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(Circulation. 2004;110:1061-1068.)
© 2004 American Heart Association, Inc.
Original Articles |
From the Department of Cardiology, Juntendo University School of Medicine, Tokyo, Japan.
Correspondence to Shinya Okazaki, MD, Department of Cardiology, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku Tokyo 113-8421 Japan. E-mail shinya{at}med.juntendo.ac.jp
Received February 10, 2004; revision received May 6, 2004; accepted May 18, 2004.
| Abstract |
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Methods and Results Seventy patients with ACS were enrolled. All patients underwent emergency coronary angiography and percutaneous coronary intervention (PCI). They were randomized to intensive lipid-lowering therapy (n=35; atorvastatin 20 mg/d) or control (n=35) groups after PCI. Volumetric intravascular ultrasound analyses were performed at baseline and 6-month follow-up for a non-PCI site in 48 patients (atorvastatin, n=24; control, n=24). LDL-C level was significantly decreased by 41.7% in the atorvastatin group compared with the control group, in which LDL-C was increased by 0.7% (P<0.0001). Plaque volume was significantly reduced in the atorvastatin group (13.1±12.8% decrease) compared with the control group (8.7±14.9% increase; P<0.0001). Percent change in plaque volume showed a significant positive correlation with follow-up LDL-C level (R=0.456, P=0.0011) and percent LDL-C reduction (R=0.612, P<0.0001), even in patients with baseline LDL-C <125 mg/dL.
Conclusions Early aggressive lipid-lowering therapy by atorvastatin for 6 months significantly reduced the plaque volume in patients with ACS. Percent change in plaque volume showed a significant positive correlation with percent LDL-C reduction, even in patients with low baseline LDL-C.
Key Words: atherosclerosis lipids plaque statins coronary disease
| Introduction |
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| Methods |
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Patient Population
Patients were enrolled between November 2001 and August 2003. Patients were eligible for inclusion if they had ACS with significant stenosis on initial coronary angiography and received PCI. ACS was defined as high-risk unstable angina, nonST-elevated myocardial infarction (MI) or ST-elevated MI. MI was diagnosed by the rise (
2 times) in serum creatine phosphokinase and positivity for troponin T. Exclusion criteria were failed PCI, diseased bypass graft, recommended CABG, cardiogenic shock, and administration of lipid-lowering drugs (statin, clofibrate, probucol or analog, nicotinic acid, or other prohibited drug) before enrollment.
PCI Procedure and Antiplatelet Therapy
PCI with or without stent placement and post-PCI management were performed in a standard manner. Intravenous heparin and oral 162 mg aspirin were administered during the procedures. After PCI, all patients received aspirin 100 mg once daily and ticlopidine 100 mg twice daily for >3 weeks and cilostazol 100 mg twice daily for 4 days.
IVUS Examination
For IVUS examinations, the same system (2.9 F, 40-MHz; Boston Scientific) was used at baseline and follow-up. All IVUS examinations were performed in the following manner. After intracoronary administration of 0.2 mg nitroglycerin, the ultrasound catheter was positioned sufficiently distal (
10 mm distal) to the PCI site. Pullback was performed automatically at 0.5 mm/s. IVUS measurements were recorded on super VHS videotape and sent to our IVUS laboratory for offline quantitative analysis.
IVUS Analysis
Plaque volume was assessed by volumetric analysis with a Netra 3D IVUS system (ScImage). Baseline and follow-up IVUS images were reviewed side by side on a display, and the target segment was selected. One target segment was determined in a non-PCI site (>5 mm proximal or distal to the PCI site) with a reproducible index side branch. Segments with marked calcification or tortuosity were avoided. If a distal protection device was used in a patient, a non-PCI site was selected proximal to the PCI site to avoid the segment affected by balloon injury of distal occlusion. Quantitative analysis was performed by an independent experienced IVUS investigator blinded to the patient groups and to the angiographic result. IVUS analyses included the vessel volume, lumen volume, and plaque volume. Standard measurements obtained included lesion length, vessel volume, and lumen volume. Plaque volume was calculated as vessel volume minus lumen volume. The percent change in plaque volume was defined as the change in plaque volume (follow-up minus baseline plaque volume) divided by the baseline plaque volume. The primary outcome was percent change in plaque volume; the secondary outcome was the correlation between percent change in plaque volume and follow-up LDL-C levels or percent LDL-C reduction.
