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Although arterial thrombosis is a major cause of morbidity and mortality, its prevention is not possible at present; likewise, its pathophysiology is not well characterized. Smoking, hyperlipidaemia, and a raised fibrinogen concentration are associated with accelerated atheroma, which accounts for the majority of arterial disease (see Chapter 36). In addition, atrial fibrillation (see Chapter 29) and valvular cardiac defects are associated with arterial embolization, but a full understanding of arterial thrombosis does not exist at present.¹⁵

The situation with venous thrombosis is somewhat different, and there have been rapid advances in the understanding, diagnosis and management of venous thrombosis (see Chapter 37) over the last few years. Venous thrombosis is primarily a disease of old age; until recently, it was thought that in the majority of cases the cause was circumstantial, with predisposing factors being immobilization and surgery, particularly to the hip, knee and pelvis, together with accessory factors such as obesity and malignancy. However, it has become clear that in up to 50% of cases of venous thrombosis, an additional underlying genetic predisposition to thrombosis becomes manifest under the above circumstances. The importance of thromboembolic prophylaxis of both surgical and medical patients at medium and high risk of developing thrombosis is increasingly recognized and practised. Likewise, the need for objective diagnosis of venous thrombosis by ultrasound examination or venography in the lower limb, and ventilation–perfusion lung scanning and pulmonary angiography in cases of suspected pulmonary embolus, has become established. Objective validation of the diagnosis of venous thromboembolic disease should always precede the initiation of treatment. Treatment should be initially with either unfractionated or low‐molecular‐weight heparin and subsequently with oral warfarin. Warfarin in the elderly is not without hazards, there being an increased chance of drug interactions; and in general, the dose required in elderly patients is somewhat lower than in younger patients. Furthermore, the risk of bleeding is increased at both high and normal INRs because of the increased incidence of underlying pathology, such as peptic ulcer, gastrointestinal malignancy, and angiodysplasia. Consequently, it is important that recommended target ranges and duration of anticoagulation are adhered to and that patients are not anticoagulated without good cause (Table 24.5).¹⁶