Pulmonary Embolism

Obstruction of pulmonary arterial circulation, most commonly by thrombus embolized from deep vein thrombosis of the lower limbs/pelvis (>90% of cases), causing ventilation-perfusion mismatch, increased pulmonary vascular resistance, and potential right ventricular strain/failure.

Classified by severity:

• Low-risk (non-massive): hemodynamically stable, no RV dysfunction

• Intermediate-risk (submassive): hemodynamically stable but with RV dysfunction (echo/CT) and/or elevated carintermediate; further subdivided intermediate-low/intermediate-high

• High-risk (massive): hemodynamic instability (sustained hypotension SBP<90, requiring vasopressors, or pulseless); highest mortality, requires aggressive reperfusion

• Sudden onset dyspnea (most common symptom), pleuritic chest pain, cough, hemoptysis (suggests pulmonary infarction)

• Tachycardia, tachypnea, hypoxia; syncope/pre-syncope (suggests significant hemodynamic compromise; high-risk feature)

• Examination: often unremarkable beyond tachycardia/tachypnea; signs of DVT present in a minority; signs of RV strain in massive PE ; raised JVP, loud P2, right-sided S3, hypotension

• Risk factors (Virchow's triad): recent surgery/immobilization, malignancy, pregnancy/postpartum, estrogen therapy, prior VTE, inherited thrombophilia, long-haul travel, obesity, trauma, central venous catheter

• Massive PE: shock, syncope, cardiac arrest ; PEA arrest should always prompt consideration of PE as a reversible cause

• Clinical probability assessment first (Wells or Geneva score):

  • Low/intermediate probability: D-dimer : if negative, PE effectively excluded; if positive, proceed to imaging

  • High probability: proceed directly to imaging (D-dimer not useful for exclusion at high pre-test probability)

• D-dimer: sensitive but non-specific (elevated in pregnancy, malignancy, infection, recent surgery, elderly) ; age-adjusted cutoffs improve specificity in older patients

• CT pulmonary angiography (CTPA): investigation of choice; direct visualization of filling defect, also assesses RV size/strain (RV:LV ratio >1 suggests significant strain)

• V/Q scan: alternative if CTPA contraindicated (renal impairment, contrast allergy) or in pregnancy

• ECG: sinus tachycardia most common; S1Q3T3, right heart strain (T-wave inversion V1-4), RBBB ; classic but insensitive

• Echocardiography: bedside assessment of RV strain in unstable patients when CTPA not immediately feasible

• Troponin/BNP: elevated in RV strain, prognostic marker for risk stratification

• Lower limb Doppler: confirms DVT source if positive, though normal doesn't exclude PE

Differentials: ACS, pneumonia, pneumothorax, pericarditis, musculoskeletal chest pain, anxiety, aortic dissection, COPD/asthma exacerbation.

Hemodynamically stable (low/intermediate-risk):

• Anticoagulation : start promptly once diagnosis confirmed (or strongly suspected while awaiting imaging in high pre-test probability):

  • DOAC (apixaban, rivaroxaban) : first-line for most; apixaban 10mg bd x7 days then 5mg bd; rivaroxaban 15mg bd x21 days then 20mg od

  • LMWH (enoxaparin 1mg/kg bd) : preferred in pregnancy, severe renal impairment, active malignancy, or if intervention anticipated

  • Warfarin: requires LMWH bridging until INR therapeutic (2-3), largely superseded except specific indications (mechanical valve, severe renal impairment, antiphospholipid syndrome)

• Duration: minimum 3 months for provoked PE with reversible risk factor; longer/indefinite for unprovoked PE or ongoing risk factors ; individualized bleeding vs. recurrence assessment

• Intermediate-high risk: closer monitoring, low threshold for escalation

Hemodynamically unstable (high-risk/massive PE) ; reperfusion indicated:

• Systemic thrombolysis: alteplase 100mg IV over 2 hours (or accelerated regimens) : first-line for confirmed massive PE with shock

• Catheter-directed thrombolysis/thrombectomy: alternative where contraindications to systemic thrombolysis exist or expertise available

• Surgical embolectomy: for absolute contraindication to thrombolysis with appropriate surgical support

• Supportive: cautious IV fluid (small boluses only : aggressive fluid worsens RV strain), vasopressor (noradrenaline) for hypotension, avoid excessive positive pressure ventilation if intubated

• ECMO: bridge to definitive therapy in refractory cardiogenic shock/cardiac arrest

IVC filter: for absolute contraindication to anticoagulation with ongoing high VTE risk, or recurrent PE despite adequate anticoagulation.

Pregnancy-specific: LMWH is anticoagulant of choice (DOACs and warfarin contraindicated), continue through pregnancy and minimum 6 weeks postpartum, total duration ≥3 months.

Referral: respiratory/cardiology for risk stratification, hematology for thrombophilia workup if unprovoked/recurrent, ICU for massive PE.