Definition of Events and Follow-Up for Major Adverse Coronary Events
Follow-up visits were scheduled every month. Cardiac events, consisting of death caused by cardiac causes, MI, recurrent angina related to the PCI vessel, or target vessel revascularization (repeated PCI or CABG), were reported. Angiographic follow-up was scheduled for all patients 6 months after PCI. Recurrent angina was defined as the presence of ischemia, either the recurrence of typical symptoms of angina or a positive exercise stress test related to the PCI vessel.
Statistical Analysis
Statistical analysis was performed with Stat View 5.0 MDSU statistical software (SAS Institute). Quantitative data are presented as mean±SD. Differences between the 2 groups with or without statin treatments were assessed with
2 test for categorical variables and with unpaired Students t test or the Mann-Whitney rank-sum test for continuous data. Correlations between percent change in plaque volume and lipid values or changes were analyzed by linear regression analysis. Event-free survival was assessed with the Kaplan-Meier method. A value of P<0.05 was considered statistically significant. For the sample size calculation, no information was available for the volumetric IVUS trial in patients with ACS. A total of 50 patients seemed appropriate to investigate the efficacy of LDL-C lowering on plaque volume and correlation between the percent change in plaque volume and LDL-C levels.
| Results |
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Follow-Up Data and Lipid Profile
Three patients in the control group received a cholesterol absorption inhibitor. No patient was withdrawn for any adverse effects in the atorvastatin group. At 6 months, LDL-C level was significantly decreased by 41.7% in the atorvastatin group compared with an increase of 0.7% in the control group (P<0.0001). HDL-C and triglyceride levels showed no significant differences in the 2 groups at baseline and follow-up (Table 3).
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Volumetric IVUS Analysis
For the target segment selection, a distal segment was selected in 10 patients in the atorvastatin group and in 11 in the control group; a proximal segment was chosen in 14 patients in the atorvastatin group and in 13 in the control group. Table 4 shows the baseline and 6-month follow-up data of volumetric IVUS analysis at the target segment. Plaque volume was significantly reduced in the atorvastatin group (13.1±12.8% decrease; P<0.0001 for baseline versus follow-up). On the other hand, it was significantly increased by 8.7±14.9% in the control group (P=0.0276 for baseline versus follow-up, P<0.0001 for atorvastatin versus control at follow-up). Figure 1 shows the percent change in cholesterol level and volumetric IVUS analysis parameters in each group. In the atorvastatin group, significant percent changes in both plaque volume and lumen volume were observed. Figure 2 shows that percent change in plaque volume had a significant positive correlation with follow-up LDL-C level (R=0.456, P=0.0011) and percent LDL-C reduction (R=0.612, P<0.0001) but no correlation with percent HDL-C gain (R=0.206, P=0.160) and baseline LDL-C level (R=0.154, P=0.295). When the patients were divided into 2 subgroups by a baseline serum LDL-C level of 125 mg/dL (median LDL-C level), plaque volume was significantly reduced in the atorvastatin group in either the LDL-C <125 mg/dL (14.7±13.2% decrease; P=0.0027 for baseline versus follow-up) or the LDL-C >125 mg/dL (10.8±11.8% decrease; P=0.043 for baseline versus follow-up) subgroup. Percent change in plaque volume showed a more significant positive correlation with percent LDL-C reduction in patients with a low baseline LDL-C (<125 mg/dL) than in those with a high baseline LDL-C (>125 mg/dL) (R=0.685, P=0.0002; R=0.462, P=0.0231, respectively; Figure 3). Figure 4 shows a representative patient from each group. Baseline and follow-up IVUS images are presented side by side. Marked enlargement of the lumen and a reduction in plaque are clearly observed in an atorvastatin patient at the non-PCI site after only 6 months of pharmacological intervention, whereas a significant reduction in the lumen and an increase in plaque area are observed in a control patient.
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Major Adverse Coronary Events
The prevalence of major adverse coronary events during 6 months of follow-up showed no significant difference between the 2 groups (8 patients each in both groups; P=0.8471). There was no case of cardiac death or target vesselrelated MI. All cases of major adverse coronary events consisted of target vessel revascularization performed for restenosis with recurrent angina in 24.2% (8 of 33) of the atorvastatin group and 25.0% (8 of 32) in the control group.
