Effects of Ageing on Aortic Circulation During Atrial Fibrillation; a Numerical Study on Different Aortic Morphologies

Abstract

Atrial fibrillation (AF) can alter intra-cardiac flow and cardiac output that subsequently affects aortic flow circulation. These changes may become more significant where they occur concomitantly with ageing. Aortic ageing is accompanied with morphological changes such as dilation, lengthening, and arch unfolding. While the recognition of AF mechanism has been the subject of numerous studies, less focus has been devoted to the aortic circulation during the AF and there is a lack of such investigation at different ages. The current work aims to address the present gap. First, we analyse aortic flow distribution in three configurations, which attribute to young, middle and old people, using geometries constructed via clinical data. We then introduce two transient inlet flow conditions representative of key AF-associated defects. Results demonstrate that both AF and ageing negatively affect flow circulation. The main consequence of concomitant occurrence is enhancement of endothelial cell activation potential (ECAP) throughout the vascular domain, mainly at aortic arch and descending thoracic aorta, which is consistent with some clinical observations. The outcome of the current study suggests that AF exacerbates the vascular defects occurred due to the ageing, which increases the possibility of cardiovascular diseases per se.

Keywords: Ageing; Aorta; Atrial fibrillation; Cardiovascular diseases; Computational fluid dynamics; Haemodynamic metrics.

Figure 1

The statistical data of aortic morphology; (a) a schematic of an aorta with a normal SAT, (b) min and max values of the mean diameter at eleven different sections, (c) diameter increase rate per decade of life, (d) curvilinear length between different sections, (e) length increase per decade of life, (f) min and max values of the mean SAT diameters at the origin, with an increase range of 0.14–0.3 mm per decade of life.

Figure 2

Geometrical specifications of young, middle age and old groups; (a) curvilinear length between different sections, (b) diameter of the aortic conduit at different sections, (c) diameter of the coronaries and SAT at their origin, (d) constructed aortic geometries for different age groups; (e) flow rates at the inlet, Q(t).

Figure 3

Validation of the numerical code against the PC-MRI data of the 31-year-old healthy volunteer; (a) the flow rates are depicted at three different cross sections (CSs) in a cardiac cycle (t_cc). CS1 is before BCA, CS2 is between BCA and LCCA and CS3 is located at DDTA, (b) a qualitative comparison of streamlines at three time points at the AA, aortic arch, and PDTA.

Figure 4

Velocity vector and axial vorticity at three different points in a cardiac cycle (a)–(c), and seven cross sections for young, middle age, and old groups; iso-surface of vorticity, Q-criterion, 1200 s⁻¹ (d)–(f), and LNH (d1)–(f1) at three timepoints in a cardiac cycle.

Figure 5

(a)–(i) Area weighted axial velocity (AV) and tangential velocity (TV) components over a cardiac cycle, (j)–(l) area-weighted, time-averaged AV and TV components. The results are shown at seven planes (Pi) in Fig. 4 for the young, middle age, and old groups during the normal, LVSD, and HFF conditions. For the LVSD cases, (d)–(f), the y-axis range is modified to clearly present the variations.

Figure 6

(a) Average flow rate through the coronary arteries, SAT, and DTA, (b) flow percentage through the coronary arteries, SAT, and DTA, and (c) mean pressure in mmHg at the level of aortic root.

Figure 7

TAWSS, OSI, and ECAP of different age groups for the normal, LVSD, and HFF.

Figure 8

Area-weighted TAWSS (Pa), OSI, ECAP (s⁻¹), and time-averaged helicity metrics (H₁, H₂) (m s²) versus age and cardiac function for six discrete compartments, including (a) SAT, (b) AA, (c) AAA, (d) DAA, (e) PDTA, and (f) DDTA; (g) heatmaps of ECAP and H₂. ECAP and H₂ increase with respect to the baseline values of the young-normal condition are shown with YN subscript.