Cardiology · Acute Coronary Syndrome
The facts most likely to be tested
Unstable angina is defined by ischemic chest pain occurring at rest, with a crescendo pattern, or of new onset that limits physical activity.
The diagnosis of unstable angina requires the absence of elevated cardiac biomarkers (specifically troponin) to distinguish it from NSTEMI.
Electrocardiogram findings in unstable angina may show ST-segment depression or T-wave inversion, but lack the ST-segment elevation seen in STEMI.
The underlying pathophysiology involves coronary artery plaque rupture with non-occlusive thrombus formation.
Initial management includes dual antiplatelet therapy with aspirin and a P2Y12 inhibitor (e.g., clopidogrel).
Patients require anticoagulation with unfractionated heparin, enoxaparin, or fondaparinux to prevent further thrombus propagation.
Beta-blockers are indicated to reduce myocardial oxygen demand by lowering heart rate and contractility, provided there are no signs of acute heart failure or cardiogenic shock.
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A 62-year-old male with a history of hypertension and hyperlipidemia presents to the emergency department with substernal chest pressure that began 2 hours ago while watching television. He reports two similar episodes of shorter duration over the past 48 hours. His physical exam is unremarkable, and his vitals are stable. An ECG shows ST-segment depression in leads V4-V6. Initial cardiac troponin levels are negative.
What is the most appropriate diagnosis?
Unstable angina
The patient presents with ischemic symptoms at rest without evidence of myocardial necrosis (negative troponin), which fulfills the diagnostic criteria for unstable angina.
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Etiology / Epidemiology
Caused by ruptured atherosclerotic plaque with non-occlusive thrombus. Primary risk factors: HTN, DM, smoking, hyperlipidemia.
Clinical Manifestations
New-onset, crescendo, or rest angina. Levine sign is the classic substernal pressure radiating to the jaw or left arm.
Diagnosis
Diagnosis is clinical + ECG (ST-depression or T-wave inversion). Troponin must be negative to exclude NSTEMI.
Treatment
Initial: Aspirin + Nitroglycerin. Avoid beta-blockers if cocaine use suspected.
Prognosis
High risk of progression to MI. TIMI score used to risk-stratify for invasive intervention.
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Epidemiology & Etiology
Occurs in patients with underlying coronary artery disease. Precipitated by a sudden decrease in myocardial oxygen supply or increase in demand. Common in patients with metabolic syndrome and chronic vascular inflammation.
Pertinent Anatomy
Involves the epicardial coronary arteries. Obstruction limits blood flow to the myocardium, specifically the subendocardium, which is most vulnerable to ischemia.
Pathophysiology
Plaque rupture leads to platelet aggregation and non-occlusive thrombus formation. Unlike STEMI, the vessel is not completely occluded, preventing transmural necrosis. Ischemia is transient, but the clinical state is acute coronary syndrome.
Clinical Manifestations
Patients present with angina pectoris that is more frequent, severe, or occurs at rest. Red flags include diaphoresis, syncope, or radiation to the neck. Physical exam is often normal, but S4 gallop may indicate decreased ventricular compliance.
Diagnosis
The ECG is the first-line diagnostic tool; look for ST-segment depression or T-wave inversion. Cardiac troponin levels must be normal to distinguish from NSTEMI. Coronary angiography is the gold standard for definitive anatomical assessment.
Treatment
Administer Aspirin (325mg) immediately. Use Nitroglycerin for pain control; contraindicated with PDE5 inhibitors due to severe hypotension. Add Clopidogrel for dual antiplatelet therapy and Heparin for anticoagulation.
Prognosis
High risk of myocardial infarction within 30 days. Patients require TIMI score or GRACE score calculation to determine the necessity of urgent cardiac catheterization.
Differential Diagnosis
NSTEMI: Troponin elevation present
STEMI: ST-segment elevation on ECG
Aortic Dissection: Tearing chest pain radiating to the back
GERD: Burning sensation relieved by antacids
Pulmonary Embolism: Pleuritic chest pain with tachycardia