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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

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Tajeddini F. , Firoozabadi B. , Pakravan H. A. , Ahmadi Tafti S. H.

Biocybernetics and Biomedical Engineering

2022

tom 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.

A comparative analysis of coronary bypass implants: Experimental and fluid-structure interaction analysis

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Changizi S. , Afrasiabian N. , Rassoli A. , Fatouraee N. , Ahmadi Tafti S. H.

Biocybernetics and Biomedical Engineering

2024

tom Vol. 44, no. 2

393--401

Bypass surgery is a commonly employed method for treating coronary artery diseases, involving the use of grafts to bypass occluded arteries. However, graft occlusion remains a concern due to mechanical disparities between the grafts and native arteries. This study aims to compare the mechanical properties of three frequently used grafts in coronary bypass surgeries: human saphenous veins, mammary arteries, and radial arteries. Stress-relaxation tests were conducted on samples obtained from these vessels, and their mechanical properties were characterized. The stress-strain curves of each sample were fitted using the quasi-linear viscoelastic (QLV) model, with MATLAB software used to extract the model’s constants. Additionally, fluid-structure simulations were performed employing the extracted viscoelastic mechanical properties of the vessels. The analysis revealed that the saphenous vein exhibited the highest elastic coefficient (0.5247) and non-linearity coefficient (0.8135) among the studied grafts. The mammary artery demonstrated nearly seven times greater viscoelasticity compared to the other graft options. Furthermore, the examination of shear stress distribution indicated lower shear stress regions in the radial and mammary artery specimens compared to the saphenous specimens. Notably, the lower wall of the host artery exhibited the greatest oscillatory shear index (OSI), with the radial specimen displaying the highest oscillation in this region compared to the other two specimens. The mechanical characterization results presented in this study hold potential applications in pathogenic and clinical investigations of heart diseases, aiding in the development of appropriate treatment approaches.