and would have allowed the appropriate discharge of 32.5% of patients without acute coronary syndrome using data collected within 2 hours of arrival (Table 3). Of those identified for discharge, 89.4% would be determined with information available at presentation, most without any laboratory testing, and the remainder would be determined safe for discharge based on repeat ECG, CK-MB, and troponin at 2 hours. This potentially allows the early discharge process to be divided into 2 sequential stages.

Figure 2. Decision tree.

Figure 3. Chest pain early discharge rule.

Table 3. Diagnostic accuracy of the rule.

Definite Acute Coronary Syndrome No Definite Acute Coronary Syndrome

Unsuitable for early discharge 163 408 571

Meet rule criteria for early discharge 2 196 198

165 604 769

Sensitivity 98.8%; specificity 32.5%; positive predictive value 28.5%; negative predictive value 99.0%.

The 2 missed patients were subsequently diagnosed with unstable angina. A 66-year-old woman was diagnosed 8 days later by outpatient nuclide stress testing, with no subsequent admission or adverse event. The other was a 52-year-old patient with a clear history of new and accelerating angina before rest pain who was treated medically for a single critical lesion not amenable to intervention. During validation, we will clarify the definition of past angina to include a recent history of typical angina of effort whether diagnosed or not.

Limitations

Although we used accepted and validated methodology,15 the Vancouver Chest Pain Prediction Rule was developed in 1 cohort of patients in a single center. We are currently beginning validation of the rule, and it will subsequently require evaluation of implementation in multiple centers. Our criterion standard for definite acute coronary syndrome was not based on mandated investigations but on a careful evaluation of all tests and visits during 30 days. It is possible that we missed some patients with silent events. The cohort was collected during day and evening hours and will require validation in patients presenting at all hours of the day. The rule is modestly complex and may be difficult to remember, which could limit its use by clinicians. However, the rule is largely intuitive, and simple memory aids (eg, pocket cards or PDA algorithms) will enhance implementation once the rule is validated. It is important to note that although our focus was on identifying patients with very low risk of acute coronary syndrome, no patients were missed with pulmonary embolism or aortic dissection. Suspicion of other life-threatening conditions requires appropriate, independent investigations. In retrospect, this rule development should have included patients 24 hours per day. Ideally, the study would be strengthened by mandating initial and 30-day imaging studies to improve the criterion standard of acute coronary syndrome. The cost implications of the Vancouver Chest Pain Rule are not yet known.

Discussion

Patients who present to the ED with chest pain fall into 3 categories: those with objective ischemia who need admission and treatment, those with a clear noncardiac cause, and those who require a diagnostic process to rule out acute coronary syndrome and other life-threatening conditions. The Vancouver Chest Pain Rule identifies 32.5% of patients who do not have acute coronary syndrome using information available in the first 2 hours of the ED visit. These very-low-risk patients are identified with minimal error, in fact including only 1.2% of those who do have unstable angina or acute myocardial infarction. This information can be integrated into the decision framework of the emergency physician who continually evaluates patients for safe and appropriate disposition.

This prediction rule is different from previous risk stratification tools. In 1988, Goldman et al6 developed a clinical/ECG algorithm that identified patients with less than 7% risk of acute myocardial infarction. This was not designed to detect patients with unstable angina and it did not improve disposition decisions relative to experienced clinician judgment alone. Limkakeng et al7 later reported that 4.9% of patients with low-risk Goldman criteria and a negative initial troponin I level experienced death, acute myocardial infarction, and revascularization within 30 days. Lee et al19 and Goldman et al20 subsequently developed a strategy to identify patients unlikely to have acute myocardial infarction and criteria to identify patients who need coronary care unit admission. These criteria required 12 to 24 hours of observation and did not facilitate early ED disposition decisions.21 Pozen et al8 developed and tested a predictive equation using 7 clinical and ECG variables. After application of this instrument, inappropriate coronary care unit admissions fell from 24% to 17%, but the 3% inappropriate discharge rate was unchanged. Selker et al10-12 modified the Pozen et al8 equation and linked it to ECG findings, creating an electronic tool called the ACI-TIPI. This tool increased the rate of appropriate discharges by unsupervised residents but did not change the performance of attending physicians. Of note, ACI-TIPI defines low risk as less than 10% chance of acute myocardial infarction or unstable angina, and few clinicians will discharge patients with this level of risk.22

