- Email: [email protected]
Comparison of Intravascular Ultrasound and Histological Findings in Culprit Coronary Plaques Between ST-Segment Elevation and Non–ST-Segment Elevation Myocardial Infarction
Comparison of Intravascular Ultrasound and Histological Findings in Culprit Coronary Plaques Between ST-Segment Elevation and NoneST-Segment Elevation Myocardial Infarction Cheol Whan Lee, MDa, Ilseon Hwang, MD, PhDb, Chan-Sik Park, MD, PhDc, Hyangsin Lee, MSd, Duk-Woo Park, MDa, Soo-Jin Kang, MDa, Seung-Whan Lee, MDa, Young-Hak Kim, MDa, Seong-Wook Park, MD, PhDa, and Seung-Jung Park, MD, PhDa,* It remains uncertain whether the histology of culprit coronary plaques differs between ST-segment elevation myocardial infarction (STEMI) and non-STEMI (NSTEMI). We compared intravascular ultrasound (IVUS) and histologic findings in coronary culprit plaques among patients presenting with STEMI and NSTEMI. Atherectomy specimens were obtained from 96 patients, 70 with STEMI and 26 with NSTEMI, who underwent directional coronary atherectomy for de novo coronary artery lesions. IVUS examinations were performed before directional coronary atherectomy. IVUS and histologic data were analyzed. Clinical characteristics were largely similar between the 2 groups; however, normal antegrade flow before angioplasty was less frequently observed in patients with STEMI than those with NSTEMI. Plaque rupture was more common on the proximal side of the minimal lumen site. There were no differences in vessel area, lumen area, calcification, plaque burden, or remodelling index at the reference and culprit sites. However, the arc of the ruptured cavity was significantly greater in patients with STEMI than those with NSTEMI (69.4 – 27.9 vs 51.8 – 20.0 , respectively, p [ 0.008). The proportion of atheroma, fibrocellular, and thrombus areas was not different between the 2 groups. Similarly, the relative areas immunopositive for CD31, smooth muscle a-actin, and CD68 were similar in the 2 groups. In conclusion, coronary culprit lesions in patients with STEMI show more severe plaque rupture with similar histologic features than those in patients with NSTEMI, supporting the idea that a large plaque rupture is more likely in STEMI patients. Ó 2013 Elsevier Inc. All rights reserved. (Am J Cardiol 2013;112:68e72) Plaque rupture and acute thrombus formation is the key mechanism of ST-segment elevation myocardial infarction (STEMI) or non-STEMI (NSTEMI).1e3 Distinguishing STEMI from NSTEMI is clinically important because their treatment and prognosis are different.4 Intravascular ultrasound (IVUS)5e7 and optical coherence tomography8e10 studies have shown that plaque rupture is identical in STEMI and NSTEMI patients with different plaque morphologies. The ruptured plaque contains numerous inflammatory cells, and inflammation is recognized as a central feature in the events leading to acute myocardial infarction.3 However, it remains uncertain whether the histology of coronary culprit plaques differs between
