USMLE Step 2 Cardiology Clinical Cases
Case 1: ST-Elevation Myocardial Infarction (STEMI) with Prehospital ECG
Clinical Vignette: A 58-year-old woman with hypertension, hyperlipidemia, and type 2 diabetes calls 9-1-1 for acute substernal chest pressure that started 30 minutes ago and radiates to her left arm. She takes aspirin, atorvastatin, lisinopril, and metoprolol. Paramedics arrive and obtain a prehospital ECG showing 3-4 mm ST-segment elevations in leads I, aVL, and V2-V6. Vital signs: BP 100/60 mmHg, HR 90 bpm, RR 16/min. Physical exam reveals clear lungs, regular rhythm, normal S1/S2, no murmurs. The catheterization laboratory is activated en route.
Questions:
- What is the diagnosis?
- What is the culprit artery?
- What is the target door-to-balloon time?
- What immediate therapies should be administered?
Key Teaching Points: This case demonstrates the critical importance of prehospital ECG acquisition and interpretation in STEMI management 1. The paramedic-to-balloon time of 46 minutes and door-to-balloon time of 23 minutes exemplify optimal systems of care. The anterior and lateral ST elevations indicate proximal left anterior descending artery occlusion.
Case 2: Unstable Angina/NSTEMI Risk Stratification
Clinical Vignette: A 72-year-old man presents to the ED with 45 minutes of substernal chest pressure that resolved 10 minutes ago with sublingual nitroglycerin. He has a history of prior MI, peripheral arterial disease, and CABG 5 years ago. He takes aspirin regularly. Vital signs: BP 145/85 mmHg, HR 88 bpm, RR 18/min, O2 sat 96% on room air. Physical exam shows clear lungs, regular rhythm, no S3 or murmurs. ECG shows T-wave inversions of 0.3 mV in leads V4-V6 and pathological Q waves in leads II, III, aVF. Initial troponin I is 0.08 ng/mL (normal <0.04 ng/mL).
Questions:
- What is the TIMI risk score for this patient?
- What is the short-term risk category (high, intermediate, or low)?
- Should this patient undergo early invasive strategy or conservative management?
- What antiplatelet and anticoagulation therapy is indicated?
Key Teaching Points: This patient has multiple high-risk features for UA/NSTEMI including prior MI, prior CABG, prolonged rest angina (>20 minutes), T-wave inversions >0.2 mV, pathological Q waves, and elevated cardiac troponin 2, 3, 4, 5. The presence of at least one high-risk feature mandates early invasive strategy with coronary angiography within 24 hours 5, 6.
Case 3: Low-Risk Chest Pain with Negative Serial Troponins
Clinical Vignette: A 45-year-old woman presents to the ED with 2 hours of atypical chest discomfort described as sharp, left-sided, worse with deep inspiration. She has no cardiac risk factors and takes no medications. Vital signs are normal. Physical exam is unremarkable. ECG shows normal sinus rhythm with no ST-segment or T-wave changes. High-sensitivity troponin I at 0 hours is 3 ng/L and at 2 hours is 4 ng/L (99th percentile: 16 ng/L). Her TIMI score is 0.
Questions:
- Can ACS be safely excluded in this patient?
- What is the false-negative rate for 30-day MACE with this testing strategy?
- Is further cardiac testing required before discharge?
- What outpatient follow-up is appropriate?
Key Teaching Points: Negative high-sensitivity troponin I at 0 and 2 hours combined with a TIMI score of 0 has a 0% false-negative rate for 30-day major adverse cardiac events, allowing safe discharge without further testing 7. This represents a validated accelerated diagnostic protocol that reduces unnecessary admissions while maintaining safety.
Case 4: Acute Decompensated Heart Failure with Cardiorenal Syndrome
Clinical Vignette: A 56-year-old man with HFrEF (EF 30%), atrial fibrillation, and recent hospitalization 3 weeks ago presents with dyspnea at rest. Home medications include valsartan, carvedilol, spironolactone, apixaban, and furosemide 40 mg daily. Vital signs: BP 120/80 mmHg, HR 110 bpm (irregularly irregular), RR 24/min, temp 36°C. Physical exam shows jugular venous distention to the angle of the jaw, bilateral crackles, and 2+ pitting edema to the knees. Labs: Na 135 mEq/L, K 3.6 mEq/L, Cl 92 mEq/L, creatinine 1.3 mg/dL (baseline 0.9 mg/dL), BUN 15 mg/dL, NT-proBNP 3,500 pg/mL (discharge value 900 pg/mL).
Questions:
- What is the appropriate initial diuretic dose?
- Should continuous infusion or bolus dosing be used?
- How should diuretic response be monitored?
- What is the significance of the elevated creatinine?
Key Teaching Points: For acute HF in patients on chronic loop diuretics, initiate intravenous furosemide at 2.5 times the home oral dose (100 mg IV in this case) 8. The DOSE trial showed that higher-dose diuretics (2.5× home dose) resulted in greater net fluid loss and weight reduction compared to lower doses, with no significant difference in renal function deterioration. The mild creatinine elevation reflects venous congestion-mediated kidney dysfunction rather than true renal injury.
Case 5: Severe Aortic Stenosis with Discordant Echocardiographic Findings
Clinical Vignette: A 78-year-old man presents with progressive exertional dyspnea (NYHA Class III) and one episode of near-syncope while climbing stairs. Physical exam reveals a delayed and diminished carotid upstroke (pulsus parvus et tardus), a late-peaking systolic crescendo-decrescendo murmur loudest at the right upper sternal border radiating to the carotids, and a single S2. Transthoracic echocardiogram shows a heavily calcified aortic valve with peak velocity 3.2 m/s, mean gradient 28 mmHg, calculated AVA 1.1 cm², and LVEF 60%.
Questions:
- Does this patient have severe aortic stenosis?
- Why is there discordance between physical exam and echocardiographic findings?
- What additional testing is required?
- What are the indications for intervention?
Key Teaching Points: When physical examination suggests severe aortic stenosis but echocardiographic gradients are lower than expected, cardiac catheterization with direct hemodynamic assessment is indicated (Class I recommendation) 9, 10. This discordance may result from poor Doppler alignment, low-flow states, or pressure recovery phenomena. The classic physical findings (delayed carotid upstroke, late-peaking murmur, single S2) in a symptomatic patient strongly suggest hemodynamically significant stenosis requiring invasive confirmation.