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Ischemic Heart Disease for USMLE Step 2

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Ischemic Heart Disease for the USMLE Step 2 Exam
Ischemic heart disease (IHD), also known as coronary artery disease (CAD), results from reduced blood flow to the myocardium, typically due to atherosclerosis in the coronary arteries. IHD includes stable angina, unstable angina, and myocardial infarction (MI), all characterized by an imbalance between oxygen supply and myocardial demand. Risk factors include hypertension, hyperlipidemia, diabetes, smoking, and family history.
Pathophysiology
  • Atherosclerosis: The primary cause of IHD. Plaque buildup in the coronary arteries narrows the vessel lumen, restricting blood flow and leading to ischemia.
  • Plaque Rupture: Unstable plaques with thin fibrous caps can rupture, causing thrombus formation that may partially or completely occlude coronary blood flow.
  • Oxygen Demand: Increased myocardial oxygen demand due to factors like exertion or stress can trigger ischemic events in patients with obstructed coronary arteries.
Clinical Syndromes
Ischemia symptoms
Stable Angina
  • Definition: Predictable chest pain that occurs with exertion and is relieved by rest or nitroglycerin.
  • Pathophysiology: Fixed coronary stenosis restricts blood flow during increased demand, causing subendocardial ischemia.
  • Symptoms: Chest pain, typically lasting less than 15 minutes, provoked by exertion or stress, and relieved by rest.
  • Diagnosis:
    • Exercise Treadmill Test (ETT): First-line test in patients with a normal ECG who can exercise.
    • Stress Imaging: Used when ETT is contraindicated or baseline ECG is abnormal.
  • Management:
    • Medications: Beta-blockers (first-line), calcium channel blockers, and nitrates.
    • Lifestyle Modification: Smoking cessation, exercise, and dietary changes to manage risk factors.
Acute Coronary Syndromes (ACS)
ACS refers to a spectrum of conditions caused by acute myocardial ischemia, including 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 that occurs at rest or with minimal exertion; NSTEMI is similar but with evidence of myocardial injury (elevated troponins).
  • Pathophysiology: Partial coronary artery occlusion caused by plaque rupture and thrombus formation.
  • Symptoms: Chest pain lasting more than 20 minutes, often at rest, and less responsive to nitroglycerin.
  • Diagnosis:
    • ECG: ST depression or T-wave inversion.
    • Biomarkers: Elevated troponins in NSTEMI, normal in UA.
  • Management:
    • Medications: Dual antiplatelet therapy (aspirin plus a P2Y12 inhibitor) and anticoagulation with heparin.
    • Risk Stratification: TIMI or GRACE score to assess the need for coronary angiography.
    • Revascularization: Coronary angiography with PCI or CABG for high-risk patients.
ST Segment Elevation Myocardial Infarction (STEMI)
  • Definition: Acute myocardial infarction with ST-segment elevation on ECG, indicating full-thickness ischemia.
  • Pathophysiology: Complete coronary artery occlusion from plaque rupture and thrombus formation.
  • Symptoms: Severe chest pain, unrelieved by rest or nitroglycerin, associated with diaphoresis, nausea, and dyspnea.
  • Diagnosis:
    • ECG: ST-segment elevation in two or more contiguous leads.
    • Biomarkers: Elevated troponin confirms myocardial injury.
  • Management:
    • Reperfusion Therapy: Primary percutaneous coronary intervention (PCI) within 90 minutes is preferred; fibrinolysis if PCI is unavailable within 120 minutes.
    • Medications: Aspirin, P2Y12 inhibitors, beta-blockers, and anticoagulation with heparin.
Secondary Prevention and Risk Factor Management
Secondary prevention aims to reduce future ischemic events and improve long-term outcomes.
  • Lifestyle Changes: Smoking cessation, a heart-healthy diet (e.g., Mediterranean diet), and regular physical activity.
  • Lipid Management: High-intensity statin therapy to lower LDL, with a target of <70 mg/dL in high-risk patients.
  • Antiplatelet Therapy: Long-term aspirin for all patients; dual antiplatelet therapy (DAPT) with aspirin and a P2Y12 inhibitor for 12 months post-PCI.
  • Blood Pressure Control: Target BP <130/80 mm Hg in patients with IHD.
  • ACE Inhibitors or ARBs: Recommended for patients with hypertension, diabetes, heart failure, or reduced left ventricular ejection fraction (LVEF <40%).
  • Beta-Blockers: For patients with a history of MI or reduced LVEF.
Key Points
  • Pathophysiology: IHD is caused primarily by atherosclerosis, which restricts blood flow, leading to myocardial ischemia.
  • Clinical Syndromes:
    • Stable Angina: Predictable chest pain with exertion, relieved by rest.
    • Unstable Angina and NSTEMI: Chest pain at rest; NSTEMI includes elevated troponin.
    • STEMI: Complete coronary occlusion with ST-segment elevation.
  • Diagnosis:
    • Stable Angina: Exercise Treadmill Test (ETT) or stress imaging.
    • ACS: ECG and troponin testing; coronary angiography for high-risk cases.
  • Management:
    • Stable Angina: Beta-blockers, nitrates, lifestyle modifications.
    • NSTEMI/UA: Dual antiplatelet therapy, anticoagulation, and risk assessment for revascularization.
    • STEMI: Immediate PCI or fibrinolysis for reperfusion.
  • Secondary Prevention: Includes antiplatelet therapy, statins, ACE inhibitors, beta-blockers, and lifestyle modifications to reduce recurrent events and improve survival.

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