 Simplified 2D Cavity Model  Flow Field Characteristics of the Simple 2D Cavity I. Introduction IV. Results • Atrial fibrillation (AFib) is the most common cardiac arrhythmia. • The risk of stroke is increased approximately 5-fold in patients with AFib. • In 91% of patients, atrial thrombi develop within the left atrium and appendage. • It is still not fully understood how the AFib-induced flow would change the hemodynamic conditions in the LA • In this study, we performed an in vitro tomographic Particle Image Velocimetry study to quantitatively characterize the pulsatile flow in the left atrium under regular (double peak) and simulated AFib (loss of A wave) waveforms. V. Conclusions CAD Model of Left Atrium • A 2D side-wall cavity model (depth-to-width ratio is 1.5) was used to examine the vortex dynamics under normal and AFib waveforms. Left atrial flow waveforms: simulated vs clinical data  3D Flow Streamlines for Normal Double-Peak LA Flow  The Cardiovascular Flow Simulator  Tomographic Particle Image Velocimetry (Tomo-PIV) II. Methodology Fluid Dynamics of the Human Left Atrium under Simulated Normal and Atrial Fibrillation Conditions: A in vitro Tomographic PIV Study Sifat K. Chowdhury, Al Habib Ullah, Zachary Posch, Yan Zhang* Department of Mechanical Engineering, North Dakota State University *Speaker; Corresponding Author: yan.zhang.4@ndsu.edu, +1(701)-231-9217 • Phase-locked planar and Tomographic Particle Image Velocimetry (PIV) were used to quantify the flow characteristics in a 2D cavity model and in a realistic LAA model, respectively • The PIV system consists of o Double-pulsed Nd:YAG lasers o Synchronizing timing unit o Four CCD cameras o Imaging processing software • A closed-loop cardiovascular flow simulator was constructed with a pulsatile flow generator to mimic the heart, under both normal and AFib waveforms, III. Test Model and Conditions  3D Left Atrium Silicone Phantom Pulmonary Veins Left Ventricle Chamber (simplified outlet) Appen dage • The refractive index (RI) matching: RI = 1.43 of the silicone model. Mixture of water-glycerin (40 % and 60 % respectively by volume)  Regular and AFib Flow Waveforms • A lump-parameter numerical model was used • The regular LA flow boundary condition features a double-peak flow (E-wave and A-wave), representing the early LV suction and the late atrial pumping effects • The simulated AFib flow was generated by smoothing out the A-wave (2nd peak). • Flow rate: 5 Liters/min • Heart rate: 75 beats per minutes Velocity vectors and out-of-plane vorticity fields of pulsatile flow past the simple cavity (a) the normal LA mitral flow and AFib flow waveforms used for experiments; (b - e) the flow fields under normal double-peak LA waveform reveals higher momentum of vortical flow inside cavity throughout the cycle; (f - i) the flow fields under AFib waveform reveals the cavity vortical flow dissipates faster after the E-wave. VI. Acknowledgement We would like to acknowledge the American Heart Association for the funding support under the AHA Institutional Research Enhancement Award (AIREA) #19AIREA34470008. • The Simple Cavity experiment results indicate that compared with the AFib waveform, the “double-peak” of the normal LA flow helps maintain the momentum of vortical flow and reduce flow stasis inside the appendage cavity. • Tomographic PIV results of LA flow suggest: • The clock-wise rotating helical flow (posterior view) is a predominant feature for LA flow, regardless of normal or AFib conditions • The secondary peak of flow under normal condition feeds into the momentum/energy of the helical flow in the LA chamber, potentially reducing flow stasis compared to Afib • The results emphasize the important role of normal atrial pulsation. Cross-Section for Tomographic PIV Measurement Volume (Volume Thickness ~10mm) Left Right Anterior Wall Posterior Wall  3D Flow Streamlines for AFib Single-Peak LA Flow Velocity Magnitude (m/s) Specific Kinetic Energy (𝒎𝟐/𝒔𝟐) Veloc