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Risk Factors for Atrial Fibrillation
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco does research for Medtronic, is a consultant for Medtronic, Novartis, and St. Jude, and is a speaker for Boston Scientific.
Source: Huxley RR, et al. Absolute and attributable risks of atrial fibrillation in relation to optimal and borderline risk factors: The Atherosclerosis Risk in Communities (ARIC) study. Circulation 2011;123:1501-1508.
The ARIC Study is a prospective epidemiologic study of atherosclerosis in four communities in the United States (Fairfax County, NC; Jackson, MS; Washington County, MD; and Minneapolis, MN). Patients were recruited for ARIC between 1987 and 1989 and had been followed sequentially since. This paper examines the relationships between baseline risk factors and later development of atrial fibrillation (AF) in this cohort.
Patients enrolled in ARIC were categorized as having an optimal AF risk factor profile if at baseline they had no history of cardiac disease, a systolic blood pressure of less than 120 and a diastolic blood pressure of less than 80 mg, no use of antihypertensive medications, a body mass index less than 25 kg/m2, a fasting serum glucose less than 100 mg/dL, and no history of antidiabetic medications or diagnosed diabetes mellitus and no smoking history. Borderline and high-risk profiles were also created using the same general categories. During follow-up through the end of 2007, incident AF and atrial flutter were diagnosed by ECGs done at study visits, the presence of an AF code in a hospital discharge, or AF listed as any cause of death on a death certificate.
The initial study group of almost 15,000 subjects included 55% women and 25% blacks and had a mean age of 54.2 years. Only 5% of the cohort had an optimal risk factor level. Just over one-quarter had one or more borderline risk factor levels. Two-thirds of the cohort had more than one elevated risk factor at study baseline. More than 80% of blacks had one or more elevated risk factors compared to approximately 60% of whites. During long-term follow-up there were 1,520 cases of incident AF. The age-adjusted incidence rates were 7.45, 4.59, 5.27, and 3.67 per 1,000 patient years among white men, white women, black men, and black women, respectively. Incident AF was strongly related to the presence of risk factors with an age-adjusted incidence rate three times higher among those with one or more elevated risk factors compared to those without any risk factors. For any category risk factor level, white men had the highest incident rate for AF and black women the lowest rate. Population-attributable fraction estimates were made showing that having ≥ 1 elevated risk factor could explain approximately 50% of AF events. Borderline risk factor presence explained an additional 6.5% of all AF events. This resulted in an estimate that modifiable risk factors were the cause of 44% of events in white men and 61% in black women. Of the population-attributable factors, elevated blood pressure was the most important contributor. Obesity and being overweight were the next two most important risk factors.
The authors conclude that maintaining an optimal risk factor could theoretically avoid more than half of the incident cases of AF. The authors argue that primary prevention strategies that enable individuals to adopt and maintain healthy diet and behavioral patterns may prevent AF.
This paper makes several interesting observations. The lower incidence of AF among blacks as opposed to whites despite the increased prevalence of risk factors among the former has been noted by other authors and is unexplained. The data also highlight that prevention of AF must start early in life. Prevention of hypertension and obesity during a patient's early and mid-adult years, rather than late treatment after these problems develop, will be necessary to prevent the atrial distention and fibrosis that so often results in AF. Unfortunately, the incidence of these risk factors is increasing, not decreasing in the U.S. population, and it's likely we'll see even more AF in future years.