Accuracy of biomarkers to diagnose acute cardiac ischemia in the emergency department: a meta-analysis

Cardiac markers in the low-risk chest pain patient

With the arrival of point-of-care cardiac marker determination, emergency physicians may be able to arrive at the diagnosis of cardiac ischemia faster than ever before. However, these tests must be used with care, as a lack of understanding about when and how they should be obtained is important both for good patient care and to avoid medicolegal pitfalls. This report reviews risk stratification of patients who present with chest pain, provides an overview of cardiac markers and literature supporting their use, and concludes with a practice guideline for the utilization of cardiac markers in the emergency department.

The sensitivity of cardiac markers stratified by symptom duration

We compared the sensitivity of three commonly used cardiac markers between two subpopulations, those who came to the Emergency Department (ED) late (6-24 h) after their symptoms began, and those who arrived earlier (<6 h), in a prospective comparative trial. Among all adult patients who presented to our ED with symptoms suggestive of acute myocardial infarction (MI), we drew serum for myoglobin, CK-MB, and troponin I upon arrival (time 0) and 2 h later. Outcomes, including acute MI, were determined. Sensitivities for all three markers between the subpopulations who arrived fewer than 6 h from symptom onset were compared to those who arrived later (6-24 h). We enrolled 346 eligible subjects, 36% of whom described cardiac symptoms as beginning 6 or more hours earlier; 14% suffered acute MIs. For time 0, the sensitivity of all three markers for acute MI was significantly higher among those subjects with symptoms of 6 or more hours' duration as compared to those with less. For troponin I, the increase in sensitivity between these two subpopulations approached 300%. At the time of the 2-h sample, the differences in sensitivities were much less and were not statistically significant. We conclude that cardiac marker values obtained at time 0 among Emergency Department patients who arrive 6 or more hours after cardiac symptom onset provide significantly higher sensitivities as compared to those obtained in patients who arrive earlier. For troponin I, the increase in sensitivity approaches threefold.

Noninvasive Imaging Techniques to Aid in the Triage of Patients with Suspected Acute Coronary Syndrome: A Review

The evaluation, treatment, and disposition of patients with symptoms suggestive of acute coronary syndrome (ACS) in the Emergency Department continues to be a clinical challenge. Many patients with suggestive symptoms are admitted to the hospital to rule out a myocardial infarction by serial enzyme tests and EKGs and receive an expedited work-up for ischemia. However, the diagnosis can be difficult, given the wide range of potentially atypical symptoms that can signal ACS, which remains a major clinical risk for patients and a liability risk for emergency physicians. This article reviews imaging technologies such as echocardiography and nuclear perfusion imaging used currently in the diagnosis of ACS and rapidly advancing technologies such as CT and MRI that may be able to visualize calcifications, plaques, occlusions, and infarctions noninvasively in real time. Some noninvasive tests used to complete an ischemia work-up after serial enzyme testing and EKGs, such as exercise EKG, stress echocardiography, and stress perfusion imaging, also are reviewed.

Advances in cardiac biomarkers

The diagnostic and prognostic roles of new and established cardiac biomarkers are continually changing. This update article discusses clinical diagnosis as a framework for directing biomarker testing. Markers are reviewed in the settings of acute coronary syndromes, decompensated heart failure, and noncardiac clinical scenarios.

The effect of cardiac troponin testing on clinical care in a veterans population: a randomized controlled trial

BACKGROUND

Cardiac troponin is more accurate than creatine kinase (CK) testing for detecting myocardial injury in patients with acute coronary syndromes (ACS), but its effects on clinical care compared with CK testing alone is open to question.

OBJECTIVE

To test the effects of troponin I on medical decisions for patients undergoing cardiac enzyme testing.

DESIGN

Randomized, controlled trial.

SETTING

Urban academic Veterans Affairs medical center.

PATIENTS

Three hundred ninety-two patients presenting to the emergency department (ED) and outpatient settings with symptoms and/or electrocardiograms suggestive but not diagnostic of ACS.

INTERVENTION

Random assignment to linked CK-troponin I (CKTnI) testing or CK testing alone.

MEASUREMENTS

ED discharge and cardiac catheterization incidence (primary); ED medication use, inpatient noninvasive testing, revascularization procedures, discharge medications, and 8-week ED visits, hospitalizations, and procedures (secondary).

RESULTS

Groups were similar in all variables except history of heart failure (CK 26.8% vs CKTnI 17.0%). ACS comprised 12.2% of the cohort. ED discharge incidence was greater in the CKTnI arm (18% vs 9.6%; relative risk [RR], 1.83; 95% CI, 1.08 to 3.31; P=.02; number needed to test=12.6; 95% CI, 4.5 to 130). Troponin testing had no significant effect on catheterization incidence (18.2% vs 14.5%; RR, 1.19; 95% CI, 0.72 to 1.92; P>.20) or other outcomes except follow-up echocardiography (13.4% vs 7.4%; RR, 2.24; 95% CI, 1.11 to 4.69; P=.02).

