Acute Coronary Syndromes Without ST-Segment Elevation

KEY FEATURES

Essentials of Diagnosis

• Distinction in acute coronary syndrome (ACS) between patients with and without ST-segment elevation at presentation is essential to determine need for reperfusion therapy

• Fibrinolytic therapy is harmful in ACS without ST-segment elevation, unlike with ST-segment elevation where acute reperfusion saves lives

• Antiplatelet and anticoagulation therapies and coronary intervention are mainstays of treatment for ACS without ST-segment elevation

General Considerations

• ACSs comprise the spectrum of unstable cardiac ischemia from unstable angina to myocardial infarction (MI)

• ACSs are classified based on the presenting ECG as either "ST-segment elevation myocardial infarction" (STEMI) or "non–ST-segment elevation acute coronary syndrome (NSTE-ACS)"

• The evolution of cardiac biomarkers allows determination of whether MI has occurred

• The universal definition of MI is a rise of cardiac biomarkers with at least one value above the 99th percentile of the upper reference limit together with evidence of myocardial ischemia with at least one of the following:

  • Symptoms of ischemia

  • ECG changes of new ischemia

  • New Q waves

  • Imaging evidence of new loss of viable myocardium or new wall motion abnormality

• ACSs is a dynamic state; patients frequently shift from one category to another, as new ST elevation can develop after presentation and cardiac biomarkers can become abnormal with recurrent ischemic episodes

CLINICAL FINDINGS

Symptoms and Signs

• Angina occurs at rest or with minimal exertion

• Substernal chest pain or discomfort that may radiate to the jaw, left shoulder, or arm

• Dyspnea, nausea, diaphoresis or syncope may either accompany the chest discomfort or may be the only symptom of ACS

• About one-third of patients with MI have no chest pain per se—these patients tend to be older, female, have diabetes, and be at higher risk for subsequent mortality

• Patients with ACS have signs of heart failure in about 10% of cases, and this is also associated with higher risk of death

DIAGNOSIS

Laboratory Tests

• Depending on the time from symptom onset to presentation, initial laboratory findings may be normal

• Markers of cardiac myocyte necrosis that may be used to identify acute MI

  • Myoglobin, creatine kinase (CK)-MB, and troponin I and T

  • High-sensitivity troponin is the recommended biomarker to diagnose acute MI

  • In patients with STEMI, these initial markers are often within normal limits as the patient is being taken to immediate reperfusion

  • In patients with MI without ST-segment elevation, it is the presence of abnormal CK-MB or troponin values that are associated with myocyte necrosis and the diagnosis of MI

• High-sensitivity troponin assays allow rapid sex-based rule out algorithms for MI in emergency departments

• Serum creatinine is an important determinant of risk

• Estimated creatinine clearance is important to guide dosing of certain antithrombotic agents, ...