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Approximately 6 million patients are evaluated in the ED setting for chest pain or symptoms suggestive of an acute coronary syndrome (ACS) each year.1 A small number of these patients will present with ST-segment elevations on their initial 12-lead ECG and go on to immediate thrombolysis or percutaneous coronary intervention. A much larger subset of these patients with chest pain will ultimately be found to have an alternative diagnosis other than ACS. Unfortunately, these patients with nonischemic chest pain often exhibit symptoms that are no different than patients with true myocardial ischemia. Indeed, no symptom alone or in combination is sufficiently discriminatory to preclude further diagnostic workup.2 Initial serologic markers of cardiac injury (total creatine phosphokinase and its MB subfraction, troponin) and ECG changes are also nondiagnostic in this subset of patients, with very poor sensitivities of 20% and 50%, respectively.3,4 Thus, emergency physicians routinely face the question of how to manage patients who are at a non-negligible risk for ischemic chest pain, but have no certain diagnostic indications of ACS on presentation to the ED.

In practice, the determination of ischemic chest pain in the ED is difficult, and errors occur. Approximately 2% to 4% of patients presenting to the ED with symptoms suggestive of myocardial ischemia are mistakenly discharged.5 The consequences of premature discharge of patients at high risk for adverse coronary events can be catastrophic, with a mortality risk nearly twice as high as those who are admitted.5 As such, physicians manage this complaint quite conservatively. This approach yields many unnecessary admissions, however, and only approximately 30% of patients admitted for a suspected myocardial infarction are ultimately diagnosed with ischemic heart disease.6 With this practice, national expenditures for admissions to rule out ACSs approach $10 billion each year.7 Many centers have adopted short-stay “chest pain units” to work toward expeditious and cost-effective management of this issue, and emergency physicians are increasingly responsible for the downstream management of these chest pain workups.

This chapter addresses the robust field of noninvasive myocardial imaging as it relates to the evaluation of patients with symptoms concerning for acute myocardial ischemia. These imaging modalities are used as a means of cardiac risk stratification, aiming to increase the diagnostic sensitivity and specificity for ACS. Furthermore, these tests help to guide patients’ management and prognosis. Each modality has its strengths and limitations, and a thorough understanding of these characteristics will guide the clinician to choose the most useful study for each patient.

Multiple imaging modalities employ the concept of stress imaging. This technique seeks to unmask coronary flow limitations that are otherwise silent at rest. Under increased metabolic demand, limited perfusion can alter the metabolic activity of the myocardium or affect regional myocardial function. The myocardial ischemic cascade (Figure 299.1-1) provides the theoretical framework for these changes. Patient symptoms and ECG changes typically occur after perfusion and regional function have been impaired. This ...

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