Stress phase angle depicts differences in coronary artery hemodynamics due to changes in flow and geometry after percutaneous coronary intervention

Abstract

The effects of changes in flow velocity waveform and arterial geometry before and after percutaneous coronary intervention (PCI) in the right coronary artery (RCA) were investigated using computational fluid dynamics. An RCA from a patient with a stenosis was reconstructed based on multislice computerized tomography images. A nonstenosed model, simulating the same RCA after PCI, was also constructed. The blood flows in the RCA models were simulated using pulsatile flow waveforms acquired with an intravascular ultrasound-Doppler probe in the RCA of a patient undergoing PCI. It was found that differences in the waveforms before and after PCI did not affect the time-averaged wall shear stress and oscillatory shear index, but the phase angle between pressure and wall shear stress on the endothelium, stress phase angle (SPA), differed markedly. The median SPA was -63.9 degrees (range, -204 degrees to -10.0 degrees ) for the pre-PCI state, whereas it was 10.4 degrees (range, -71.1 degrees to 25.4 degrees ) in the post-PCI state, i.e., more asynchronous in the pre-PCI state. SPA has been reported to influence the secretion of vasoactive molecules (e.g., nitric oxide, PGI(2), and endothelin-1), and asynchronous SPA ( approximately -180 degrees ) is proposed to be proatherogenic. Our results suggest that differences in the pulsatile flow waveform may have an important influence on atherogenesis, although associated with only minor changes in the time-averaged wall shear stress and oscillatory shear index. SPA may be a useful indicator in predicting sites prone to atherosclerosis.

Fig. 1.

The vascular centerline and segmented cross sections of the right coronary artery (RCA).

Fig. 2.

The reconstructed surface of the original stenosed RCA (left) and stenosis-free vascular geometry (right) modeled based on the original (closed up around the stenosis).

Fig. 3.

Velocity waveforms acquired with a commercial intravascular ultrasound-Doppler probe ComboWire (Volcano) at 1.0-kHz sampling rate at the proximal RCA of patients 1 (left) and 2 (middle) with a severe stenosis, and mean ± SD waveforms of 10 patients without angiographically significant stenosis (right).

Fig. 4.

Pressure waveforms acquired with a commercial intravascular pressure probe ComboWire (Volcano) at 1.0-kHz sampling rate at the proximal RCA of patients 1 (left) and 2 (middle) with a severe stenosis, and mean ± SD waveforms of 10 patients without angiographically significant stenosis (right).

Fig. 5.

Normalized amplitude of harmonics for the velocity (top, left) and pressure (top, right) waveforms, and amplitude of impedance (bottom, left) and impedance phase angle (IPA; bottom, right) for each harmonic before and after percutaneous coronary intervention. Patient 1 (cf. Figs. 3 and 4, left) was chosen as the most apparent case. V_n and P_n, amplitude of nth harmonics for velocity and pressure, respectively; i.e., the amplitude was normalized by that of 0th harmonic which is the average over the cardiac cycle.

Fig. 6.

Velocity profiles at various time moments during a cardiac cycle based on before- (left) and after-stent (right) waveform. r and R, radial coordinate in the cross section and radius of the lumen, respectively.

Fig. 7.

Comparison of time-averaged wall shear stress (TAWSS) between 4 computational states. A and B, states 1 to 4 from top. Geom, geometry. Note: color versions of Figs. 7–10 and 13 can be found with the online version of this article via hyperlink to the originally submitted manuscript.

Fig. 8.

Comparison of oscillatory shear index (OSI) between 4 computational states. A and B, states 1 to 4 from top.

Fig. 9.

Comparison of stress phase-angle (SPA) between 4 computational states. A and B, states 1 to 4 from top.

Fig. 10.

Comparison of wall shear stress (WSS)-flow rate phase angle (WQPA) between 4 computational states. A and B, states 1 to 4 from top.

Fig. 11.

Temporal variations of flow (Q) and WSS in a straight pipe for before- (left) and after-stent (right) waveforms.

Fig. 12.

Flow-WSS phase angle for the first 10 harmonics for straight pipe cases. Deg, degree.

Fig. 13.

Normalized axial velocity profiles on the centerline of cross sections L1–L4 (from top to bottom) in accelerating (left), at the peak (middle), and at decelerating (right) phases. V_max, maximal velocity magnitude in the cross section. Horizontal axis denotes relative location on the centerline, and positive and negative signs correspond to pericardial- and epicardial-facing side. Positive velocity means the flow to downstream.

Fig. 14.

WSS and flow rate variation at a point on the wall in the recirculation region for states 1 (left) and 2 (right).