Heart rate variability in atrial fibrillation related to left atrial size.
The purpose of this investigation was to determine whether heart rate variability (HRV) in atrial fibrillation (AF) can be related to any echocardiographic-derived measurements of cardiac dimensions or function. AF is characterized by marked HRV. Although HRV in normal sinus rhythm has been studied and shown to have important clinical implications, there have been relatively few published reports dealing with the phenomenon in AF. This study examines HRV in AF taking into account the influence of heart rate. HRV measurements were obtained in 38 patients with persistent AF who had undergone 24-hour ambulatory electrocardiographic monitoring. Taking into account a strong heart rate dependence of the HRV measurements, regressions were calculated. The relations were then re-examined using the differences (diff) in HRV from the expected for the average RR intervals. No significant correlations were found between unadjusted HRV measurements and any clinical features or echocardiographic variables. However, taking into account heart rate relations, with negative HRVdiff signifying less HRV than expected, reduced HRV correlated with increasing left atrial and left ventricular dimensions. On multivariate regression analysis, left atrial dimension emerged as an independent determinant of HRV. Also, HRV was greater in patients with lone AF than in those with cardiac disorders. HRV in AF is highly rate dependent. Unless this influence is taken into account, important relations may be obscured. When HRVdiff are related to echocardiographic measurements, increasing left atrial dimensions correlate with less HRV.