A patient who has had chest pain for several hours is admitted with a diagnosis

Use of Echocardiography in Chest Pain Units and Clinical Algorithms

Chest pain units specializing in evaluation of patients presenting with acute chest pain have become widely used, particularly for patients at lower risk.37 Although data suggest the short-term risk of clinically relevant adverse events such as life-threatening arrhythmia, inpatient ST segment elevation myocardial infarction, cardiac or respiratory arrest, or death is low in those with negative serial biomarkers, nonconcerning vital signs, and nonischemic ECG findings,38 clinical algorithms using a variety of additional testing strategies have been developed and evaluated by clinical outcomes. For example, Gibler and colleagues developed a “Heart ER Program,” a diagnostic and treatment program for patients with chest pain in an urban tertiary care ED.39 More than 1000 patients with symptoms suggestive of acute coronary syndrome were enrolled. Patients with known coronary artery disease, acute ST segment shift, hemodynamic instability, or a clinical presentation consistent with unstable angina were admitted directly. 2D echocardiography and graded exercise testing were performed on all patients at the end of a 9-hour observation period. The results determined the disposition of the patient. The vast majority of patients were discharged from the ED (82.1%), whereas only 15% were admitted for further evaluation. Of patients admitted, 34% were found to have a cardiac cause for their symptoms. Stress echocardiography can be safely used in those patients at low risk, after an initial 6-hour observation period.40

A group in Italy evaluated 6723 intermediate-risk patients in the ED presenting with chest pain and a nondiagnostic ECG.41,4 In general, older atients or those with multiple risk factors or nondiagnostic ECGs had SPECT imaging, younger patients and those with only one or no risk factors and normal ECGs underwent treadmill exercise testing, and those unable to exercise or with an uncertain or nondiagnostic exercise treadmill testing or SPECT results underwent dobutamine stress echocardiography. Although the multiple types of testing performed make interpretation of their results more difficult, this protocol enabled them to make the early diagnosis of coronary artery disease in 22% of their chest pain unit patients, with early discharge in 78%.

A subsequent manuscript reported on approximately 500 patients with recent chest pain, but without ischemic myocardial infarction changes or definite evidence of coronary artery disease after a 6-hour workup including troponin levels. Patients unable to exercise or who had left bundle branch block or poor echocardiographic windows were excluded. Patients had exercise echocardiography and exercise methoxy iso butyl isonitrile (MIBI) scan within 24 hours, and patients with abnormal troponin levels at any time or positive stress tests were recommended for angiography. Endpoints for the study were a stenosis of greater than 50% on catheterization or cardiovascular events at 6 months. The exercise echocardiogram was positive in 20% of the cohort; the exercise MIBI was positive in 24%. Fourteen patients with negative exercise echocardiograms were ultimately diagnosed with coronary artery disease, versus 13 patients with negative exercise MIBI. The sensitivity of exercise echocardiography and exercise MIBI for the ultimate diagnosis of coronary artery disease in this study was similar (85% vs. 86%), whereas the specificity of exercise echo was slightly higher (95% vs. 90%), leading to a higher likelihood ratio for a positive exercise echocardiography test.42

In 2010, Parato and colleagues published a study of 403 patients presenting with chest pain, normal ECG, and cardiac troponin admitted to a cardiologist run chest pain unit.43 They underwent serial resting echocardiograms, ECG, and cardiac markers. A total of 49 patients were diagnosed with acute coronary syndrome; 33% of these were due to regional wall motion abnormalities on echocardiogram. The shortest interval between admission and acute coronary syndrome diagnosis was in those diagnosed with echocardiography, and the most common culprit vessel in this group was the circumflex.

Alduous and coinvestigators recently evaluated the incremental value of stress testing (a mixture of exercise treadmill testing and DSE) in 709 patients presenting to the ED with low- to intermediate-risk acute chest pain and negative serial troponins.44 In this single center study, stress testing identified an additional 34 patients (4.5%) with inducible ischemia who subsequently underwent revascularization during the index hospitalization. Of note, randomized data suggest that involvement of patients at low risk of acute coronary syndrome in decision-making about observation unit admission and options for subsequent testing through the use of a decision aid was associated with a lower rate of observation unit admission and no major adverse events, although the cohort was small (n = 204).45

Potential Expansion of the Use of Chest Pain Units for Intermediate-Risk Patients

