  Atrial fibrillation (AF) is considered the most common human arrhythmia.
Around 99\% of thrombi in non-valvular AF are formed in the left atrial
appendage (LAA). Studies suggest that abnormal LAA haemodynamics and the
subsequently stagnated flow are the factors triggering clot formation. However,
the relation between LAA morphology, the blood pattern and the triggering is
not fully understood. Moreover, the impact of structures such as the pulmonary
veins (PVs) on LA haemodynamics has not been thoroughly studied due to the
difficulties of acquiring appropriate data. On the other hand, in-silico
studies and flow simulations allow a thorough analysis of haemodynamics,
analysing the 4D nature of blood flow patterns under different boundary
conditions. However, the reduced number of cases reported on the literature of
these studies has been a limitation. The main goal of this work was to study
the influence of PVs on left atrium (LA) and LAA haemodynamics. Computational
fluid dynamics simulations were run on 52 patients, the largest cohort so far
in the literature, where different parameters were individually studied:
pulmonary veins orientation and configuration; LAA and LA volumes and its
ratio; and flow velocities. Our computational analysis showed how the right
pulmonary vein height and angulation have a great influence on LA
haemodynamics. Additionally, we found that LAA with great bending with its tip
pointing towards the mitral valve could contribute to favour flow stagnation.
