Aim: Idiopathic paroxysmal atrial fibrillation (AF) occurs in patients with apparently normal heart. Its mechanisms may be complex and are poorly understood. The aim of the study was to evaluate whether patients with idiopathic AF have any structural abnormality that may explain the occurrence of AF.
Methods and results: A case-control study was undertaken including 60 consecutive patients (mean age 48 +/- 12 years; 75% men) with idiopathic AF admitted to the emergency department. Sixty sex- and age-matched healthy volunteers made up the control group. An echocardiogram was performed in all patients and volunteers to assess the left atrial (LA) and ventricular (LV) dimensions and valvular function. LV diastolic function was also evaluated by analysis of the LV inflow and pulmonary vein flow velocity patterns and tissue Doppler imaging of the mitral annulus. All AF patients showed normal echocardiographic studies with similar LV dimensions, ejection fraction, and diastolic function when compared with normal controls. However, patients with AF had larger LA dimensions (27 +/- 3 vs. 24 +/- 3 mm/m(2)), LA area (10 +/- 2 vs. 8 +/- 2 mm(2)/m(2)), and LA volume (27 +/- 9 vs. 19 +/- 6 mL/m(2)) (P < 0.05 for all). Among patients with AF, there were no differences in LA size between patients with a first episode or recurrent paroxysmal episodes.
Conclusion: Patients with idiopathic AF showed larger left atria when compared with controls, there being no differences between patients with a first episode or a recurrence. This suggests the presence of an enhanced substrate to develop idiopathic lone AF.