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Patient-specific fluid-structure interaction simulation of the LAD-ITA bypass graft for moderate and severe stenosis: A doubt on the fractional flow reserve-based decision

Tajeddini Farshad, Firoozabadi Bahar, Pakravan Hossein Ali, Ahmadi Tafti Seyed Hossein

Biocybernetics and Biomedical Engineering

2022

Vol. 42, no. 1

143--157

Fractional flow reserve (FFR)-based decision improves the outcomes of percutaneous coronary intervention (PCI) for some patients, while its effectiveness in improving the results of coronary artery bypass graft (CABG) is unclear, in particular for moderate stenosis. It may be due to the fact that FFR cannot take into account the impacts of competitive flow (CF), intimal hyperplasia (IH), as well as compliance mismatch (CMM). As a result, two questions arise 1) whether FFR is a sufficient factor to decide to perform the CABG for patients with moderate to severe stenosis or not and 2) whether post-operative FFR shows the effectiveness of a graft. To shed light on this matter, two patient-specific models of LAD-ITA graft, consisting of two different severities of stenosis (moderate and severe), were simulated using two-way FSI simulation. It was observed that although both pre- and postoperative FFRs for moderate stenosis were higher, CF is more intense for moderate stenosis than severe one. Also, it was seen that CM and IH are more likely to occur in the bed, toe, and heel areas of a bypass graft performed for moderate stenosis. All in all, it can be concluded that in the case of moderate stenosis, pre- and post-operative FFRs might not be a suitable index for making the decision about performing or deferring CABG and also the effectiveness of the graft. Under such circumstances, it seems rational to use CFD in a wider range to investigate patients with moderate stenosis before the operation.

Primary stenosis progression versus secondary stenosis formation in the left coronary bifurcation: A mechanical point of view

Jahromi Reza, Pakravan Hossein Ali, Saidi Mohammad Said, Firoozabadi Bahar

Biocybernetics and Biomedical Engineering

2019

Vol. 39, no. 1

188--198

Biomechanical forces and hemodynamic factors influence the blood flow and the endothelial cells (ECs) morphology. These factors behave differently beyond the coronary artery stenosis. In the present study, unsteady blood flow in the left coronary artery (LCA) and its atherosclerotic bifurcating vessels, left anterior descending (LAD) and left circumflex (LCX) arteries, were numerically simulated to investigate the risk of plaque length development and secondary plaque formation in the post-stenotic areas. Using fluid–structure interaction (FSI) model, compliance of arterial wall and vessel curvature variations due to cardiac motion were considered. The arteries included plaques at the beginning of the bifurcation. Stenosis degree varied from 40% to 70% based on diameter reduction. Healthy coronary artery was also reconstructed to compare with the atherosclerotic arteries. Circumferential and longitudinal strains of ECs as well as wall shear stress (WSS) were computed in different locations downstream of the stenosis. It was concluded that the most critical regions experiencing low circumferential strain and low WSS were located proximal to the plaque throat, and the effects of these parameters intensified by stenosis degree. The results proposed that primary plaque length progression is more probable than secondary plaque formation distal to the stenosis when the stenosis degree increases.