ULTRASTRUCTURAL CHARACTERISTICS OF CELLULAR REACTION AFTER EXPERIMENTALLY-INDUCED LESIONS IN THE ARTERIAL VESSEL

Restenosis after angioplasty occurs with an incidence of 20-50 % and remains a major drawback. Certain randomized studies suggest that a bigger post-angioplasty lumen predicts a better long-term outcome. Conversely other studies showed a better outcome with limited injury. The present study aimed to investigate the depth of the lesion and relate this to cellular alterations after graded vascular injury. Method: Vessel segments of 30 pigs underwent injury using a directional atherectomy catheter. Vessels were assigned according to the extent of injury to Group 1 (intima lesion) or Group 2 (media injury). 2 hours to 7 days after injury, 68 arteries showing 41 intimal and 27 media lacerations were excised and processed for histology and transmission electron microscopy. Results: Immediately after injury, thrombus formation was found at the site of the altered segment. A marked, transient infiltration of polymorphonuclear leukocytes (PMN) occurred only if the media was lacerated, starting within the first hours and increasing up until the 12 hours time point. The cellular infiltration was followed by a transformation of contractile myocytes to a synthetic subtype. The ratio of myofilaments to organelles decreased. A pronounced myoproliferative response was found in Group 2 after 7 days (p < 0.01), whereas only moderate tissue hyperplasia was seen in Group 1. Conclusion: The data presented provide evidence that the cellular alteration of injured vessels begins immediately. Subsequent to an initial temporary PMN infiltration, an activation of local myocytes occurs at a very early stage. In particular, a myoproliferative response was found only after deep injury with rupture of the internal elastic lamina.