Assessment of Doppler-derived aortic flow in atrial fibrillation using beats with equal subsequent cycles

Background: Prior studies have demonstrated that during atrial fibrillation (AF), beats with equal preceding and pre-preceding R-R intervals, defined as intervals differing less than 5%, could be used to determine the mean values instead of measuring over 20 cardiac cycles. It is not known whether beats with interval difference less than 10% could be used in the same way. Methods: In 120 patients with AF, Doppler aortic flow time-velocity integral was determined for at least 20 consecutive cardiac cycles. The values at beats with interval difference of less than 5% and less than 10% were chosen. These were then compared with the measured average values over all cardiac cycles. Results: Agreement and mean percentage difference analyses revealed that the accuracy of measurements using inter-beat variability less than 10% was similar to that using less than 5% for 2- and 3-beat analyses provided the R-R intervals were longer than 500 milliseconds. The values at beats with cycle lengths shorter than 500 milliseconds were usually far below the average values. The mean percentage differences were not significantly different between methods using interval differences of less than 5% and less than 10% for 3-beat analysis (2.83% vs. 2.97%, p = 0.269). Moreover, it is relatively easy to obtain beats with interval difference less than 10%. The median numbers of beats required finding 3 beats with inter-beat variability of less than 10% and less than 5% were 9 and 16, respectively. Conclusions: Averaging 3 beats with R-R interval difference less than 10% and cycle lengths longer than 500 milliseconds can be applied to accurately estimate Doppler-derived aortic flow for patients with AF.