Pulmonary embolism Study Guide

📖 Core Concepts Pulmonary embolism (PE) – blockage of a pulmonary artery by material that traveled from elsewhere, most often a deep‑vein clot from the leg. Virchow’s triad – the three forces that promote clot formation: stasis (immobility, pregnancy), endothelial injury (surgery, catheter), and hypercoagulability (cancer, estrogen, inherited thrombophilias). Clinical probability tools – Wells score and PERC rule estimate pre‑test likelihood and dictate the need for further testing. Imaging hierarchy – CTPA is first‑line; V/Q scan or lower‑limb ultrasound are alternatives when CTPA is contraindicated. Risk stratification – PESI/sPESI classes predict 30‑day mortality; hemodynamic instability (hypotension, shock) denotes massive PE. --- 📌 Must Remember Wells score interpretation: >6 = high, 2–6 = moderate, <2 = low probability. PERC rule: In low‑risk patients, no PERC criteria → no further testing. Criteria = age > 50 yr, HR > 100, O₂ < 95 %, unilateral leg swelling, recent surgery/trauma, prior DVT/PE, hemoptysis, hormone use. D‑dimer cut‑off: < 500 µg/L excludes PE in low/moderate probability; age‑adjusted = age × 10 µg/L for patients > 50 yr. First‑line imaging: CTPA (high accuracy, non‑invasive). Anticoagulation targets: Warfarin INR 2.0–3.0; DOACs (rivaroxaban, apixaban) can start without injectables; dabigatran & edoxaban need initial heparin/fondaparinux. Duration of therapy: ≥ 3 months; extend to 6 months or indefinite if no reversible risk factor or recurrent events. Massive PE treatment: Systemic thrombolysis (tPA) unless contraindicated; consider catheter‑directed thrombolysis or surgical thrombectomy if refractory. PESI mortality: Class I–II ≈ 1 % 30‑day mortality; Class III–V up to 24 %. --- 🔄 Key Processes Assess clinical probability Apply Wells → categorize (high/medium/low). If low risk, run PERC; if any PERC positive → proceed to D‑dimer. Laboratory testing Obtain D‑dimer; interpret with age‑adjusted cut‑off if >50 yr. Normal D‑dimer + low/moderate probability → PE excluded. Imaging algorithm Positive D‑dimer or moderate/high Wells → order CTPA. Contraindication to contrast → V/Q scan or lower‑limb compression US (if DVT found, treat as PE). Therapeutic cascade Start rapid anticoagulation (UFH, LMWH, or fondaparinux). Bridge to oral agent (warfarin or DOAC) per drug‑specific protocol. For massive PE with hemodynamic compromise → evaluate for thrombolysis, CDT, or surgery. Risk stratification & disposition Calculate PESI/sPESI → determine inpatient vs outpatient management. Monitor for right‑ventricular dysfunction (echo, biomarkers). --- 🔍 Key Comparisons Small (subsegmental) vs Large (central) PE Location: peripheral vs central pulmonary arteries. Symptoms: pleuritic pain common in small; severe dyspnea, hypotension in large. Hemodynamics: small usually hemodynamically stable; large often cause tachycardia, hypotension, shock. DOACs: Rivaroxaban/Apixaban vs Dabigatran/Edoxaban Loading: Rivaroxaban & Apixaban → no prior injectable needed. Requirement: Dabigatran & Edoxaban → need 5‑day heparin/fondaparinux lead‑in. CTPA vs V/Q scan CTPA: high accuracy, works in most patients, uses iodinated contrast. V/Q: preferred when contrast contraindicated (renal failure, allergy, pregnancy). --- ⚠️ Common Misunderstandings “Normal ECG rules out PE.” Only 12–50 % show S1Q3T3; sinus tachycardia is the most common finding. “All subsegmental emboli need anticoagulation.” Evidence suggests many patients do well without anticoagulation; decision should weigh bleeding risk. “A positive D‑dimer always means PE.” D‑dimer is non‑specific; must be interpreted in the context of clinical probability. --- 🧠 Mental Models / Intuition “Clot‑to‑lung pipeline” – Think of a DVT as a train that can either stop in the leg (no PE) or reach the lung (PE). Immobility, injury, and hypercoagulable states are the “track switches” that push the train forward. “Risk‑test‑treat loop” – Start with risk (Wells), apply a test (PERC/D‑dimer/CTPA), then treat (anticoagulation ± thrombolysis). If any step is negative, you can stop early, saving resources. --- 🚩 Exceptions & Edge Cases Pregnancy – Use LMWH throughout; avoid warfarin (teratogenic) and most DOACs (insufficient data). Cancer‑associated PE – Prefer LMWH over warfarin or DOACs for better outcomes. Renal insufficiency – Consider V/Q scan or bedside ultrasound; avoid contrast‑based CTPA and dose‑adjust LMWH. Age‑adjusted D‑dimer – For patients >50 yr, raise cut‑off to age × 10 µg/L to improve specificity. --- 📍 When to Use Which Low‑risk patient + negative PERC → No further testing. Low‑/moderate‑risk + positive PERC or not assessed → D‑dimer; if normal, stop. Positive D‑dimer or high Wells → CTPA (unless contraindicated). Contraindication to contrast → V/Q scan; if V/Q non‑diagnostic, perform leg compression US. Hemodynamically unstable (massive PE) → Immediate thrombolysis (tPA) unless bleeding risk high; consider CDT or surgery if thrombolysis fails or contraindicated. Outpatient management → Low PESI/sPESI class, stable vitals, no RV dysfunction, reliable follow‑up. --- 👀 Patterns to Recognize Tachycardia + hypoxia + pleuritic chest pain → classic triad pointing toward PE. Sudden dyspnea + syncope + hypotension → massive PE → urgent reperfusion needed. Right‑axis deviation + S1Q3T3 on ECG → suggest right‑ventricular strain → higher risk. Elevated troponin/BNP + RV dysfunction on echo → intermediate‑high risk PE (consider closer monitoring or early thrombolysis). --- 🗂️ Exam Traps “Any positive D‑dimer confirms PE.” – D‑dimer is a rule‑out test; a positive result requires imaging. “Absence of pleuritic pain excludes PE.” – Large central emboli often lack pleuritic pain. “S1Q3T3 is pathognomonic.” – Low specificity; many other conditions (e.g., COPD exacerbation) can mimic it. “All patients with PE need 6‑month anticoagulation.” – Minimum is 3 months; longer only if no reversible risk factor or recurrent events. “Warfarin is first‑line for cancer‑associated PE.” – LMWH is preferred per guidelines. ---