ESSENTIALS OF DIAGNOSIS
Distinction in 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.
ACSs comprise the spectrum of unstable cardiac ischemia from unstable angina to acute MI. ACSs are classified based on the presenting ECG as either ST-segment elevation MI (STEMI) or non–ST-segment elevation MI (NSTEMI). This allows for immediate classification and guides determination of whether patients should be considered for acute reperfusion therapy. The evolution of cardiac biomarkers then allows determination of whether MI has occurred.
ACSs represent a dynamic state in which 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.
Chest pain is one of the most frequent reasons for emergency department visits. Algorithms have been developed to aid in determining the likelihood that a patient has an ACS and, for those patients who do have an ACS, the risk of ischemic events and death.
Patients with ACSs generally have symptoms and signs of myocardial ischemia either at rest or with minimal exertion. These symptoms and signs are similar to the chronic angina symptoms described above, consisting of 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 ACSs have signs of HF in about 10% of cases, and this is also associated with higher risk of death.
Many hospitals have developed chest pain observation units to provide a systematic approach toward serial risk stratification to improve the triage process. In many cases, those who have not experienced new chest pain and have insignificant ECG changes and no cardiac biomarker elevation undergo treadmill exercise tests or imaging procedures to exclude ischemia at the end of an 8- to 24-hour period and are discharged directly from the emergency department if these tests are negative.
Depending on the time from symptom onset to presentation, initial laboratory findings may be normal. The markers of cardiac myocyte necrosis (myoglobin, CK-MB, and troponin I and T) may all be used to identify acute MI, although high-sensitivity troponin is the recommended biomarker to diagnose acute MI (see ...