Structural determinants of lumen narrowing after angioplasty in atherosclerotic nonhuman primates

Purpose: The relationship between lumen narrowing, intimal hyperplasia, and wall remodeling after angioplasty was explored in a nonhuman primate model of atherosclerosis. Methods: Cynomolgus monkeys (n = 37) used in long-term atherosclerosis studies underwent left iliac artery balloon injury. The uninjured right iliac artery served as a reference segment for intraanimal comparisons. One month later iliac arteries were fixed by perfusion (100 mm Hg) and removed for cross-sectional analysis to determine mean values for lumen area (LA), intimal area (IA), internal elastic lamina area (IELA), plaque burden (IA/IELA), and depth of wall injury. Values for each balloon-injured iliac artery were normalized to the contralateral uninjured iliac artery (percent of control), and linear regression analysis was performed comparing LA with IA, with IELA, and with depth of injury. Comparisons were also made between those arteries that remained dilated 1 month after balloon injury (LA greater than or equal to 140%; n = 13) and those that renarrowed (LA less than or equal to 100%; n = 14). Results: For all 37 animals, LA 1 month after balloon injury correlated well with IELA (r = 0.72; p < 0.001) but not with IA (r = 0.10; p = 0.54), suggesting that changes in artery size rather than neointimal mass determined lumen caliber. When comparing arteries that remained dilated (n = 13) with those that renarrowed (n = 14), there were no differences in depth of wall injury (injury depth: 0, no injury; 1, intima; 2, IEL; 3, media; 4, EEL; 2.1 +/- 0.3 vs 1.6 +/- 0.3; p = 0.12), neointimal accumulation (IA, 507% +/- 118% vs. 421% +/- 81% of control; p = 0.55), or plaque burden (IA/IELA, 0.39 +/- 0.04 vs 0.37 +/- 0.06; p = 0.71), respectively. However, wall size defined as IELA was significantly smaller in arteries that renarrowed than in those that remained dilated (IELA, 115% +/- 14% vs 230% +/- 19% of control; p < 0.001). Conclusions: Restenosis after angioplasty has been attributed to intimal hyperplasia, equating loss of lumen caliber with neointimal mass. The data presented herein suggest that lumen narrowing after arterial wall injury may have little to do with intimal mass per se, but rather that a change in wall caliber or wall narrowing is the cause of restenosis.