Farkouh et al120 extended the use of a chest pain unit in a separate portion of the ED to include patients at an intermediate risk of adverse clinical outcome based on the previously published Agency for Health Care Policy and Research guidelines for the management of USA (see Table 7-14). They reported a 46% reduction in the ultimate need for hospital admission in intermediate-risk patients after a median stay of 9.2 hours in the chest pain unit. Extension of the use of chest pain units to intermediate-risk patients in an effort to reduce inpatient costs is facilitated by making available diagnostic testing modalities, such as treadmill testing and stress imaging (ECHO or NUC), 7 days a week.121

Management

Patients with atypical or mild symptoms, negative admission ECG, and normal initial cTn level should be observed in a chest pain unit. If the patient has no continuing angina and serial ECG and troponin assays are normal, a noninvasive test (exercise test, stress myocardial perfusion imaging, and stress echocardiography) could be performed before or early after discharge to decide for specific treatments. Some centers have specific protocols using hsTn or coronary CTA as discussed earlier. Other patients with no high-risk features such as ongoing or recurrent chest pain, new ST-T changes or elevated biomarkers in serial assessments, could be admitted to a step-down or regular unit. Patients with any of these high-risk criteria or those in a moderate to high-risk category based on risk stratification protocols should be admitted to an intensive coronary unit. General considerations in patients with possible or definite NSTE-ACS are summarized in Table 23.2.

Specific treatments in the acute phase of NSTE-ACS are directed either to alleviate ischemia and related symptoms or to prevent adverse cardiac events including myocardial infarction, heart failure, and death. Nitrates, beta-blockers, and calcium blockers are usual selections to achieve the first goal while antiplatelet and anticoagulants are used to target the second aim. Invasive approaches and revascularization help to achieve both therapeutic goals.

In addition to acute-phase treatments, after hospital discharge, all measures should be taken to control risk factors and prevent further events. Statins not only have an important therapeutic value in the acute phase but also have a pivotal role in reducing recurrent events.

Exercise Testing

The use of exercise testing is relatively safe and can identify patients at very low risk for cardiac events.21-25 Box 13-1 provides indications and contraindications for exercise testing in an ED or chest pain unit. In one series of 1000 clinically low-risk patients presenting to the ED with chest pain between 1993 and 1998, Amsterdam and colleagues21 performed exercise testing using a modified Bruce protocol and reported that 13%, 64%, and 23% of the exercise tests were normal, abnormal, or nondiagnostic, respectively. There were no deaths in the next 30 days regardless of the exercise test results and those with a normal exercise test were discharged directly from the ED. Of the 640, 125, and 235 patients who had a negative, positive, or nondiagnostic test, a myocardial infarction was diagnosed in 1, 4 and 0 patients, respectively. Similar results have been reported by others and are summarized in an AHA statement on the role of exercise testing for chest pain evaluation in the ED.25

Class I

1.

The history, physical examination, 12-lead ECG, and initial cardiac marker tests should be integrated to assign patients with chest pain into one of four categories: a noncardiac diagnosis, chronic stable angina, possible ACS, and definite ACS. (Level of evidence: C)

Patients with definite or possible ACS, but whose initial 12-lead ECG and cardiac marker levels are normal, should be observed in a facility with cardiac monitoring (e.g., chest pain unit), and a repeat ECG and cardiac marker measurement should be obtained 6 to 12 hours after the onset of symptoms. (Level of evidence: B)

In patients in whom ischemic heart disease is present or suspected, if the follow-up 12-lead ECG and cardiac marker measurements are normal, a stress test (exercise or pharmacologic) to provoke ischemia may be performed in the emergency department, in a chest pain unit, or on an outpatient basis shortly after discharge. Low-risk patients with a negative stress test can be managed as outpatients. (Level of evidence: C)

Patients with definite ACS and ongoing pain, positive cardiac markers, new ST-segment deviations, new deep T-wave inversions, hemodynamic abnormalities, or a positive stress test should be admitted to the hospital for further management. (Level of evidence: C)

Patients with possible ACS and negative cardiac markers who are unable to exercise or who have an abnormal resting ECG should undergo a pharmacologic stress test. (Level of evidence: B)

Patients with definite ACS and ST-segment elevation should be evaluated for immediate reperfusion therapy. (Level of evidence: A)

By integrating information from the history, physical examination, 12-lead ECG, and initial cardiac marker tests, clinicians can assign patients into one of four categories: noncardiac diagnosis, chronic stable angina, possible ACS, and definite ACS.

