USMLE Guide: Acute Coronary Syndrome

Introduction

Acute Coronary Syndrome (ACS) refers to a spectrum of clinical presentations related to insufficient blood supply to the heart muscle. It includes unstable angina (UA), non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI). ACS is a critical condition requiring immediate medical attention and intervention. This USMLE guide aims to provide a comprehensive overview of ACS, including its pathophysiology, clinical presentation, diagnosis, and management.

Pathophysiology

ACS is primarily caused by the rupture of an atherosclerotic plaque within a coronary artery, leading to partial or complete occlusion. The rupture exposes the underlying thrombogenic material, resulting in platelet aggregation and the formation of a thrombus. The thrombus can partially or completely obstruct the coronary artery, leading to myocardial ischemia and subsequent clinical manifestations.

Clinical Presentation

1. Unstable Angina (UA): Characterized by new-onset or worsening angina symptoms, occurring at rest or with minimal exertion. The symptoms are often severe, prolonged, and not relieved by nitroglycerin.
2. Non-ST-segment Elevation Myocardial Infarction (NSTEMI): In addition to UA symptoms, NSTEMI is diagnosed based on elevated cardiac biomarkers, such as troponin, indicating myocardial necrosis.
3. ST-segment Elevation Myocardial Infarction (STEMI): Presents with persistent ST-segment elevation on electrocardiogram (ECG), along with symptoms consistent with myocardial ischemia. Elevated cardiac biomarkers confirm myocardial necrosis.

Diagnosis

1. History and Physical Examination: Assess for typical symptoms such as chest pain, dyspnea, diaphoresis, and radiation to the left arm or jaw. physical examination may reveal signs of heart failure or abnormal heart sounds.
2. Electrocardiogram (ECG): A crucial tool for diagnosing ACS. ST-segment elevation in specific leads indicates STEMI, while ST-segment depression or T-wave inversions suggest NSTEMI or UA.
3. Cardiac Biomarkers: Serial measurements of cardiac biomarkers, particularly troponin, help differentiate UA from NSTEMI and confirm myocardial necrosis.
4. Coronary Angiography: Invasive procedure to visualize coronary arteries and identify any significant stenosis or occlusion. It provides valuable information for selecting appropriate management strategies.

Management

1. Antiplatelet Therapy: Aspirin should be administered immediately, followed by P2Y12 inhibitors (e.g., clopidogrel, ticagrelor) to prevent further platelet aggregation.
2. Anticoagulation: Low-molecular-weight heparin (LMWH) or unfractionated heparin should be initiated to prevent thrombus formation and extension.
3. Pain Relief: Sublingual nitroglycerin is the initial treatment for angina symptoms. Opioids can be used for severe pain not relieved by nitroglycerin.
4. Revascularization: Percutaneous coronary intervention (PCI) is the preferred revascularization strategy, involving the use of stents to restore blood flow. Thrombolytic therapy can be considered if PCI is not readily available.
5. Secondary Prevention: Statins, beta-blockers, angiotensin-converting enzyme inhibitors (ACE inhibitors), and lifestyle modifications (smoking cessation, exercise, healthy diet) are crucial for long-term management and reducing the risk of future cardiovascular events.

Remember, ACS is a medical emergency requiring prompt diagnosis and treatment to minimize myocardial damage and improve patient outcomes.

Note: This USMLE guide provides a concise overview of ACS, but it is essential to refer to comprehensive textbooks and guidelines for more in-depth study.

References:

• Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 11th Edition.
• American College of Cardiology/American Heart Association Guidelines for the Management of Patients With Acute Coronary Syndromes.