| Discussion |
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Several serial IVUS studies have indicated that cholesterol lowering could retard the progression of atherosclerosis; however, they did not demonstrate significant plaque regression in patients with stable coronary artery disease.12,13 In a recent study in stable angina, the plaque volume reduction by statin treatment was not significant compared with control, although this study showed a 4-fold-greater increase in plaque hyperechogenicity.13 In contrast, the present study demonstrated plaque regression by aggressive lipid lowering over a relatively short period of time after ACS. This early regression in ACS may be explained by the difference in target plaque characteristics between ACS and stable coronary artery disease. Previous large-scale intervention trials suggest that they have very different clinical processes. It was reported that in ACS the rate of death or nonfatal MI was 10.4% among patients who received immediate invasive treatment with medical treatment and 14.1% among patients who received medical therapy alone.14 In contrast, stable angina patients were found to have a better clinical outcome. In SAPAT, the rate of death or nonfatal MI was <2%.15 This substantial prognostic difference suggests that patients with ACS have vulnerable plaques leading to recurrent clinical events; on the other hand, patients with stable angina have rather stable plaques. Indeed, previous clinical studies have demonstrated that patients with ACS had vulnerable plaque at the culprit lesion and in other branches of the coronary tree. An angiographic study showed that most MI occurs at sites at which only mild to moderate luminal stenosis previously existed.16 Those infarct-related lesions usually showed complex morphology that was histologically vulnerable.17 These studies suggest that coronary plaques in ACS have vulnerable morphology that is prone to regression by aggressive lipid lowering, as indicated in the present study.
The analyzed target segments in the present study in which significant regression was observed were nonculprit lesions proximal or distal to the culprit lesion. Goldstein et al18 reported the presence of additional multiple complex angiographic lesions in 39.5% of ACS patients, and these lesions were associated with increased incidence of recurrent ACS. Rioufol et al19 observed all 3 coronary trees in patients with ACS by IVUS. They found
2 ruptured plaques in 79% of patients. These studies suggest that ACS seems to be associated with the overall coronary instability that is responsible for the frequent recurrence rate even after acute treatment of the culprit lesions. Thus, the beneficial effect of aggressive lipid lowering on the nonculprit lesions in the present study may contribute to prevention of recurrent events. Indeed, recent statin trials indicated that early statin treatment in patients with ACS could produce a significant advantage in short-term follow-up.811 The MIRACL study investigated the efficacy of early statin treatment on recurrent coronary events within 16 weeks and found a significant 16% reduction in events.9
The mechanisms of the beneficial effect of acute statin treatment in ACS are not fully understood. Because efficacy was observed as early as 16 weeks, instead of the LDL-C-lowering effect, direct effects of statins, including recovery of impaired endothelial function and/or an anti-inflammatory effect and/or an antithrombotic effect, have been proposed. In the present study, we documented significant plaque regression in the atorvastatin group, with a significant positive correlation between percent LDL-C reduction and follow-up LDL-C level and percent change in plaque volume during only a 6-month period. Thus, aggressive LDL-C lowering itself should be an important mechanisms for event reduction by early statin treatment after ACS. In a recent observational study, Von Birgelen et al20 documented a positive correlation between baseline LDL-C level and annual change in plaque size of the left main trunk during
12 months of follow-up in cross-sectional analysis of IVUS measurements. Although the study demonstrated significant enlargement of the lumen area in the low baseline LDL-C (120 mg/dL) group, regression of plaque area was not observed, and only retardation of the progression was found. Similar correlation was not found between baseline LDL-C and percent change in plaque volume in the present study because pharmacological intervention modified the lipid profile. A significant correlation was observed between percent LDL-C reduction and follow-up LDL-C level and percent change in plaque volume. Moreover, this correlation was found even in patients with a low baseline LDL-C level (<125 mg/dL). Thus, plaque regression by aggressive LDL-C lowering could be attributable to the acute effect of statins in ACS, independent of the baseline LDL-C level.
Study Limitations
This study consisted of only 48 ACS patients with volumetric IVUS analysis; however, high-quality IVUS images in both the acute phase of ACS and follow-up allowed us to identify a significant difference in plaque volume between the atorvastatin and control groups in a short period. We could not perform tissue characterization in this study. Future study should address the detailed mechanisms of acute plaque stabilization by statins in patients with ACS.
Conclusions
Our study demonstrated that early aggressive lipid-lowering therapy by atorvastatin for 6 months significantly reduced the plaque volume in patients with ACS. Percent change in plaque volume showed a significant positive correlation with percent LDL-C reduction, even in patients with a low baseline LDL-C (<125 mg/dL). Thus, aggressive lipid lowering by statins immediately after ACS onset may be an attractive treatment strategy, regardless of the baseline serum LDL-C level.
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