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Ischemic Heart Disease for USMLE Step 1

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Ischemic Heart Disease for the USMLE Step 1 Exam
Ischemic heart disease (IHD), or coronary artery disease (CAD), is caused by reduced blood flow to the myocardium, usually due to atherosclerosis. IHD encompasses stable angina, unstable angina, and myocardial infarction (MI). The main risk factors are hypertension, hyperlipidemia, diabetes, smoking, and family history.
Pathophysiology
  • Atherosclerosis: The main cause of IHD. It involves lipid accumulation within the arterial intima, forming atherosclerotic plaques that narrow the coronary arteries and reduce blood flow.
  • Plaque Rupture: Unstable plaques with thin fibrous caps can rupture, leading to thrombus formation and potential coronary artery occlusion.
  • Myocardial Oxygen Demand: Imbalance between oxygen supply and demand triggers myocardial ischemia.
Clinical Syndromes
Ischemia symptoms
Stable Angina
  • Definition: Predictable chest pain with exertion, relieved by rest or nitroglycerin.
  • Pathophysiology: Fixed coronary artery stenosis limits blood flow during increased myocardial demand, resulting in transient subendocardial ischemia.
  • Symptoms: Chest pain or pressure lasting under 15 minutes, typically brought on by exertion or stress.
  • Diagnosis:
    • Exercise Treadmill Test (ETT): Initial test for patients able to exercise, evaluating for ECG changes suggestive of ischemia.
    • Stress Imaging: Used when ETT is contraindicated or baseline ECG is abnormal.
  • Management:
    • Medications: Beta-blockers (first-line), nitrates, and calcium channel blockers.
    • Lifestyle Modifications: Control of blood pressure, cholesterol, and smoking cessation.
Acute Coronary Syndromes (ACS)
ACS includes unstable angina, NSTEMI, and STEMI.
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Unstable Angina (UA) and Non-ST Segment Elevation Myocardial Infarction (NSTEMI)
  • Definition: UA is chest pain at rest or worsening angina; NSTEMI has similar symptoms but with myocardial injury indicated by elevated troponins.
  • Pathophysiology: Plaque rupture and partial coronary artery occlusion lead to decreased blood flow.
  • Symptoms: Prolonged chest pain at rest, often lasting more than 20 minutes.
  • Diagnosis:
    • ECG: ST depression or T-wave inversion.
    • Biomarkers: Elevated troponins in NSTEMI; normal in unstable angina.
  • Management:
    • Medications: Antiplatelet agents (aspirin and P2Y12 inhibitors), anticoagulants (heparin), and beta-blockers.
    • Risk Stratification: Assess need for invasive coronary angiography based on risk factors.
ST Segment Elevation Myocardial Infarction (STEMI)
  • Definition: Acute MI with ST-segment elevation on ECG, indicative of full-thickness ischemia.
  • Pathophysiology: Complete coronary artery occlusion from plaque rupture and thrombus formation.
  • Symptoms: Severe, prolonged chest pain unresponsive to rest or nitroglycerin, often associated with diaphoresis, nausea, and dyspnea.
  • Diagnosis:
    • ECG: ST-segment elevation in two or more contiguous leads.
    • Biomarkers: Elevated troponin levels confirm myocardial injury.
  • Management:
    • Reperfusion Therapy: Primary percutaneous coronary intervention (PCI) within 90 minutes is preferred. If PCI is unavailable, fibrinolysis within 30 minutes.
    • Medications: Aspirin, P2Y12 inhibitors, beta-blockers, and anticoagulation with heparin.
Risk Factor Modification and Prevention
Secondary prevention in IHD focuses on lifestyle changes and medications to prevent recurrence.
  • Lifestyle Changes: Smoking cessation, healthy diet, regular physical activity.
  • Lipid Management: High-intensity statin therapy to lower LDL levels.
  • Antiplatelet Therapy: Long-term aspirin; dual antiplatelet therapy (DAPT) for 12 months post-PCI.
  • Blood Pressure Control: Aim for BP <130/80 mm Hg.
  • Beta-Blockers and ACE Inhibitors: Long-term beta-blockers for patients with reduced ejection fraction or previous MI. ACE inhibitors in patients with hypertension, diabetes, or heart failure.
Key Points
  • Pathophysiology: Atherosclerosis reduces blood flow, with plaque rupture leading to thrombosis in acute cases.
  • Types of IHD:
    • Stable Angina: Predictable chest pain with exertion, relieved by rest.
    • Unstable Angina and NSTEMI: Chest pain at rest; NSTEMI shows elevated troponins.
    • STEMI: Complete coronary artery occlusion with ST-segment elevation.
  • Diagnostic Tests:
    • Stable Angina: Exercise Treadmill Test (ETT) or stress imaging.
    • ACS: ECG and troponin testing, with coronary angiography for high-risk cases.
  • Management:
    • Stable Angina: Beta-blockers, nitrates, lifestyle modifications.
    • NSTEMI/UA: Antiplatelet and anticoagulant therapy; invasive approach if high risk.
    • STEMI: Immediate reperfusion with PCI or fibrinolysis.
  • Secondary Prevention: Includes lifestyle changes, antiplatelet therapy, statins, ACE inhibitors, and beta-blockers to prevent recurrent events.

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