The Impact of the Geometric Characteristics on the Hemodynamics in the Stenotic Coronary Artery

Abstract

The alterations of the hemodynamics in the coronary arteries, which result from patient-specific geometric significances are complex. The effect of the stenosis on the blood flow alteration had been wildly reported, but the combinational contribution from geometric factors required a comprehensive investigation to provide patient-specific information for diagnosis and assisting in the decision on the further treatment strategies. In the present study, we investigated the correlation between hemodynamic parameters and individual geometric factors in the patient-specific coronary arteries. Computational fluid dynamic simulations were performed on 22 patient-specific 3-dimensional coronary artery models that were reconstructed based on computed tomography angiography images. Our results showed that the increasing severity of the stenosis is associated with the increased maximum wall shear stress at the stenosis region (r = 0.752, P < 0.001). In contrast, the length of the recirculation zone has a moderate association with the curvature of the lesion segment (r = 0.505, P = 0.019) and the length of the lesions (r = 0.527, P = 0.064). Moreover, bifurcation in the coronary arteries is significantly correlated with the occurrence of recirculation, whereas the severity of distal stenosis demonstrated an effect on the alteration of the flow in the upstream bifurcation. These findings could serve as an indication for treatment planning and assist in prognosis evaluation.

Fig 1. The geometric characteristics include severity of stenosis, tortuosity of the lesion segment, curvature of the lesion segment, angle of the lesion and length of the lesion.

A: Tortuosity (T) was taken as the ratio of the length from the ostium of the coronary segment to 1 cm distal to the stenosis (L) to the distance between the ends of the segment (C). B: The severity of the stenosis is the ratio of the cross-section area in the remain lumen at the stenosis and the healthy proximal segment. C: Curvature (unit: 1/m) of the stenotic artery segment was measured, of which the ends of the segment were 1cm proximal to the stenosis and 1cm distal to the stenosis. D: The angle of the lesion was measured at the immediate distal edge of the lesion (unit: degree). E: The length of the lesion was also measured (unit: mm).

Fig 2. Validation of the calculation is provided by comparing calculated FFRCT to the measurement FFR.

A: Agreement between the FFRCTA and FFR is evaluated by Bland-Altman agreement test, the mean±SD bias of is 0.00269 ± 0.01899. B: Agreement between FFRCT and FFR is also evaluated by linear regression that R² = 0.974 with 95% confident interval.

Fig 3. The correlation analysis of FFRCT and the severity of the stenosis.

The correlation factor R2 was 0.617 with 95% confident interval. 19 out 22 cases were included in the confident interval and close to the range while 3 cases showed diversion.

Fig 4. The FFRCT distribution in the coronary arterial geometries with stenosis.

The FFRCT at the stenosis decreased as the severity of the stenosis increased. Degree of the stenosis in A, B and C was 57%, 76,6% and 86.4%, the corresponding FFRCT value was 0.687, 0.603 and 0.57, respectively.

Fig 5. Relationship among stenosis severity, tortuosity, curvature, angle, lesion length with wall shear stress in the reconstructed patient-specific coronary arteries.

A: effect of stenosis severity (percent diameter stenosis) on maximum wall shear stress; B: effect of tortuosity on maximum wall shear stress; C: effect of curvature on maximum wall shear stress; D: effect of lesion length on maximum wall shear stress; E: effect of angle of the lesion segment on maximum wall shear stress. Third-order nonlinear cur fit with 95% confident interval is shown in A with R² equals 0.521.

Fig 6. The effect of stenosis severity on the recirculation zone.

Streamline of the flow distribution are illustrated (unit: m/s). The length the recirculation increase with the severity of the stenosis. Severity of the stenosis in A, B, C and D is 28.2%, 57%, 76.6% and 86.3% with the corresponding length of the recirculation zone is 0 mm, 5.02 mm, 6.48 mm to 16.77 mm, respectively. Recirculation zone is not only seen at the downstream of the stenosis, but also at the upstream bifurcation (labeled with red cross-star in C).

Fig 7. The streamline of the flow distribution color-coded with velocity magnitude.

The pulsatile effect of the blood flow on the distribution of the recirculation. A, B, C and D illustrated 4 time points during one cardiac cycle. A: The recirculation disappeared at the low flow rate; B, C and D: The area of the recirculation zone varied along with the flow rate while the lengths of the recirculation zone were relatively consistence (5mm).

Fig 8. Relationship among stenosis severity, tortuosity, curvature, angle, lesion length with length of recirculation zone in the reconstructed patient-specific coronary arteries.

A: effect of curvature on maximum wall shear stress; B: effect of stenosis severity (percent diameter stenosis) on maximum wall shear stress; C: effect of tortuosity on maximum wall shear stress; D: effect of lesion length on maximum wall shear stress; E: effect of angle of the lesion segment on maximum wall shear stress.

Fig 9. The distribution of the flow and the corresponding WSS distribution in the stenotic coronary artery.

A: The streamline of the flow distribution color-coded with velocity magnitude showed that blood flow is separated at the downstream of the stenosis, leading to the occurrence of the recirculation zone (red arrow) (unit: m/s). Severe stenosis (>80%) resulted in the increasing of the resistance of the vascular bed, leading to the flow reversal at the upstream bifurcation (yellow cross-star). B: The vessel wall shear stress distribution showed that the maximum wall shear stress is found at the distal stenosis (red cross-star), disturbance of the flow is found in downstream, leading to the altered distribution of the wall shear stress (red frame) (unit: Pa). C and D: The streamline of the flow distribution color-coded with velocity magnitude in the cross-section area showed a more significant secondary flow pattern at the upstream (as in C labeled with yellow cross-star corresponding to the location showed in A) compare to that at the downstream of distal stenosis (as in D labeled with red arrow corresponding to the location showed in A) (unit: m/s).

Fig 10. The streamlines of the flow distributions color-coded with velocity magnitude.

Increasing of the resistance due to the distal stenosis leads to the flow reversal at the upstream bifurcation that blood flow is redistributed to the side branch as showed in A (unit: m/s). Examples of the disappearing of the recirculation zone at the downstream of the stenosis as showed in B (unit: m/s).