Myocardial Infarction, Acute Non–ST-Segment Elevation

KEY FEATURES

ESSENTIALS OF DIAGNOSIS

• New or worsening symptoms of myocardial ischemia (angina pectoris or its equivalents)

• New or worsening ECG changes of myocardial ischemia (ST-wave depression or T-wave inversion on ECG in 2 or more contiguous leads)

• Positive biologic markers for myocardial injury (ie, troponin I or T)

GENERAL CONSIDERATIONS

• Acute non–ST-segment elevation myocardial infarctions (NSTEMIs) make up about two-thirds to three-quarters of all admissions to cardiac care units

• Usually caused by unstable plaque characterized by fissure or rupture of the fibrous cap

• Platelet aggregation leading to thrombus formation ensues

• Vasoconstriction occurs secondary to endothelial dysfunction

• Most episodes occur without antecedent increase in myocardial oxygen demand

• Worsening of stable coronary artery disease may be triggered by:

  • – Severe anemia

  • – Thyrotoxicosis

  • – Acute tachyarrhythmias

  • – Hypotension

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

• Angina that lasts up to 20–30 minutes or longer

• Symptoms may occur at rest or during minimal accustomed exertion

• Associated symptoms occur such as sweating and fatigue

• Dyspnea with or without chest pain may be a primary manifestation

• Recurrence of ischemic symptoms within 4 weeks after a myocardial infarction or percutaneous coronary procedure or coronary artery bypass graft surgery

PHYSICAL EXAM FINDINGS

• No typical abnormal physical finding

• S₃ or S₄

• Transient ischemic mitral regurgitation

• Features of left ventricular dysfunction

• Hypotension may occur depending on the extent of myocardial involvement or secondary to an arrhythmia

DIFFERENTIAL DIAGNOSIS

• Stable angina pectoris

• Variant angina

• Unstable angina

• Aortic dissection

• Acute myopericarditis

• Acute pulmonary embolism

• Esophageal reflux

• Cholecystitis

• Peptic ulcer disease

• Cervical radiculopathy

• Costochondritis

• Pneumothorax

DIAGNOSTIC EVALUATION

LABORATORY TESTS

• CBC to exclude anemia

• Basic metabolic panel (especially creatinine and potassium)

• Cardiac troponin I or T

• Brain natriuretic peptide

ELECTROCARDIOGRAPHY

• 12-lead ECG (patients with resting ST-segment depression are considered high risk)

IMAGING STUDIES

• Echocardiogram to evaluate:

  • – Regional wall motion analysis

  • – Left ventricular function

  • – Valvular heart disease

• In patients in whom medical management is chosen, stress perfusion study may be done > 48 hours after the last episode of chest pain for further risk stratification

DIAGNOSTIC PROCEDURES

• Coronary angiogram

TREATMENT

CARDIOLOGY REFERRAL

• All patients with NSTEMI should be seen by a cardiologist

HOSPITALIZATION CRITERIA

• All patients should be hospitalized

MEDICATIONS

• General:

  • – Oxygen if hypoxemic

• Pain relief and anti-ischemic agents:

  • – Sublingual nitroglycerin followed by IV if necessary

  • – Morphine sulfate if nitrates fail to ...