Randomized trial of therapy with platelet antiaggregants for threatened stroke. 2: Observations on the pathogenesis and natural history of threatened stroke.

Transient cerebral ischemia and stroke may occur despite previous occlusion of the artery supplying the appropriate part of the brain. After occlusion of the internal carotid artery, emboli may pass from the "stump" of the occluded artery to later produce transient cerebral ischemia or a stroke. Transient cerebral ischemia and stroke are due to a variety of conditions, some of which are strongly correlated with platelet thromboembolism, while others have little primary relation to thrombosis. The impact of this on therapeutic considerations is obvious. Thromboembolism related to myxomatous degeneration of the mitral valve (mitral valve prolapse) is a factor to consider in determining the cause of a stroke in a younger person. The prognosis for the different varieties of threatened stroke is incompletely known. When due to arteriosclerosis of the large cerebral arteries, transient cerebral ischemia and minor strokes pose a cumulative threat for a major stroke or death of 13% in the first year, 22% in the second year and 30% in the third year.