Quantification of disturbed coronary flow by disturbed vorticity index and relation with fractional flow reserve

Background and aims: The relation between FFR and local coronary flow patterns is incompletely understood. We aimed at developing a novel hemodynamic index to quantify disturbed coronary flow, and to investigate its relationship with lesion-associated pressure-drop, and fractional flow reserve (FFR).

Methods: Three-dimensional angiographic reconstruction and computational fluid dynamics were applied to simulate pulsatile coronary flow. Disturbed vorticity index (DVI) was derived to quantify the stenosis-induced flow disturbance. The relation between DVI and pressure-drop was assessed in 9 virtual obstruction models. Furthermore, we evaluated the correlation between DVI, FFR, hyperemic flow velocity, and anatomic parameters in 84 intermediate lesions from 73 patients.

Results: In virtual models, DVI increased with increasing flow rate, stenosis severity, and lesion complexity. The correlation between DVI and pressure-drop across all models was excellent (determination coefficient R² = 0.85, p < 0.001). In vivo, DVI showed a correlation with FFR (rho (ρ) = -0.74, p < 0.001) that was stronger than the relations of FFR with hyperemic flow velocity (ρ = -0.27, p=0.015), lesion length (ρ = -0.36, p=0.001) and percent diameter stenosis (ρ = -0.40, p < 0.001).

Conclusions: DVI, a novel index to quantify disturbed flow, was related to pressure-drop in virtual obstruction models and showed a strong inverse relation with FFR in intermediate lesions in vivo. It supports the prognostic value of FFR and may provide additional information about sources of energy loss when measuring FFR.