In 1992, Baxt23 and Baxt and Skora24 “trained†neural networks to recognize acute myocardial infarction and, in 1993, Jonsbu et al25 developed a sensitive computer-derived algorithm. Doyle et al26 studied 9 algorithms but found none that improved clinical decisionmaking. The recently described Thrombolysis in Myocardial Infarction (TIMI) Risk score27 is an excellent stratification tool but was derived from studies of patients with objective evidence of acute coronary syndrome and has not been validated in undifferentiated ED patients with chest discomfort. The Erlanger protocol28 is an intense 2-hour assessment that includes serial ECGs, 2 CK-MB and troponin measurements, clinical judgment, and nuclear stress testing. It is the most detailed published protocol designed to facilitate early discharge but requires nuclear imaging to increase sensitivity from 80% to 99%. None of the above stratification tools help clinicians identify patients who are safe to discharge after a brief ED evaluation.

Recent American College of Cardiology/American Heart Association14 guidelines recommend that all patients with a compatible history have serial marker testing until 9 hours after symptom onset, followed by provocative testing. Applying this guideline in the ED, where most patients have ill-defined chest discomfort, could greatly increase diagnostic and ED bed utilization without a corresponding improvement in patient outcomes. The ED/AHCPR guidelines and the Toronto Heart Centre ACS Guidelines29 recommend excluding patients with discomfort because of other causes from the diagnostic pathway, but neither suggests a process for identifying these patients.

The Vancouver Chest Pain Rule is unique in its ability to identify very-low-risk patients who are suitable for early discharge. It is also unique in that it identifies patients in a clinically logical stepwise process with a minimum of investigations. First, age, initial history, and ECG findings identified 56 of 198 patients who ultimately meet rule criteria. A further 121 patients were identified based on initial CK-MB and low-risk pain characteristics. The last 21 patients were identified by the absence of changes in the ECG or serum markers during 2 hours. If disposition according to the rule was implemented in this stepwise manner, ED lengths of stay and investigational costs could be reduced substantially in many settings.

Some would argue that the age criteria might result in missing younger patients with myocardial infarction, but age is in fact a powerful predictor, and the low-risk group younger than 40 years is also defined by a near-normal ECG and the absence of past myocardial infarction or angina. Marsan et al30 recently studied 1032 patients younger than 40 years and presenting with chest pain and found that those with no cardiac history and either no cardiac risk factors or a normal ECG result had less than 0.5% 30-day risk of acute coronary syndrome.

We found that CK-MB at a low threshold was consistently a better discriminator than any level of troponin, surprising because many studies suggest troponin is the superior marker. Our findings are not unique, and at least 1 other investigator has reported that CK-MB was more predictive of acute coronary syndrome than troponin early in the patient's presentation.31 Laboratory technicians used the Triage (Biosite) point-of-care device, and we attribute the greater discriminatory power of CK-MB over troponin to its better analytic performance within the normal range. The reported 99th percentile for troponin on the Triage point-of-care device is actually the detection limit (0.19 μg/L), whereas the 95th percentile for CK-MB (usual cutoff) is well above the detection limit (0.75 μg/L). de Winter et al32 determined that an increase in CK-MBmass greater than 2 μg/L represents the critical difference between 2 results for the detection of myocardial damage. We hypothesize that it is the absence of a critical increase over baseline value (median 1.5 μg/L) that underlies the discriminatory power of a CK-MB level less than 3 μg/L. In comparison, present troponin methods do not permit the detection of a change within the normal range.

