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Ischemic Heart Disease for USMLE Step 3

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Ischemic Heart Disease for the USMLE Step 3 Exam
Ischemic heart disease (IHD), or coronary artery disease (CAD), occurs when coronary blood flow is insufficient to meet myocardial oxygen demand, usually due to atherosclerosis. IHD includes stable angina, unstable angina, and myocardial infarction (MI). Risk factors include hypertension, hyperlipidemia, diabetes, smoking, obesity, and family history of early CAD.
Pathophysiology
  • Atherosclerosis: The primary cause of IHD, characterized by lipid deposition in the coronary arteries. Plaques may calcify and narrow vessel lumen, reducing myocardial perfusion.
  • Plaque Rupture and Thrombosis: Unstable plaques can rupture, triggering thrombus formation and partial or complete occlusion of coronary arteries, which can precipitate ACS.
  • Imbalance in Oxygen Supply and Demand: Increased oxygen demand or reduced supply can cause ischemia, manifesting as angina or myocardial infarction.
Clinical Syndromes
Ischemia symptoms
Stable Angina
  • Definition: Predictable chest pain that occurs with exertion and is relieved by rest or nitroglycerin.
  • Pathophysiology: Fixed coronary artery stenosis limits blood flow during increased myocardial demand, causing subendocardial ischemia.
  • Symptoms: Chest pain lasting less than 15 minutes, typically provoked by exertion or emotional stress, and relieved by rest.
  • Diagnosis:
    • Exercise Treadmill Test (ETT): First-line test in patients with a normal ECG and ability to exercise.
    • Pharmacologic Stress Imaging: Used when ETT is contraindicated or baseline ECG is abnormal.
  • Management:
    • Medications: Beta-blockers (first-line), nitrates, and calcium channel blockers.
    • Lifestyle Changes: Smoking cessation, dietary modifications, and physical activity to control risk factors.
Acute Coronary Syndromes (ACS)
ACS includes unstable angina, NSTEMI, and STEMI, all resulting from acute myocardial ischemia.
Unstable Angina (UA) and Non-ST Segment Elevation Myocardial Infarction (NSTEMI)
  • Definition: UA is chest pain at rest or with minimal exertion; NSTEMI involves elevated troponins, indicating myocardial injury.
  • Pathophysiology: Partial coronary artery occlusion due to plaque rupture and thrombus formation.
  • Symptoms: Chest pain lasting over 20 minutes, unrelieved by rest or nitroglycerin.
  • Diagnosis:
    • ECG: ST depression or T-wave inversion.
    • Biomarkers: Elevated troponins in NSTEMI, normal in UA.
  • Management:
    • Antithrombotic Therapy: Dual antiplatelet therapy (aspirin and a P2Y12 inhibitor) and anticoagulation with heparin.
    • Risk Stratification: Use TIMI or GRACE scores to determine the need for invasive intervention.
    • Revascularization: Coronary angiography and possible PCI for high-risk patients.
ST Segment Elevation Myocardial Infarction (STEMI)
  • Definition: Acute MI with ST-segment elevation, indicating full-thickness myocardial ischemia.
  • Pathophysiology: Complete coronary artery occlusion from thrombus formation.
  • Symptoms: Severe, prolonged chest pain unrelieved by rest or nitroglycerin, often accompanied by nausea, diaphoresis, and dyspnea.
  • Diagnosis:
    • ECG: ST-segment elevation in at least two contiguous leads.
    • Biomarkers: Elevated troponin confirms myocardial injury.
  • Management:
    • Reperfusion Therapy: Primary PCI within 90 minutes is preferred; fibrinolysis is an option if PCI is unavailable within 120 minutes.
    • Adjunct Medications: Aspirin, P2Y12 inhibitors, beta-blockers, and heparin.
Secondary Prevention and Risk Factor Management
Secondary prevention in IHD aims to reduce recurrent events and improve long-term survival.
  • Lifestyle Modifications: Smoking cessation, heart-healthy diet, and regular physical activity.
  • Lipid Management: High-intensity statin therapy, with a target LDL <70 mg/dL in high-risk patients.
  • Antiplatelet Therapy: Aspirin for all patients long-term; dual antiplatelet therapy (DAPT) for at least 12 months post-PCI.
  • Blood Pressure Control: Target BP <130/80 mm Hg in IHD patients.
  • ACE Inhibitors or ARBs: Recommended for patients with hypertension, diabetes, heart failure, or reduced left ventricular ejection fraction (LVEF <40%).
  • Beta-Blockers: Long-term therapy for patients with prior MI or low LVEF.
Key Points
  • Pathophysiology: IHD is primarily due to atherosclerosis and is characterized by an imbalance in myocardial oxygen supply and demand.
  • Types of IHD:
    • Stable Angina: Predictable chest pain with exertion, relieved by rest.
    • ACS:
    • Unstable Angina and NSTEMI: Chest pain at rest; NSTEMI includes elevated troponins.
    • STEMI: Complete coronary artery occlusion with ST-segment elevation.
  • Diagnosis:
    • Stable Angina: Exercise Treadmill Test (ETT) or stress imaging.
    • ACS: ECG and troponin for diagnosis; angiography in high-risk cases.
  • Management:
    • Stable Angina: Beta-blockers, nitrates, and lifestyle modifications.
    • NSTEMI/UA: Dual antiplatelet therapy, anticoagulation, and invasive strategy if high risk.
    • STEMI: Immediate PCI or fibrinolysis for reperfusion.
  • Secondary Prevention: Focuses on lifestyle changes, antiplatelet therapy, statins, ACE inhibitors, and beta-blockers to reduce recurrent events and improve outcomes.

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