[Stent-induced changes of coronary morphology--pathologic-anatomic and experimental findings after balloon expansion]

Restenosis after coronary stenting still remains a major limitation of implanted endoluminal endoprostheses. To minimize-device related complications, a better understanding of the mechanisms leading to vessel wall alterations is needed.

To study the morphological effects of coronary stenting in correlation to design changes of the endoprostheses after intraluminal dilation.

1) Postmortem analysis of the changes in coronary artery morphology and venous bypass specimens of 35 stents inserted in 27 patients (24 hours up to 4 years after implantation). 2) Standardized postmortem stenting of 20 highly stenosed (> 90% in postmortem selective coronary angiography) and calcified coronary artery segments. Artifact-free microscopical analysis and measurements were performed on cross sections obtained by methylmethacrylate embedding and hard-cut grinding histological preparation.

Light microscopy revealed inhomogeneous stent expansion in all artery cross sections resulting in twisted stent filaments. Calcified plaque areas were not deformed by the stent dilation. In eccentric stenoses only over-dilation of the fibrotic plaque segments led to enlargement of the vessel's cross section. Dissections were seen on the edges of atherosclerotic plaques reaching into the arterial medial lamina. Underlying vessel morphology and not implantation pressure determined stent symmetry. Ruptured stent filaments were a seldom but crucial complication of changes in stent design after balloon dilation.

The expansion pattern of coronary stents is determined mostly by the underlying degree of atherosclerotic disease, which is the major factor influencing results of coronary stenting and leading to limiting thrombotic and myofibroblastic stent occlusions.