Continuous ST-Segment Monitoring: 3 Case Studies in Progressive Care

Three case studies in this article demonstrate the use of a protocol for continuous ST-segment monitoring among patients in intensive care units and progressive care units.For patients in intensive care units (ICUs) and progressive care units (PCUs), a particular area of interest in the cardiac waveform is the ST segment. Depression or elevation of the ST portion of the waveform in at least 2 electrocardiography (ECG) leads that view the same surface of the heart indicates possible ischemia and resulting risk for myocardial infarction or death.1 Recently, an expert consensus document2 was published that provided a universal definition of myocardial infarction, giving specific guidelines regarding the degree of changes in the ST segment that are significant. For example, new ST-segment depression of only 0.5 mm or more in 2 contiguous leads meets criteria for potential manifestation of acute myocardial ischemia (in absence of left ventricular hypertrophy and left bundle branch block).2A static 12-lead ECG has been the tool used to evaluate changes in ST segments. However, the added technology of continuous ST-segment monitoring for hospitalized cardiac patients has been available for more than a decade, allowing clinicians to be notified by audible alarm and enabling trends in these small changes to be reviewed before an intermittent or scheduled 12-lead ECG,3 potentially before a patient becomes symptomatic.4 The purpose of this article is to provide a brief review of studies and guidelines that support the use of continuous ST-segment monitoring, and to present 3 case studies demonstrating use of a protocol for continuous ST-segment monitoring among patients in PCUs and ICUs. Each case study is followed by a discussion of what was learned and the related practice implications.Continuous monitoring of ST segments in real time allows accurate prediction of prognosis of critically ill patients, including patients experiencing acute coronary syndrome (ACS).5–9 Additionally, continuous ST-segment monitoring among cardiac patients has been useful for evaluating the effectiveness of interventions such as administration of thrombolytic agents10–12 or platelet inhibitors13–15 and percutaneous interventions,8,16 as well as for detection of perioperative ischemia.17,18Fesmire19 evaluated whether ST-segment monitoring via serial ECGs obtained every 20 minutes would result in a change in treatment that would not have been predicted from a standard 12-lead ECG obtained at admission. Researchers evaluated 678 patients with chest pain and suspected ACS who lacked clinical ECG criteria for emergent reperfusion therapy in order to determine whether continual 12-lead ST-segment monitoring with automated serial ECG resulted in a significant change in therapy (administration of thrombolytic agents, emergent percutaneous coronary interventions, or intensive treatment with intravenous heparin or nitroglycerin) during the initial evaluation in the emergency department. Patients were categorized into 1 of 4 risk categories that were based on clinical and ECG criteria for urgency of reperfusion. Researchers19 reported that serial 12 leads for ischemia monitoring led to a significant change in therapy for 26 patients (14.6% of high-risk patients and 1.1% of low-risk patients).Consensus guidelines for cardiac monitoring were published as a scientific statement from the American Heart Association by Drew and colleagues: specifically for continuous ST-segment monitoring in 199920 and more comprehensive guidelines for cardiac monitoring in 2004.21 Specific guidelines for length of monitoring are available from the scientific statement and in a summary table from Sandau and Smith.22 According to these guidelines, patients who should receive continuous ST-segment monitoring include the following:Ischemia monitoring via continuous ST-segment monitoring is available on most cardiac monitoring equipment in US hospitals and can provide a helpful indication of which patients may be experiencing ischemia. However, although all ICU and PCU nurses may monitor for heart rate and dysrhythmias, a 2001 survey of critical care nurses indicated that only about half of critical care units in the United States used available technology to monitor continuously for changes in the ST segment, with the most common reason being lack of interest among physicians.23Based on the guidelines from the scientific statement, the American Association of Critical-Care Nurses published a practice alert in 2004 (revised in 2008),24 recommending a standard of practice for continuous ST-segment monitoring. Depression or elevation of 1 to 2 mm in the ST segment lasting for a least 1 minute warrants further assessment.The practice alert recommended that continuous