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Maureen Smith is a clinical nurse specialist in critical care in the Nasseff Heart Center at United Hospital. She directs critical care orientation at United Hospital and teaches electrocardiography courses for Allina Hospitals and Clinics.
To purchase electronic or print reprints, contact The InnoVision Group, 101 Columbia, Aliso Viejo, CA 92656. Phone, (800) 899-1712 or (949) 362-2050 (ext 532); fax, (949) 362-2049; e-mail, reprints{at}aacn.org.
To learn more about ST-Segment Monitoring, read "ST-Segment Changes in Right Ventricular Paced Rhythms" by
Michele M. Pelter and Mary G. Carey in the American Journal of Critical Care, 2006;15:231-232.
Now that you’ve read the article, create or contribute to an online discussion about this topic using eLetters. Just visit www.ccnonline.org and click "Respond to This Article" in either the full-text or PDF view of the article.
None reported.
Corresponding author: Dr. Kristin Sandau, Bethel University, Department of Nursing, 3900 Bethel Dr, St Paul, MN 55112 (e-mail: K-Sandau{at}bethel.edu).
To aid in implementing consensus guidelines, we describe a nurse-directed hospital-wide protocol with interdisciplinary agreement on continuous ST-segment monitoring. We begin with a review of current guidelines for continuous ST-segment monitoring among hospitalized patients. Results of a brief survey of hospital use of continuous ST-segment monitoring in our community are provided to facilitate discussion of the extent of implementation of the guidelines into practice. We also review research studies and discuss current limitations of continuous ST-segment monitoring. Finally, we present implications for further research to clarify best-practice use of continuous ST-segment monitoring.
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Guidelines for In-Hospital Electrocardiographic Monitoring |
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 Top Guidelines for In-Hospital... Patients Who May Benefit...Community Survey of Use...Review of StudiesPractical Limitations of...Our Protocol: Education and...Implications for ResearchImplications for PracticeConclusionPRIME POINTSReferences |
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In light of the newly published consensus guidelines for universal definition of myocardial infarction by experts from the American Heart Association (AHA), American College of Cardiology, and other relevant organizations,5 more continuous and accurate ST-segment monitoring is needed. The consensus guidelines5 describe ECG manifestations of acute myocardial ischemia (in absence of left ventricular hypertrophy and left bundle branch block) as new ST-segment elevation at the J-point in 2 contiguous leads, with the cutoff points of more than 2 mm in men or more than 1.5 mm in women in leads V2 and V3 and/or more than 1 mm in other leads. The J-point is located at the point where the QRS segment ends. Contiguous leads that provide information on surface areas of the heart are found in Table 1
.5–8 The guidelines also describe acute myocardial ischemia as ST-segment depression of greater than 0.5 mm in 2 contiguous leads and/or T-wave inversion greater than 1 mm in 2 contiguous leads with a prominent R wave.
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In 2001, Patton and Funk4 reported on the uniformity of continuous ST-segment monitoring as a standard of practice in the United States. A random sample (n=192) of clinical nurse specialists and nurse managers were surveyed by US mail. Only 54.2% of respondents indicated that their departments used continuous ST-segment monitoring to detect ischemia in patients with ACS.
In 2004, a scientific statement of practice standards for ECG monitoring in the hospital was published by the AHA and endorsed by the American Association of Critical-Care Nurses (AACN) and the International Society of Computerized Electrocardiology.3 The comprehensive best-practice standards were created to facilitate safe and effective monitoring for cardiac dysrhythmias, QT-segment monitoring, and ischemia monitoring and included guidelines for continuous ST-segment monitoring in certain patients.
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Patients Who May Benefit From ST-Segment Monitoring |
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)9–15 based on research evidence and expert opinion to make recommendations about which patients should have continuous ST-segment monitoring.
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Community Survey of Use of Continuous ST-Segment Monitoring |
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Why is continuous ST-segment monitoring not a consistent standard of practice across hospitals? Probable reasons include a lack of awareness of the consensus guidelines or a published protocol, lack of acceptance by physician and nurse leaders who may be awaiting the results of clinical trials to support a stronger level of evidence, and lack of education for nurses about what to do when findings on continuous ST-segment monitoring are abnormal.
