Impact of cardiac phase selection on computational fluid dynamics analysis

The selection of cardiac phase in coronary computed tomography angiography (CCTA) may affect computational fluid dynamics (CFD)-derived hemodynamic metrics; however, this influence is not well-quantified, particularly in anomalous coronary anatomies. This study aims to evaluate how cardiac phase selection impacts CFD outcomes in normal and anomalous coronary arteries.

Multiphase CCTA datasets were analyzed from 40 patients: 30 with systolic and diastolic reconstructions (10 inter-arterial anomalous right coronary artery [ARCA], 10 myocardial bridging [MB], 10 normal) and 10 additional normals with mid-diastolic and diastolic reconstructions. Geometric differences among phases were measured. CFD-derived parameters, including time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), and CCTA-derived fractional flow reserve (CT-FFR), were calculated. Phase-dependency was assessed by (i) comparing proximal right coronary artery (pRCA) and proximal left anterior descending artery (pLAD) measurements in normal systole vs. diastole and mid-diastole vs. diastole; (ii) comparing pRCA measurements in ARCA vs. normal, and pLAD measurements in MB vs. normal, for systole and diastole.

Luminal area differences among phases in pRCA and pLAD segments demonstrated group-distance interactions (p ​< ​0.05). Absolute relative differences in OSI were significantly smaller in pLAD for MB group (median 5.31% [IQR 2.61%-7.46%]) versus normal group (15.99% [6.23%-31.98%]; p ​= ​0.0125). While TAWSS, OSI, and RRT exhibited phase-dependency, this was neither specific to patient cohorts nor coronary artery territories. The variation of relative differences in CT-FFR (maximum 2.4%) was generally lower than that in TAWSS (21.3%), OSI (63.9%), and RRT (28.1%), with all relative differences of the four parameters showing no significant variation from zero.

The coronary geometry showed clear phase-dependency. The phase dependency should not be ignored when CCTA is used to quantify TAWSS, OSI and RRT. Standardizing cardiac phase selection in CCTA-based CFD analyses is crucial for improving accuracy and clinical consistency.