ST-segment monitoring should ideally include use of all 12 leads. If technology is not available for all 12 leads to receive continuous ST-segment monitoring, the nurse should use the most appropriate leads for ST-segment monitoring, depending on the patient’s needs and risk for ischemia and/or dysthymia.Several clinicians have published helpful practical recommendations for implementation of continuous ST-segment monitoring into practice.3,25–31 Sandau and Smith22 provided the first complete nursing practice standard and protocol for continuous ST-segment monitoring in order to equip other institutions with a sample of practical application of consensus guidelines; this protocol is reprinted in the TableT1. The following case studies are provided as examples of consensus guidelines being translated into practice.Nasseff Heart Center at United Hospital has had a protocol in place for continuous ST-segment monitoring since the early 1990s. We currently have 3 ICUs and 5 PCUs, and our protocol for continuous ST-segment monitoring is actively used throughout these departments. The following 3 case studies from our heart center were chosen to illustrate the use of the protocol for continuous ST-segment monitoring. Each of the patients in the case studies experienced signs or symptoms of ACS, and each displayed characteristics that required critical thinking and adaptation of monitoring. The following case studies on continuous ST-segment monitoring include (1) monitoring of silent ischemia limited by inappropriate alarm levels, (2) selecting an appropriate lead for monitoring response to interventions, and (3) monitoring in patients with cardiac risk factors and comorbid conditions.A 73-year-old woman was admitted with chest and shoulder pain. Six years before this admission, she had a stent placed in the left anterior descending coronary artery (LAD). She underwent coronary angiography and had the following interventions: a 90% occluded diagonal vessel was reduced to 20% occlusion, an 80% calcified midcircumflex artery was treated via angioplasty and 2 drug-eluting stents were placed (a side branch was compromised with possible spasm). The procedure was technically difficult because of her tortuous and calcified vessels. The patient was hypertensive during the procedure, spent 1 night in the ICU, and had no changes in her morning 12-lead ECG. She transferred to a PCU, where she initially began an uneventful recovery.On the second morning following her procedure, the patient offered a vague complaint of “not feeling well.” She had a small emesis after breakfast and mild transient hypotension, and she refused her cardiac rehabilitation session. She had no chest or shoulder pain. Although telemetry showed elevation of the ST segment in the display lead, no audible telemetry alarm or strip recording had occurred throughout the day because the ST-segment alarm had been set at only a message-level alarm (Figure 1A). This alarm resulted in a visual notification on the telemetry screen, with no audible alarm and no automatically generated printout of a strip. The cardiologist rounded at 4 PM and, upon viewing the telemetry display, noted that the patient’s ST segments were profoundly elevated (Figure 1B). An immediate 12-lead ECG confirmed marked ST-segment elevation in the inferior leads. Although 3 measurements of troponin T levels had been normal upon admission, a stat analysis indicated an abnormal troponin T level (0.52 ng/mL). The patient was subsequently returned to the cardiovascular laboratory, where a drug-eluting stent was successfully placed in the proximal portion of the first diagonal branch of the right coronary artery. She was discharged home 2 days later without further complications.This case study illustrates the usefulness of continuous ST-segment monitoring for detecting both asymptomatic and symptomatic ischemia. However, this monitoring tool is dependent on staff nurses being able to recognize the seriousness of such changes. Additionally, the ST alarm of 2 mm should be set to an alarm level that is audible and that automatically generates a telemetry strip to distinguish it from less immediate alarms. This important lesson resulted in a practice change.The clinical nurse specialist requested biomedical personnel to adjust the preset on all monitors so that ST-segment changes of 2 mm or greater registered as a “warning level” rather than a “message level” alarm, thus giving staff a more urgent notice. This practice change resulted in a continuous audible alarm and automatic generation of a printed strip showing the ST-segment change. The clinical nurse specialist reinforced to the staff nurses the clinical significance of an ST-segment alarm of 2 mm or greater and told them to use the “full disclosure” capability available on our monitoring system to view all