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Unprovoked Pulmonary Thromboembolism — Complete Clinical Review

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1. Definition & Terminology

Important update (Harrison's, p. 7731): Current guidelines (ESC 2019, updated recommendations) no longer support the strict terminology of "provoked" vs. "unprovoked," as it is potentially misleading and not directly helpful for decision-making about anticoagulation duration. Instead, the focus is on identifying ongoing risk factors and recurrence risk to guide treatment.

Categories Based on Risk Factor Presence:

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2. Epidemiology

• PE is the 3rd most common acute cardiovascular emergency globally, after myocardial infarction and stroke.
• Annual incidence: ~100–200 per 100,000 persons in the general population.
• ~30–40% of all PE episodes are classified as unprovoked.
• Mortality: 30-day mortality is ~10–15% overall; higher in massive PE (>50%).
• Recurrence risk is highest in unprovoked PE:
  • ~10% at 1 year
  • ~30% at 5 years
  • ~50% at 10 years (if anticoagulation stopped)

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3. Pathophysiology

Virchow's Triad (Foundation)

Hemodynamic Consequences

1. Obstruction of pulmonary vessels → increased pulmonary vascular resistance (PVR)
2. Elevated PVR → acute right ventricular (RV) pressure overload
3. RV dilation → interventricular septal shift (D-sign on echo/CT)
4. Reduced LV filling → decreased cardiac output → systemic hypoperfusion
5. Myocardial ischemia: RV wall tension rise + coronary perfusion pressure fall
6. Reflex hypoxic vasoconstriction + neurohormonal activation amplify PVR

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4. Inherited Thrombophilias (Common in Unprovoked PE)

Harrison's (p. 3508): Factor V Leiden and prothrombin G20210A mutation are established risk factors for DVT and PE; their contribution to arterial thrombosis is much less defined. Arterial and venous thrombosis do share common risk factors, notably age and metabolic syndrome.

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5. Clinical Presentation

Symptoms (variable, nonspecific)

• Dyspnea — most common (~73–80%)
• Pleuritic chest pain (~44–66%)
• Cough (~34%)
• Hemoptysis (~13%) — suggests pulmonary infarction
• Syncope or presyncope — especially in massive PE (~14%)
• Anxiety, diaphoresis

Signs

• Tachycardia (HR >100) — most common sign
• Tachypnea (RR >20)
• Fever (low-grade, usually <38.5°C)
• Hypoxia (SaO₂ <95%)
• Hypotension/shock — massive PE
• Signs of DVT: unilateral leg swelling, calf tenderness, erythema
• S₁Q₃T₃ on ECG (classic but insensitive), RV strain pattern
• Loud P₂, right-sided S₃, JVD, tricuspid regurgitation murmur

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6. Risk Stratification

Wells Criteria for PE

Revised Geneva Score (alternative, fully objective)

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7. Severity Classification

PESI (Pulmonary Embolism Severity Index)

• Class I–II: 30-day mortality <2% (low-risk; outpatient treatment candidate)
• Class III–V: increasing mortality risk up to >25%

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8. Diagnostic Workup

Step-by-Step Algorithm

Suspected PE
     ↓
Calculate Wells score
     ↓
PE Unlikely (≤4)          PE Likely (>4)
     ↓                          ↓
D-dimer                    CTPA immediately
     ↓
Negative → PE excluded
Positive → CTPA
     ↓
CTPA positive → Treat
CTPA negative → Lower limb compression ultrasound

Key Investigations

CT Pulmonary Angiography (CTPA) — Gold Standard

• Sinus tachycardia (most common)
• S₁Q₃T₃ pattern (right ventricular strain)
• New RBBB
• T-wave inversions in V₁–V₄
• Right axis deviation

• Often normal
• Westermark sign (oligemia distal to obstruction)
• Hampton's hump (wedge-shaped pleural-based opacity — infarction)
• Fleischner sign (enlarged pulmonary artery)

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9. Management

A. Immediate Resuscitation (Massive PE)

• Supplemental oxygen / intubation if needed (use with caution — reduces preload)
• Vasopressors: norepinephrine first-line for shock
• Fluid resuscitation: 500 mL cautious bolus only (excessive fluids worsen RV dilation)
• Avoid intubation if possible — positive pressure ventilation reduces RV preload dangerously

B. Anticoagulation — Cornerstone of Treatment

Acute Phase (First 5–21 days):

Long-term Anticoagulation (Months 1–3+):

C. Duration of Anticoagulation — Critical Decision

Harrison's (p. 7731): Extended oral anticoagulation of indefinite duration should be considered for patients with a first episode of PE and:

• (a) No identifiable risk factor (classic unprovoked PE)
• (b) A persistent risk factor (cancer, APS, hereditary thrombophilia)
• (c) A minor transient or reversible risk factor (e.g., OCPs, long travel)

