Role of intimal hyperplasia and arterial remodeling after balloon angioplasty - An experimental study in the atherosclerotic rabbit model

The arterial response to injury appears to be an important factor in the development of restenosis. Traditionally, intimal hyperplasia has been thought to be the primary mechanism responsible for restenosis. However, recent studies have found that arterial remodeling is a major determinant of lumen loss after balloon angioplasty. In this study, we evaluated the actual separate contributions of intimal hyperplasia and arterial remodeling to the restenotic process after balloon angioplasty in the atherosclerotic rabbit model. One month after induction of focal atherosclerotic lesions, femoral arteries were randomized to receive treatment with either two or six balloon inflations. One group of rabbits was euthanized immediately after angioplasty to evaluate the initial degree of injury with each dilatation strategy (''acute group''), and the rest were euthanized 28 days after angioplasty (''chronic group''). Arteries that had been treated with six inflations had a higher injury score than those treated with two (4.0+/-3.0 versus 1.9+/-1.5, P<.05). In the chronic group, there was a significant increase in intimal area in the six inflation-treated arteries compared with the two-inflation group (0.617+/-0.06 versus 0.432+/-0.05 mm(2), P<.004). However, there was no significant difference in lumen cross-sectional area between groups. By multivariate analysis, the most important independent predictor of lumen area was the external elastic lamina (EEL) area, although the degree of intimal thickening was also a significant independent predictor. There was a strong, positive correlation between intimal area and EEL area: the larger the intimal area, the larger the EEL area (r=.703, P<.0001). The intimal area was similar in both restenotic and nonrestenotic lesions. In contrast, EEL area was significantly larger (due to remodeling) in nonrestenotic lesions. This study confirms previous findings that the degree of injury determines the degree of neointimal proliferation and supports recent findings that chronic arterial remodeling plays a major role in the final lumen area. Understanding and controlling the remodeling process rather than concentrating solely on intimal hyperplasia may yield better results after balloon angioplasty in the future.