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Review of Studies |
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Significance of Continuous ST-Segment Monitoring for Evaluation of Interventions
Jernberg et al17 found that use of multilead ST-segment monitoring in patients with ACS allowed prospective identification of patients who had the best response to longer treatment with low-molecular-weight heparin, thus resulting in lower rates of mortality, myocardial infarction, and revascularization (35.3% vs 53.4%; relative risk reduction, 34%; P=.01). Researchers in a substudy18 of the Global Utilization of Streptokinase and TPA for Occluded Coronary Arteries (GUSTO-I) trial concluded that recurrent ST-segment elevation as detected via continuous ST-segment monitoring was an independent predictor of mortality, even after consideration of multiple clinical risk factors in the GUSTO mortality model.
In a multisite, prospective, comparative study of 1777 patients, Maas et al19 found that age, heart rate, and late ST-segment elevation were independent risk factors for adverse clinical outcomes. ST subgroupings resulted in significant stratification for both low- and high-risk patients for the composite end points (in-hospital death and combined death, reinfarction, or congestive heart failure). Maas et al concluded that continuous ST-segment monitoring is helpful in assessing response to therapy, especially in high-risk patients more than 70 years old.
In patients with ACS, transient myocardial ischemia is an independent predictor of worse outcomes. In a study20 conducted at various sites in Canada, 681 patients admitted with non–ST-elevation ACS were randomly assigned to receive either enoxaparin or intravenous unfractionated heparin. At 30 months, patients with ST-segment shifts were more likely to die (17.7% vs 5.8%; P<.001) and to reach the composite end point for worse outcomes (24.6% vs 11.1%; P < .001) than were patients without such shifts. After adjustments for risk scores, the presence of ST-segment shifts on continuous ECGs was a stronger independent predictor of mortality than were the findings on admission 12-lead ECGs.20 Several other investigators reported that using continuous ST-segment monitoring helped to predict patients’ severity of disease at a variety of time points: during hospitalization,19,21,22 after discharge,23 and in long-term follow-up.24
In the first study involving a comprehensive evaluation of ST-segment changes before, during, and after percutaneous coronary intervention, Terkelsen et al25 performed continuous ST-segment monitoring in 92 patients with ST-elevation myocardial infarction, from ambulance through the percutaneous procedure until 90 minutes after the procedure. The results indicated that a prespecified ST-monitoring classification was useful for stratifying patients at the time of percutaneous coronary intervention into groups at low, intermediate, and high risk. Terkelsen et al25 recommended use of continuous ST-segment monitoring for an early indication of the degree of reperfusion after percutaneous intervention.
Akkerhuis et al26 performed a meta-analysis of 3 prospective clinical trials (n=995) with retrospective blinded analysis of recordings of continuous monitoring done in a core laboratory. They found that the number of ischemic episodes in 24 hours was directly proportionate to the probability of cardiac events at 5 and 30 days. After known baseline predictors of worse outcomes were controlled for, each transient ischemic event was predictive of a 25% increase in the risk of death or myocardial infarction at 5 and 30 days. Akkerhuis et al26 concluded that integration of continuous ST-segment monitoring via a 12-lead ECG system was warranted in the emergency and coronary care departments to enable early identification of patients who may benefit from early revascularization.
Finally, in an ongoing study, Drew et al27 are investigating whether prehospital ST-segment monitoring with telephone transmission of ST events to the target hospital can improve hospital time-to-treatment in patients with ACS. Results from this study will add to the body of literature and may provide support for the use of continuous ST-segment monitoring in a prehospital environment.
Significance of Continuous ST-Segment Monitoring for Patients Vulnerable to Silent Ischemia
Patients with silent or unrecognized ischemia may benefit from continuous ST-segment monitoring. Reported rates of silent ischemia among hospitalized patients vary, from 21% to 77%, depending on the type of patient, hours of monitoring, and method of continuous ST-segment monitoring.17,28–30 Gunnarsson et al31 reported that continuous, real-time multilead ST-segment monitoring was as accurate as or more accurate than standard 12-lead ECG monitoring.