available leads to check for ST-segment elevation in a patients whose alarms are triggered. The clinical nurse specialist also increased nurses’ awareness of a standing order for critical care nurses to obtain a 12-lead ECG after 15 minutes of sustained ST-segment changes even in the absence of any symptoms, and to call the physician after ST-segment changes noted on telemetry alarms are confirmed via 12-lead ECG.A 79-year-old man was admitted to the ICU with a history of hypertension, cigarette use (1 pack a day), and severe coronary artery disease not amenable to intervention. He had chest pain and an elevated level of troponin T (0.92 ng/mL), exhibiting 1- to 1.5-mm ST-segment elevation in inferior leads (II, III, and aVF) and possible posterior ischemia manifested by reciprocal changes (tall R waves) in V3 and V4 (Figure 2A), suggesting ACS with non–Q-wave myocardial infarction. Five days after admission, the patient was on a PCU and progressing well with clopidogrel bisulfate, aspirin, and a β-blocker. He was further treated with intravenous antibiotics, intermittent continuous positive airway pressure, and diuretics for a diagnosis of left-sided pneumonia and renal insufficiency. He began to complain of pleuritic left-sided chest pain and a headache. Although 1 sublingual nitroglycerin brought relief, his oxygen saturations were only 85% even after his oxygen support was titrated up to 6 L of oxygen per nasal cannula. The patient was receiving continuous cardiac monitoring for 7 leads, with leads V1 and II chosen as display leads. However, continuous ST-segment monitoring never triggered alarms, as the ST segment on lead II appeared only 1 mm elevated. A 12-lead ECG showed 2-mm elevation of the ST segment in leads III and aVF, as well as marked depression of the ST segment in V2 through V6 (Figure 2B). The primary physician came to the unit and ordered sublingual nitroglycerin and intravenous morphine. The patient was transferred to the ICU for intravenous infusion of nitroglycerin and morphine titrated to relieve angina. The nurses were able to adjust monitoring leads so that continuous ST-segment monitoring could be used to match the leads with ST-segment changes shown on the 12-lead ECG.The case study provides a reminder for nurses to check the 12-lead ECG in order to select the most appropriate lead to display and monitor for ST-segment changes. For this patient, V1 showed no ischemia on admission; therefore, the nurse may have found that switching to leads III and V3 (leads of concern shown by 12-lead ECG) would be more helpful for continuous monitoring of this patient. Although our monitors, like many telemetry monitors, allow only 1 chest lead to be monitored at a time, nurses can manually switch the chest lead to detect ST-segment changes in other affected leads.Nurses are encouraged to use patients’ 12-lead ECG to determine the lead most indicative of ischemia, injury, or infarction for a particular patient and then to select this lead as the primary lead for continuous ST-segment monitoring. In this case, continuous ST-segment monitoring was also useful to monitor whether interventions such as nitroglycerin and morphine were helpful in reducing ischemia. For example, the nurse could evaluate the effect of interventions by checking for a lessening of ST-segment elevation in lead III and a lessening of ST-segment depression in V3. A helpful table for selecting the best leads for viewing suspicious coronary arteries was provided by Sandau and Smith.22A 67-year-old man with a history of schizophrenia who had chest pain and shortness of breath with productive sputum was brought to the hospital by paramedics. Coronary risk factors included a history of cigarette smoking (1 pack per day) until 2 days earlier, hypertension, and type 2 diabetes mellitus; he was unaware of his lipid status. Home medications included a histamine2 blocker (for acid reflux symptoms) and an angiotensin-converting enzyme inhibitor (for hypertension). An echocardiogram from about 1 year earlier showed a normal ejection fraction of 60% to 65%. Hypoxemia noted on admission was thought to be due to chronic obstructive pulmonary disease. His ECG initially revealed sinus tachycardia (heart rate, 130/min). Although the initial 12-lead ECG was of poor quality because of his respiratory effort, it appeared to show ST-segment depression in the inferolateral leads as well as ventricular hypertrophy (Figure 3A). Subsequent ECGs showed a ventricular rate slowing to 91/min, P pulmonale, and continued ST-segment depression in the inferolateral leads. Blood tests revealed a level of troponin T that increased from admission (0.02 ng/mL) to 0.31 ng/mL and 0.26 ng/mL through the night.The patient’s condition was stabilized with oxygen, and he was started on a course of antibiotics for presumed