Chronic stable angina may also be diagnosed in this setting, and patients with this diagnosis should be managed according to the ACC/AHA guidelines for the management of patients with chronic stable angina.74

Studies published since the guidelines were printed include the excellent review from Amsterdam and colleagues75 and other reports that have described the use of immediate exercise testing to evaluate a large, heterogeneous group of low-risk patients with chest pain.76–79

Cardiac Imaging in Patients with Suspected MI

Diagnosis of MI can be made in the presence of evidence of new regional wall-motion abnormalities in echocardiography, myocardial scars in MRI or in nuclear tests, or an intracoronary thrombus during coronary angiography in combination with a significant rise and/or fall of cardiac troponin even in the absence of clinical symptoms. Transthoracic echocardiography (TTE) should always be available in chest pain units and emergency rooms. TTE allows detection of regional wall abnormalities and helps detect signs of other nonischemic causes of chest pain such as myocarditis, valvular disease, cardiomyopathy, pulmonary embolism, or aortic dissection. Another advantage of echocardiography is the detection of complications of MI such as ventricular wall rupture, secondary mitral valve regurgitation after papillary muscle rupture, or ischemia (Flachskampf et al., 2011). Myocardial disease can best be assessed with cardiac MRI. Multidetector computed tomography for anatomical evaluation of coronary arteries may be helpful in patients with low to intermediate pretest probability for ACS. In such patients, a normal CT scan can exclude coronary artery disease (Samad et al., 2012).

Neurologic Testing

Routine electroencephalography (Chapter 403) is not helpful because a single study may be normal, even in epileptic patients. Structural brain diseases rarely cause episodic loss of consciousness, and routine brain imaging studies are indicated only in patients with focal neurologic findings. Carotid Doppler (Chapter 414) studies can document stenosis, but unconsciousness requires bihemispheric dysfunction. Transcranial Doppler or magnetic resonance angiography of the basilar artery is indicated only in patients with symptoms suggestive of brain stem ischemia.

Treatment

Treatment of syncope depends on the underlying cause. Proximate to the syncopal episode, hospital admission (e.g., observation in a chest pain unit or its equivalent) is recommended when the cause of syncope is unclear, especially in elderly patients, otherwise fragile or worrisome patients, or those suspected of having a cardiac or cerebrovascular cause, or if the syncope resulted in significant injury. Patients at highest risk have a systolic blood pressure below 90 mm Hg, a history of myocardial infarction or heart failure, a complaint of shortness of breath, an abnormal initial ECG, or a hematocrit less than 30%.

Until the cause of the syncope is determined and treated, patients should be instructed to avoid situations that may cause injury as a result of the syncope, especially if there is no prodrome and episodes are frequent. Careful consideration should be given to driving restrictions, which may be mandatory depending on local laws, and restrictions on dangerous work-related activity (e.g., for pilots, heavy machine operators, bus drivers) until definitive therapy is given.

In patients with a cardiac cause of syncope, targeted treatments include valve replacement for aortic stenosis (Chapter 75); medications for hypertrophic cardiomyopathy (Chapter 60); cardioversion, a pacemaker, an implantable cardioverter-defibrillator, ablation, or medications for tachyarrhythmias (Table 62-3; Chapters 63 through 65Chapter 63Chapter 64Chapter 65); and fluid repletion for orthostatic hypotension.

In patients with neurocardiogenic syncope, behavioral guidance should encourage an increased intake of fluid and salt, as well as the avoidance of situations that precipitate symptoms. Patients should also be taught how to tense their arms and legs and grip their hands during prodromal symptoms to increase peripheral resistance and systemic blood pressure.2 If neurocardiogenic syncope recurs despite education and lifestyle changes, fludrocortisone (0.1 mg/day, starting dose) can expand intravascular volume but has not been proved to prevent syncope. Midodrine (usually 10 mg three times daily), an α1-receptor agonist and vasoconstrictor, has shown potential benefit,3 but other α-agonists have not. Paroxetine (20 mg/day), a selective serotonin re-uptake inhibitor, reduced recurrent neurocardiogenic syncope in one trial of very symptomatic patients but otherwise has been disappointing.3 In randomized trials, β-blockers have not been useful. Pacemakers do not reduce recurrent neurocardiogenic syncope,4 but they are very effective in patients with cardioinhibitory syncope as a result of severe bradycardia.3

