Abstract
Introduction:
In patients with atrial fibrillation, pulmonary embolism and right atrial (RA) thrombus are less common than stroke and left atrial (LA) thrombus. Prior studies have linked thrombus formation to decreased blood flow velocity (stasis) promoting blood clotting. We hypothesized LA stasis is more evident than RA stasis.
Methods:
Whole heart 4D flow MRI was performed in n=70 subjects: 33 AF patients in sinus rhythm (SR) during imaging (AF-SR, age = 62±10 years), 29 AF patients in AF (AF-afib, age = 67±12 years), and 8 age-matched controls (age = 59±5 years). 3D segmentation (MIMICS, Materialise, USA) of the LA and RA geometry was performed to calculate the flow velocity distribution for all atrial voxels and cardiac time frames. Velocity histograms normalized by the total number of entries (figure 1A) were used to assess mean and median atrial velocities and the % of LA and RA with velocities <0.2m/s (stasis).
Results:
Compared to controls (LA = 0.20±0.2m/s, RA = 0.19±0.02m/s), both LA and RA velocities were significantly reduced in AF-SR (LA = 0.16±0.03m/s, RA = 0.16±0.04m/s, p<0.03) and even further in AF-afib patients (LA = 0.13±0.03m/s, RA = 0.13±0.04m/s, p<0.001). Atrial stasis was more pronounced in AF-afib (LA = 82±13%, RA = 80±16%, p<0.001) and AF-SR (LA = 72±15%, RA = 69±20%, p<0.04) than in controls (LA = 53±10%, RA = 53±13%). No significant RA vs LA differences were noted, Figure 1 shows significant associations (p<0.01) between LA and RA mean velocity (R2=0.40) and stasis (R2=0.36) in figure 1B. RA/LA mean velocity ratio (1.0±0.2, range=0.6-2.0) and RA/LA stasis ratio (1.0±0.3, range=0.3-2.2) were not significantly different.
Conclusions:
In both controls and AF patients, there was no evidence for increased stasis in the LA vs RA. Although stasis likely contributes to clot formation, other factors such as atrial geometry in combination with individual LA vs. RA flow differences may account for the more prevalent formations in the LA vs. the RA.