Study On Hemodynamics Of Dilated Myocardial Ischemia Induced By Coronary Artery Aneurysm

Coronary artery aneurysm(CAA)is a coronary artery segment which exceeds twice the diameter of an adjacent normal segment.CAA can lead to dilated myocardial ischemia,patients with CAAs show clinical symptoms similar to those with coronary artery stenosis.Although the clinical symptoms are similar,the mechanisms of stenosis and dilated myocardial ischemia are not the same.However,the mechanism of dilated myocardial ischemia has not been thoroughly studied.Aiming at the hemodynamic mechanism of myocardial ischemia induced by CAA,the research contents are mainly divided into the following two aspects:(1)Hemodynamic mechanism of blood stolen phenomenon in CAAs.In the clinic,the presence of uncomplicated CAAs can lead to a decrease in distal blood flow,namely blood stolen phenomenon,which leads to myocardial ischemia.A lumped parameter model and a geometrical multiscale model of the cardiovascular system with different diameter CAAs were established to observe the blood flow in the CAAs and to simulate the blood stolen phenomenon.The effects of different diameters of CAAs on the severity of blood stolen phenomenon were explored and the mechanism of the phenomenon was clarified.(2)Hemodynamic of intraluminal thrombosis in CAAs.Abnormal hemodynamic environment in CAA makes it easy to form thrombus,which leads to myocardial ischemia.A geometrical multiscale model of the cardiovascular system with 1,3 and 5times diameter CAAs was established.The wall shear stress(WSS),oscillatory shear index(OSI),relative particle retention time(RRT)and vorticity parameters were observed.The effects of diameter of CAAs on the hemodynamic environment of CAAs were explored,and the hemodynamic mechanism of intraluminal thrombosis in CAAs was discussed.The results show that:(1)The presence of CAA led to an abnormal systolic peak and backward flow during the prophase of diastole in the upstream,and a decrease of downstream blood flow.CAAs with 2,3,5 and 7 times diameter resulted in 5.21%,9.57%,14.78% and 20% decrease of downstream blood flow,respectively.With the increase of the diameter of CAAs,the downstream blood flow decreases,and even the diastolic backward flow phenomenon appeared in the upstream.CAAs with 5 and 7times diameter caused 2.7% and 11.6% of the upstream diastolic backward flow,respectively.(2)The proportion of area with low WSS(< 0.1037Pa)in 5 times diameter model was 2.05%,that with 3 times diameter model was 0.97%.The area percentage of high OSI(> 0.003)was 12.58% in 5 times diameter model,and that with 3 times diameter model was 9.63%.The average RRT and vorticity of 5 times diameter model were significantly higher than that of 3 times diameter model.The mean RRT of 5 times diameter model was 28 times higher than that of normal blood vessel.The conclusions are as follows:(1)The model established in this study can well simulate the blood stolen phenomenon.Numerical simulation results are generally consistent with clinical observations and the mechanism of dilated myocardial ischemia induced by the blood stolen phenomenon is revealed: a CAA can be considered a low pressure chamber.During systole,the blood flows into the CAA;and in the diastolic phase,due to the elasticity of the wall of the CAA,the backward flow phenomenon occurs upstream of the CAA,blood cannot flow downstream normally,so that part of the blood flow in the CAA returns to the aortic root,eventually leading to dilated myocardial ischemia.With the expansion of the CAA,the elasticity of the wall of the CAA increases,the blood stolen phenomenon will be more severe.(2)CAAs are characterized by low velocity,large area of low shear,high shear in some areas,high OSI,long particle retention time and high vorticity.These phenomena are more serious with the increase of diameter of CAAs.Combined with the vorticity contour and WSS contour,it can be observed that the distribution of hemodynamics in CAAs satisfies the condition of thrombosis formed by platelets.Platelets aggregate in the high vorticity region of the CAA neck,then activate in the high WSS region,and finally adhere to the low WSS region,resulting in thrombosis.Through the study of hemodynamics in coronary artery system and CAA,it is shown that the phenomenon of coronary aneurysm stealing caused by elasticity of CAA wall and the formation of intraluminal thrombosis caused by abnormal hemodynamic environment are two important mechanisms of dilated myocardial ischemia induced by CAA.