Airway, breathing, and circulation (ABCs), obtain and interpret 12-lead ECG within 10 minutes of arrival to identify a STEMI and need for emergent revascularization, establish intravenous (IV) access, place patient on cardiac monitor with continuous pulse oximetry, have resuscitation equipment available, consider serial ECGs, obtain troponin, aspirin load if no contraindications, and nitroglycerin, oxygen, and analgesia as indicated.
Acute coronary syndrome (ACS) represents a spectrum of clinical diseases that result from an acute mismatch of myocardial oxygen supply and demand leading to myocardial ischemia or infarction. ACS includes ST-segment elevation myocardial infarction (STEMI), non-ST-segment elevation myocardial infarction (NSTEMI), and unstable angina (UA). When the severity and duration of ischemia are sufficient to cause necrosis of myocardial tissue, the result is acute myocardial infarction (AMI). AMI is further divided into multiple subtype classifications: When considering ACS, type 1 AMI is the result of a coronary event with acute occlusion followed by thrombus formation and vasospasm. Type II AMI is the result of secondary ischemia due to increased oxygen demand or decreased supply.
The most prominent presenting symptom of ACS is usually diffuse chest discomfort, often described as a crushing pressure-like sensation. Presenting symptoms of ACS are variable and can include combinations of chest pain, pressure, heaviness, or discomfort that can radiate to the upper extremities, neck, abdomen, back, or jaw. Other associated symptoms can include diaphoresis, nausea, vomiting, shortness of breath, lightheadedness, confusion, presyncope, syncope, and fatigue. Vague associated symptoms can be subtle and without chest pain, especially in women, elderly individuals, and those with comorbid conditions such as diabetes.
ACS is most commonly due to coronary artery atherosclerosis, the long-term result of a cascade of chronic inflammatory processes that lead to the development of plaques. The fibrous cap over the plaques may be unstable and can rupture, leading to a platelet-rich thrombosis, which can partially or completely obstruct blood flow. Usually, ischemic symptoms at rest develop when coronary vessel stenosis exceeds 95% obstruction. Risk factors for atherosclerotic disease include hypertension, hyperlipidemia, diabetes, smoking, increased weight, increased age, male sex, renal insufficiency, sedentary lifestyle, Western diet, and family history of atherosclerotic disease. In the United States, ACS is most common in the sixth decade of life and has a male-to-female ratio of 3:2. Approximately 900 000 Americans experience AMI per year, and 30% of these individuals die within 30 days.
Less common causes of arterial obstruction that can result in ACS include embolic events, vasospasm, and coronary artery dissection. ACS may also occur as a result of diffuse myocardial ischemia and infarction in the setting of noncardiac disease such as severe anemia, hypoxemia, or sepsis. Rarely, acute rupture of the ventricular wall can occur in late-presenting cases of myocardial infarction.
ACS is a major cause of morbidity and mortality throughout the world; however, while overall cases have declined, cases of NSTEMI have risen due to increasingly sensitive troponin assays.
ACS represents a spectrum of disease severity that is differentiated by ECG findings and serum cardiac enzyme (troponin) levels:
- STEMI – New ST segment elevation at the J point in 2 contiguous leads on ECG and elevated cardiac enzyme levels.
- NSTEMI – Elevated cardiac enzyme levels without ST elevations. New horizontal or downsloping ST depressions and/or T-wave inversions in 2 or more contiguous leads may or may not be present on ECG.
- UA – Chest pain and/or other symptoms of ischemia that are new, worsening, or occurring at rest in the absence of abnormal cardiac enzyme levels. ST-segment depressions and T-wave inversions may or may not be present on ECG. This is distinguished from stable angina, in which chronic coronary artery disease causes chest discomfort that is provoked by exertion or stress and resolves spontaneously with rest or nitroglycerin in a predictable manner.