a Department of Medicine, University of Ulsan, Seoul, Korea; Department of Pathology, School of Medicine, Keimyung University, 194 Dongsan-Dong, Choong-Ku, Daegu, Korea; cDepartment of Pathology, Asan Medical Center, University of Ulsan, Seoul, Korea; and dAsan Institute of Life Science, University of Ulsan, Seoul, Korea. Manuscript received January 15, 2013; revised manuscript received and accepted February 26, 2013. CW Lee and I Hwang contributed equally to this article. Supported by Grant A120045 from the Korean Health Technology R&D Project, Ministry of Health & Welfare, Republic of Korea. See page 72 for disclosure information. *Corresponding author: Tel: 82-2-3010-3150; fax: 82-2-486-5918. E-mail address: [email protected] (S.-J. Park). b
0002-9149/13/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.amjcard.2013.02.050
STEMI and NSTEMI patients. In the present study, we compared IVUS and histologic findings in coronary culprit plaques from patients with STEMI and NSTEMI. Methods Specimens of coronary atherosclerotic plaques from 96 consecutive patients with either STEMI (n ¼ 70) or NSTEMI (n ¼ 26) were obtained from a local biobank that collects atherectomy-derived tissues. Patient demographic and clinical characteristics, and the procedures applied to each patient were prospectively recorded. Patients were considered suitable for directional coronary atherectomy if they had a significant stenotic lesion with a large plaque burden but lacked heavy thrombi in a nontortuous epicardial coronary artery >3 mm in diameter.11,12 Each sample corresponded to a de novo lesion from a single patient. Directional coronary atherectomy was performed with a Flexi-Cut catheter (Abbott Laboratories/Guidant Vascular Interventions, Santa Clara, California) under IVUS guidance. The study protocol was approved by the local Institutional Review Committee, and all patients provided written informed consent. Following intracoronary administration of 0.2 mg nitroglycerin and the guide wire passage, IVUS examinations were performed before directional coronary atherectomy using a motorized transducer pullback system (0.5 mm/sec) www.ajconline.org
Coronary Artery Disease/Culprit Plaque Morphologies in Myocardial Infarction Table 1 Clinical characteristics Characteristics
69
Table 2 Intravascular ultrasound findings STEMI (n ¼ 70)
NSTEMI (n ¼ 26)
p Value
Age (yrs) 55.5 10.5 60.0 8.3 0.051 Male/female 62/8 20/6 0.194 Current smoker 33 (47.1%) 9 (34.6%) 0.272 Diabetes mellitus 13 (18.6%) 5 (19.2%) 0.941 Hypertension 35 (50%) 14 (53.8%) 0.738 Total cholesterol (mg/dl) 194.6 50.4 176.4 27.7 0.084 Triglyceride (mg/dl) 196.1 130.3 129.0 49.2 0.002 HDL cholesterol (mg/dl) 35.2 8.4 39.5 11.3 0.063 Hs-CRP (mg/dl) 4.5 6.0 4.7 5.9 0.912 Multivessel coronary disease 32 (45.7%) 13 (50%) 0.708 Culprit coronary artery 0.057 Left anterior descending 43 (61.4%) 9 (34.6%) Left circumflex 8 (11.4%) 4 (15.4%) Right 19 (27.1%) 13 (50%) TIMI flow grade 3 at baseline* 7 (10%) 16 (61.5%) <0.001 Medications at the time of DCA Aspirin 70 (100%) 26 (100%) 1.0 Clopidogrel 70 (100%) 26 (100%) 1.0 ACEI/ARB 4 (6%) 4 (15%) 0.128 Beta blockers 8 (11%) 8 (31%) 0.024 Calcium antagonists 8 (11%) 7 (27%) 0.063 Statins 19 (27%) 13 (50%) 0.035 ACEI ¼ angiotensin-converting enzyme inhibitor; ARB ¼ angiotensin receptor blocker; DCA ¼ directional coronary atherectomy; hs-CRP ¼ high-sensitivity C-reactive protein; TIMI ¼ thrombolysis in myocardial infarction. * Antegrade TIMI flow grade 3 through the coronary culprit lesion before coronary angioplasty.