Kress et al15 used continuous 3-lead Holter monitors with blinded ST-segment analysis by a cardiologist to detect myocardial ischemia in ICU patients receiving mechanical ventilation who had risk factors for coronary artery disease. Ischemia was defined as ST-segment elevation or depression of more than 0.1 mV from baseline. Myocardial ischemia was detected among 24% of patients, who subsequently had a longer ICU stay (mean, 17.4 days; SD, 17.5 vs mean, 9.6 days; SD, 6.7; P=.04) than did patients without ischemia. The study involved patients receiving continuous ST-segment monitoring to detect ischemia while being awakened from sedation. Continuous ST-segment monitoring was a more helpful end point than troponin T level for detecting myocardial ischemia because many patients had preexisting troponin leaks that could not be "undone" and because continuous ST-segment monitoring provided real-time data (rather than a static troponin marker).
Certain populations of patients with coronary ischemia, such as women and patients with diabetes mellitus, may have atypical anginal symptoms. In a large study20 of patients with myocardial infarction, 33% did not have chest pain on arrival at the hospital. Patients without chest pain, compared with patients with chest pain, were significantly more likely to be women, have diabetes, or have prior heart failure. Additionally, patients with myocardial infarction without chest pain had a longer delay before going to a hospital (mean, 7.9 vs 5.3 hours); were less likely to have a diagnosis of confirmed myocardial infarction at the time of admission (22.2% vs 50.3%); and were less likely to receive thrombolysis or primary angioplasty (25.3% vs 74.0%), aspirin (60.4% vs 84.5%), β-blockers (28.0% vs 48.0%), or heparin (53.4% vs 83.2%).
In another study,32 patients with myocardial infarction without chest pain had a 23.3% in-hospital mortality rate compared with a rate of 9.3% among patients with chest pain. Pope et al33 also reported that failure to hospitalize patients who had acute myocardial infarction or unstable angina (missed diagnoses) was significantly related to the absence of typical features of cardiac ischemia.
Less well-recognized populations of patients vulnerable to silent ischemia may include patients with confusion and patients who cannot communicate effectively (eg, patients who are sedated and intubated, mentally impaired, or experiencing acute delirium). Continuous ST-segment monitoring may be helpful in detecting silent ischemia. Once ischemia is detected, interventions can be initiated that increase chances for maintaining viable myocardial tissue. In this era of widespread interventional capability, nurses caring for cardiac patients should examine available technology that alerts caregivers to changes in cardiac status.
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Practical Limitations of Continuous ST-Segment Monitoring |
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In addition to concerns about continuous ST-segment monitoring, general bedside ECG monitoring has concerns related to quality assurance that must be addressed. Drew et al35 identified several weaknesses of ECG monitoring, including lack of skin preparation before ECG patches are applied and inaccurate placement of ECG leads. If the lead that overlies the current of injury is not the one selected for continuous ST-segment monitoring, a sense of false assurance may result, with potential for missed ischemia.
Even when ECG patches are correctly placed and maintained by knowledgeable nurses, certain limitations exist in current bedside ST-segment monitoring. Most current in-hospital monitors do not detect T-wave inversion, which may be the only objective sign of reversible ischemia in some patients. Also, physically restless or combative patients may create artifacts that trigger false alarms, requiring that ST monitoring be turned off so that staff do not become accustomed to ignoring ST alarms and to prevent patients from being burdened with meaningless alarms.
Education for Continuous ST-Segment Monitoring
Education of nurses responsible for ECG monitoring needs to be ongoing and evidence based. Results of a study36 in which nurses’ ability to differentiate ischemic from nonischemic ECG patterns was evaluated were disappointing; only 19% of nurses were able to correctly identify the presence or absence of ischemia in all 6 scenarios. However, Johanson et al37 found that after the majority of critical care nurses in their sample attended a 2-day symposium on vectorcardiographic interpretation and analysis, bedside nurses’ evaluations of ST trend curves were equal to evaluations done in a core laboratory.
Initial education must be supported by ongoing assessment of competency. Lead selection and placement based on the priority monitoring needs of each patient are a core education component. This level of education may require more than a single introductory class to ECG monitoring. It may also require unit policies that match monitoring lead selection to the population of patients served. Additionally, accuracy of lead placement may require close supervision of unlicensed assistants or float nurses, who may be placing or repositioning telemetry patches. Periodic quality assurance audits are needed to verify the lead placement skills of staff.
