SummaryThe difference in neointimal stent coverage (NSC) between ruptured segments and adjacent nonruptured segments in infarct-related lesions (IRL) of acute myocardial infarction after bare metal stent (BMS) implantation was evaluated using coronary angioscopy. Serial angioscopic observations were performed for 19 IRLs immediately after the implantation of a BMS and at 1-month and 6-month follow-up. Stented segments were divided into the ruptured segment and the nonruptured segment based on the presence of a thrombus. The grade of NSC was divided into 0 = complete exposure, 1 = partial coverage, or 2 = complete coverage. The grade of plaque color was classified semiquantitatively as 0 = white, 1 = light yellow, or 2 = intense yellow. The existence of a thrombus was also determined. The grade of NSC in the ruptured segment was lower than that of the nonruptured segment at each follow-up. The grade of plaque color at the 1-month follow-up was higher in the ruptured segment than in the nonruptured segment. At 6 months, the grade of plaque color was similar between the ruptured and nonruptured segments. In all cases, thrombi existed in the ruptured segments immediately after stenting. Although thrombi still remained frequently at 1-month, most had disappeared at the 6-month follow-up. Neointimal proliferation of the ruptured segment in IRL advanced slowly in comparison to the adjacent nonruptured segment. The presence of an atherosclerotic yellow plaque and a thrombus may affect the delayed neointimal coverage after BMS implantation. (Int Heart J 2010; 51: 7-12) Key words: Acute myocardial infarction, Stent, Neointima, Plaque R ecently, a late thrombosis after stent implantation has emerged as a major clinical concern regardless of the type of stent, such as a bare metal stent (BMS) or a drug-eluting stent, because it is a life-threatening complication.1-3) The principal mechanisms of the late stent thrombosis are delayed endothelialization, lack of neointimal stent coverage (NSC), and the presence of persistent uncovered stent struts. 4,5) Several follow-up studies after stent implantation using coronary angioscopy demonstrated that NSC had an effect on plaque stabilization due to the complete sealing of the stent by the neointima underlying the ruptured plaque regardless of any unstable clinical settings, such as an acute myocardial infarction (AMI).
6,7)Moreover, NSC after stent implantation has a different time course between patients with an AMI and those with stable angina pectoris. 7,8) The major causes of an AMI are understood to be the disruption of atherosclerotic vulnerable plaques and subsequent thrombus formation and a vulnerable plaque is recognized as yellow by coronary angioscopy.9-11) Although a coronary stent is deployed on the ruptured segment, the location of the stent extends to the nonruptured segment beyond the ruptured segment. Angioscopic plaque morphology between the ruptured and nonruptured segments is quite different. The ruptured segment is defined as the site of a vulnerable yellow pl...