Atrial fibrillation as an independent risk factor for stroke: the Framingham Study.

Abstract

The impact of nonrheumatic atrial fibrillation, hypertension, coronary heart disease, and cardiac failure on stroke incidence was examined in 5,070 participants in the Framingham Study after 34 years of follow-up. Compared with subjects free of these conditions, the age-adjusted incidence of stroke was more than doubled in the presence of coronary heart disease (/?< 0.001) and more than trebled in the presence of hypertension (p<0.001). There was a more than fourfold excess of stroke in subjects with cardiac failure (/><0.001) and a near fivefold excess when atrial fibrillation was present (/»<0.001). In persons with coronary heart disease or cardiac failure, atrial fibrillation doubled the stroke risk in men and trebled the risk in women. With increasing age the effects of hypertension, coronary heart disease, and cardiac failure on the risk of stroke became progressively weaker (p<0.05). Advancing age, however, did not reduce the significant impact of atrial fibrillation. For persons aged 80-89 years, atrial fibrillation was the sole cardiovascular condition to exert an independent effect on stroke incidence (/><0.001). The attributable risk of stroke for all cardiovascular contributors decreased with age except for atrial fibrillation, for which the attributable risk increased significantly (/><0.01), rising from 1.5% for those aged 50-59 years to 23.5% for those aged 80-89 years. While these findings highlight the impact of each cardiovascular condition on the risk of stroke, the data suggest that the elderly are particularly vulnerable to stroke when atrial fibrillation is present The powerful independent effect of atrial fibrillation reported here is in accord with the findings of recent randomized clinical trials in which >50% of stroke events were prevented by warfarin anticoagulation. (Stroke 1991^2:983-988)A lthough hypertension is the strongest risk fac-/ \ tor for stroke, age and the presence of other J. \ . risk factors may modify or enhance the effect of increased blood pressure on stroke occurrence. Impaired cardiac function, overt or occult, increases stroke incidence at all levels of blood pressure. In hypertensive persons coronary heart disease, cardiac failure, and particularly atrial fibrillation are associated with increased stroke risk. 5 -7 Atrial fibrillation, which is frequently associated with hypertension, coronary heart disease, and cardiac failure, becomes increasingly prevalent among persons aged >70 years.8 It has been suggested that Received December 21, 1990; accepted April 23, 1991. atrial fibrillation is a risk "marker" for stroke and that the increased stroke incidence in persons with this arrhythmia is a result of age and associated cardiovascular abnormalities. 910 To help address this issue, we have extended our previous study and examined in detail the relative impacts of hypertension, coronary heart disease, cardiac failure, and atrial fibrillation on the incidence of stroke in the Framingham Study. 8 We took advantage of the 110 additional initial stroke events, a...

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