The most frequently cited reason (27%) a sample of critical care nurses gave for not using ST monitoring was the lack of interest by physicians.4 This finding clearly indicates that practice changes in cardiac monitoring need interdisciplinary attention. Possibly, cardiologists are not aware of the consensus guidelines for cardiac monitoring. Thus, interdisciplinary discussion and agreement on ECG monitoring protocols is imperative.38
Finally, a shift in thinking about ECG monitoring beyond heart rates and dysrhythmias is needed to match the current culture of aggressive intervention. The emphasis in cardiac management has shifted from observing development of a pathological q wave (a sign of irreversible transmural myocardial damage) and supportive management to prevention and rapid intervention when ST-segment changes that may indicate reversible ischemia are detected. Early intervention, particularly of an occluded left anterior descending artery, may prevent death of the myocardium and thus prevent development of heart failure.39 Nurses in rural hospitals without an in-house physician often base their decisions on ST segments noted on the initial 12-lead ECG. For example, ST-segment results influence whether or not a level I hospital is contacted for transfer of a patient with ACS. Early and accurate identification of ischemia requires that acute care nurses use critical thinking about a monitoring process they understand well.
Critical Thinking in Lead Selection
Unfortunately, the leads selected for monitoring a particular patient may be based on habit or a unit protocol rather than a nurse’s critical thinking about the patient’s priority for monitoring. For patients who have undergone cardiac surgery, lead V6 is understandably often used to avoid placing a lead near the sternum. Like lead V1, V6 is helpful for identifying intraventricular conduction defect and distinguishing between ventricular ectopy and aberrancy. However, V6 may not be the best lead for observing abrupt reocclusion, depending on the artery that was revascularized (see Table 1
). For example, if a patient’s revascularized vessels were the right coronary artery and the left anterior descending artery, the best leads would be III and V2 or V3.40,41
Many units have equipment capability to select only 1 precordial (chest) lead and 1 limb lead and therefore have routinely used V1 or V6 (as ideal arrhythmia leads) and II (as ideal limb lead) for monitoring all patients.41 Although these leads may provide classic ECG waveforms, they may be problematic, depending on the nurse’s primary aim. For example, if a nurse wants to monitor for frequency of a patient’s premature ventricular contractions, use of a standard V1 lead may be adequate. Similarly, if the nurse’s intent is to monitor for recurrence of atrial fibrillation, then the commonly selected lead II may be appropriate. However, if the priority for monitoring involves a patient who has had recent revascularization of the left circumflex artery, the nurse may miss abrupt reocclusion if only leads V1 and II are selected for monitoring. The nurse would more correctly select a lead that monitors the lateral surface of the heart (I, aVL, or V5–V6).
Ideally, nurses should base lead selection on the priority monitoring needs of each patient. Although this concept seems simple, it requires more than an introductory class in ECG monitoring. Nurses responsible for cardiac monitoring should receive the appropriate ongoing education to enhance critical thinking about tailoring lead selection to a patient’s need.
Daleiden and Schell42 attributed the underuse of continuous ST-segment monitoring to technical problems (false alarms, inadequate hardware or software for accurate ST analyses), lack of practice standards, and lack of consensus by physicians about the need for continuous ST-segment monitoring. The authors42 provided clear, succinct instructions for nurse leaders considering implementation of ST-segment monitoring technology. A particular focus included clinical education of staff nurses, physicians, and monitor technicians, who should be able to place leads correctly (initial and ongoing), recognize changes in the ST segment (ongoing elevation vs resolution), recognize abrupt reocclusion after a coronary intervention, recognize false alarms, and incorporate patients’ symptoms and hemodynamic status along with a rhythm in order to better interpret the clinical significance of changes in the ST segment.
Utilization Protocols
Guidelines for protocols for continuous ST-segment monitoring have been offered by Drew and Funk,43 Leeper,2,44 and Flanders.38,45 A handful of nurses have published clinical papers describing how continuous ST-segment monitoring is used in their institution. One of the earliest reports came from nurses in Australia,46 who described the ease of use of this noninvasive technology and who used 2 case studies to illustrate how continuous ST-segment monitoring via 12-lead ECG provided additional diagnostic information in a patient who underwent emergency percutaneous intervention during a myocardial infarction and a patient who received thrombolytic therapy for an anteroseptal myocardial infarction. In the latter patient, continuous ST-segment monitoring provided early detection of poor perfusion, so the patient was able to undergo subsequent successful percutaneous coronary reperfusion.
Crater et al47 used case studies to illustrate how nurses in the coronary care unit at Duke University Medical Center, Durham, North Carolina, monitored ST segments via a real-time portable 12-lead system. The authors offered a risk stratification model of patients with ST-segment monitoring for house officers to use during triage for ACS. A specific nursing protocol was not given.
