A numerical study of the hemodynamic effect of the aortic valve on coronary flow

Abstract

During diastole, coronary perfusion depends on the pressure drop between the myocardial tissue and the coronary origin located at the aortic root. This pressure difference is influenced by the flow field near the closing valve leaflets. Clinical evidence is conclusive that patients with severe aortic stenosis (AS) suffer from diastolic dysfunction during hyperemia, but show increased coronary blood flow (CBF) during rest. Transcatheter aortic valve implantation (TAVI) was shown to decrease rest CBF along with its main purpose of improving the aortic flow and reducing the risk of heart failure. Physiological or pathological factors do not provide a clear explanation for the increase in rest CBF due to AS and its decrease immediately after TAVI. In this manuscript, we present a numerical study that examines the impact of AS and TAVI on CBF during rest conditions. The study compares the hemodynamics of five different 2D numerical models: a baseline "healthy valve" case, two AS cases and two TAVI cases. The analysis used time-dependent computational fluid-structure interaction simulations of blood flow in the aortic root including the dynamics of the flexible valve leaflets and the varying resistance of the coronary arteries. Despite its simplifications, our 2D model succeeded to capture the major effects that dominate the hemodynamics in the aortic root and to explain the hemodynamic effect that leads to the changes in CBF found in in vitro and clinical studies.

Validation and Extension of a Fluid–Structure Interaction Model of the Healthy Aortic Valve

“…Whilst there is consensus that the haemodynamics established within the aortic root plays a key role in the proper valve function 4 , 38 , 40 , 48 and optimum flow to the coronary arteries, there is no agreement on the specific mechanisms involved. 3 , 36 , 49 Although the Valsalva sinuses are commonly indicated to promote fluid recirculations, which in turn act upon the leaflets, some investigations report that these vortices form within the sinuses in early systole, 15 , 33 , 52 while others claim that these structures only occur during late systole. 16 , 35 , 43 The number and locations of these vortices are also disputed, with contrasting research indicating multiple vortices within each sinus, 15 a single vortex fully contained within each sinus 43 or a vortex only partially within the sinus.…”

New Insights into Valve Hemodynamics

“…While CAO risk is currently evaluated based only on the anatomic location of the coronary ostia, numerical models can help to quantitatively assess flow dynamics. 65,66 The circularity and size of the valve orifice can be highly dependent on patient anatomy, especially with self-expandable TAVI devices. Clearly, it is undesirable to have a non-circular valve, and this phenomenon has been generally been addressed by the supra-annular design of the TAVI device.…”

Computational fluid dynamics: a primer for congenital heart disease clinicians

“…For the interested reader, reviews on fluid structural interaction applications in modeling cardiovascular disease are included. [25][26][27]…”

“…This is particularly true if the problem’s geometry possesses symmetry that allows for 2D representation. 24 , 25 Because CFD is a computationally intensive task, with single problems taking hours or days to solve, simplifying assumptions like this are an important part of pre-processing. Below are additional aspects that must be considered.…”