A STROKE that occurs when the flow of blood to a part of the brain is interrupted by a partial or complete THROMBOSIS of the supplying artery or ARTERIES, or by a clot of blood that has detached itself from elsewhere in the circulatory system – for instance, a deep vein thrombosis (DVT) – and blocked a cerebral artery. Stroke is the second most common cause of death worldwide. Its treatment is difficult and prevention is best targeted at those who are at the highest absolute risk of stroke, because such people are likely to derive the greatest benefit. They may have had a previous ischaemic stroke or TRANSIENT ISCHAEMIC ATTACKS (TIA), coronary heart disease (see HEART, DISEASES OF) or PERIPHERAL VASCULAR DISEASE.

About 80 per cent of patients survive an acute stroke and they are at risk of a further episode within a few weeks and months; about 10 per cent in the first year and 5 per cent a year after that. HYPERTENSION, smoking, HYPERLIPIDAEMIA and raised concentration of blood sugar, along with OBESITY, are significant pointers to further strokes and preventive steps to reduce these factors are worthwhile, although the reduction in risk is hard to assess.