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Our Protocol: Education and Protocol for Standard Practice |
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In Nasseff Heart Center of the 572-bed United Hospital, continuous ST-segment monitoring was implemented in the early 1990s. Currently a 5-electrode ECG lead is used. Each staff nurse on the ICU or progressive care unit is required to pass a basic cardiac rhythms test. Nurses new to cardiac monitoring receive a 24-hour basic course, divided into 3 days over a period of up to 2 weeks, followed by verification of competency on the clinical unit. Both intermediate and advanced ECG classes (8 hours each) are encouraged but are not mandatory. Because only introductory content on ST-segment monitoring is provided in the basic cardiac rhythm course, all new nurses receive further individualized instruction from the assistant nurse manager on their units on the protocol for use of continuous ST-segment monitoring. This personalized instruction includes how to assess for patients who do not benefit from continuous ST-segment monitoring. New nurses are taught how to turn off the default alarm and how to answer and adjust alarm settings and are reminded of the parameters of as-needed 12-lead ECG.
Interdisciplinary agreement was sought so that the standard practice for using continuous ST-segment monitoring would be accepted by cardiologists, hospitalists, cardiac rehabilitation professionals, and nurses. A key decision by the interdisciplinary group was policy wording that stipulated that the ST alarm default must be the "on" setting for all patients. Thus, nurses must manually turn ST alarms to "off " for patients who meet exclusion criteria (Table 3). Before notifying a physician about an ST alarm, the nurse first verifies that the patient’s patches are correctly placed and that the alarm is not due to an artifact, particularly an artifact caused by movement of the patient.48
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The as-needed ECG is rarely required because nurses turn off continuous ST-segment monitoring alarms when appropriate. For example, a patient admitted to rule out ACS for whom tests for cardiac markers are normal and diffuse ST changes are apparent will have continuous ST-segment monitoring discontinued after a physician confirms a diagnosis of pericarditis. Similarly, for a patient who has declined further intervention but continues to have alarms on ST-segment monitoring, the nurse can request an order from a physician to increase alarm limits to prevent continual alarms.
Minor modifications to the original protocol were made after case studies of actual patients were reviewed. Case studies provided learning opportunities to enhance patients’ outcomes, nurses’ education, and interdisciplinary discussions. Case studies may also provide a forum for discussion among institutions for how to incorporate consensus guidelines into actual practice. An article will be published later in Critical Care Nurse in which case studies are used to illustrate practical application of a protocol and related education for continuous ST-segment monitoring.
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Implications for Research |
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Additional research is needed to better clarify which populations of patients will benefit from continuous ST-segment monitoring, as well as the length of time monitoring should be applied. For example, analysis of coarse atrial fibrillation based on changes in the ST segment is currently difficult. Further study is needed on normal variations in the ST segment after cardiac surgery. Finally, identifying the most efficient bedside monitoring equipment that minimizes interference with the healing of sternal incisions, is user friendly, and is cost-effective may improve use of this technology.
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Implications for Practice |
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Hospitalists and cardiologists need to partner with staff nurses in applying the protocols of continuous ECG monitoring used in hospitals where the physicians admit patients. If continuous ST-segment monitoring is initiated as a new policy in a hospital, nurse leaders in education and practice should consider measuring outcomes before and after the implementation. Nurses need to learn from each other, especially about policies for increasing alarm limits and when to request an ECG.
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Conclusion |
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In our hospital, we implemented the use of continuous ST-segment monitoring with a well-defined protocol developed by a cardiovascular clinical nurse specialist and approved by an interdisciplinary team. The protocol included strategies to verify accuracy of continuous ST-segment monitoring alarms and to obtain a 12-lead ECG before calling a physician, thus avoiding unnecessary telephone calls for potentially false-positive alarms. Translation of consensus guidelines into actual practice policies helped
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PRIME POINTS |
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Acknowledgments |
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References |
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This article has been cited by other articles:
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  K. E. Sandau, S. Sendelbach, J. Frederickson, and K. Doran National Survey of Cardiologists' Standard of Practice for Continuous ST-Segment Monitoring Am. J. Crit. Care., March 1, 2010; 19(2): 112 - 123. [Abstract] [Full Text] [PDF]
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
