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

Restenosis after angioplasty occurs with an incidence of 20-50 % and r emains a major drawback. Certain randomized studies suggest that a big ger post-angioplasty lumen predicts a better long-term outcome. Conver sely other studies showed a better outcome with limited injury. The pr esent study aimed to investigate the depth of the lesion and relate th is to cellular alterations after graded vascular injury. Method: Vesse l 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 a fter injury, 68 arteries showing 41 intimal and 27 media lacerations w ere excised and processed for histology and transmission electron micr oscopy. Results: Immediately after injury, thrombus formation was foun d 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 tran sformation of contractile myocytes to a synthetic subtype. The ratio o f myofilaments to organelles decreased. A pronounced myoproliferative response was found in Group 2 after 7 days (p < 0.01), whereas only mo derate tissue hyperplasia was seen in Group 1. Conclusion: The data pr esented provide evidence that the cellular alteration of injured vesse ls begins immediately. Subsequent to an initial temporary PMN infiltra tion, an activation of local myocytes occurs at a very early stage. In particular, a myoproliferative response was found only after deep inj ury with rupture of the internal elastic lamina.