Implementation

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Implementation of a CPU approach in an emergency setting is nearly as challenging as evaluating the patients themselves. Several syner-gistic components are required to adequately, efficiently, and cost-effectively evaluate this patient population, including

1) Sufficient and dedicated space to evaluate and observe the patients

2) Nursing staff and other ED personnel that are knowledgeable and dedicated to this approach

3) Emergency physician staff that can be responsible for these patients

4) Collaboration of cardiologist colleagues on the protocols, testing, follow-up, and admission procedures

5) Availability of nuclear cardiology and radiology colleagues for the emergent performance and reading of nuclear imaging studies

6) Laboratory personnel to run serial cardiac biomarker measurements

7) Primary care physicians that understand the scope and limitations of a CPU evaluation for follow-up

Various physical models exist for CPUs. Several of these models are illustrated in Table 1 and Figs. 1 and 2. In Table 1, the Medical College of Virginia protocol integrates the use of radionuclide

Table 1

Medical College of Virginia CPU protocol

Table 1

Medical College of Virginia CPU protocol

Level

AMI risk

ACS risk

Strategy

Disposition

1

Very high

Very high

Fibrinolysis/PCI

CCU

2

High

High

ASA, heparin, NTG, GP Ilb/IIIa

CCU

3

Moderate

Moderate

Markers + nuclear imaging

9-h observations

4

Low

Mod or low

Nuclear imaging

Home and OP stress test

5

Very low

Very low

As needed

Home

Abbreviation: AMI, acute myocardial infarction.

Abbreviation: AMI, acute myocardial infarction.

testing into a five-level risk stratification program. Figs. 1 and 2 demonstrate protocols for the University of Cincinnati and the Mayo Clinic, respectively. Both protocols integrate myocardial necrosis testing by cardiac biomarkers and functional exercise testing. Each model takes into account the specific patient population, cardiologist collaboration, nuclear imaging availability, and ED resources to design the optimal CPU for that hospital.

Most of these units are located in an area adjacent to, but separate from, the general emergency patient population. Often the CPU protocol patients are evaluated in conjunction with other observation unit (OU) protocols. As these patients are frequently in the ED for 6 hours or more, it is desirable to provide many of the inhospital comforts generally not available in a traditional ED. These comforts may include hospital beds, meals, television sets, and telephones, which greatly improve patient satisfaction. This space allocation and additional patient resources may be prohibitive for some hospital physicians, nurses, and administrations considering the start-up of a new CPU and, thus, some of these protocols are performed within the regular department using basic ED resources. This alternative can be suboptimal as the increased time required for CPU protocols can hamper ED patient throughput, lowering patient satisfaction.

A successful CPU also requires a nursing staff dedicated to the care of these patients with special needs. These patients require frequent assessment, close monitoring, noninvasive testing, and serial cardiac biomarker testing and ECG acquisition. These tasks are generally in excess of those expected for a typical emergency patient and may require additional training and staffing as appropriate for the individual institution and ED. The overall success of the unit depends on adherence to the systematic evaluation protocol by nursing personnel.

Although most of these patients are placed on CPU protocols that do not require constant

Fig. 1. University of Cincinnati "Heart ER'' strategy. Data from [5] Gibier et al, Ann Emerg Med 1995;25:1-8 and [17] Storrow et al, Circulation 1998;98:1-425.
Fig. 2. Mayo Clinic Strategy.

emergency physician interaction, they must be continually re-evaluated and re-assessed while in the CPU. ACS is a dynamic process and can easily progress over the course of the patient's stay in the CPU. Symptom changes, cardiac biomarker positivity, and ECG ST-segment variation should prompt immediate therapy and potential intervention in the cardiac catheterization laboratory. The emergency physician must stay integrally involved with the patient to provide this increased level of therapy. A successful CPU requires the cooperation of many health care professionals in the ED and around the participating institution. An absolutely critical component of successful CPU operation is the collaboration and cooperation of cardiologists and radiologists. Cardiology involvement in CPU protocols is necessary for many reasons. Formulation, knowledge, and acceptance of CPU protocols particular for each institution requires active participation and expertise of the cardiologists. In addition, many CPU protocols successfully use provocative testing with radionuclide echocardiography, or standard graded exercise testing, and these tests generally require the interpretation of a cardiologist [5-10].

While collaboration between emergency medicine and cardiology is intuitive, integration with nuclear cardiologists and radiologists is also pivotally important to the success of every CPU.

Radionuclide perfusion imaging has emerged as an important tool in many centers for assessing patients who present with and without known cardiovascular disease and also in evaluating the patient presenting to the ED with possible ACS. Technetium-99 (Tc-99) sestamibi tomographic imaging is the most common agent currently being used in patients presenting to the ED with suspected ACS [11,12]. Studies have shown that positive rest perfusion imaging accurately identifies patients at high risk for adverse cardiac events [13]. Radionuclide perfusion imaging has thus become a cornerstone of evaluation for many units [14,15].

The diagnostic sensitivity of myocardial perfusion imaging is, in part, dependent on the timing of injection in relation to the cessation of chest pain. The major obstacles for radionuclide studies have traditionally included cost and accessibility. The perfusion agents have a 6- to 12-hour shelf life and, thus, have to be prepared several times a day to be available for acute imaging. Collaboration with nuclear cardiology and radiology colleagues is paramount for this reason. Timely evaluation of these patients requires immediate access to these studies and timely reading and reporting of the results by expert readers.