and a commercial scanner (SCIMED/Boston Scientific, Natick, Massachusetts) consisting of a rotating 40-MHz transducer. IVUS measurements were taken by a colleague who was blind to the clinical data. A ruptured plaque was defined as a plaque containing a cavity that communicated with the lumen and that also showed an overlying residual fibrous cap fragment. A thrombus was defined as an intraluminal mass with a layered or lobulated appearance, showing evidence of blood flow (microchannels) within the mass, and demonstrating speckling or scintillation. Using computerized planimetry, the external elastic membrane (EEM) and lumen cross-sectional area (CSA; mm2) were measured in culprit and reference segments. When there was a thrombus in the cavity, the area occupied by the thrombus was included in the cavity area measurement. Cavity length was measured between the proximal and distal edges of the cavity, and the arc of the ruptured cavity was measured from the middle of the lumen. A reference segment was defined as the most normal-appearing cross section within a 5 mm region proximal and distal to the lesion but before any side branch. The remodeling index was calculated as the lesion EEM CSA divided by the mean reference EEM CSA, and the plaque burden was calculated as plaque þ media CSA divided by EEM CSA. Tissue specimens were formalin-fixed and embedded in donor paraffin blocks. Tissue microarrays were produced by reembedding tissues from the preexisting donor paraffin
Variable
STEMI (n ¼ 70)
NSTEMI (n ¼ 26)
p Value
Lesion length (mm) Thrombus Plaque morphology Hyperechoic Mixed Hypoechoic Attenuated plaque Calcium, superficial Plaque rupture Rupture location vs minimal lumen site Proximal Same Distal Proximal reference EEM CSA (mm2) Lumen CSA (mm2) Distal reference segment EEM CSA (mm2) Lumen CSA (mm2) Minimal lumen site EEM CSA (mm2) Lumen CSA (mm2) Plaque burden (%) Remodeling index Rupture site EEM CSA (mm2) Lumen CSA (mm2) Plaque burden (%) Arc of cavity, degree Cavity length (mm) Cavity area (mm2) Remodeling index
26 11 61 (87%)
25 14 21 (81%)
0.715 0.432 0.15
20 13 37 39 47 62
(29%) (19%) (53%) (56%) (67%) (89%)
10 (39%) 8 (31%) 8 (31%) 16 (62%) 22 (85%) 22 (85%)
38 (61%) 3 (5%) 21 (34%)
14 (64%) 4 (18%) 4 (18%)
17.3 5.0 9.5 2.9
16.3 6.0 9.2 4.2
0.145 0.691
10.8 4.0 6.2 2.4
10.7 4.6 6.1 2.5
0.899 0.834
0.608 0.091 0.602 0.090
14.5 1.2 91 1.1
4.3 0.4 4 0.2
14.9 1.3 90 1.1
6.0 0.5 5 0.2
0.742 0.082 0.178 0.251
15.3 3.0 81 69 2.2 1.2 1.1
3.9 1.6 8 28 2.1 1.8 0.2
15.6 3.2 78 52 2.1 1.2 1.1
6.2 1.5 11 20 2.0 1.2 0.3
0.835 0.537 0.171 0.008 0.935 0.949 0.759
blocks into an array on a recipient paraffin block. Sections from the master block were cut with a microtome, mounted on microscope slides, and used for subsequent staining procedures. Standard hematoxylin and eosin staining was performed to determine cellularity and general morphologic features. The area of each plaque was measured with a microscopic image analysis system (Motic Images Advanced 3.2, Motic, Xiamen, China). Plaques were classified as atheromatous (i.e., with necrotic cores and cholesterol clefts, but without connective tissue matrix) or fibrocellular portions. All slides were graded by 2 pathologists (C.-S. Park and I. Hwang) who were blinded to the clinical status of the patient. Discrepancies among their findings were resolved by discussion. Sections of each tissue specimen were stained with monoclonal antibodies (mAbs) against smooth muscle a-actin (1:200, mouse antihuman macrophage antibody clone 1A4; DAKO, Carpinteria, California), CD31 (1:200, mouse antihuman endothelial cell antibody clone WM59; BD Biosciences, Franklin Lakes, New Jersey), and CD68 (1:200, mouse antihuman macrophage antibody clone KP-1; DAKO). Staining was performed with the Envision-Plus Immunostaining Kit and 3,3-diaminobenzidine or 3-amino-9-ethylcarbazole as the chromogen, according to the manufacturer’s instructions
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Figure 1. Representative images of intravascular ultrasound (AeD) and corresponding atherectomy histology (EeJ) in patients with STEMI (A, B, EeG) or NSTEMI (C, D, HeJ). The culprit lesions on IVUS examination show greater rupture in STEMI (A, B) than in NSTEMI (C, D) patients. However, immunohistochemical staining reveals similar positive areas of CD31 (E, H), CD68 (F, I), and smooth muscle a-actin (G, J) in patients with STEMI or NSTEMI. Magnification 400.