CONCLUSIONS

In a veterans population undergoing cardiac enzyme testing, CKTnI testing led to more ED discharges than CK testing alone but had no effect on inpatient care and was associated with more echocardiograms in a follow-up period.

Diagnostic performance of venous lactate on arrival at the emergency department for myocardial infarction

OBJECTIVES

To determine the sensitivity of the venous lactate level at presentation for acute myocardial infarction (AMI) in emergency department (ED) patients with chest pain.

METHODS

A prospective, double-blind observational study was done in a tertiary care ED. From January to April 2000, all consecutive patients presenting with chest pain were eligible. Lactate level was obtained on arrival and compared with two criterion standards for the diagnosis of AMI: the World Health Organization (WHO) and the Joint European Society of Cardiology/American College of Cardiology Committee (ESC/ACC) classifications. A lactate level greater than 1.50 mmol/L was considered positive.

RESULTS

Between January and April 2000, 718 patients were enrolled. By the WHO criteria, 64 patients suffered an AMI, of whom 59 had an elevated lactate level, yielding a sensitivity of 92% (95% CI = 86% to 99%), a specificity of 44% (95% CI = 40% to 48%), and a negative predictive value (NPV) of 98% (95% CI = 97% to 99%). For all patients presenting with more than two hours of chest pain (n=34), the lactate level was elevated. When using the ESC/ACC criteria, 100 patients sustained an AMI, of whom 88 had an elevated lactate level, yielding a sensitivity of 88% (95% CI = 82% to 94%), a specificity of 46% (95% CI = 42% to 50%), and an NPV of 96% (95% CI = 94% to 98%).

CONCLUSIONS

Venous lactate level at presentation is highly sensitive for the diagnosis of AMI, particularly in patients with more than two hours of chest pain. Given its limitations in specificity and ability to detect creatine kinase-MB-negative/troponin-positive microinfarcts, further research is needed to determine how lactate can complement other cardiac enzymes in risk-stratifying all acute coronary syndromes.

Missed acute cardiac ischemia in the ED: limitations of diagnostic testing

Correctly identifying and appropriately triaging patients who present to the ED with the broad range of symptoms suggestive of acute cardiac ischemia (ACI: unstable angina pectoris [UAP] and acute myocardial infarction [AMI]) remains one of the greatest challenges in EM. Although a number of diagnostic technologies have been described to aid in this triage process, each of these tests or technologies has limitations. We report a case series in which either the use of adjuncts with unknown performance or tests with known but not considered limitations could have contributed to the failure to appropriately triage and treat patients with ACI. Each case illustrates different aspects of this clinical challenge. One case illustrates the hazards of reliance on a single set of negative cardiac biomarkers. The limitations of a negative exercise electrocardiographic stress test (ETT) are illustrated in the second case. Finally, the limitations of a negative coronary angiogram, the "gold standard" test for symptomatic coronary artery disease, are discussed. We review the literature on technologies to aid in the evaluation of patients who present to the ED with symptoms suggestive of ACI.

Risk stratification and the management of non-ST-segment elevation acute coronary syndromes: the role of antiplatelet therapy

Risk stratification is crucial in guiding the acute management of non-ST-segment elevation (NSTE) acute coronary syndromes (ACS). An early invasive strategy (catheterization/revascularization) in conjunction with aggressive antiplatelet and anticoagulant therapy offers the most effective means of reducing ischemic complications in intermediate- and high-risk patients. In low-risk patients, stress testing serves to indicate whether a secondary prevention strategy or elective catheterization/percutaneous coronary intervention and GP IIb/IIIa inhibition is more appropriate. NSTE ACS also confers a long-term risk of recurrent cardiovascular events, regardless of whether initial management follows a medical or interventional approach. Combination aspirin and clopidogrel therapy is effective for secondary prevention across the spectrum of NSTE ACS patients, regardless of risk or initial treatment strategy (conservative or invasive). Long-term aspirin and clopidogrel therapy addresses the thrombotic component of atherothrombosis, while combined beta-blocker, ACE inhibitor, and statin therapy is directed against the atheroma.

Application of the principles of evidence-based medicine to laboratory medicine

The principles of evidence-based medicine and the consequent search for robust evidence on outcomes plays a central role in the practice of laboratory medicine. The core of the evidence lies in an explicit recognition of the clinical question(s) that the test result can address. Studies that focus on the relevant patient cohort and clinical setting for the test, and identify the appropriate outcome measure will generate information that can be used to guide use of the test, identify the benefits, and thereby support the case for investment of resources to deliver the service.

