Impact of Boundary Conditions on the Computational Assessment of Fractional Flow Reserve

Abstract

Coronary artery disease (CAD) may leads to myocardial ischemia, the main cause of death worldwide. Nowadays, fractional flow reserve (FFR) is considered the gold standard procedure to assess risk of myocardial ischemia in presence of CAD. The FFR index is defined as the ratio of intravascular blood pressure before and after the arterial lesion under maximal hyperemia conditions.Therefore, FFR is obtained through an invasive procedure, which requires specialized cardiologist and dedicated medical instrumentation and consequently it is expensive and not risk free. In recent years, the computational biomechanics community has been developing tools for the FFR estimation using computational fluid dynamics (CFD) and medical image based models (hereafter FFRce), receiving increasing interest from cardiologists around the world. The implementation of these models as diagnosis tools has the potential to improve patient's experience, decrease the number of unnecessary invasive studies and reduce economic costs associated to diagnosis and treatment of CAD. Most of past and current literature focused on proposing computational solutions for the estimation of FFR, nevertheless, they generally lack comprehensive sensitivity analyses assessing the implications of changes in the hemodynamics parameters.Here, we present an exhaustive analysis on physiologic parameters that translate into boundary conditions (BC) of the computational model.Specifically, we study the impact of the coronary flow reserve (CFR), the flow distribution in the coronary tree and the coronary steal on the FFRce.We employed a set of 10 coronary computed tomography angiography (CCTA) images to construct the patient specific arterial models and solve the full 3D CFD problem.Blood flow was modeled using the Navier-Stokes equations for rigid domains, i.e. arterial compliance was neglected.One measurement of invasive FFR is available for each patient, and the value is used as reference to assess the variations due to changes in the BC. The impact of such variations in the BC is extensively discussed.