Chapter 122: Unstable Angina and Non-ST-Elevation Myocardial Infarction

INTRODUCTION

Unstable angina (UA) and non-ST-elevation MI (NSTEMI) are acute coronary syndromes with similar mechanisms, clinical presentations, and treatment strategies.

CLINICAL PRESENTATION

UA includes (1) new onset of severe angina, (2) angina at rest or with minimal activity, and (3) recent increase in frequency and intensity of chronic angina. NSTEMI is diagnosed when symptoms of UA are accompanied by evidence of myocardial necrosis (e.g., elevated cardiac biomarkers). Pts with NSTEMI may present with symptoms identical to STEMI—the two are differentiated by ECG findings.

PHYSICAL EXAMINATION

May be normal or include diaphoresis, pale cool skin, tachycardia, S₄, basilar rales; if large region of ischemia, may demonstrate S₃, hypotension.

ELECTROCARDIOGRAM

May include ST depression and/or T-wave inversion; unlike STEMI, there is no Q-wave development.

CARDIAC BIOMARKERS

Cardiac-specific troponins (specific and sensitive markers of myocardial necrosis) and CK-MB (less sensitive marker) are elevated in NSTEMI. Small troponin elevations may also occur in pts with heart failure, myocarditis, pulmonary embolism, and other conditions in Table 122-1.

TABLE 122-1Causes of Elevated Cardiac Troponin Reflecting Direct Myocardial Damage Other Than Spontaneous Myocardial Infarction (Type 1)

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TABLE 122-1 Causes of Elevated Cardiac Troponin Reflecting Direct Myocardial Damage Other Than Spontaneous Myocardial Infarction (Type 1)

CARDIAC

NON-CARDIAC OR SYSTEMIC

Tachyarrhythmias

Congestive heart failure

Hypertensive emergencies

Infection/inflammation (e.g., myocarditis, pericarditis)

Stress cardiomyopathy (Tako-Tsubo cardiomyopathy)

Structural heart disease (e.g., aortic stenosis)

Aortic dissection

Coronary spasm

Cardiac procedures (endomyocardial biopsy, ablation, CABG, PCI)

Infiltrative diseases (e.g., amyloidosis, hemochromatosis, malignancy)

Pulmonary embolism/pulmonary hypertension

Trauma (e.g., electrical shock, burns, blunt chest wall)

Hypo or hyperthyroidism

Toxicity (e.g., anthracyclines, snake venom)

Renal failure

Sepsis, shock

Stroke or other acute neurologic event

Extreme endurance efforts (e.g., ultra-marathon)

Rhabdomyolysis

Source: Data from Newby LK et al: J Am Coll Cardiol 60:2427, 2012; Roffi M: Eur Heart J 37:267, 2016.

TREATMENT

TREATMENT Unstable Angina and Non-ST-Elevation Myocardial Infarction

First step is appropriate triage based on likelihood of coronary artery disease (CAD) and acute coronary syndrome (Fig. 122-1) as well as identification of higher-risk pts. Pts with low likelihood of active ischemia are initially monitored by serial ECGs and serum cardiac biomarkers, and for recurrent chest discomfort; if these are negative, stress testing (or CT angiography if probability of CAD is low) can be used for further therapeutic planning.

Therapy of UA/NSTEMI is directed (1) against the inciting intracoronary thrombus, and (2) toward restoration of balance between myocardial oxygen supply and demand. Pts with the highest-risk scores benefit the most from aggressive interventions.

ANTITHROMBOTIC THERAPIES

Aspirin (325 mg initially, then 75–100 mg/d).
Platelet P2Y12 receptor antagonist (unless excessive risk of bleeding or immediate coronary artery bypass grafting [CABG] likely): Clopidogrel ...

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