An early discharge strategy such as the one developed here defines patients safe for early discharge and reduces the number who require more definitive testing but also defines the companion group of patients who are not clearly “safe†and require further investigations. To maximize diagnostic efficiency, a more prolonged “chest pain unit†rule-out strategy should be applied to patients without objective ischemia who do not meet early discharge criteria.

In summary, the Vancouver Chest Pain Rule defines a group of chest pain patients who can be safely discharged from the ED in the first few hours after arrival. If validated in an independent cohort, it will improve the process of diagnostic decisionmaking in patients presenting with chest pain.

The authors are grateful for the support and data supplied by the physicians and nurses at St. Paul's Hospital, Vancouver, Canada, and for the dedication of Patti Lawson, BA, and Courtney Barker.

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From the University of British Columbia (Christenson, Innes, McKnight, Thompson, Wong, Yu, Boychuk, Grafstein, Rosenberg, Gin, Anis, Singer); St. Paul's Hospital (Christenson, Innes, Thompson, Boychuk, Grafstein, Rosenberg); Vancouver Hospital (McKnight, Gin); and the Center for Health Evaluation and Outcome Sciences (Christenson, Innes, Grafstein, Wong, Yu, Anis, Singer) Vancouver, British Columbia, Canada

Address for correspondence: Jim Christenson, MD, Department of Emergency Medicine, St. Paul's Hospital, 1081 Burrard Street, Vancouver, British Columbia V6Z 1Y6, Canada; 604-806-8985, fax 604-806-8798

Supervising editor: Judd E. Hollander, MD

Author contributions: DM, HR, EY, EG, FR, AA, and JS helped design the study, analyzed the data, and reviewed the manuscript. BB helped design the study, collected data, and reviewed the manuscript. JMC, GI, and CRT conceived and helped design the study, collected data, and wrote the manuscript. JMC takes responsibility for the paper as a whole.

Funding and support: Canadian Institutes of Health research grant MOP 53102 and Heart and Stroke Foundation of British Columbia and Yukon Grant. Materials for analysis of some laboratory testing were donated by Biosite.PII: S0196-0644(05)01440-X doi:10.1016/j.annemergmed.2005.08.007 © 2006 American College of Emergency Physicians. Published by Elsevier Inc. All rights reserved.

[Ace844]

Jeeze, I'm surprised that you guys don't really use "risk statification" as an assessment tool....Like for instance, don't you all feel it would be useful to "startify" a patient whom yoiu were considering "terfing to BLS"?!?!?!? The examples abound... What do you all think?

Out here,

ACE844

[AZCEP]

Anyone that is doing an assessment is performing risk stratification, although to a lesser extent.

The 12 lead ECG and knowledge of the TIMI score are the most common tools that I use. The patient's history/medications also come into play, but again that is part of the initial assessment. I would rather "over-triage" someone to a PCI facility that isn't having the big one, than the other way around.

Keep the cardiologists in business.

[Dustdevil]

Anyone that is doing an assessment is performing risk stratification, although to a lesser extent.

Agreed. The majority of the time, my 12-lead is going to tell me what I need to know. If it doesn't, then I still maintain a high index of suspicion. I certainly wouldn't delay my 12-lead by playing a numbers game. And if the 12-lead results are positive, the whole point of the numbers game becomes moot.

[Ridryder 911]

Agreed, mainly is it is going to be Hx.. hx.. hx... 12 lead will determine initial treatment. STEMI from Non-STEMI enough hopefully I can either get them thrombolyzed or straight to cath lab...

Most of this is done simultaneously, maybe not in this format though.. I am surprised they are so interested in Tropin I.. yes, it is the best lab marker, it has hx of delay marker up to 6 hrs. ...

Thanks Ace...

Be safe,

R/R 911

[Ace844]

Agreed. The majority of the time, my 12-lead is going to tell me what I need to know. If it doesn't, then I still maintain a high index of suspicion. I certainly wouldn't delay my 12-lead by playing a numbers game. And if the 12-lead results are positive, the whole point of the numbers game becomes moot.

