Pulmonary embolism

Definition and risk factors. Pulmonary embolism (PE) is obstruction of the pulmonary arterial tree, usually by thrombus embolising from a deep vein of the leg or pelvis. Risk factors follow Virchow's triad: immobility, hospitalisation, stroke with hemiplegia, hip fracture and arthroplasty, malignancy, previous VTE, heart failure, dehydration, sepsis, oestrogens and thrombophilia. Advancing age is an independent risk factor, and PE is both commoner and more often fatal in the old.

Clinical features and the diagnostic trap. Sudden breathlessness, pleuritic chest pain, haemoptysis, tachypnoea, tachycardia, syncope and hypotension. PE shares fever, cough, chest pain and dyspnoea with pneumonia; the clues that favour PE are clear lung fields on the chest radiograph, a context favouring venous thromboembolism, or clinical signs of deep vein thrombosis. Conversely, a pulmonary infarct produces signs shared with pneumonia and is very often secondarily infected. In older patients PE presents atypically with unexplained breathlessness, delirium, falls, syncope or new atrial fibrillation, and is a common missed diagnosis at autopsy.

Risk-stratified diagnostic approach. First ask whether the patient is haemodynamically unstable. If stable, apply a validated pre-test probability score (Wells or revised Geneva) and, if low/intermediate, measure D-dimer — a negative result excludes PE. D-dimer specificity falls with age, so use the age-adjusted cut-off (age × 10 µg/L in patients over 50), which substantially reduces unnecessary imaging in the elderly. If D-dimer is raised or probability is high, perform CT pulmonary angiography. Use a V/Q or V/Q-SPECT scan when there is renal impairment or contrast allergy. If unstable, perform bedside echocardiography for right ventricular dilatation and strain and treat immediately.

Supporting investigations. ECG — sinus tachycardia is commonest; S1 Q3 T3 is classic but uncommon; also right axis deviation, RBBB and anterior T-wave inversion (V1–V4). Chest radiograph usually normal or shows oligaemia (Westermark), a wedge-shaped peripheral opacity (Hampton hump), raised hemidiaphragm or a small effusion. ABG — hypoxaemia with hypocapnia and a widened A–a gradient. Troponin and BNP for right ventricular injury and prognosis. Compression ultrasound of the legs supports the diagnosis when imaging is not possible.

Severity stratification. High-risk (massive) — persistent hypotension or shock; mortality > 15%. Intermediate-risk (submassive) — normotensive but with right ventricular dysfunction on imaging and/or raised troponin; subdivided into intermediate-high (both positive) and intermediate-low. Low-risk — sPESI = 0 (the simplified PESI counts age > 80, cancer, chronic cardiopulmonary disease, heart rate ≥ 110, systolic BP < 100, SpO < 90%), 2 permitting early discharge and outpatient treatment.

Treatment. Start therapeutic anticoagulation immediately once PE is suspected with high probability, before confirmation, unless bleeding risk is prohibitive. DOACs are first-line — apixaban 10 mg twice daily for 7 days then 5 mg twice daily, or rivaroxaban 15 mg twice daily for 21 days then 20 mg daily; dabigatran and edoxaban need 5 days of LMWH lead-in. Use LMWH in severe renal impairment and pregnancy and warfarin for antiphospholipid syndrome. For high-risk PE give systemic thrombolysis (alteplase 100 mg over 2 hours); if thrombolysis is contraindicated or fails, use catheter-directed therapy or surgical embolectomy. Routine thrombolysis is not given in intermediate-risk PE (PEITHO showed reduced decompensation but excess major and intracranial bleeding, especially over 75). Duration: provoked by a transient factor 3 months; unprovoked or persistent risk factor extended/indefinite, with reduced-dose apixaban 2.5 mg twice daily or rivaroxaban 10 mg daily thereafter. Reserve an IVC filter for absolute contraindication to anticoagulation.

Catheter-based reperfusion is now supported by randomised evidence. The PEERLESS trial (Circulation 2025) randomised 550 patients with intermediate-risk PE to large-bore mechanical thrombectomy versus catheter-directed thrombolysis and found a significantly better composite outcome with thrombectomy (win ratio 5.01), driven by less clinical deterioration or need for bailout therapy and less post-procedural intensive care use, with shorter hospital stay and fewer 30-day readmissions. STORM-PE (2025) then showed mechanical thrombectomy improved right-ventricular recovery compared with anticoagulation alone. These approaches are attractive in older patients because they avoid systemic thrombolysis and its intracranial bleeding risk, but the decision must still be made by a Pulmonary Embolism Response Team (PERT).