The laboratory must also be supportive of a CPU. Ideally, bedside point-of-care testing for cardiac biomarkers provides rapid data collection for these patients as creatine-kinase myocardial band (CK-MB) and, in particular, the troponins I (Tnl) and T (TnT) allow risk stratification to be performed expeditiously [16]. A collaborative relationship between emergency physicians and labo-ratorians can ensure a consistent and effective evaluation of patients in the CPU.

Finally, primary care physicians must be supportive of the CPU and willing to have patients evaluated in this protocol-driven process. Communication between emergency physicians and the patient's primary care physician can then assure careful follow-up and patient compliance with lifestyle changes and treatment recommendations after evaluation.

Examples of chest pain units

Over the years, several manifestations of CPUs have evolved. Each of these models has been successfully adopted by specific institutions for its patient populations. An individual institution should carefully evaluate their patient population, physician expertise, physical structure, staffing model, and hospital environment to most adequately determine their optimal CPU protocol.

For instance, the University of Cincinnati Center for Emergency Care ''Heart ER,'' established in October 1991, was one of the first ED-based CPUs. Patients at low to moderate risk for ACS are admitted to the Heart ER for a protocol-driven evaluation of their chest discomfort. The serial cardiac biomarkers CK-MB and troponin T levels are drawn at 0, 3, and 6 hours after presentation to the ED. The original protocol used continuous ST-segment trend monitoring, which has since been discontinued. Graded exercise testing or Tc-99 sestamibi radionuclide scanning is now performed depending on patient's functional status and test availability. Patients having negative evaluations in the Heart ER are released to home with careful follow-up as an outpatient [5].

In the first 2131 consecutive patients evaluated over a 6-year period, 309 (14.5%) required admission and 1822 (85.5%) were released to home from the ED. Of admitted patients, 94 (30%) were found to have a cardiac cause for their chest pain. Follow-up of 1696 patients discharged from the Heart ER to home yielded 9 cardiac events (0.53%, confidence interval [CI], 0.24%-1.01%; 7 percutaneous transluminal coronary angioplasty, 1 coronary artery bypass grafting, 1 death) [17]. These data suggest that the Heart ER program provides a safe and effective means for evaluating low- to moderate-risk patients who present with possible ACS to the ED.

Other institutions also have developed effective chest pain center strategies. The Medical College of Virginia has an elegant protocol that triages chest pain patients into five distinct levels (see Table 1) [14,18]. Level 1 patients have ECG criteria for acute myocardial infarction (AMI) while level 5 patients have clearly noncardiac chest discomfort. The triage level dictates further diagnostic measures and treatment. Intermediate level patients (levels 2 and 3) include individuals with variable probability of unstable angina. These patients are admitted to the CCU for diagnostic testing for ACS while less acute patients (level 4) undergo serial cardiac biomarker determination and Tc-99 sestamibi radionuclide imaging from the ED.

The University of California at Davis protocol uses a novel use of immediate exercise treadmill testing without serial cardiac biomarker determination. In a recent study of 1000 patients, 13% were positive and 64% were negative for ischemia. The remaining 23% of the patients had non-diagnostic tests. No adverse effects exist from exercise testing and no mortality occurred in either of the patient evaluation groups at 30-day follow-up. The authors concluded that immediate exercise testing of low-risk patients is safe and accurate for the determination of which patients can be safely discharged from the ED [6]. A careful history is required to ensure that only low- to moderate-risk patients for ACS are exercised acutely in the ED.

The Mayo Clinic separates patients into low-, intermediate-, and high-risk categories according to Agency for Health Care Policy Research (AHCPR) guidelines. Intermediate-risk patients are evaluated with CK-MB levels at 0, 2, and 4 hours while undergoing continuous ST-segment monitoring and 6-hour observation. If this evaluation is negative, an ECG exercise test, a nuclear stress test, or an echocardiographic stress test is performed. Patients with positive or equivocal evaluations are admitted, whereas patients having negative evaluations are discharged to home with a 72-hour follow-up [19].

Lastly, Brigham and Women's Hospital divides patients into three groups: unstable angina or AMI, possible ischemia, and nonischemic. Patients with unstable angina or AMI are admitted, whereas nonischemic chest pain patients are discharged from the CPU. The intermediate, or ''possible ischemia,'' group either undergoes exercise treadmill testing with a 6-hour period of observation or a 12-hour period of observation. At the end of the observation period, stable patients are discharged to home. Nichol and colleagues [20] evaluated the impact of this pathway approach in a retrospective cohort of 4585 patients and found that a 17% reduction in admissions and an 11% reduction in length of stay would occur if even fewer than 50% of eligible patients for observation and exercise testing had participated.

Each institution has constructed its CPU protocols to suit its patient population, physician expertise, and resource availability to optimize chest pain evaluation. Each hospital and patient population represents a unique environment with specific needs and resources that must be reflected in the ultimate CPU design and implementation.

Once the patient "passes" the CPU protocol and apparently does not have ACS, the individual can be discharged safely to home and appropriate follow-up arranged. Adequate attention must be given to the cause of the patient's discomfort even if it is determined not to be cardiac in nature. Testing for other noncardiac chest pain, including gastrointestinal or psychiatric disease, must then be performed. Patients also require outpatient provocative testing, if not received in the CPU protocol, to further delineate their cardiac risk caused by fixed coronary artery lesions. These tests must be followed and acted on by a primary care physician.

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