Keywords: coronary artery, stenosis, stent, wall shear stress, computer simulation.

The advantages of stents over angioplasty include larger acute gains in luminal diameter and better long-term patency and clinical outcomes [1,2]. Nevertheless, stents provoke absolutly later luminal loss than balloon angioplasty [3,4] and carry the additional risk of thrombosis. Therefore, in-stent restenosis has become a big problem to be solved by interventional cardiologists. The objective of the present study is to evaluate the effects of stenting shapes on flow velocity and wall shear stress in angulated coronary stenosis by computer simulation.

Following stenting shapes, optimally revascularized angulated coronary arteries were divided into two models: Model 1 with the angle change of less than 15 degrees Model 2 with the angle change of more than 15 degrees according to the angular difference between pre- and post-stenting. Coronary angiograms and Doppler ultrasound measurements in patients with angulated coronary stenosis were obtained. Inlet wave velocity form was obtained from in vivo intracoronary Doppler data and used for the input data of the computer simulation.

For effective numerical analysis of hemodynamics, the finite volume method was used. The viscosity of working fluid is set to 0.00345 Pa.s, which is the same as the viscosity of blood at the infinite shear rate. The governing equations are discretized with a non-staggered grid system. The fully implicit scheme is used to solve the physiologic flow problem, where the time step is set to be 0.01second.

Spatial distributions of blood flow velocity and recirculation areas were drawn for the coronary models. Wall shear stresses in the intracoronary stent models were calculated by using three-dimensional computer simulations.

The velocity vectors of the pre-stenting models revealed very high flow velocity toward the outer walls of the coronary artery models due to critical coronary stenosis and flow separation, flow recirculation, as well as a flow attachment phenomenon in the inner walls. The velocity vectors of the post-stenting models revealed the reduced peak flow velocity in the same coronary artery and no flow recirculation area. The frictional force exerted by flowing blood at the endothelium of the artery has been repeatedly implicated in the pathogenesis of atherosclerosis and vascular remodeling after percutaneous transluminal balloon angioplasty or coronary stenting. In the present study, the same flow disturbances mentioned above, such as flow seperation, recirculation, and reattachment, occurred in the curved inner wall of the coronary artery stenosis model before stenting, which phenomena were due to the differences of flow velocity and decreased arterial diameter. Therefore, fatty streaks and fibrous plaque may be developed on the inner wall of a curve due to low local flow velocity and low wall shear stress. The high shear stress and flow velocity was disappeared after stenting. This study suggests that local flow characteristics may play a part of the atherogenesis in curved areas, especially in coronary arteries under physiologic situations. These insights have provided the basis for the rational design of promising new therapeutic strategies for cardiovascular diseases. In the results, when temporal and spatial shear stress fluctuations in post-stenting status was presented in Model 2, a higher percent diameter stenoses occured at follow-up angiograms, which may indicate negative effects of the temporal gradient of shear stress on the healing process after stenting.

Model 1 has so less degree of angle change after stenting that the angulation was not enough to make disturbed flow to be adequately straightened compared with Model 2. The in-stent restenosis occurs due to so many factors that we cannot say that the flow property inside of the stented lesion mainly takes the responsibility of restenosis. Further experimental studied under various conditions of in vitro and in vivo biologic cases are needed. Finally, these results will be used for coronary intervention to prevent the restenosis of coronary arterial disease and its progression. The emerging paradigm of biomechanical activation of endothelial cells promises to be a conceptually rich and pathophysiologically relevant area for future investigation.

1

P.W. Serruys, P. de Jaegere, F. Kiemeneij, C. Macaya, W. Rutsch, G. Heyndrickx, H. Emanuelsson, J. Marco, V. Legrand, P. Materne, J. Belardi, U. Sijwart, A. Colombo, J. Goy, P. van den Heuvel, J. Delcan, M. More, "A comparison of balloon-expandable-stent implantation with balloon angioplasty in patients with coronary artery disease", N. Eng J. Med., 331, 489-495, 1994. doi:10.1056/NEJM199408253310801

2

D.L. Fischman, M.B. Leon, D.S. Baim, R.A. Schatz, M.P. Savage, I.M. Penn, K. Detre, L. Veltri, D.R. Ricci, M. Nobuyoshi, M.W. Cleman, R.R. Heuser, D. Almond, P.S. Teirstein, R.D. Fish, A. Colombo, J. Brinker, J. Moses, A. Shaknovich, J. Hirshfeld, S. Bailey, S. Ellis, R. Rake, S. Goldberg, "A randomized comparison of coronary artery-stent placement and balloon angioplasty in the treatment of coronary artery disease", N. Engl. J. Med, 331, 496-501, 1994. doi:10.1056/NEJM199408253310802

3

R.E. Kuntz, R.D. Safian, M.J. Levine, G.J. Reis, D.J. Diver, D.S. Baim, "Novel approach to the analysis of restenosis after the use of three new coronary devices", J. Am Coll Cardiol, 19, 1493-1499, 1992.

4

D. Kim, H.M. Kwon, B.K. Lee, Y. Jang, S.H. Suh, S.S. Yoo, H.S. Kim, "Hemodynamic effects of the geometric dimensions of graft vessels in coronary artery bypass graft models", J. Kor Med Sci., 13, 263-268, 1998.

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