NIIGATA, JAPAN. Metabolic syndrome (MS) is defined as a combination of risk factors for atherosclerosis including obesity, high blood pressure (hypertension), insulin resistance (glucose intolerance), and dyslipidemia (elevated cholesterol and triglycerides). The diagnosis of MS is made when at least 3 of the following criteria are met:

• Elevated body mass index (BMI) – greater than 30 kg/sq m*
• Elevated triglycerides – greater than 150 mg/dL
• Low high-density cholesterol (HDL) – less than 40 mg/dL in men and 50 mg/dL in women
• Elevated blood pressure – greater than 130/85 and/or history of treated hypertension
• Impaired glucose tolerance
• *NOTE: Because the incidence of obesity in Japan is only 2-3% as compared to 20-30% in western countries, a cut-off value for obesity of only 25 kg/square meter was used in this study.

A group of American and Japanese researchers now report that metabolic syndrome is not only a risk factor for atherosclerosis and cardiovascular disease, but also significantly increases the risk of developing atrial fibrillation (AF). Their study involved 28,449 Japanese men and women enrolled in the Niigata Association for Comprehensive Health Promotion and Research Study. The mean age of enrolment in the study was 59 years and 66% of participants were women. At baseline MS was diagnosed in 13-16% (depending on definition of impaired glucose tolerance) of the participants, but none had AF. After a 4.5-year follow-up period, AF had been diagnosed in 265 subjects corresponding to an annual incidence rate of 0.41% in men and 0.13% in women. The annual incidence rate of AF was 0.19% in participants without MS and 0.33% in those with MS, thus indicating that MS along with age and gender (males were 3 times more likely to develop AF than were women) are potent risk factors for AF.The risk of developing AF increased with the number of MS components diagnosed in individual participants. The relative risk increase associated with the components were as follows:

• Obesity – 64%
• Hypertension – 69%
• Low HDL cholesterol – 52%
• Impaired glucose tolerance – 44%

An elevated level of triglycerides was not associated with an increased risk of AF. The researchers speculate that inflammation and oxidative stress may be common factors in both MS and AF and that hypertension and obesity can cause atrial stretch and dilation resulting in a structural substrate predisposing to AF.

Watanabe, H, et al. Metabolic syndrome and risk of development of atrial fibrillation. Circulation, Vol. 117, March 11, 2008, pp. 1255-60