The Impact of Left Atrium Appendage Morphology on Stroke Risk Assessment in Atrial Fibrillation: A Computational Fluid Dynamics Study

Abstract

Atrial fibrillation (AF) carries out a 5-fold increase in stroke risk, related to embolization of thrombi clotting in left atrium (LA). Left atrial appendage (LAA) is the site with the highest blood stasis which causes thrombus formation. About 90 % of the intracardiac thrombi in patients with cardioembolic events originally develop in the LAA. Recent studies have been focused on the association between LAA anatomical features and stroke risk and provided conflicting results. Haemodynamic and fluid dynamic information on the LA and mostly on the LAA may improve stroke risk stratification. Therefore, the aim of this study was the design and development of a workflow to quantitatively define the influence of the LAA morphology on LA hemodynamics. Five 3D LA anatomical models, obtained from real clinical data, which were clearly different as regard to LAA morphology were used. For each LAA we identified and computed several parameters describing its geometry. Then, one LA chamber model was chosen and a framework was developed to connect the different LAAs belonging to the other four patients to this model. These new anatomical models represented the computational domain for the computational fluid dynamics (CFD) study; simulations of the hemodynamics within the LA and LAA were performed in order to evaluate the interplay of the LAA shape on the blood flow characteristics in AF condition. CFD simulations were carried out for five cardiac cycles. Blood velocity, vorticity, LAA orifice velocity, residence time computed in the five models were compared and correlated with LAA morphologies. Results showed that not only complex morphologies were characterized by low velocities, low vorticity and consequently could carry a higher thrombogenic risk; even qualitatively simple morphologies showed a thrombogenic risk equal, or even higher, than more complex auricles. CFD results supported the hypothesis that LAA geometric characteristics plays a key-role in defining thromboembolic risk. LAA geometric parameters could be considered, coupled with the morphological characteristics, for a comprehensive evaluation of the regional blood stasis. The proposed procedure might address the development of a tool for patient-specific stroke risk assessment and preventive treatment in AF patients, relying on morpho-functional defintion of each LAA type.

Demonstration of Patient-Specific Simulations To Assess Left Atrial Appendage Thrombogenesis Risk

“…Taken together, our results indicate that flow patterns inside the LAA are not as complex as in the LA body or the LV, which we attribute to the strong geometrical confinement of the flow inside the appendage. These flow patterns led to elevated blood residence in the LAA compared to the LA body, in agreement with previous CFD results [3,8,15,18,19,22], and the consensus that thrombi form preferentially in the LAA. Patients with impaired atrial function also showed a trend for blood stasis to appear near the mitral annulus, since their weaker LA body vortex systems caused decreased stirring compared to normals.…”

“…In the LAA, normal wall kinetics drove inward and outward flow jets. By contrast, flow inside the LAA was similar to a lid-driven cavity flow in subjects with impaired booster and reservoir function, consistent with Masci et al's [19] data. Additionally, our subject with impaired reservoir function and normal booster function experienced hybrid LAA flow dynamics that oscillated between lid-driven cavity flow during LA diastole, and a weak outflow jet during LA systole.…”

“…While previous CFD studies suggested that reduced wall motion impairs LA blood transit [18,19,22], there is a lack of systematic data about how functional parameters such as EFLA affect this transit. We demonstrated that LAA TR has a clear dependence on EFLA.…”

“…Several CFD studies have explored the effect of LAA geometry on blood flow but, taken together, have offered ambiguous results. Bosi et al [3] found that LAA morphologies that are clinically associated with higher stroke incidence have impaired blood washout, whereas other studies [8,19] reported that LAA stasis depends critically on additional factors such as PV inflow patterns.…”

Brain–heart interaction after acute ischemic stroke

“…The current understanding of heart disease corroborates that cardiac remodeling is a common consequence of chronic myocardial or arrhythmic dysfunctions [56]. A pre-clinical study demonstrated that focal AIS and subsequent catecholamine release are followed by long-term cardiac dysfunction and remodeling [56,57]. In this setting, metoprolol was tested and found to slow down cardiac remodeling and inhibit sympathetic activity [57].…”