Atrial fibrillation - risk marker for stroke

Article Abstract:

The risk of stroke increases with age, and is related to rapid and irregular heart beats, or atrial fibrillation. Nonvalvular atrial fibrillation (without heart valve disease) is related to the development of arterial emboli (fragments of clotted tissue obstructing arteries), and signals a five-fold increase in the risk of ischemic stroke (due to diminished blood supply). Ischemic stroke eventually occurs in up to 35 percent of patients with nonvalvular atrial fibrillation; the percentage of affected patients is even higher if symptomless stroke damage is considered. Narrowing of the carotid artery, which carries blood to the brain, is twice as likely in patients with atrial fibrillation, but does not seem to be related to the occurrence of stroke. Evidence is growing that atherosclerosis (fatty plaque formation) within the ascending aorta, the main artery carrying blood from the heart, is a source of emboli. In the absence of other cardiopulmonary disease or high blood pressure, atrial fibrillation is associated with a very low risk of stroke, suggesting that the condition itself does not cause stroke, but may be a marker for or increase the risk of other cardiovascular diseases. The different causes of stroke help explain the different responses to warfarin (coumadin) and aspirin therapy. Aspirin may be more effective in preventing strokes in patients with emboli due to heart valve abnormalities or ruptured arterial plaques, while warfarin may be more effective in preventing stasis-related stroke, usually due to clots developing in the left side of the heart when normal circulation is compromised. A direct comparison of aspirin and warfarin therapy is now underway. Three long-term studies of stroke prevention confirm that patients with nonvalvular atrial fibrillation may be candidates for treatment with either drug. However, the danger of hemorrhage must be weighed, especially in elderly patients with a history of falls. The therapeutic challenge is to choose the right drug and, if warfarin is chosen, to maintain an appropriate clotting time (to prevent bleeding and hemorrhage). With warfarin therapy, clotting time is outside of normal limits approximately one-third of the time. (Consumer Summary produced by Reliance Medical Information, Inc.)

Causes of, Physiological aspects, editorial

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Preliminary report of the stroke prevention in atrial fibrillation study

Article Abstract:

Atrial fibrillation, rapid, irregular contractions of the atria, the chambers of the heart to which blood returns from the body or the lungs, is associated with a considerably increased rate of ischemic stroke, a sudden decrease in blood flow to the brain. It is not known whether the administration of drugs that prevent blood clot formation would prevent stroke in people with atrial fibrillation. To answer this question, a large number of patients (1,244) with atrial fibrillation not due to rheumatic heart disease or prosthetic heart valves, and who were under treatment in several medical centers, received warfarin (an anti-coagulant), aspirin, or a placebo (inactive) drug. After a little more than a year, there was such a clear reduction in the rates of stroke or embolism (blood clot that lodges in a vessel) among patients receiving either aspirin or warfarin (1.6 percent per year) as compared with those receiving a placebo (8.3 percent), that investigators were led to eliminate the placebo treatment. The reduction in the rate of stroke or embolism was far greater than the slight increase in rate of hemorrhage (less than 1.0 percent per year). That aspirin prevented stroke and embolism in these atrial fibrillation patients was surprising. The patients in this part of the study were all 75 years old or younger; the effect of aspirin for older people was not determined. The relative merits of aspirin and warfarin in preventing these events will not be known until more data have been collected. (Consumer Summary produced by Reliance Medical Information, Inc.)

Care and treatment, Stroke patients, Cerebrovascular disease, Cerebrovascular disorders

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Randomized trials of warfarin for atrial fibrillation

Article Abstract:

A series of five clinical trials examined the use of the anticoagulant warfarin to prevent strokes in patients with nonrheumatic atrial fibrillation, or rapid heart beat. Patients with nonrheumatic atrial fibrillation have a higher risk of stroke than other individuals and this risk increases with age. The clinical trials were consistent in finding that warfarin was effective in preventing strokes in patients suffering from atrial fibrillation. It is easier to examine all the risks and benefits of a new drug with multiple clinical trials than with single studies. Observation of the same results in multiple clinical trials provides evidence that the results are valid. The clinical trials examining the use of warfarin found that it reduces the number of strokes among patients with atrial fibrillation by two thirds or more. Warfarin should still be prescribed cautiously because many risks are associated with its use.

Editorial

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