4. Treatment protocols for chest pain patients

When patients present to an emergency department with chest pain, the first step is to determine if they are experiencing a myocardial infarction, since action must take place immediately if myocardial damage is to be minimized. To assure rapid treatment many hospitals developed 'fast track' protocols to facilitate thrombolytic therapy for appropriate patients with myocardial infarction. Unfortunately, despite guidelines and protocols promoting rapid administration of thrombolytic therapy, few hospitals consistently achieve this goal. The myocardial infarction triage and intervention (MITI) [4] trial evaluated heart attack care in hospitals, observing that hospitals provided better cardiac care when involved in a research study compared with when they were not in a clinical study. These inconsistencies within the same emergency departments highlighted the fact that 'preparedness' is a critical component of heart attack care and that emergency departments need some form of sustaining influence to maintain vigilance and provide optimal cardiac care.

However, optimal cardiac care is not achieved solely through guidelines for thrombolytic therapy. Annually, over 5.5 million patients in the US present to the emergency department with chest pain, but eventually only 10-15% are diagnosed with an acute myocardial infarction [15,16]. Although management strategies for patients with myocardial infarction are well defined [22,23], treatment of chest pain patients with atypical or nondiagnostic symptoms is less clear. When unsure of a definitive diagnosis many physicians will admit the patient to the coronary care unit to be safe. An estimated 50-60% of emergency department chest pain patients are admitted to coronary care units and most are found to be free of cardiac disease.

This conventional approach to treating patients with undiagnosed chest pain, however, contains major shortcomings. First, although the incidence of myocardial infarction patients misdiagnosed has been reduced, an estimated 5% of chest pain patients fall through the cracks and are mistakenly sent home where they experience a myocardial infarction. Of this number, approximately 16% will die from complications associated with their heart attack [7-10]. Second, this is an expensive way to treat chest pain patients. Approximately 70% of patients admitted to coronary care units do not develop a myocardial infarction during observation and are discharged with no significant disease found [9,15]. In the US alone, these 'unnecessary' admissions account for an estimated 1.6 million hospital days and a total cost exceeding $4 billion annually [24].

Chest pain centers address the shortcomings in the conventional approach by presenting an effective strategy for managing both sets of patients with chest pain. Patients presenting to chest pain centers with chest pain or discomfort are subject to a comprehensive and systematic triage plan [25]. In addition to promoting fast track treatment protocols for opening blocked coronary vessels, through the appropriate use of thrombolytic therapy or angioplasty, the triage plan aids the clinician in attaining a 'proper diagnosis.' Chest pain patients with an uncertain diagnosis are no longer automatically admitted to cardiac care, but are observed, evaluated and placed into one of five clinical tracks, depending on the probability of myocardial ischernia (Fig. 1).

The chest pain center provides standardized, yet accelerated protocols for a quicker more precise evaluation of patients than does the traditional inpatient [11, 12]. Patients in these units undergo a series of protocol-driven tests that quickly provides sufficient evidence to definitively rule out a myocardial infarction. Additionally, serial testing of patients for biochemical markers of cardiac damage allows risk stratification of the group, facilitating appropriate treatment. Whether they enter chest pain centers or the emergency department, patients with obvious signs of acute myocardial infarction and ST segment elevation are placed in Track I and require prompt treatment with thrombolytic agents. After initiating therapy, usually within 30 min of arrival, patients are admitted to the coronary care unit. Achieving this goal is estimated to have an annual life savings potential of 15 000 additional patients [26].

Track II represents patients with non-Q-wave myocardial infarction (NQMI), or severe progressive unstable angina (UA). A high rate of mortality can be associated with these patients, and they are treated and stabilized in chest pain centers until they can be admitted into the coronary care unit. The patient can be 'cooled down' through the appropriate use of aspirin, heparin and, most recently, GP Ilb/Illa platelet receptor inhibitors, pending decisions regarding cardiac catheterization and patient management. Recent clinical trials suggest that the appropriate use of GP Ilb/Illa receptor inhibitors may reduce progression to myocardial infarction, reduce the magnitude of an infarction that still occurs, and improve outcomes if angioplasty, with or without stenting, is part of the treatment regimen [27-33]. Other studies are underway to evaluate the appropriate use of these agents with thrombolytics. The primary concern when combining potent antiplatelet and antithrombotic agents will be the increased risk of major bleeding, intracranial hemorrhage, or thrombocytopenia. If a surgical procedure is required, the antiplatelet therapy should be discontinued, and platelet infusion may be necessary. Chest pain center specialists can treat these patients effectively without compromising later treatment options.

A second level of care provided by chest pain centers involves the evaluation of patients with potential myocardial ischemia. After acute myocardial infarction is ruled out, chest-pain patients are further evaluated and differentiated, based on the likelihood of myocardial ischemia. Patients are assigned to Track III (moderate probability) or Track IV (low probability) (Fig. 1). Since some 40-60% of acute myocardial infarction patients have experienced prodromal symptoms in the week before the acute event, effective management of these Track III and IV patients offers the greatest likelihood of avoiding infarction. Early and effective management, both behavioral and pharmacological, of these individuals may forestall or possibly avoid acute incidents. At the same time, the observation period allows identification of the higher risk patients in Track III who may eventually be admitted to the coronary care unit, but can be treated appropriately until that decision is clear. The remaining patients in Track III and IV denote a group that has experienced an ischemic episode and are more likely to benefit from observational management of their disease. Because of the fear inherent in this type of event these patients are 'teachable.'

Track III and IV patients (60% of presenters) have become, perhaps, the most important subset of patients in chest pain center strategy. Although, the majority of these patients can be safely discharged for outpatient follow-up, a small percentage of myocardial infarction patients show atypical presentations.

Traditionally, these patients were released, with the inherent risk of post-discharge infarction, or required a 2- to 3-day inpatient stay in the coronary care unit. However, after a 6- -to 8-h period in the chest pain clinic, with the use of biochemical markers and possibly stress testing, 80% of these patients can be safely discharged. The overall goal of chest pain centers is to keep accidental discharge of patients with myocardial infarction to less than 0.1%. This high quality care is provided at one-half the cost of a traditional rule-out [34]. Track V patients (15% of presenters) represent a group of patients that may, or may not, have experienced a cardiac event. If the chest pain can be determined to be non cardiac, often by obtaining a complete clinical and patient history (for example, establishing that the patient had been hit in the chest with an elbow during a ball game), the patients are sent home. The importance of good interviewing skills should not be overlooked with any of these groups. To avoid accepting a cardiac origin for their pain, patients will often offer plausible explanations once the pain has past.

Triage of chest pain patients represents another milestone in the treatment of acute ischemic coronary syndromes. Chest pain centers provide for the rapid treatment of patients with acute myocardial infarction, but promote the more aggressive treatment of patients with unstable angina or even early stages of ischemic disease. This opens the possibility of a more aggressive community awareness program for early recognition of prodromal symptoms since chest pain centers are more capable than emergency departments or hospitals to sort out low-probability ischemic patients and handle large numbers of patients. Thus, as the paradigm shifts to early intervention, heart attack avoidance care can be emphasized, although this may result in larger number of patients presenting to chest pain centers with milder symptoms of chest pain (Fig. 2). Chest pain centers are designed to use standardized protocols to efficiently and accurately diagnose and treat these patients, without being overburdened.

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