pulmonary embolism

The Great Masquerader

Obstruction of pulmonary arteries by thrombus (usually from DVT), air, or fat. Management is dictated by haemodynamic stability, not clot size.

diagnosis

Symptoms (dyspnoea, pleuritic pain, haemoptysis) are non-specific. Use a structured approach to avoid over-testing.

1. pre-test probability (wells score)

Different from DVT Wells.

• Score > 4 (PE Likely): Skip D-dimer $\to$ CTPA.
• Score $\le$ 4 (PE Unlikely): Apply PERC Rule.

2. rule-out criteria (low risk only)

• PERC Rule (Pulmonary Embolism Rule-out Criteria):
  • Prerequisite: Low clinical gestalt (belief that PE is unlikely).
  • Must meet ALL 8: Age <50, HR <100, SaO2 >94%, no haemoptysis, no exogenous oestrogen, no prior VTE, no surgery/trauma <4w, no unilateral leg swelling.
  • If Negative: PE excluded (risk <2%). No testing.
  • If Positive: Order D-dimer.

3. imaging

• CT Pulmonary Angiogram (CTPA): Gold standard.
  • Contraindications: Severe renal failure, anaphylaxis to contrast.
• V/Q Scan:
  • Preferred in severe renal failure or pregnancy (if CXR normal).
  • Reported as High/Intermediate/Low probability.

risk stratification

Prognosis depends on blood pressure and RV function.

Category	Definition	Markers	Management
Massive (High Risk)	Hypotension (SBP <90 for >15 min) or shock.	Positive	Thrombolysis + UFH
Submassive (Intermediate)	Normotensive but RV strain present.	Positive RV dysfunction (Echo/CT) or $\uparrow$ Troponin.	Anticoagulation + Close Monitoring. Rescue lysis only if decompensating.
Low Risk	Normotensive, no RV strain.	Negative	Anticoagulation (often outpatient).

management: stable (low/intermediate)

• Pharmacotherapy: Start anticoagulation immediately.
  • Apixaban (Preferred): 10 mg PO BID $\times$ 7 days $\to$ 5 mg PO BID.

  • evidence: apixaban safety (2025 update)

  • Apixaban vs Rivaroxaban:

  • • COBRRA (ISTH 2025 Abstract): RCT showing Apixaban has significantly less bleeding (NNT~27) vs Rivaroxaban.

  • • Bea et al. (JAMA IM 2025): Large observational study (n=163k) corroborating these findings (lower major bleeding and lower recurrence with Apixaban).

  • • Impact: Apixaban is the standard of care for acute PE.

• Outpatient Management:
  • Safe for Low Risk patients.
  • Tools: Hestia Criteria or sPESI score (0 points = low risk).
• Subsegmental PE:
  • Controversial. Small clots in distal vessels.
  • Treat if: Active cancer, severe symptoms, high D-dimer, or poor cardiopulmonary reserve.
  • Observe (Serial US): If incidental, asymptomatic, and no DVT found on leg ultrasound.

management: unstable (massive)

• ABC: Oxygen, fluids (cautious—RV is failing; volume overload worsens septal bowing and LV filling).
• Anticoagulation: Unfractionated Heparin (UFH) IV.
  • Preferred over LMWH due to short half-life if lysis/procedure needed.
• Reperfusion:
  • Systemic Thrombolysis: Alteplase (tPA) 100 mg IV over 2 hours.
  • Contraindications: Recent intracranial haemorrhage, active bleed, recent neurosurgery.
  • Catheter-Directed Lysis: If high bleed risk or systemic lysis failed (requires IR).
  • ECMO: Bridge to embolectomy in refractory shock.

exam trap: "the big clot"

Do NOT thrombolyse based on clot size or RV strain alone if the patient is normotensive (Submassive PE).

• Evidence (PEITHO Trial): Thrombolysis in intermediate-risk PE reduced decompensation but significantly increased intracranial haemorrhage and stroke.
• Strategy: Watch and wait. Lyse only if BP drops.

ivc filters

choosing wisely

“IVC Filters are likely the wrong answer.”

• Indication: Only if Acute Proximal DVT/PE AND Absolute Contraindication to anticoagulation (e.g., active GI bleed).
• Do NOT use: As an “adjunct” to anticoagulation (no mortality benefit, doubles DVT risk).
• Plan: Must be retrieved as soon as anticoagulation is safe.

special considerations: pregnancy

clinical pearl: cus first

In pregnant patients with suspected PE, start with Leg Ultrasound (CUS).

• If Positive: Treat for VTE (diagnosis confirmed, no radiation).
• If Negative: Proceed to chest imaging.

• Imaging Choice (CTPA vs V/Q):
  • CTPA: Lower fetal radiation, higher maternal breast radiation.
  • V/Q: Higher fetal radiation (still safe), lower maternal breast radiation. Preferred if CXR normal to spare breast tissue.
• Management:
  • LMWH (Dalteparin/Tinzaparin) is mandatory.
  • Contraindicated: DOACs (fetotoxicity), Warfarin.

complications

• CTEPH (Chronic Thromboembolic Pulmonary Hypertension):
  • Dyspnoea persisting >3 months post-PE.
  • Screen: Echocardiogram.
  • Confirm: V/Q Scan (more sensitive than CT for chronic/organized clots).
  • Treat: Pulmonary endarterectomy (surgical cure).

related pages: Deep Vein Thrombosis, Warfarin, Anticoagulant Reversal, Shock