Body mass index is an independent determinant of left atrial size

Obesity is a risk factor for atrial fibrillation (AF) but the mechanisms underlying this association are unclear. We aimed to assess whether body mass index (BMI) is an independent determinant of left atrial size, in subjects in sinus rhythm.

Subjects were consecutive ambulatory patients aged >/=18 years who underwent outpatient transthoracic echocardiography at a major metropolitan teaching hospital in Sydney, Australia. At the time of examination, age, sex, height and weight were measured. Left atrial (LA) area was measured on ultrasound by planimetry. Left ventricular (LV) function and LV posterior wall thickness were measured by M-mode.

Of 4859 consecutive subjects who underwent outpatient echocardiography at our institution over a three-year period, we analysed echocardiographic data from 2534 aged >/=18 years with confirmed sinus rhythm, normal LV contractility and no evidence of significant aortic or mitral valve disease. In these subjects (age 47+/-16.6 years, BMI 27.1+/-6.1, 53% male), BMI was a significant predictor of LA size (p<0.001), independent of the significant influences of LV end-diastolic volume and LV posterior wall thickness. Average LA size was 18.5+/-4.0 cm(2) in those with normal BMI, 20.7+/-4.5 cm(2) in the overweight and 22.3+/-4.1cm(2) in obese subjects (p for trend <0.001).

Obesity is associated with increased left atrial size in subjects undergoing clinically indicated echocardiography, independent of the effects of left ventricular size and posterior wall thickness. This may contribute, at least in part, to the rising incidence of atrial fibrillation in the community.