(DAKO). Briefly, samples were incubated with primary antibodies (diluted in antibody diluent, DAKO) for 1 hour, washed twice (5 min each) with Tris-buffered saline/Tween20, incubated with secondary antibodies conjugated with horseradish peroxidase (HRP)-labeled polymer (DAKO) for 1 hour, and washed again. As negative controls, adjacent sections were stained with species- and isotype-matched irrelevant antibodies, including normal rabbit immunoglobulin G (Abcam, Cambridge, UK). The immunopositive area was calculated as the ratio of the area of positively stained regions to the total plaque area. Continuous variables are expressed as means SD or medians with interquartile ranges. Categorical variables are expressed as frequencies. Continuous variables were compared by Student t tests or Mann-Whitney U tests, and
categorical variables were analyzed using the chi-squared test. Statistical significance was defined as a 2-sided p value <0.05. Results Clinical characteristics were largely similar between the 2 groups, except lipid profiles and medications (Table 1). The median age was 57 years; 18.8% of the patients had diabetes mellitus, and 51.0% had hypertension. The median time from onset of chest pain to angioplasty was 4 hours for STEMI (n ¼ 70) and 48 hours for NSTEMI (n ¼ 26). Normal antegrade flow before angioplasty was less frequently observed in patients with STEMI than in patients with NSTEMI. At the time of the index procedure, beta
Coronary Artery Disease/Culprit Plaque Morphologies in Myocardial Infarction Table 3 Histological findings Variable
STEMI (n ¼ 70)
NSTEMI (n ¼ 26)
Histology Atheroma 18.3 (0.1e42) 20.3 (0.2e43.1) Fibrocellular area 55.1 (31.6e85.5) 70.9 (45.2e86.1) Thrombus 1.7 (0e13.6) 0.9 (0e5.6) Calcium 0 (0e0.1) 0 (0e0.1) 391 (240e648) Total plaque area (mm2) 346 (250e528) Immunohistochemistry CD31 1.1 (0.4e3.4) 0.7 (0.3e3.5) CD68 9.1 (1.1e21.6) 5.7 (1.3e10.4) 3.0 (1.7e5.7) 3.5 (1.2e7.7) Smooth muscle a-actin
p Value 0.240 0.327 0.474 0.404 0.307 0.471 0.550 0.993
Data are expressed as percent-positive areas (immunostained area/total plaque area 100), and as median values with interquartile ranges.
blockers and statins were less frequently used in patients with STEMI than in those with NSTEMI. IVUS data are shown in Table 2. A thrombus was observed in 87.1% of patients with STEMI, compared with 80.8% of patients with NSTEMI (p ¼ 0.432). Plaque rupture was more commonly observed at the proximal side of the minimal lumen site. Proximal and distal reference measurements were similar in the 2 groups. Likewise, there were no significant differences in EEM CSA, lumen CSA, calcification, plaque burden, or remodelling index at the rupture and minimal lumen sites, and the ruptured cavity area was similar in the 2 groups. However, the arc of the ruptured cavity was significantly greater in patients with STEMI than in those with NSTEMI (69.4 27.9 vs 51.8 20.0 , respectively, p ¼ 0.008). Representative cases of plaque rupture and corresponding histopathology are shown in Figure 1. Histological findings are summarized in Table 3. The proportion of atheroma, fibrocellular, and thrombus areas was not different between the 2 groups. The relative areas immunopositive for CD31 (1.1 [0.4e3.4] vs 0.7 [0.3e3.5], p ¼ 0.471), and CD68 (9.1 [1.1e21.6] vs 5.7 [1.3e10.4], p ¼ 0.550) were similar between the 2 groups. Likewise, the proportion of areas immunopositive for smooth muscle a-actin was not different between the 2 groups. Discussion This study showed that coronary culprit lesions in patients with STEMI had a lesser normal antegrade flow before angioplasty and a larger plaque rupture than those with NSTEMI. Unlike angiographic and IVUS findings, histologic features including CD31- and CD68-immunopositive areas were not different between STEMI and NSTEMI patients; therefore, other factors may be responsible for the types of acute myocardial infarction after plaque rupture. Plaque rupture occurs during the course of atherosclerosis, but only a few patients with ruptured plaques may develop acute myocardial infarction. In autopsy studies, plaque rupture is present in w70% of individuals who died after acute myocardial infarction, with the remaining w30% of deaths associated with plaque erosion or calcified nodules.1e3 However, it remains uncertain why some plaque ruptures trigger STEMI, whereas others trigger NSTEMI.