Chest Pain and Acute Coronary Syndromes, and Acute Myocardial Infarction

Chest pain accounts for approximately 6 million annual visits to emergency departments in the United States, making chest pain the second most common complaint in the emergency department.10 ACS are life-threatening causes of chest pain seen in the emergency department and include unstable angina, non–ST segment elevation MI (NSTEMI), and acute MI or ST segment elevation MI. Less than 15% to 30% of patients who present to the emergency department with nontraumatic chest pain have ACS, however.11,12 An important challenge is to identify patients with ACS appropriately and admit them to the appropriate setting for further care. For the evaluation and management of patients with acute chest pain, prediction models have markedly improved our ability to estimate risk, and cost-effectiveness analyses have helped guide the development of new paradigms and the incorporation of new technologies.13

In addition to treating patients with ACS, the CICU has traditionally been considered appropriate for monitoring patients with acute chest pain until ACS is diagnosed or excluded. Increasing health care costs have created pressures, however, to increase the efficiency of CICUs. Possible strategies seek to decrease resource use by identifying low-risk patients for initial triage or early transfer to lower levels of care. The application of management algorithms and the development of intermediate care units are allowing for a distinction between intensive coronary care and careful coronary observation.14 The development of chest pain units located in the emergency department is an another alternative to CICU admission. These units are safe, effective, and a cost-saving means of ensuring that patients with unstable angina who are considered to be at intermediate risk of cardiovascular events receive appropriate care.15 Patients at low clinical risk can receive immediate exercise testing in the chest pain unit if the appropriate diagnostic modalities are available. This approach is accurate for discriminating low-risk patients who require admission from patients who can be discharged to further outpatient evaluation.16

Several reports have detailed strategies to identify high-risk patients early. To achieve more appropriate triage to the CICU of patients presenting with acute chest pain, Goldman and coworkers17 used clinical data on 1379 patients at two hospitals to construct a computer protocol to predict the presence of MI. This protocol was tested prospectively, and it had a significantly higher specificity (74% versus 71%) in predicting the absence of infarction than physicians deciding whether to admit patients to the CICU, and it had a similar sensitivity in detecting the presence of infarction (88% versus 87.8%). Decisions based solely on the computer protocol would have reduced the admission of patients without infarction to the CICU by 11.5% without adversely affecting the admission of patients in whom emergent complications developed that required intensive care.

In another study,18 the acute cardiac ischemia time-insensitive predictive instrument (ACI-TIPI) was used to triage patients with symptoms suggestive of acute cardiac ischemia to the CICU, telemetry unit, ward, or home. Use of ACI-TIPI was associated with reduced hospitalization among emergency department patients without acute cardiac ischemia. Appropriate admission for unstable angina or acute infarction was not affected. If ACI-TIPI is used widely in the United States, its potential incremental impact is estimated to be more than 200,000 fewer unnecessary hospitalizations and more than 100,000 fewer unnecessary CICU admissions.18

In a cost-effectiveness analysis, Fineberg and colleagues19 found that for patients with a 5% probability of infarction, admission to a CICU would cost $2.04 million per life saved and $139,000 per year of life saved compared with intermediate care. For the expected number of such patients annually in the United States, the cost would be $297 million to save 145 lives.

In another study by Goldman and associates,20 a set of clinical features was defined; if these features were present in the emergency department, they were associated with an increased risk of complications. These clinical features included ST segment elevation or Q waves on the electrocardiogram (ECG) thought to indicate acute MI, other ECG changes indicating myocardial ischemia, low systolic blood pressure, pulmonary rales above the bases, or an exacerbation of known ischemic heart disease. The risk of major complications in patients with acute chest pain can be estimated on the basis of the clinical presentation and new clinical observations made during the hospital course. These estimates of risk help in making rational decisions about the appropriate level of medical care for patients with acute chest pain.