Agreed, mainly is it is going to be Hx.. hx.. hx... 12 lead will determine initial treatment. STEMI from Non-STEMI enough hopefully I can either get them thrombolyzed or straight to cath lab...

Most of this is done simultaneously, maybe not in this format though.. I am surprised they are so interested in Tropin I.. yes, it is the best lab marker, it has hx of delay marker up to 6 hrs. ...

Thanks Ace...

Be safe,

R/R 911

That brings up a good point that I'd like to hear some of you address. How has the field use of 12 leads affected your use of narcotics for chest pain? If the EKG is negative for signs of an MI, does that make analgesia contraindicated in your protocols or judgement, or the judgement of your online medical control? Or do you still treat the pain the same way as you would have otherwise without a 12 lead?

"DustDevil, Rid, AZEP, et.al.& all others",

I not to long ago sat thru an EM lecture taught by the director of the RI Hosp. ER. This lecture was on "Risk stratification of chest pain patients, treatment modalities and litigious risk." Essentially, what it boiled down to in regards to this discussion is this. 1.) A 12 lead ECG is 98% specific and 50% sensitive. In short, just because you have a "normal" 12 lead doesn't mean your patient isn't having a myocardial event.....As a matter of fact, you could get the same sensitivity of info by a simple coin toss.... (Remember: the 12 lead is just a snap shot of a few millisecond in time)B.) This is why one needs at least 3 sets of - enzymes and a period of observation, "to rule out" if you will. c.) Tort law has now made it a patient’s "right" to be pain free. It is your duty to try to alleviate it. D.) The "pain" felt in MI can and will usually absolve when the underlying etiology has been appropriately treated, i.e.: MIO2 has been restored with blood flow, etc... The reason most often MSO4 is given isn't so much for the minimal vaso-dilitory effects as anxiety control, and "perception of pain decrease".

Lastly, your decision to treat or not to treat a CP patient's "pain" should have nothing to do with whether you have changes on the 12 lead. As a matter of fact there is an overwhelming amount of evidence which shows that pain can completely devoid of an ischemic event...Among the many reasons I decided to start this "discussion," was because I have recently run into a spate of Medics who don't di this, but do rely on the 12 lead & occasionaly PMH as a sole indicator of whether the patient's having cardiac related chest pain. I have tried to get myself in the practice of soing risk statification as part of my assessment. It just seemed to me that it was happening alot less than it should be pre-hospital. So thus I am curious about how you all practice, and if you don't do so, why? Next as "AZEP," said he does TIMI, etc..as part of his assessment, I think that his doing so is amlso among the minority and as you can see above, there is more to the "strata" than just the TIMI criteria..

Hope this helps,

Ace844

[Ace844]

(Published Online First: 30 December 2005. doi:10.1136/hrt.2005.073122

Heart 2006;92:905-909

© 2006 by BMJ Publishing Group Ltd & British Cardiovascular Society

CARDIOVASCULAR MEDICINE

Validity of the GRACE (Global Registry of Acute Coronary Events) acute coronary syndrome prediction model for six month post-discharge death in an independent data set

P J Bradshaw @ D T Ko*, A M Newman, L R Donovan and J V Tu,

Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada

Correspondence to:

Dr Pamela Bradshaw

School of Population Health, University of Western Australia, M431 Clifton Street Campus, Nedlands, WA 6009, Australia; pamela@sph.uwa.edu.au)

Objective: To determine the validity of the GRACE (Global Registry of Acute Coronary Events) prediction model for death six months after discharge in all forms of acute coronary syndrome in an independent dataset of a community based cohort of patients with acute myocardial infarction (AMI).

Design: Independent validation study based on clinical data collected retrospectively for a clinical trial in a community based population and record linkage to administrative databases.

Setting: Study conducted among patients from the EFFECT (enhanced feedback for effective cardiac treatment) study from Ontario, Canada.

