Effects of Vessel Tortuosity on Coronary Hemodynamics: An Idealized and Patient-Specific Computational Study

Abstract

Although coronary tortuosity can influence the hemodynamics of coronary arteries, the relationship between tortuosity and flow has not been thoroughly investigated partly due to the absence of a widely accepted definition of tortuosity and the lack of patient-specific studies that analyze complete coronary trees. Using a computational approach we investigated the effects of tortuosity on coronary flow parameters including pressure drop, wall shear stress, and helical flow strength as measured by helicity intensity. Our analysis considered idealized and patient-specific geometries. Overall results indicate that perfusion pressure decreases with increased tortuosity, but the patient-specific results show that more tortuous vessels have higher physiological wall shear stress values. Differences between the idealized and patient-specific results reveal that an accurate representation of coronary tortuosity must account for all relevant geometric aspects, including curvature imposed by the heart shape. The patient-specific results exhibit a strong correlation between tortuosity and helicity intensity, and the corresponding helical flow contributes directly to the observed increase in wall shear stress. Therefore, helicity intensity may prove helpful in developing a universal parameter to describe tortuosity and assess its impact on patient health. Our data suggest that increased tortuosity could have a deleterious impact via a reduction in coronary perfusion pressure, but the attendant increase in wall shear stress could afford protection against atherosclerosis.

Increased Coronary Tortuosity Is Associated with Increased Left Ventricular Longitudinal Myocardial Shortening

“…16 Although TCA itself results in abnormal distribution of shear, this form of arterial remodeling which results in multiple gradual rather than focal sharp bends during systole would more evenly distribute shear forces and reduce the net pressure drop across the epicardial artery. 7,26 In other words, the gradual bends of TCA may increase shear and heterogeneity of shear during diastole, but it serves as a “shear absorber” to evenly distribute shear during exaggerated shortening along the major axis. This concept implies that tortuosity may not necessarily be a maladaptive process, which could potentially explain the lower incidence of CAD, a disease also influenced by shear heterogeneity, in those with TCA and the neutral effect of TCA on cardiovascular outcomes.…”

“…2,5,6 Fluid dynamic modeling suggests that stress-induced ischemia may be attributable to a reduction in distal coronary artery perfusion pressure from viscous and turbulence energy losses. 7,8 The physiologic reasons for TCA are unclear. Pre-clinical studies where elastases and collagenases were used to alter arterial morphology together with genetic and pathologic analysis of rare clinical disorders such as arterial tortuosity syndrome have indicated that arterial tortuosity arises from abnormalities in arterial elastin fibers and extracellular matrix.…”

The hemodynamic complexities underlying transient ischemic attacks in early-stage Moyamoya disease: an exploratory CFD study

“…The circle of Willis is characterized by highly tortuous morphology, which dictates swirl and helical flow structure to the blood flow field 39 . When the flow passes through a region of high tortuosity, the streamlines (which are locally tangent to the velocity vector field) undergoes spatial curvature creating regions of forced vortices which is sometimes called helical structures 40 . In the case of pulsatile flow, the local acceleration term increases the swirl generation effects.…”

Coronary fractional flow reserve measurements of a stenosed side branch: a computational study investigating the influence of the bifurcation angle

“…In order to visualize the flow patterns inside the coronary bifurcations, the local normalized helicity was calculated. This quantity has been widely adopted in the cardiovascular field of biomechanical engineering to describe the arrangement of fluid streams into spiral patterns [ 35 , 37 – 42 ]. Positive and negative local normalized helicity values point out clockwise and counter-clockwise rotating fluid structures along the main flow direction, respectively.…”