bronchitis. He had no further complaints of chest pain. A psychiatrist was consulted because of the patient’s labile mood and paranoid comments about the “people doing witchcraft” around him. On day 2 of his stay, he had mild but sustained ST-segment depression of only 1 mm in the inferior leads on telemetry, particularly in lead II. The nurse acknowledged the alarm and used the full disclosure capability to print additional leads (Figure 3B). The nurse followed protocol and verified that the telemetry patches were placed correctly and that the patient was supine. The attending hospitalist was called to view a 12-lead ECG (Figure 3C) obtained concurrently with a printout of a telemetry strip. Because the 12-lead ECG showed only 1 mm of ST-segment depression in leads II, III, and aVF, the hospitalist asked that the limits for the ST-segment alarm be increased to stop the alarming. However, approximately 2½ hours later, the ST-segment depression on telemetry began alarming at 4 mm (Figure 3D). The hospitalist was called again, and because the patient had no complaints of chest pain and no increased needs for oxygen, he started treatment with aspirin and metoprolol and an ECG was ordered for the following morning.The next day the patient began to complain of chest pain. A hospitalist attributed the “epigastric discomfort” to the patient not receiving his home dose of histamine2 blocker, noting that the morning level of troponin T had decreased to 0.15 ng/mL. However, a cardiologist was consulted. The cardiologist agreed that an increase in troponin level upon admission was presumed to be due to the patient’s initial tachycardia and hypoxemia, and that the patient had a myocardial infarction at the time of admission. The option of angiography was presented to the patient because of his risk factors. Although the patient had initially refused angiography, he agreed to start treatment with intravenous heparin, undergo stress testing, and consider action based on the findings.After a positive dobutamine stress test in which his ejection fraction was calculated at 38%, the patient underwent angiography, which revealed 99% occlusion of the circumflex branch of the left coronary artery, 70% occlusion of the LAD, and total occlusion of the right coronary artery. Angioplasty was performed successfully on the LAD and 2 areas of the circumflex branch. Two drug-eluting stents were placed (in the proximal circumflex branch and the LAD). The lesion in the right coronary artery was reported to be well collateralized.This patient clearly displayed characteristics of a patient at risk for silent ischemia. Diabetes mellitus32 and his mental health issues could interfere with his ability to perceive and communicate anginal symptoms. It is possible that differences in the telemetry strip and the 12-lead ECG may reflect a lack of voltage standardization in telemetry systems versus 12-lead systems. Currently, most clinicians still consider the standard static 12-lead ECG necessary, and thus a 12-lead ECG should be obtained to provide definitive diagnosis in the context of the patient’s clinical manifestations. The ST-segment alarm is one of several pieces of clinical assessment, not a diagnostic confirmation. In this case, however, the standard 12-lead ECG alone did not show marked changes in the ST segment. Rather, the repeated ST-segment alarms added a piece to the patient’s comprehensive clinical picture, which indicated a need for angiography that subsequently confirmed marked occlusion of a vessel.This case study demonstrates the interdisciplinary discussion that must occur in addressing ST-segment alarms. Nurses are encouraged to continue to talk with hospitalists and cardiologists about the most appropriate response to these alarms.Patients experiencing ACS require rapid initial assessment as well as ongoing assessment for ischemia, injury, and infarction. Continuous ST-segment monitoring can provide additional data to supplement a patient’s risk factors, cardiac biomarkers, and clinical assessment, broadening the critical care nurse’s picture of whether ischemia is present, worsening, or resolving. We used case studies such as these as opportunities for continued learning and to modify our monitoring protocol. Our 10 years of clinical experiences have provided us with conviction that continuous ST-segment monitoring is a technology that will continue to be enhanced, both by improvements in protocols and by monitoring technologies required to meet the needs of clinicians who require more user-friendly ways of monitoring trends in ST-segment changes in ACS patients.We thank the nursing staff involved with cardiac monitoring at United Hospital, Clinical Equipment Services of United Hospital, the Allina ECG Course faculty, and Victor Tschida, md, past medical director of the Nasseff Heart Center.