Triage in Moderate-Risk Patients with
Chest Pain: The Emerging Role of
Real-Time Continuous ECG Monitoring
Mitchell W. Krucoff, MD, FACCDirector, Ischemia Monitoring Laboratory
Duke University Medical Center
Durham, NC
Director, Cardiac Catheterization Laboratory
Durham VA Medical Center
Durham, NC
Quick Overview
Introduction
Rapid and accurate evaluation of patients presenting with chest pain has been a unique area of progress in Emergency Department (ED) care over the past decade. Like the evolution of specialized resources in Coronary Care Units (CCU) in the 1960s and 1970s, Chest Pain Centers (CPCs) have focused ED attention on the identification and treatment of patients with unstable coronary syndromes (unstable angina, acute myocardial infarction [AMI]). Efficiency of triage and evaluation not only support more rapid definitive diagnosis and reduced time to therapy, but also help optimize resource utilization in an era of cost consciousness.As enhanced awareness of acute coronary syndromes crosses emergency medicine-cardiology boundaries, so do the tools with which such patients may be evaluated. Continuous electrocardiographic (ECG) monitoring combines elements previously familiar from interpretation of the standard diagnostic 12-lead ECG, with the interpretation of serial ECGs, as a noninvasive, inexpensive part of the evaluation of chest pain patients. Technical automation and progressive integration of this technology into the CPC environment will better define in which patients the information adds most. This article reviews the potential of this tool.
ECG Monitoring in High- and Low-Risk Patients
The vast majority of work with continuous ECG monitoring has been done in patients with coronary risk factors, persistent chest pain, and ST-segment elevation in multiple leads, ie, high-risk patients with AMI who warrant thrombolytic or interventional therapy. Continuous ECG monitoring in these patients is useful for the noninvasive detection of cyclic flow changes, reperfusion, or reocclusion of an infarct artery.At the other end of the spectrum, in patients with atypical clinical histories, no classic coronary risk factors and nondiagnostic ECGs, caution must be exercised in interpreting continuous ECG information. The specificity of ECG changes in this very low-risk population is poor, and labile elements of the ECG, such as T-waves or elevated J-points, may show changes over time in the absence of ischemia.
The most challenging area of application is in patients who present with worrisome symptoms, who have coronary risk factors, and who initially have nondiagnostic ECGs-one of the most common scenarios faced by ED staff and especially those in CPCs. In these patients rapidly available, objective ECG evidence of an acute coronary syndrome could be particularly useful for triage and therapy. This article will also review some of the concepts from ECG monitoring most salient to such evaluation.
The "Nondiagnostic" ECG
Classic ECG interpretation incorporates a broad array of morphologic patterns into categories referred to as "normal" or "nonspecific," especially in the repolarization pattern known as the ST segment. It must first be understood that these descriptors are largely statistically based over population studies, with variable application to specific individual patients. A "normal" appearance on ECG may be highly abnormal for an individual if his or her own personal ECG was previously abnormal. Continuous ECG monitoring automatically compares each ECG using the patient's own previous ECG as a template. Using this "self-referenced" approach, any changes from the presenting ECG are detected, independently of whether the changes represent physiologic improvement or deterioration. Thus, a patient who is ischemic at presentation may be detected by ECG improvement after nitroglycerin, or a patient who is actually okay at presentation may show ischemic changes in later ECGs, even though each at first had only nondiagnostic ECG changes. When such serial changes are brought to attention by automated measurements made by the ECG monitor, the bedside clinician can add the interpretative dimension, determining whether the ECG represents physiologic improvement or deterioration based on the whole patient assessment.Transient and Asymptomatic Ischemia and the
Static ECG:
A Problem of Undersampling, a Solution by Continuous Monitoring
Unlike the prolonged insult that produces myocardial necrosis and infarction,
ischemia by definition implies reversible dysfunction, ie, a transient insult.
The combined pathophysiologic factors that produce ischemia, such as platelet
deposition, local coronary vasoconstriction, and elevations in heart rate
and blood pressure, may either become active or be relieved in a matter
of seconds. To document such events requires a focused and efficient strategy.
Scenarios such as the patient who calls 911 because of chest pain who is
pain free on arrival at the ED, or the patient who has chest pain in the
ED that is gone by the time an ECG cart is connected, are all too familiar.
