Australia & New Zealand Society of Vascular Surgeons

Aim Myointimal Hyperplastic(MIH) stenoses within vein grafts arise focally rather than with a generalised distribution. The reason for the distribution of stenoses remains to be adequately explained. We investigated local haemodynamic parameters within bypass grafts employing 3-dimensional(3D) Computational Fluid Dynamics(CFD) techniques applied to in-vivo measurements. These parameters are otherwise impossible to measure directly. Methods Patients underwent baseline MRI scanning(2D time-of-flight acquisition sequences) after surgery to obtain 3D anatomical models of their grafts. Duplex ultrasound data was also saved digitally(Phillips ATL5000 and HDI-Lab software,Washington,USA) at baseline and after follow-up for comparison. Computer generated 3D geometrical datasets and ultrasound acquired flow waveforms (haemodynamic boundary conditions) were combined and used for CFD modelling. Physical parameters such as wall shear stress(WSS) and oscillatory shear index(OSI) could then be solved computationally (using modified engineering-based software) to produce computerised graphical and numerical outputs. Results The computer generated maps revealed striking variability in the haemodynamic parameters within and between individual grafts. Numerical data indicate there is considerable variability in magnitude of flow-related forces throughout the graft (spatially) and during the cardiac cycle (temporally). Conclusions This novel use of CFD modelling can produce 3D images or maps of local haemodynamic conditions in vein bypass grafts. The significant regional variability may help to explain the local haemodynamic determinants of vein graft wall remodelling and the focal distribution of MIH stenoses within grafts.