Effects of heart rate on flow velocity of the left atrial appendage in patients with nonvalvular atrial fibrillation

Background and hypothesis: Flow velocity of the left atrial appendage (LAA) is thought to be important in thrombus formation in association with blood stasis and the development of spontaneous echo contrast. The effects of heart rate on peak flow velocity of the LAA have not been studied in patients with nonvalvular atrial fibrillation. Methods: Using transesophageal Doppler echocardiography, peak flow velocity of the LAA was measured at the junction between the left atrium and the LAA during left ventricular (LV) systole and diastole in 21 patients with nonvalvular atrial fibrillation. In six cases, the average peak flow velocity of the LAA for 10 consecutive beats with moderately long R-R intervals (LI beats) was compared with those for 3-5 consecutive beats with extremely short R-R intervals (SI beats). Results: Average peak flow velocity of the LAA during LV diastole was significantly higher than that during LV systole (26.5 +/- 15.7 vs. 19.3 +/- 10.4 cm/s, p < 0.01). In SI beats, average peak flow velocity of the LAA was significantly lower than that in LI beats (17.1 +/- 12.1 vs. 21.2 +/- 12.9 cm/s, p < 0.01). Conclusion: An increased heart rate reduced the peak flow velocity of the LAA in patients with nonvalvular atrial fibrillation, which would promote blood stasis in the LAA.