In these scenarios the significance of a nondiagnostic ECG is obscured by
the fact that the clinical syndrome of chest pain has abated entirely by
the time the ECG is taken. Continuous ECG monitoring eliminates the "missed
opportunities" or undersampling of the clinical syndrome by capturing
ST-segment changes of even the most transient events.At the other end of the spectrum, some patients with only mild or fleeting chest pain may have prolonged and severe periods of myocardial ischemia. It has now been widely demonstrated that for every episode of anginal chest pain, three to five equally severe episodes can be documented by an array of objective markers of ischemia with no subjective patient awareness. With routine observation of the population in Framingham, 50% of all myocardial infarctions were discovered only retrospectively. These data imply that for every ECG taken in response to an episode of chest pain, 75% to 80% of the potential diagnostic ECG information available is missed in routine clinical practice. The shortcomings of the current standard or "event" (chest pain)-driven ECG are erased by real-time ECG monitoring. Using the patient as his or her own baseline for comparison, ST-segment changes are detected when they violate ischemic thresholds, regardless of whether the patient reports symptoms.
Quick Overview
Temporal Patterns of Ischemic Syndromes:
Primary Role of the ED in ECG Monitoring
For all of the unpredictability of acute coronary syndromes, certain patterns
are remarkably consistent. Temporal patterns of ischemic activity are generally
consistent in their tendency to occur in "bursts" or "hot"
periods, followed by a progressive reduction in their incidence and severity.
This means that the first few hours of evaluation in patients presenting
with chest pain-hours that are most frequently spent in the ED-are most
likely to provide diagnostic information if such information is properly
gathered. Extrapolating from other experiences with acute coronary syndromes,
it is probable that 80% to 90% of the diagnostic information obtained in
24 hours of monitoring will be acquired in the first 2 to 4 hours. The complete
absence of ischemia over 3 hours of continuous ECG monitoring in a suspicious
syndrome may support admission to a ward bed rather than a CCU bed. Transient
episodes of asymptomatic ischemia may support administration of heparin
or nitroglycerin to prevent progression to a more severe insult. In this
particular respect, the physiology of greatest concern and the logistics
of the ED converge, when sampled continuously, to provide a uniquely rich
source of information for diagnosis and management.
Nondiagnostic ST Elevation and Depression
It is not uncommon for "nondiagnostic" ECGs acquired for chest pain evaluation to include ST elevation or depression. Therapeutic decisions in such patients frequently include consideration of thrombolytic therapy, with enormous consequences when withheld from patients who need it or when administered to patients who do not. Continuous ECG monitoring establishes the nature of ST elevation over a matter of minutes, during which time transmural ischemia escalates rapidly and frequently develops a more malignant, less equivocal morphology (or resolves abruptly to isoelectric levels). The one thing ischemic ST elevation or "injury current" rarely does is stay at a fixed level of deviation over sustained periods.ST-segment depression can provide some similar characteristics to ST elevation. Subtle conduction abnormalities, left ventricular hypertrophy, electrolyte abnormalities, or certain medications such as digoxin may all cause 100 to 200 Uv ST-segment depression. Like ST elevation, ischemic ST-segment depression rarely remains at a fixed level of deviation in a patient being actively treated with nitroglycerin or other anti-ischemic medications. Over the course of monitoring, ischemic ST depression is suggested either by worsening or by normalization, while other causes are suggested by fixed, unchanging levels of deviation.
Risk Stratification: Other Quantitative ECG Indices
Patients diagnosed with ischemic chest pain by continuous ECG monitoring may also be further risk stratified by quantitative ECG indices, including the duration of ischemic episodes, the peak amplitude of deviation, and the number of precordial leads deviated. Response or lack of response to therapy may help decide whether a patient should be directed to a CCU bed or directly to invasive therapy.Limitations of the ECG, Independent of Monitoring:
Evaluating the Patient With a Truly Nondiagnostic ECG
Continuous real-time ECG monitoring has enormous potential for chest pain
evaluation, but is not without limitations. Currently, many commercial manufacturers
produce relatively crude, difficult to use, noise-sensitive or bulky systems,
all of which are logistical problems in a busy environment such as the ED.
