Pathogenesis:
- Most emboli -> proximal DVT of lower extremities above the knee (MC: ileofemoral DVT)
- DVT dislodges -> vena cava -> right heart -> pulmonary circulation -> obstruct part of the pulmonary artery -> ↑ alveolar dead space (hypoxemia + hypercarbia -> tachypnea) -> vascular constriction -> pulmonary hypertension
- When 50% of lung vasculature is involved -> ↑ RV workload -> right-sided HF
- Massive PE: when > 2\3 of one lung is involved
High risk:
- Age (>60), obesity
- Recent surgery (esp orthopedic)
- Cancer history
- Immobile pts (esp hospitalized), travelling
- Acquired thrombophilia: lupus anticoagulant, nephrotic (loss of antithrombin III), oral contraceptives
- Inherited thrombophilia: factor V Leiden mutation, protein C and S def, antithrombin III def
- Pregnancy: risk continues until 2 months after delivery
Clinical presentation:
- Sudden onset of dyspnea and tachypnea
- Cough
- Pleuritic chest pain
- Hemoptysis (only w\ infarction; rare bc of lung’s dual circulation ‘bronchial + pulmonary’)
- Thigh or calf swelling
- Syncope in large PE
- PE: rales tachycardia, S4, shock in massive PE, low-grade fever, ↓ BS, dull percussion
Investigations:
» If high clinical suspicion -> start anti-coagulant (don’t wait for test results)
ABG: hypoxemia, ↑ A-a gradient, respiratory alkalosis
D-dimer: most sensitive for thromboembolic ds. Useful as an adjunct test in a low-risk pts. Little value if pretest probability is high
CXR:
- Normal, atelectasis, pleural effusion, hemi diaphragm elevation
- Westermark sign: lack of vascular markings (oligemia) distal to PE
- Hampton bump: wedge-shaped infiltrate due to pulmonary infarct
CT angio: initial test for PE
- Positive -> 100% treat PE
- Negative -> consider peripheral PE
Pulmonary angiogram: gold standard -> filling defect
- Negative angiogram excludes clinically relevant PE
Duplex US: for DVT
V\Q scan: in PE; perfusion defect w\ normal ventilation.
- Normal -> rule out PE
- High-probability -> treat w\ heparin
- Low\intermediate-probability -> go with the clinical suspicion
- Low clinical suspicion -> rule out PE
- High clinical suspicion -> do duplex US
- Positive duplex -> treat DVT (same as PE)
- Negative\uncertain duplex -> do pulmonary angio
ECG: most commonly sinus tachycardia, or evidence of right heart strain (due to pulmonary HTN) -> large S wave in lead I, deep Q wave in lead III, T wave inversion in lead III “S1, Q3, T3”
Treatment:
» Heparin (LMWH or unfractionated) + warfarin for 5-7 days (or until therapeutic INR) -> then continue on warfarin for 6 mo
- A pt w\ recurrent PE or DVT despite heparin treatment? Consider Heparin-induced thrombocytopenia (which, paradoxically, is associated with thromboembolic events after giving heparin for 5-7 days) (occurs in both unfractionated and LWMH ‘but less’)
- What to do? Monitor plt while on heparin and stop it if plt ↓ by < 50% -> give new anti-coagulants (Argatroban or Lepirudin)
- In pts w\ preexisting protein C deficiency -> warfarin skin necrosis (bc protein C has a shorter half-life than factors 1972 -> “transient hypercoagulable state”
- Contraindication: eye\neurosurgery -> use IVC filter (placed below the renal veins to prevent renal V thrombosis)
» If massive PE: defined as hemodynamically unstable by either:
- Hypotension (systolic <90)
- A drop in BP > 40 mmHg persisting for > 15 mins
- Treatment: give thrombolytics (tPA, streptokinase)
» Intermediate PE: defined as hemodynamically stable + either or both of:
- Right heart strain by echo
- Positive cardiac enzymes
- To prevent chronic swelling w\ DVT (post-thrombotic \postphlebitic syndrome)? Compression stockings
- Fat embolism (3 days after long bone fracture; acute dyspnea, petchiae in neck + axilla, confusion) -> supportive treatment (no anticoagulation)
- Duration of treatment: minimum of 3 mo -> then asses risk of bleeding -> if none; continue for another 3 mo
- The risk of recurrence if unprovoked: in 1 yr is 10%, in 5 yrs is 30%, in 10 yrs is 50%
Download the PDF version: here
References:
- Toronto notes
- The Johns Hopkins Internal Medicine Board Review
- Master the boards
- Step up to medicine