Patients: Randomly selected men and women hospitalised for AMI between 1999 and 2001.

Main outcome measure: Discriminatory capacity and calibration of the GRACE prediction model for death within six months of hospital discharge in the contemporaneous EFFECT AMI study population.

Results: Post-discharge crude mortality at six months for the EFFECT study patients with AMI was 7.0%. The discriminatory capacity of the GRACE model was good overall (C statistic 0.80) and for patients with ST segment elevation AMI (STEMI) (0.81) and non-STEMI (0.78). Observed and predicted deaths corresponded well in each stratum of risk at six months, although the risk was underestimated by up to 30% in the higher range of scores among patients with non-STEMI.

Conclusions: In an independent validation the GRACE risk model had good discriminatory capacity for predicting post-discharge death at six months and was generally well calibrated, suggesting that it is suitable for clinical use in general populations.

(Published Online First: 26 October 2005. doi:10.1136/hrt.2005.072975

Heart 2006;92:735-740

© 2006 by BMJ Publishing Group Ltd & British Cardiovascular Society

CARDIOVASCULAR MEDICINE

Admission N-terminal pro-brain natriuretic peptide and its interaction with admission troponin T and ST segment resolution for early risk stratification in ST elevation myocardial infarction

E Björklund1 @ T Jernberg3, P Johanson3, P Venge4, M Dellborg3, L Wallentin4, B Lindahl2, the ASSENT-2 and ASSENT-PLUS Study Groups

1 Department of Cardiology, University Hospital of Uppsala, Uppsala, Sweden

2 Uppsala Clinical Research Centre, University Hospital of Uppsala, Uppsala, Sweden

3 Clinical Experimental Research Laboratory, Sahlgrenska University Hospital/Östra, Göteborg, Sweden

4 Department of Clinical Chemistry, University Hospital of Uppsala, Uppsala, Sweden

Correspondence to:

Dr Erik Björklund

Department of Cardiology, University Hospital, 751 85 Uppsala, Sweden; erik.bjorklund@akademiska.se)

Objective: To assess the long term prognostic value of N-terminal pro-brain natriuretic peptide (NT-proBNP) on admission and its prognostic interaction with both admission troponin T (TnT) concentrations and resolution of ST segment elevation in fibrinolytic treated ST elevation myocardial infarction (STEMI).

Design and setting: Substudy of the ASSENT (assessment of the safety and efficacy of a new thrombolytic) -2 and ASSENT-PLUS trials.

Patients: NT-proBNP and TnT concentrations were determined on admission in 782 patients. According to NT-proBNP concentrations, patients were divided into three groups: normal concentration (for patients 65 years, 184 ng/l and 268 ng/l and for those > 65 years, 269 ng/l and 391 ng/l in men and women, respectively); higher than normal but less than the median concentration (742 ng/l); and above the median concentration. For TnT, a cut off of 0.1 µg/l was used. Of the 782 patients, 456 had ST segment resolution (< 50% or 50%) at 60 minutes calculated from ST monitoring.

Main outcome measures: All cause one year mortality.

Results: One year mortality increased stepwise according to increasing concentrations of NT-proBNP (3.4%, 6.5%, and 23.5%, respectively, p < 0.001). In receiver operating characteristic analysis, NT-proBNP strongly trended to be associated more with mortality than TnT and time to 50% ST resolution (area under the curve 0.81, 95% confidence interval (CI) 0.72 to 0.9, 0.67, 95% CI 0.56 to 0.79, and 0.66, 95% CI 0.56 to 0.77, respectively). In a multivariable analysis adjusted for baseline risk factors and TnT, both raised NT-proBNP and ST resolution < 50% were independently associated with higher one year mortality, whereas raised TnT contributed independently only before information on ST resolution was added to the model.

Conclusion: Admission NT-proBNP is a strong independent predictor of mortality and gives, together with 50% ST resolution at 60 minutes, important prognostic information even after adjustment for TnT and baseline characteristics in STEMI.