Diagnosis of myocardial injury by biochemical markers: problems and promises

The role of biochemical markers in the diagnosis of acute coronary syndromes has increased considerably in the past decade. The World Health Organization previously defined acute myocardial infarction as a combination of at least 2 of 3 components: symptoms consistent with acute myocardial infarction, electrocardiogram changes diagnostic of acute myocardial infarction, and an enzyme pattern with classic rise and fall. Measurement of creatine kinase and its MB fraction by various assays was the gold standard for the diagnosis. Troponins are more specific and sensitive markers for myocardial injury, and their increasing utilization has resulted in a broadening of the definition of acute myocardial infarction to incorporate high-risk acute coronary syndromes. Previously, traditional enzyme evaluation left patients with small amounts of cellular death undiagnosed; these patients were categorized as having unstable angina or, worse, noncardiac chest pain. Newer markers now identify these patients as a subgroup at high risk for cardiac death or cardiac events. Newer therapeutic interventions and a more invasive strategy have been shown to improve outcomes in this high-risk subgroup. Increased specificity has also reduced the number of patients who undergo extensive, expensive, and invasive evaluations for noncardiac syndromes due to false elevations of traditional markers. This article comprehensively reviews the evolution of biochemical markers for the diagnosis of acute myocardial infarction, addressing their promise for improving delivery of care and outcomes and their technical and diagnostic pitfalls.

Cardiorespiratory physical assessment for the acutely ill: 2

The second of this two-part article aims to develop advanced cardiovascular and respiratory knowledge to enhance practice for the nurse caring for an acutely ill patient on a general ward. The first part dealt with the core aspects of care in respiratory and cardiovascular physical assessment, including respiratory function and failure, pulse oximetry, oxygen therapy, fluid therapy, pulse measurement, blood pressure and electrocardiogram monitoring (Vol 11(11): 750-8). As the use of critical care beds within trusts becomes more difficult to manage, with ever-increasing patient dependency and occupancy figures remaining high, critically ill patients are likely to remain in wards longer or be discharged from a critical care environment earlier. These patients will require more frequent, direct, non-invasive and invasive monitoring to ensure that they do not deteriorate, and that any deteriorations are detected early and managed effectively. The skills and information discussed here will help nurses advance their practice and improve the quality of their care.

Cardiac markers of acute coronary syndromes: is there a case for point-of-care testing?

OBJECTIVE

Major challenges for physicians include selection of effective tests in the time-sensitive identification and management of patients with acute coronary syndromes (ACS). We review whether cardiac marker testing performed at the point-of-care (POC) has an impact on clinical management and guidance of intervention for ACS patients.

DESIGN AND METHODS

Evidence from recently published studies and meta-analyses supports the efficacy of cardiac markers. Technologies and specifications of all currently available POC tests for monitoring cardiac markers are surveyed. Finally, a series of questions to investigate the utility of cardiac markers, and their measurement by POC tests, for clinical management and guidance of therapy for ACS patients, are addressed.

RESULTS

Cardiac troponins are clearly the best markers for the definitive detection of myocardial infarction. Compelling evidence for the utility of troponins in risk stratification and guidance of intervention for ACS patients has resulted in inclusion of cardiac markers in clinical guidelines. Rapid multi-analyte POC tests, few of which exhibit harmony with central laboratory assays, have facilitated the use of cardiac markers for clinical management and guidance of therapy.

CONCLUSIONS

Given the need to minimize vein-to-brain time, it is expected that point-of-care testing of cardiac markers will take a leading role in management of ACS patients.

Diagnosing acute cardiac ischemia in the emergency department: a systematic review of the accuracy and clinical effect of current technologies

STUDY OBJECTIVE

Acute cardiac ischemia (ACI) encompasses the diagnoses of unstable angina pectoris and acute myocardial infarction (AMI). Accurate diagnosis and triage of patients with ACI in the emergency department should increase survival for these patients and reduce unnecessary hospital admissions.

METHODS

We conducted a systematic review of the English-language literature published between 1966 and December 1998 on the accuracy and clinical effect of diagnostic technologies for ACI. We evaluated prospective and retrospective studies of adult patients who presented to the ED with symptoms suggesting ACI. Outcomes were diagnostic performance (test sensitivity and specificity) and measures of clinical effect. Meta-analyses were performed when appropriate. A decision and cost-effectiveness analysis was conducted that investigated various diagnostic strategies used in the diagnosis of ACI in the ED.

RESULTS

We screened 6,667 abstracts, reviewed 407 full articles, and included 106 articles articles in the main analysis. Single measurements of biomarkers at presentation to the ED have low sensitivity for AMI, although they have high specificity. Serial measurements greatly increase the sensitivity for AMI while maintaining their excellent specificity. Diagnostic technologies to evaluate ACI in selected populations, such as electrocardiography, sestamibi perfusion imaging, and stress ECG, may have very good to excellent sensitivity; however, they have not been sufficiently studied. The Goldman Chest Pain Protocol has good sensitivity (about 90%) for AMI but has not been shown to result in any differences in hospitalization rate, length of stay, or estimated costs in the single clinical effect study performed. Its applicability to patients with unstable angina pectoris has not been evaluated. The use of an Acute Cardiac Ischemia-Time-Insensitive Predictive Instrument led to the appropriate triage of 97% of patients with ACI presenting to the ED and reduced unnecessary hospitalizations.

CONCLUSION

Many of the current technologies remain underevaluated, especially regarding their clinical effect. The extent to which combinations of tests may provide better accuracy than any single test needs further study.