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INTRODUCTION AND EPIDEMIOLOGY

About 7 million patients with chest pain present to a U.S. ED each year.1 Of these, more than 50% are placed into an observation unit or admitted to the hospital, yet only about 10% are eventually diagnosed with an acute coronary syndrome (ACS).2-6 Still, approximately 2% of patients with acute myocardial infarctions (AMIs) are not diagnosed on initial presentation to the ED.2 We discuss the features and approach that help differentiate ACS from other causes of chest pain. Chapter 49, “Acute Coronary Syndromes,” and Chapter 51, “Low-Probability Acute Coronary Syndromes,” discuss management of these specific syndromes.

Acute chest pain is the recent onset of pain, pressure, or tightness in the anterior thorax between the xiphoid, suprasternal notch, and both midaxillary lines. ACS includes AMI and acute ischemia (unstable angina). AMI is defined by myocardial necrosis, evident from elevation of cardiac biomarkers, and is classified by ECG findings into ST-segment elevation myocardial infarction (STEMI) or non–ST-segment elevation myocardial infarction (NSTEMI). Unstable angina is a clinical diagnosis defined by chest pain or an equivalent (neck, upper extremity pain) from inadequate myocardial perfusion that is new or occurring with greater frequency, less activity, or at rest. Patients with unstable angina do not have pathologic ST-segment elevation on ECG or cardiac biomarker elevation, but they are at risk of eventual myocardial damage absent recognition and treatment.

PATHOPHYSIOLOGY

The chest wall, from the dermis to the parietal pleura, is innervated by somatic pain fibers. Neurons enter the spinal cord at specific levels corresponding to the skin dermatomes. Visceral pain fibers are found in internal organs, such as the heart, blood vessels, esophagus, and visceral pleura. Visceral pain fibers enter the spinal cord and map to areas on the parietal cortex corresponding to cord levels shared with somatic fibers. Stimulation of visceral or somatic afferent pain fibers results in two distinct pain syndromes. Pain from somatic fibers is usually easily described, precisely located, and often experienced as a sharp sensation. Pain from visceral fibers is generally more difficult to describe and imprecisely localized. Patients with visceral pain are more likely to describe it as discomfort, heaviness, pressure, tightness, or aching. Visceral pain is often referred an area of the body corresponding to adjacent somatic nerves, which explains why pain from an ACS may radiate to the neck, jaw, or arms. Factors such as age, sex, comorbid illnesses, medications, drugs, and alcohol may interact with psychological and cultural factors to alter pain perception and communication.

CLINICAL FEATURES

INITIAL ASSESSMENT

Patients with abnormal vital signs, ECG findings of ischemia or injury, a history of prior coronary artery disease, multiple atherosclerotic risk factors, or any abrupt, new, or severe chest pain or dyspnea should be quickly placed into a treatment bed. Initiate cardiac monitoring and IV access, and ...

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