Non-invasive Quantification of Coronary Artery Disease in Arterial Bifurcations Using CCTA and CFD: Comparison to Fractional Flow Reserve Measurements

Recent advances in coronary computed tomography angiography (CCTA) allow the calculation of various functional indices of coronary artery disease (CAD). smartFFR is our proposed new index for the assessment of the significance of coronary stenoses in coronary bifurcations. The aim of the current study is to compare smartFFR with the Fractional Flow Reserve (FFR) values deriving from direct invasive pressure measurements from a dedicated pressure wire. In the context of the SMARTool study, 22 patients with chest pain symptoms and intermediate pre-test likelihood of CAD underwent CCTA as well as FFR measurement. The 22 left arterial branches which included the LAD and the LCx were reconstructed using our in-house developed software. We performed two computational blood flow simulations for each case to calculate the smartFFR for each 3D model. Regarding the inlet, the average patient-specific pressure at rest was applied as a boundary condition. Assuming a myocardial blood flow of 2 ml/s and 6 ml/s during rest and under stress for the Left Main artery, respectively, we calculated the flow for each branch using Murray's law and applied it as outlet boundary conditions. smartFFR was calculated for each branch by computing the ratio of distal to proximal pressure for a range of flows between 0 and 4 ml/s, normalized by the respective ratio of a normal artery. The required average process time was less than 20 min. Strong correlation (r = 0.88, P < 0.0001) was found between the two methods. All pathological cases presenting ischemia, were correctly categorized by our method as hemodynamically significant lesions. smartFFR demonstrated a high diagnostic accuracy for distinguishing hemodynamically significant lesions in a matter of minutes, and may represent a valid non-invasive tool for comprehensive characterization of CAD.