Despite these findings, the implementation of these algorithms in clinical practice by physicians without specific training in their use has been minimal.21,22 This situation may relate to physicians’ reporting that they are too busy, are unsure of the value of the algorithms, and are concerned about the consequences of inappropriately discharging patients who are later found to have had MI.23

A more recent analysis by Tosteson and colleagues24 indicates that the CICU usually should be reserved for patients with a moderate (≥21%, depending on the patient's age) probability of acute MI, unless patients need intensive care for other reasons. Clinical data suggest that only patients with ECG changes of ischemia or infarction not known to be old have a probability of acute MI this high. A summary has been developed that outlines the location to which chest pain patients should be admitted (Table 3-2).25

Another important issue to consider is the length of stay in the CICU after patients are admitted. If patients are initially triaged to the CICU, the lack of cardiac enzyme abnormalities or recurrent chest pain during the first 12 hours of hospitalization are parameters that can be used to identify patients for whom a 12-hour period of CICU observation is sufficient to exclude acute MI.26 In a study by Weingarten and colleagues,27 physicians caring for patients with chest pain who were at low risk for complications received personalized written and verbal reminders regarding a guideline that recommended a 2-day hospital stay. Use of the practice guideline recommendation with concurrent reminders was associated with a decrease in length of stay from 3.54 ± 4.1 days to 2.63 ± 3 days and a total cost reduction of $1397 per patient. No significant difference was noted in complications, patient health status, or patient satisfaction when measured 1 month after hospital discharge.

The European Society of Cardiology and American College of Cardiology restructured the definition of acute MI in 2000 (Table 3-3).28 The principal revision compared with the previous World Health Organization definition29 is the inclusion of biomarkers, specifically troponin, as a necessary component. There have been some attempts to assess the new definition and the widespread introduction of troponin measurement on CICU admitting practices. One study by Amit and colleagues30 was a retrospective cohort study in which all admissions to the CICU the year before and after the introduction of troponin measurement and the updated MI definition were examined. There was a 20% increase in the number of CICU admissions, driven by a 141% increase in the number of NSTEMIs. Length of stay in the CICU decreased by 1 day for all ACS patients, and the 30-day mortality for acute MI did not change significantly. In another study by Zahger and associates,31 the number of NSTEMI patients increased by 33% after the definition change, whereas the number of patients with ST segment elevation MI remained the same. There was no change in the number of CICU beds at the participating institutions. The proportion of patients given the diagnosis of NSTEMI increased significantly more in centers with high use of troponin. These changes have a significant impact on resource use.

Given this increased demand for a relatively fixed resource, the question of whether all NSTEMI patients need to be admitted to the CICU arises. The CRUSADE registry32 showed that patients with NSTEMI often receive excess doses of antithrombotic therapy, and that dosing errors occur more often in vulnerable populations and predict an increased risk of major bleeding. Some institutions have interpreted these data to indicate that all NSTEMI patients should be admitted to the CICU because a maximally observed setting may limit excess dosing and bleeding complications.

At our institution, it is practice for only NSTEMI patients who are high risk by the TIMI risk score33 to be admitted to the CICU. The lower risk NSTEMI patients are admitted to a telemetry unit with cardiac nurses. There is preliminary evidence that admission of patients with initially uncomplicated chest pain with a relatively low probability of acute MI to a stepdown unit does not place at increased risk those who eventually “rule in” for MI.34 Regardless of specific setting, the adherence to clinical pathways offers the potential to improve the care of patients with ACS while reducing the cost of care.35

Prehospital Care

The extension of the CCU into the prehospital phase involves a shift in thinking from the CCU as a fortress, inside which excellent clinical care can be divorced from the chaos of the external world. Instead, we now know that applying the same principles of evidence, using outcomes studies and clinical trials, can improve the fate of patients in the highest-risk situation—before reaching the hospital—and that we can have a major effect in the period of highest risk in the hospital, the emergency department (ED).

Acute cardiac care begins with the basic principle of encouraging those with symptoms to enter the care system as quickly and efficiently as possible. Most people with symptoms of myocardial ischemia do not seek help quickly, and when they do, most do not call 911 or other emergency medical services (EMS); rather, they arrange nonmedical transport to an emergency facility.24,25 Though these statements simply present the facts, they belie the underlying complexity of this principle. First, it is based on the assumption that the public understands or can recognize the symptoms of ischemia and the implications of delay. Without those two concepts, people at risk will not enter the system quickly or efficiently. Although the implications of delay may be relatively simple to teach, accurate symptom recognition is difficult even for medically trained personnel, and this has fueled the widespread use of chest pain units. Further, we have limited understanding of what influences even knowledgeable people in the decisions they make when confronted with potential ischemic symptoms. Coupled with wide variability in EMS systems and in patient perceptions of them, fulfilling the basic principle of patients’ quick entry into the care system is a great challenge to successful prehospital cardiac care.

