ULTRASTRUCTURAL CHARACTERISTICS OF CELLUL AR REACTIONS IN THE ARTERIAL VESSEL SYSTEM TO EXPERIMENTAL LESIONS INDUCED BY A CATHETER SYSTEM

After angioplasty, restenosis remains the major drawback of the proced ure with an incidence of between 20-40%. It is a matter of concern whe ther the cellular alterations start immediately after directional athe rectomy (DA) and if they are dependent on the depth of the lesion. Met hod: Cellular alterations immediately after DA were investigated using peripheral atherectomy in normal vessels of 30 pigs (A. femoralis, A. carotis communis). DA was used to remove material. The arteries were assigned to two groups according to the depth of vessel injury. (Group 1: lesions to the intima; Group 2: lesions to the media.) 68 arteries with 41 intimal and 27 media lacerations were excised 4 to 24 hours l ater and processed for transmission electron microscopy, histology and immunohistochemistry. Results: Immediately after DA, thrombus formati on at the site of the altered segment was found. A transient infiltrat ion of polymorphonuclear leukocytes (PMN) occurred, especially if the media was lacerated, followed by the transformation of contractile smo oth muscle cells (SMC) into the synthetic subtype. A marked myoprolife rative response was found in Group 2 whereas only moderate tissue hype rplasia was seen in Group 1. Conclusion: The present data provides evi dence that cellular alteration of the atherectomized vessel begins imm ediately after atherectomy. Subsequent to the initial temporary PMN in filtration, an activation of local SMC occurs at a very early stage. T hese effects and, in particular, a myoproliferative response were foun d lesions injured the internal elastic membrane, while only minor effe cts were seen when the lesion affected the intimal layer.