Background and objective

The instantaneous wave-free ratio (iFR) has been proposed to estimate the hemodynamic severity of atherosclerotic stenosis in coronary arteries. The atherosclerotic stenosis in a proximal coronary artery could change its distal microcirculatory resistance (MR). However, there is a lack of investigation about the effect of MR variation on the blood flow and iFR of stenotic coronary arteries. We aim to investigate the changes of blood flow and iFR caused by distal MR variation.

Methods

Four three-dimensional models of coronary arteries were reconstructed from the computed tomography images of two normal cases and two cases with 74.9% and 96.4% (in area) stenoses in a large branch of left anterior descending artery (LAD). Computational fluid dynamics simulation was performed on each model under 6 MR situations: hyperemia as the reference situation, resting when MR was multiplied by 8/3 in all outlet branches, h-one-1.5 and h-one-2 when MR was multiplied by 1.5 and 2.0 in one branch (the stenotic, or the corresponding branch in normal case) of LAD, h-branches-1.5 and h-branches-2 when MR was multiplied by 1.5 and 2.0 in the stenotic/corresponding and its cognate branches. Flow rate and iFR of each outlet branch were then calculated and compared between different MR situations to investigate the effect of MR variation on flow rate and iFR.

Results

In the 74.9% stenosed and normal cases, referring to the hyperemia situation, the increase of MR in any branch significantly decreased its flow rate and increased its iFR, with limited effect on the flow rate (<3%) and iFR (<0.01) of other branches. However, in the 96.4% stenosed case, the doubled MR in the stenosed branch (h-one-2) significantly increased the flow rate (>10%) and iFR (>0.05) of its cognate branches.

Conclusion

The increase of MR in a normal or mildly stenosed branch of coronary artery decreases its blood flow and increases its iFR, with limited effect on other branches. Whereas, the increase of MR in a severely stenotic large branch could significantly increase the flow velocity and iFR of its cognate branches.

中文翻译：

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微循环阻力对冠状动脉血流和瞬时无波比率的影响：计算研究。

背景和目标

提出了瞬时无波比（iFR）来评估冠状动脉粥样硬化狭窄的血流动力学严重程度。冠状动脉近端的动脉粥样硬化狭窄可改变其远端微循环阻力（MR）。但是，目前尚无关于MR变化对冠状动脉狭窄的血流和iFR的影响的研究。我们旨在调查由远端MR变化引起的血流和iFR的变化。

方法

从两个正常病例和两个在左前降支大动脉（LAD）分支中有74.9％和96.4％（面积）狭窄的病例的计算机断层扫描图像重建四个冠状动脉三维模型。在6种MR情况下对每个模型进行了计算流体动力学模拟：充血作为参考情况，当MR乘以所有出口分支的8/3时处于静息状态，当MR乘以MR时乘以h-one-1.5和h-one-2。当MR分别在狭窄/对应分支及其同源分支中分别乘以1.5和2.0时，LAD，h-branches-1.5和h-branches-2的一个分支（狭窄，或正常情况下相应的分支）中的1.5和2.0

结果

在74.9％的狭窄和正常情况下，参考充血情况，任何分支中MR的增加都会显着降低其流速并增加其iFR，但对流速（<3％）和iFR（<0.01）的影响有限其他分支机构。但是，在96.4％狭窄的病例中，狭窄分支（h-one-2）中的MR翻倍会显着增加其同源分支的流速（> 10％）和iFR（> 0.05）。

结论

正常或轻度狭窄的冠状动脉分支中MR的增加会减少其血流量并增加其iFR，而对其他分支的作用有限。而严重狭窄的大分支中MR的增加可能会显着增加其同源分支的流速和iFR。