The National Heart, Lung, and Blood Institute-sponsored Rapid Early Action for Coronary Treatment (REACT) trial26 randomized communities to a massive public-relations effort or conventional approaches to attempting to improve responses to symptoms of possible ischemia. The trial showed no effect on time to treatment, appropriate diagnoses, or improved outcomes, but it did show an improvement in the use of EMS as the mode of transport. These results and those of previous studies suggest a need for more-targeted education and refocus of these efforts. Patient delay (prehospital delay) is the major factor in treatment delay, and it has not changed substantially in the reperfusion era.27,28 Efforts to understand the factors predisposing to delay and to define and target educational efforts to high-risk, high-yield populations may ultimately be a better approach than massive public-education efforts.

In a substudy, the REACT investigators29 showed that the decision to use EMS depended on the person's thinking about the symptoms: those who lived alone, those who thought that their symptoms were serious enough to take nitroglycerin, and those who were prompted to “go quickly” by others used EMS. Those who called their doctors were less likely to use EMS. Further, communities that had an EMS prepayment plan tended to have greater EMS use than communities in which individuals paid out of pocket (as fee for service) for EMS.

Despite these difficulties, given that the risk of life-threatening arrhythmias and death is greatest in the first few hours after MI,30 earlier access to life-saving technology is a crucial part of any community cardiac care program. This technology includes the following four main elements: (1) extensions of interventions available in the hospital, for example, the defibrillator; (2) the 12-lead ECG; (3) acute reperfusion therapy; and (4) other drugs.

Time to defibrillation is a critical variable in determining the likelihood of surviving a cardiac arrest. The ultimate approach to this problem is implantation of an automated internal cardioverter/defibrillator (ICD). Even with the expanded Multicenter Automatic Defibrillator Implantation Trial (MADIT)-2 criteria,4,31 this approach is unlikely to meet the need for primary prophylaxis against sudden death because a patient must have already experienced major dysrhythmia or MI to meet these criteria. Another approach is wider distribution of automated external cardioverter defibrillators (AECDs). A recent pilot study from Germany reported a threefold improvement in meaningful recovery from cardiac arrest in the community when AECDs were introduced,32 and the positive results of deploying AECDs in casinos in Las Vegas have been much discussed.33

The standard 12-lead ECG completes the loop for modern acute care of people with thrombosis-induced MI, given that both pathophysiology and definitive therapies have been established for this condition. The standard 12-lead ECG that provides key diagnostic information in patients with ACS symptoms is commonly performed by EMS personnel before hospital arrival. More modern technology can provide wireless ECG transmission from the scene to a handheld liquid crystal display (LCD) to support the on-call cardiologist making triage decisions.34 A recent study showed that 50% of patients with ECG interpretation of “acute MI” by trained emergency medical technologists and 85% with cardiologist concurrence of “acute MI” will have an acute thrombotic occlusion confirmed during attempted primary percutaneous coronary intervention (PCI).35 Further, the ability of practicing cardiologists to make both the same ECG diagnosis and the same reperfusion triage decision on paper and on the LCD of a handheld device has been reported.36,37 Trials have shown that prehospital transmission of ECGs to cardiologists is associated with a 50-minute reduction in door-to-balloon times.38,39 Recently, a large registry-based observational study of more than 12,000 patients confirmed that prehospital ECG acquisition is associated with a greater use of reperfusion therapy and improved reperfusion times.40

The ST segment has been the portion of the ECG typically used to provide both diagnostic and prognostic information. Ischemia-induced terminal distortion of the QRS complex, however, has been shown to be superior to ST-segment measurements in predicting final acute MI size and assessing the possible effects of fibrinolytic therapy.41 Also, comparative quantitative changes in T waves and infarction-induced initial distortion of the QRS complex have been shown to add to historical timing in the prediction of limiting MI size through reperfusion therapy.42

