Step 3 CCS: Pulmonary Embolism

Pulmonary embolism CCS cases test your ability to rapidly risk-stratify, anticoagulate, and identify massive PE requiring thrombolytics. You must navigate the Wells score → D-dimer → CT angiography algorithm cleanly, initiate heparin before imaging confirmation if clinical suspicion is high, and recognize right ventricular strain as a marker of severity requiring escalation.

Clinical Approach — What Attendings Do First

The First Minute

  • Supplemental O2 to SpO2 ≥92%, hemodynamic assessment (BP, HR)
  • If high clinical suspicion: start heparin immediately, do not wait for CTPA
  • Order CT pulmonary angiography STAT — the diagnostic gold standard
  • If too unstable for CT: bedside echocardiogram looking for RV dilation/strain
  • 12-lead ECG (sinus tachycardia most common; S1Q3T3 is classic but rare; right heart strain pattern)

Key Orders

  • Unfractionated heparin 80 units/kg IV bolus → 18 units/kg/hr (check aPTT in 6 hours, target 60-80 sec)
  • CT pulmonary angiography with IV contrast
  • D-dimer ONLY if Wells score ≤4 (low-intermediate probability) — high-probability patients go straight to CTPA
  • BNP or troponin (markers of RV strain — prognostic, not diagnostic)
  • CBC, BMP, PT/INR, ABG if hypoxic
  • Echocardiogram if hemodynamically significant (RV dilation = submassive/massive PE)
  • Lower extremity duplex ultrasound (identify DVT source — affects IVC filter decision)

Time-Sensitive Actions

  • Massive PE (SBP <90): alteplase 100 mg IV over 2 hours — do not delay for imaging if clinically obvious
  • If CTPA contraindicated (contrast allergy, severe CKD): order V/Q scan or lower extremity duplex
  • For massive PE in cardiac arrest: consider catheter-directed thrombolysis or surgical embolectomy (consult)
  • Transition from heparin to DOAC (rivaroxaban or apixaban) once stable — order before discharge

Common CCS Pitfalls

  • Ordering D-dimer in a high-probability patient — wastes time; go straight to CTPA
  • Waiting for imaging to start heparin when suspicion is high — delays critical anticoagulation
  • Not ordering echocardiogram for hemodynamically significant PE — RV strain changes management
  • Forgetting to identify provoked vs unprovoked PE — determines duration of anticoagulation
  • Not ordering hypercoagulability workup in unprovoked PE in young patients (factor V Leiden, antiphospholipid)

Frequently Asked Questions

Should I start heparin before CTPA confirmation on a CCS PE case?

Yes — if clinical suspicion is high (Wells score >6), start heparin immediately while awaiting imaging. For intermediate probability, it is still reasonable to anticoagulate while waiting for CTPA. Unfractionated heparin 80 units/kg IV bolus then 18 units/kg/hr, or enoxaparin 1 mg/kg SQ q12h if stable with normal renal function. Do not delay anticoagulation for hours waiting for CT results.

When do I use thrombolytics for PE on CCS?

Systemic thrombolysis (alteplase 100 mg IV over 2 hours) is indicated for massive PE: sustained hypotension (SBP <90 for >15 minutes), cardiac arrest, or refractory shock despite pressors and heparin. Submassive PE (normal BP but RV strain on echo/CT) is controversial — consider thrombolytics if clinical deterioration despite heparin. On CCS, order echocardiogram to assess RV function in any hemodynamically significant PE.

What is the long-term anticoagulation plan after PE on CCS?

Provoked PE (surgery, immobilization, OCP): anticoagulate for 3 months. Unprovoked PE: at least 3-6 months, then reassess for extended therapy. Recurrent unprovoked PE: indefinite anticoagulation. DOACs (rivaroxaban, apixaban) are preferred over warfarin for most patients. Cancer-associated PE: LMWH or DOAC (edoxaban, rivaroxaban). Before discharge on CCS, order the correct anticoagulant with follow-up plan.

Related Organ System Topics

Pulmonology

Pulmonary medicine on USMLE Step 3 includes obstructive and restrictive lung diseases, acute respiratory failure, pulmonary embolism, and pneumonia management.

Cardiology

Cardiovascular disease is one of the highest-yield areas on USMLE Step 3, spanning acute coronary syndromes, heart failure, arrhythmias, and valvular disease.

Hematology

Hematology on USMLE Step 3 covers anemias, coagulation disorders, leukemias, lymphomas, and thrombocytopenia.

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