Well-designed CPCs may have the foresight to hard-wire systems with effective
ST-segment monitoring capabilities or complete 12-lead ECG monitoring capabilities,
or may at least leave sufficient space for portable systems. In addition
to the technical limitations, physiologic limitations in interpretability
bear mention. Patients with bundle-branch blocks or ventricular pacemakers
may have such abnormal baseline ST-segment levels that small changes in
heart rate may produce artifactual but measurable deviation relative to
those baseline levels. No ECG monitoring system currently supports heart
rate correction for the acquisition of ST-segment measurements. Patients
with suspicious chest pain and no ECG changes at all may have severe disease
in any of several locations well described anatomically, including the circumflex
artery, the apical left anterior descending, or certain global ischemia
such as in left main coronary disease. Management of such patients could
be augmented by rapid assay serum markers or echocardiography.Ideally, as the result of future research and regression modeling, the relative contribution of elements of the history, physical exam, laboratory tests, and ECG for diagnosis and therapy in patients with chest pain will emerge in a substantial and useful combination. In such a model, continuous ECG monitoring in patients at moderate risk for unstable coronary syndromes will certainly play a large and practical role.
References
1 Krucoff MW, Wagner NB, Pope JE, et al. The portable programmable microprocessor-driven real-time 12-lead electrocardiographic monitor: a preliminary report of a new device for the noninvasive detection of successful reperfusion or silent coronary reocclusion. Am J Cardiol. 1990;65:143-148.
2 Krucoff MW, Jackson YR, Start KS, et al. Electrocardiographic patterns of impending coronary closure independent of unstable anginal symptoms. Predisposing Conditions for Acute Ischemic Syndromes. 1989:96-105.
3 Krucoff MW, Sawchak ST, Pope JE, et al. Rethinking classical ECG patterns of ischemia and infarction. The Newspaper of Cardiology. 1993:2-44.
4 Krucoff MW. Comprehensive ischemia monitoring in unstable coronary syndromes. Coronary Acute Care. 1990:2-10.
5 Krucoff MW, Wagner BL, Sigmon KN, et al, and the TAMI 7 Study Group. The relative roles of clinical variables and continuous ST segment monitoring for "real time" noninvasive detection of reperfusion in the TAMI 7 trial. Circulation. 1991;84:II-117.
6 Gibler WB, Runyon JP, Levy RC, et al. A rapid diagnostic and treatment center for patients with chest pain in the emergency department. Ann Emerg Med. 1995;25:1-7.
7 Gibler WB, Sayre MR, Levy RC. Serial 12-lead electrocardiographic monitoring in patients presenting to the emergency department with chest pain.
J Electrocardiol. 1993;26(suppl):238-243.
Return to Index of Articles for Clinician;
Volume 14.4
- Faculty Listing 3
- Introduction: Community Message in Acute Myocardial Ischemia 4
- Concept of Community Chest Pain Centers in Emergency Departments 5
- Reawakening Awareness of the Importance of Prodromal Symptoms in the Shifting Paradigm to Early Heart Attack Care (EHAC) 7
- The Role of Emergency Medicine in the Future of American Medical Care: A Summary of the Josiah Macy, Jr, Foundation Conference 12
- From ACC/AHA Guidelines to Best Practice: Can "Acute MI Report Cards" Save Lives?Measuring Quality of Care for Patients With Cardiovascular Disease 16
- Improving Lay Responses to Cardiovascular Emergencies and the Potential of Shifting the Paradigm to Early Heart Attack Care 18
- National Survey of Chest Pain Centers Rationale and Potential Results 21
- Outpatient Rule-Out Myocardial Infarction in Observation Units 22
- Reducing Time to Thrombolytic Treatment 24
- Intervention Programs to Reduce Patient Delays in Acute Myocardial Infarction 29
- Public Education Using the Early Heart Attack Care Program Shawnee Mission Medical Center 31
- School Component: Early Heart Attack Care Program Development and Evaluation 33
- Educational Strategies to Prevent Prehospital Delay in Patients at High Risk for Acute Myocardial Infarction 36
- Precipitating Factors in Acute Cardiovascular Disease 41
- Use of Myocardial Perfusion Imaging in the Emergency Department for Risk Stratification 44
- The Evolution of Chest Pain Centers: The Impact of Technological Advances on the Evaluation of Patients With Possible Acute Ischemic Coronary Syndrome 47
- Critical Pathways for Triage and Treatment of Chest Pain Patients in the Emergency Department 53
- Chest Pain Centers: An Emerging Model for the Emergency Evaluation of Chest Pain and Treatment of Acute Myocardial Infarction 56
- The Key to Success in the Chest Pain Emergency Department: The Observational Role of theNurse 59
- Triage in Moderate Risk Patients With Chest Pain: The Emerging Role of Real-Time Continuous ECG Monitoring 61
- Diffusion of Innovations: The Introduction and Impact of the Chest Pain Emergency
- Department and its Comparison to the Coronary Care Unit Development 64
- Economics of Chest Pain Centers: What Really Matters? 68
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