Chiastra Claudio, Iannaccone Francesco, Grundeken Maik J, Gijsen Frank J H, Segers Patrick, De Beule Matthieu, Serruys Patrick W, Wykrzykowska Joanna J, van der Steen Antonius F W, Wentzel Jolanda J
Department of Cardiology, Biomedical Engineering, Erasmus MC, Rotterdam, The Netherlands.
Laboratory of Biological Structure Mechanics (LaBS), Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, Milan, Italy.
Biomed Eng Online. 2016 Aug 5;15(1):91. doi: 10.1186/s12938-016-0211-0.
Coronary hemodynamics and physiology specific for bifurcation lesions was not well understood. To investigate the influence of the bifurcation angle on the intracoronary hemodynamics of side branch (SB) lesions computational fluid dynamics simulations were performed.
A parametric model representing a left anterior descending-first diagonal coronary bifurcation lesion was created according to the literature. Diameters obeyed fractal branching laws. Proximal and distal main branch (DMB) stenoses were both set at 60 %. We varied the distal bifurcation angles (40°, 55°, and 70°), the flow splits to the DMB and SB (55 %:45 %, 65 %:35 %, and 75 %:25 %), and the SB stenoses (40, 60, and 80 %), resulting in 27 simulations. Fractional flow reserve, defined as the ratio between the mean distal stenosis and mean aortic pressure during maximal hyperemia, was calculated for the DMB and SB (FFRSB) for all simulations.
The largest differences in FFRSB comparing the largest and smallest bifurcation angles were 0.02 (in cases with 40 % SB stenosis, irrespective of the assumed flow split) and 0.05 (in cases with 60 % SB stenosis, flow split 55 %:45 %). When the SB stenosis was 80 %, the difference in FFRSB between the largest and smallest bifurcation angle was 0.33 (flow split 55 %:45 %). By describing the ΔPSB-QSB relationship using a quadratic curve for cases with 80 % SB stenosis, we found that the curve was steeper (i.e. higher flow resistance) when bifurcation angle increases (ΔP = 0.451Q + 0.010Q (2) and ΔP = 0.687Q + 0.017Q (2) for 40° and 70° bifurcation angle, respectively). Our analyses revealed complex hemodynamics in all cases with evident counter-rotating helical flow structures. Larger bifurcation angles resulted in more pronounced helical flow structures (i.e. higher helicity intensity), when 60 or 80 % SB stenoses were present. A good correlation (R(2) = 0.80) between the SB pressure drop and helicity intensity was also found.
Our analyses showed that, in bifurcation lesions with 60 % MB stenosis and 80 % SB stenosis, SB pressure drop is higher for larger bifurcation angles suggesting higher flow resistance (i.e. curves describing the ΔPSB-QSB relationship being steeper). When the SB stenosis is mild (40 %) or moderate (60 %), SB resistance is minimally influenced by the bifurcation angle, with differences not being clinically meaningful. Our findings also highlighted the complex interplay between anatomy, pressure drops, and blood flow helicity in bifurcations.
人们对冠状动脉分叉病变特有的血流动力学和生理学尚未完全了解。为了研究分叉角度对分支病变冠状动脉内血流动力学的影响，我们进行了计算流体动力学模拟。
根据文献创建了一个代表左前降支-第一对角支冠状动脉分叉病变的参数模型。直径遵循分形分支定律。近端和远端主支狭窄均设定为60%。我们改变远端分叉角度（40°、55°和70°）、流向主支和分支的血流分配比例（55%:45%、65%:35%和75%:25%）以及分支狭窄程度（40%、60%和80%），共进行了27次模拟。计算所有模拟中主支和分支（FFRSB）的血流储备分数，其定义为最大充血时远端狭窄平均压力与主动脉平均压力之比。
比较最大和最小分叉角度时，FFRSB的最大差异在分支狭窄40%的情况下为0.02（与假定的血流分配无关），在分支狭窄60%、血流分配55%:45%的情况下为0.05。当分支狭窄为80%时，最大和最小分叉角度之间FFRSB的差异为0.33（血流分配55%:45%）。对于分支狭窄80%的情况，用二次曲线描述ΔPSB-QSB关系时，我们发现当分叉角度增加时曲线更陡（即血流阻力更高）（40°和70°分叉角度时，ΔP分别为0.451Q + 0.010Q²和0.687Q + 0.017Q²）。我们的分析揭示了所有情况下复杂的血流动力学，伴有明显的反向螺旋流结构。当存在60%或80%的分支狭窄时，较大的分叉角度会导致更明显的螺旋流结构（即更高的螺旋度强度）。还发现分支压降与螺旋度强度之间具有良好的相关性（R² = 0.80）。
我们的分析表明，在主支狭窄60%和分支狭窄80%的分叉病变中，较大的分叉角度会使分支压降更高，表明血流阻力更高（即描述ΔPSB-QSB关系的曲线更陡）。当分支狭窄为轻度（40%）或中度（60%）时，分支阻力受分叉角度的影响最小，差异无临床意义。我们的研究结果还突出了分叉处解剖结构、压降和血流螺旋度之间复杂的相互作用。
