טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentShofty Rona
SubjectThe Influence of Intravascular Stents on the Proliferative
Process
DepartmentDepartment of Medicine
Supervisor Professor Rafael Beyar


Abstract

    The purpose of implanted stents is to prevent the acute recoil following balloon angioplasy and reduce restenosis in the longer time range. At present, the  restenosis rate of  stented coronaries ranges between 10-25% and remains an unresolved problem of the stenting procedure.

The study objectives are:

     1.Characterization of the parameters involved in the restenotic process.

     2. Analysis of stent mediated injury with respect to the inflammatory response, the  

         vascularization  and their interrelationship at various points in time.

     3.Assessment of the influence of mechanical properties of stents on the

         interrelationship between injury and proliferation.

     4.Assessment of the effect of structural and mechanical characteristics of various   

        stent types on each of the parameters involved in restenosis and on the  

        proliferative process with reference to stent location and times of follow-up.

192 stents of various types, implanted in an animal model (swine), and 5646 histological sections were analysed . The relationship between injury and proliferation was shown to be affected by various stent properties and to depend on other factors such as inflammation and vascularization. The correlation between increased intimal thickness and vascularization emphasized their interdependence in  response to arterial wall injury.

Evaluation of the neovascularization and its role in the proliferative process has contributed to the understanding of the arterial response mechanism. Follow-up with time and location as reference criteria allowed highlighting variations in coronary response to different stent properties.

Short stents cause a more limited proliferative response than long ones. Reaction to stents in the left anterior decending artery is followed by increased proliferation and injury as compared to the right coronary artery. Rigid and long stents cause more injury and correspondingly a greater proliferative response in the left than in the right coronary arteries. Flexible stents in these vessels elicit a more limited response throughout the entire stent length.

Each expansion mechanism has its specific reaction kinetics. The self-expanding stent initially causes a greater proliferative response than the balloon expandable stent, however a lower restenosis is observed in the long run.

The study examines  the various interactions between the proliferative response and its accompanying factors,  deals with the clinical significance of response elicited by the various stent types and contributes to the establishment of a standard methodology for the evaluation of coronary stents in the animal model.