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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- PE classically presents with acute dyspnea, pleuritic chest pain, tachycardia, tachypnea, and hypoxemia
- Use pretest probability: PERC can rule out PE in very low-risk patients; D-dimer is used in low/intermediate-risk patients; CTPA is used when probability is high or D-dimer is positive
- Stable PE: anticoagulation with DOAC or heparin depending on setting, renal function, pregnancy, cancer, and severity
- Massive PE = hemodynamic instability; treat with systemic thrombolysis unless contraindicated
- Submassive PE = RV strain or biomarkers without hypotension; anticoagulation is standard, with escalation if deterioration occurs
Overview
Pulmonary embolism is a form of venous thromboembolism in which clot obstructs pulmonary arterial flow. Most emboli originate from proximal lower-extremity or pelvic deep veins. Clinical severity ranges from incidental small PE to obstructive shock and cardiac arrest. Risk stratification determines both diagnostic pathway and treatment intensity.
Epidemiology
Venous thromboembolism affects hundreds of thousands of people annually in the United States and is a major cause of preventable hospital death. Incidence increases with age, hospitalization, surgery, malignancy, obesity, pregnancy, estrogen exposure, and prior VTE.
Clinical Features
Symptoms
Sudden dyspnea, often unexplained by lung examination
Pleuritic chest pain and cough
Hemoptysis from pulmonary infarction
Syncope, severe chest pain, or sense of impending doom
Calf pain, swelling, or recent unilateral leg symptoms suggesting DVT
Postoperative or postpartum acute dyspnea
Signs
Tachycardia and tachypnea are the most common signs
Hypoxemia with clear lungs
Unilateral leg swelling or tenderness
Hypotension, shock, or cardiac arrest
Loud P2, JVD, or right ventricular heave in severe PE
Investigations
First-line
Clinical probability scoreWells or revised Geneva score guides testing. PERC can rule out PE only in very low-risk patients
D-dimerHigh sensitivity but low specificity. Use only in low/intermediate probability patients. Age-adjusted cutoff is age x 10 ng/mL FEU for patients >50 years
CT pulmonary angiographyFirst-line imaging for most patients with positive D-dimer or high pretest probability; shows intraluminal filling defect
Second-line
V/Q scanUse when CTPA is contraindicated, such as severe contrast allergy or pregnancy with normal chest X-ray in selected cases
Lower-extremity compression ultrasoundIf positive for proximal DVT in a patient with PE symptoms, treatment can proceed when chest imaging is not feasible
ECG and troponin/BNPSinus tachycardia is most common. RV strain pattern, elevated troponin, or BNP suggests higher-risk PE
Specialist
EchocardiographyUse in unstable suspected PE when CTPA is unsafe; RV dilation/strain supports massive PE management
Catheter pulmonary angiographyReserved for catheter-directed therapy or rare diagnostic uncertainty
1
Initial stabilization
- Assess hemodynamic status immediately: hypotension defines high-risk massive PE
- Oxygen, IV access, cardiac monitoring, and cautious fluids if RV failure is present
- Vasopressors such as norepinephrine for obstructive shock
- Start anticoagulation promptly when PE is likely and bleeding risk is acceptable
2
Anticoagulation
- Stable outpatient or inpatient PE: DOACs such as apixaban or rivaroxaban are preferred for many patients
- Unfractionated heparin is preferred if thrombolysis, procedure, severe renal failure, or rapid reversibility may be needed
- Low-molecular-weight heparin is preferred in pregnancy and often used in malignancy depending on bleeding risk and drug interactions
- Minimum treatment duration is usually 3 months; extend if unprovoked PE, recurrent VTE, active cancer, or persistent risk factors
3
Massive PE
- Systemic thrombolysis with alteplase for PE causing sustained hypotension, shock, or cardiac arrest unless contraindicated
- If thrombolysis contraindicated or fails: catheter-directed therapy or surgical embolectomy
- Do not choose catheter-directed therapy over systemic thrombolysis as the routine next step in a classic Step 2 CK massive PE stem
4
Submassive and low-risk PE
- Submassive PE has RV dysfunction or positive biomarkers without hypotension; treat with anticoagulation and monitor closely
- Low-risk PE may be treated outpatient if stable, low bleeding risk, reliable follow-up, and adequate social support
- IVC filter only when acute VTE exists and anticoagulation is contraindicated or recurrent PE occurs despite adequate anticoagulation
Complications
- Obstructive shock: Massive PE acutely increases RV afterload and reduces LV preload
- Right ventricular failure: RV dilation, septal bowing, elevated troponin, and BNP indicate higher risk
- Pulmonary infarction: Pleuritic pain, hemoptysis, and wedge-shaped Hampton hump
- Chronic thromboembolic pulmonary hypertension: Persistent dyspnea and pulmonary hypertension after PE
- Bleeding: Major complication of anticoagulation or thrombolysis
USMLE Step 2 CK Exam Tips
- 1Most common ECG finding in PE is sinus tachycardia, not S1Q3T3
- 2Low-risk patient who is PERC negative needs no D-dimer and no imaging
- 3Positive D-dimer does not diagnose PE; it triggers imaging in the correct pretest probability group
- 4High clinical probability PE goes straight to CTPA, not D-dimer
- 5Massive PE with hypotension = systemic alteplase unless contraindicated
- 6Unstable suspected PE unable to go to CT: bedside echo showing RV strain supports thrombolysis in the right clinical context
- 7IVC filter is not first-line; use only if anticoagulation is contraindicated or fails
practicetest your knowledge on pulmonary embolismApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — respiratory and beyond.
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