31. Deep vein thrombosis (DVT); pulmonary embolism

Deep vein thrombosis (DVT) and pulmonary embolism

DVT is thrombus formation in the deep venous system, most often in the lower limb. Pulmonary embolism (PE) occurs when thrombotic material embolises to the pulmonary arterial circulation.
Virchow triad explains thrombosis: venous stasis, endothelial injury and hypercoagulability. Risk factors include surgery, trauma, immobility, malignancy, pregnancy/postpartum state, oestrogen therapy, previous VTE, thrombophilia and acute medical illness.
Proximal DVT (popliteal or above) carries greater PE risk than isolated distal calf DVT. PE increases pulmonary vascular resistance and may cause right ventricular strain, reduced left ventricular filling and obstructive shock.

DVT may cause unilateral leg swelling, calf/thigh pain, tenderness, warmth, erythema and pitting oedema; some cases are asymptomatic. Physical signs alone cannot confirm or exclude DVT.
PE commonly causes sudden dyspnoea, pleuritic chest pain, tachypnoea, tachycardia, hypoxaemia, cough or haemoptysis. Syncope, hypotension and shock suggest high-risk PE.
Massive iliofemoral thrombosis may cause phlegmasia alba or cerulea dolens, with severe swelling, pain, cyanosis and threatened limb viability.

Estimate pre-test probability using a validated clinical score such as the Wells score. D-dimer is useful to exclude VTE in patients with low/intermediate probability when a sensitive assay is used; it is nonspecific and often elevated after surgery, in pregnancy, cancer and infection.
Compression duplex ultrasound is the first-line test for suspected lower-limb DVT. Repeat imaging may be needed if initial ultrasound is negative but suspicion remains.
CT pulmonary angiography is the usual imaging test for suspected PE in suitable patients. Ventilation-perfusion scanning is an alternative when CT contrast is unsuitable or in selected pregnancy pathways.
ECG, chest radiograph, troponin, BNP and echocardiography help assess severity and alternative diagnoses; they do not independently exclude PE. In haemodynamically unstable patients, bedside echo may identify acute RV strain while urgent treatment is arranged.
Differential diagnoses include cellulitis, ruptured Baker cyst, muscle injury, chronic venous disease, heart failure, pneumonia, acute coronary syndrome and aortic disease.

Start anticoagulation promptly when VTE is confirmed and may be started while awaiting imaging if clinical probability is high and bleeding risk is acceptable. Options include direct oral anticoagulants, low-molecular-weight heparin or unfractionated heparin depending on renal function, pregnancy, cancer, haemodynamic status and procedures.
Treat for at least three months in most patients with a first proximal DVT/PE; longer treatment is considered for unprovoked, recurrent or persistent-risk VTE after balancing bleeding risk.