• Rivaroxaban 10 mg OD (EINSTEIN-CHOICE trial) — reduces recurrence, low bleeding
• Apixaban 2.5 mg BD (AMPLIFY-EXT trial) — superior to placebo, similar bleeding to placebo
• Aspirin — inferior to DOACs for recurrence prevention; only if anticoagulation refused

D. Thrombolysis (Systemic)

E. Catheter-Directed Therapy (CDT)

• Catheter-directed thrombolysis (CDT): lower dose tPA directly into thrombus via pulmonary artery catheter
• Catheter-directed mechanical thrombectomy: rheolytic, aspiration, or ultrasound-facilitated
• Indications: Massive/submassive PE when systemic thrombolysis contraindicated or failed
• EKOS system (ultrasound-accelerated CDT): reduces clot burden with lower bleeding risk

F. Surgical Embolectomy

• Reserved for: massive PE with failed/contraindicated thrombolysis; large central thrombus
• 30-day mortality: 20–30% in experienced centers
• May be performed with or without cardiopulmonary bypass

G. IVC Filter

• Indications:
  • Absolute contraindication to anticoagulation
  • Recurrent PE despite adequate anticoagulation
• Retrievable filters preferred — retrieve once anticoagulation can be resumed
• Do not routinely add IVC filter to anticoagulation (does not improve mortality; increases DVT risk — PREPIC trial)

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10. Special Situations in Unprovoked PE

Thrombophilia Testing

• Test after completing acute anticoagulation (results unreliable during anticoagulation)
• Testing for antithrombin, protein C, protein S requires being off warfarin ≥2 weeks; being off DOACs ≥2 days
• Who to test: Young patients (<50), family history of VTE, recurrent unprovoked VTE, unusual site thrombosis (mesenteric, cerebral), APS suspicion
• Testing does not change initial management; influences long-term anticoagulation decisions

Occult Malignancy Screening

• ~4–10% of unprovoked PE patients harbor occult malignancy
• Recommended workup:
  • Minimum: History, physical exam, standard bloodwork, chest X-ray, age-appropriate cancer screening (mammogram, Pap smear, colonoscopy, PSA)
  • Limited CT scan of abdomen/pelvis if not already performed
  • Full-body PET-CT: not routinely recommended, controversial cost-benefit

Antiphospholipid Syndrome (APS)

• Test with: anticardiolipin antibodies (IgG/IgM), anti-β₂-glycoprotein I (IgG/IgM), lupus anticoagulant
• Requires 2 positive tests ≥12 weeks apart for diagnosis
• Management: Warfarin (INR 2–3); DOACs are inferior in triple-positive APS (TRAPS trial) — avoid DOACs in confirmed APS

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11. Prognosis & Recurrence

• Evaluate at 3–6 months post-PE: echocardiogram, V/Q scan
• Treatment: pulmonary endarterectomy (PEA) (curative in operable disease), balloon pulmonary angioplasty (BPA), riociguat (medical therapy)

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12. Predictors of Recurrence (to Guide Indefinite Anticoagulation)

• HERDOO2 rule (for women): low recurrence risk if ≤1 of: hyperpigmentation/edema/redness (leg), D-dimer ≥250 μg/L, obesity (BMI ≥30), age ≥65 — these women may safely stop anticoagulation
• Vienna Prediction Model: uses sex, location (DVT vs. PE), D-dimer
• DASH score: D-dimer, Age, Sex, Hormonal therapy — ≤1 point = low risk of recurrence

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13. Summary Algorithm for Unprovoked PE Management

Confirmed Unprovoked PE
        ↓
Acute anticoagulation (LMWH/DOAC/UFH)
        ↓
Risk stratify (PESI, echo, biomarkers)
        ↓
Massive PE ──→ Thrombolysis / Embolectomy / CDT
        ↓
Stable → Continue anticoagulation ≥3 months
        ↓
Assess: bleeding risk vs. recurrence risk
Screen for occult malignancy
Thrombophilia testing (after acute treatment)
        ↓
Extended/Indefinite anticoagulation (strongly preferred in unprovoked PE)
Use reduced-dose DOAC after 6 months if appropriate
        ↓
Follow-up echo/V-Q at 3–6 months to rule out CTEPH

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Key References

• Harrison's Principles of Internal Medicine, 21st Edition (pp. 3508, 7731)
• ESC Guidelines on Pulmonary Embolism (2019, updated 2022)
• EINSTEIN-PE, AMPLIFY, AMPLIFY-EXT, PEITHO, EINSTEIN-CHOICE, Hokusai-VTE trials
• PREPIC trial (IVC filters)
• TRAPS trial (DOACs in APS)
• HERDOO2 rule, Vienna Prediction Model, DASH score