Instantaneous wave-free ratio (iFR), an invasive index of coronary artery, can evaluate the functional performance of vascular stenosis without pharmacological vasodilators. The purpose of this study is to develop a 0D/3D coupling method that predicts iFR from CTA to non-invasive assess the myocardial ischemia. The 0D/3D coupling method was used to perform a numerical simulation by coupling the lumped parameter model (LPM; 0D sub-model) and 3D vascular sub-models. This work studies iFR of different stenosis in the left anterior descending (LAD) artery by reducing the local diameter.

In this study, the three-dimensional (3D) geometry of coronary arteries was reconstructed from coronary computed tomography (CT) images. Virtual surgery were implemented on the 3D model with a different stenosis in the LAD by reducing the local diameter (40%, 50%, 60%, 75% and 90%). The lumped parameter models of this study were as described by Taylor et al [1]. The inlet of 3D models was coupled with a LPM of the heart, while all the systemic outlets were coupled with a LPM of the systemic block. Moreover, the coronary outlets were coupled with the coronary micro-circulation block. Five 3D models shared the same 0D part since the patient’s peripheral vascular structure were not changed with different stenosis.

The pressure, flow rate and iFR of native coronary artery of five models were calculated and illustrated. With the increase of the degree of stenosis, the mean flow of LAD was gradually decreased as followed: 81.18 ml/min, 79.64 ml/min, 77.47 ml/min, 64.22 ml/min, 12.79 ml/min. The iFR used the ratio of distal coronary pressure to the pressure observed in the aortic pressure over the wave-free period (WFP). The WFP begins 25% into diastole and ends 5ms before the end of diastole [2]. Moreover, the mean resistance of cardiac cycle and wave-free period were illustrated. Compared to the resistance of cardiac cycle, the resistance of the WFP decreased 51.25%. And the iFR contour of different stenosis models were illustrated. With the increase of the degree of the stenosis, the iFR value gradually reduced as follow: 0.97, 0.95, 0.91, 0.68, 0.06. When the degree of stenosis was more than 75%, iFR was less than 0.86 (the critical value of myocardial ischemia). This promising simulation method provides a combined anatomic-physiology-functional evaluation of coronary artery disease with the aim of improving clinical diagnostic accuracy.