When the prehospital ECG is perceived to indicate acute coronary thrombosis and the clinical situation is appropriate, early reperfusion therapy can be started intravenously by emergency medical technicians, by rapid administration in the ED, or by PCI in the catheterization laboratory. Electronic transmission of 12-lead ECGs to the hospital ED has been shown to reduce the time to reperfusion via primary PCI by 50 minutes.38,39,43 The administration of fibrinolytic therapy in the field, also predicated on the availability of 12-lead ECGs at the scene, now has been tested in multiple clinical trials. A systematic overview showed reduced mortality with prehospital versus hospital administration of fibrinolytic therapy,44 and a pilot trial of field fibrinolysis suggested outcomes comparable with direct PCI.45 For the most part, field administration of fibrinolytic therapy in the United States has been limited by concerns about liability and the absence of physicians in ambulances. In countries such as France, the system supports the effort, but it is unclear in the United States whether appropriately trained nonphysician personnel can safely give prehospital fibrinolytic or other medical therapy unless there is direct exchange of clinical and ECG information with an on-call physician. When they become available, the results of the ASsessment of the Safety and Efficacy of a New Thrombolytic Agent (ASSENT)-III Plus study, in which patients from around the world were treated with fibrinolytic therapy in the field by personnel with various clinical backgrounds, should help to address these concerns.

Until reforms in medical liability can be addressed and the safety of prehospital therapy given by nonphysicians is clearly shown and accepted, the first consideration in the United States should be to ensure that all EMS units can capture and transmit in-field 12-lead ECGs. Prehospital services then can focus on timely transfer of patients with acute MI to regional centers capable of rapid administration of fibrinolytic therapy or performance of PCI. For rural areas with long transit times to the nearest hospital, however, improved technology, including electronic transmission of ECGs from the field to on-call physicians, should drive consideration of in-field treatment if qualified nonphysician personnel are available. Development of hybrid, but perhaps safer, alternative approaches to full-dose fibrinolysis also could be an answer. Regardless, in addition to understanding patient-related factors in responding to symptoms and using EMS, broad standardization of EMS services and their improved coordination with regional acute cardiac care facilities will be necessary to enhance prehospital care.

In patients with ACS who are not candidates for acute reperfusion therapy, the amount of depression in the ST segment of the initial ECG has been shown to have value in early risk stratification.46 Unlike STEMI, it has been difficult to show a dramatic time-dependency of outcome after giving effective therapies in NSTE ACS. Thus, it is difficult to know whether the expense of supplies and training needed for prehospital administration of pharmacologic therapy, other than aspirin and acute therapies such as oxygen, nitrates, and morphine, is warranted. However, having ECG information available from the field should aid in patient triage on arrival and inform decisions for early invasive management strategies. Such information also could improve the likelihood of evidence-based therapies being started early on arrival as well as help identify patients eligible for clinical trials, particularly if integrated with input from on-call cardiology services at the receiving hospital.

Future prehospital cardiac care of patients with ACS may be enhanced by the availability of both practice guidelines and access to the medical literature via handheld devices. Even a simple innovation—such as a new way to provide quantitative information from the 12-lead ECG to the handheld device of the on-call cardiologist—might be useful. A new display of the ECG with all 24 views around “clock faces” surrounding schematic images of the heart, in both the frontal and transverse planes, has been introduced.47 This might provide added decision support for the cardiologist's interpretation of the initial ECG by indicating the spatial location of the acute ST-segment deviation for more precise localization of the culprit lesion within the coronary artery. A substudy of the Global Use of Strategies To Open occluded coronary arteries (GUSTO) I and II trials has suggested the value of this method.48

Chest Pain Units

The United States is leading the way with the development of chest pain units [CPU]. This advance in the management of acute chest pain presentations to hospital emergency departments is promoted by the Society of Chest Pain Units [http://www.scpcp.org/]. More than a quarter of a century ago the first chest pain center opened in St. Agnes Hospital in Baltimore, MD.1,2 CPU were initially developed to facilitate rapid assessment of chest pain patients and the subsequent treatment of patients with acute myocardial infarction.3-5 Research has shown that CPU are accepted as a safe and cost-effective method of assessing low-risk patients presenting with acute chest pain.4,6,7 In the United States, the number of chest pain centers is estimated to be ∼1200 and is increasing rapidly.8-11 The main purpose of CPU is to improve outcomes for individuals with a suspected acute myocardial infarction.12 Chest pain units are rapidly evolving not only in the United States, but also in Australia, United Kingdom, Brazil, and other countries around the world.12-15

More information on chest pain units can be found in Amsterdam EA, Kirk JD. Chest pain units. Cardiol Clin 2005;23(Nov).