Atrial fibrillation: relation to the metabolic syndrome, smoking, and development of a clinical risk score.

Abstract

This document provides information on the pathophysiology and epidemiology of atrial fibrillation, along with details on three manuscripts that together form the basis of a doctoral thesis. Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical practice and poses a great economic burden on the healthcare system. Some well known cardiovascular risk factors, such as smoking and the metabolic syndrome, have not been widely studied in the context of AF. In addition, the majority of studies on AF have used primarily white cohorts from North America and Europe.

This dissertation reports the associations of the metabolic syndrome and smoking with incident AF, and provides a 10-year risk prediction score for AF using the Atherosclerosis Risk in Communities (ARIC) study. The ARIC study is a bi-racial cohort of almost 16,000 participants followed since the baseline examination in 1987-1989.

The first manuscript describes the association of the metabolic syndrome and the individual components of the metabolic syndrome with risk of incident AF over a mean follow-up of 15.4 years. A 67% increased risk of incident AF was reported for individuals with compared to those without the metabolic syndrome at baseline. Most of the metabolic syndrome components were associated with an increased AF risk, and of the individual components, elevated blood pressure appeared to contribute most to AF risk. In addition, a monotonically increasing risk of AF with increasing number of metabolic syndrome components was observed.

In the second manuscript, the associations of smoking status and amount with incident AF in ARIC were examined, and a systematic literature review on prospective cohort studies investigating the effects of smoking on AF incidence was conducted. Current and former smokers exhibited a 98% and 30% increased risk of developing AF compared to never smokers. The risk of incident AF increased with increasing cigarette-years of smoking, and appeared to be somewhat greater among current smokers than former smokers with similar cigarette-years of smoking. However, no consistent association was apparent in previously published studies on smoking and incident AF.

A 10-year risk score for AF was developed using risk factors commonly measured in clinical practice for the third manuscript. The risk score had good discrimination and better predicted who would develop AF than the Framingham AF risk score applied to the ARIC cohort. In addition, the Framingham and ARIC coronary heart disease risk scores did not predict the 10-year risk of AF well, highlighting the importance of a separate risk score to predict AF.