71
IVUS studies have shown that ruptured plaques in culprit lesions of acute coronary syndrome have smaller lumens, greater plaque burdens, and more thrombus than in stable angina.5e7 In this study, the arc of the ruptured cavity, but not the area of the ruptured cavity, was larger in patients with STEMI than in those with NSTEMI. These findings indicate a bigger tear of the culprit plaques in STEMI patients compared with NSTEMI patients because lumen and vessel sizes at the sites of plaque rupture were similar between the 2 groups. High-resolution optical coherence tomography revealed that patients with STEMI have greater plaque disruption and smaller minimal lumen area than those with NSTEMI.8e10 Furthermore, a ruptured plaque with the aperture open-wide against the direction of coronary flow was more often seen in STEMI, indicating that the morphology of the culprit lesions may affect clinical presentation after plaque rupture.10 However, aspiration thrombectomy is usually required to visualize the culprit plaques before optical coherence tomography examination, which can damage the fibrous cap with artificial plaque rupture and make it difficult to interpret their findings. Plaques vulnerable to rupture are commonly composed of a thin fibrous cap with higher macrophage infiltration and a large lipid core, indicating that inflammation drives the rupture of the coronary culprit plaques.1e3 In addition, coronary atherosclerotic plaques prone to rupture contain a large amount of red blood cells caused by the hemorrhage of blood vessels into the plaque,13,14 supporting the notion that neovascularization also contributes to the growth of atherosclerotic lesions and is a key factor in plaque destabilization leading to rupture. However, few data are available on in vivo histologic comparisons between STEMI and NSTEMI. In the present study, CD31 (endothelial cell marker)- and CD68 (macrophage marker)-immunostaining areas in coronary culprit plaques were not different between STEMI and NSTEMI patients; therefore, factors other than angiogenesis and inflammation seem to be responsible for the development of either STEMI or NSTEMI after plaque rupture. Ruptured plaques in patients with acute coronary syndrome have stronger tissue factor expression than those in patients with stable angina,15,16 and clinical manifestations may depend on the extent and severity of thrombus formation and the degree of collateral flow to the jeopardized myocardium. In our study, the culprit lesions had total occlusion and severe plaque rupture more frequently in patients with STEMI than in those with NSTEMI. Therefore, it seems likely that a greater plaque rupture exposes more thrombogenic parts of the atherosclerotic plaque, leading to total occlusion of the coronary culprit lesion with STEMI. Study limitations should be noted. First, atherectomy tissues were extracted from selected lesions in large vessels, because calcified, tortuous, or small vessels are not suitable for directional coronary atherectomy. It may not be possible to generalize our findings to lesions at sites other than large vessels. Second, systemic blood factors that increase thrombogenicity around ruptured plaques were not measured. Third, the site of IVUS evaluation and section of tissue specimen may not have been at the same location. Finally, the relatively low resolution of IVUS precludes
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a detailed assessment of the ruptured plaque, including fibrous cap thickness.
9.
Disclosures The authors have no conflicts of interest to disclose. 1. Falk E, Shah PK, Fuster V. Coronary plaque disruption. Circulation 1995;92:657e671. 2. van der Wal AC, Becker AE, van der Loos CM, Das PK. Site of intimal rupture or erosion of thrombosed coronary atherosclerotic plaques is characterized by an inflammatory process irrespective of the dominant plaque morphology. Circulation 1994;89:36e44. 3. Libby P. Inflammation in atherosclerosis. Nature 2002;420:868e874. 4. García-García C, Subirana I, Sala J, Bruguera J, Sanz G, Valle V, Arós F, Fiol M, Molina L, Serra J, Marrugat J, Elosua R. Long-term prognosis of first myocardial infarction according to the electrocardiographic pattern (ST elevation myocardial infarction, non-ST elevation myocardial infarction and non-classified myocardial infarction) and revascularization procedures. Am J Cardiol 2011;108:1061e1067. 5. Maehara A, Mintz GS, Bui AB, Walter OR, Castagna MT, Canos D, Pichard AD, Satler LF, Waksman R, Suddath WO, Laird JR Jr, Kent KM, Weissman NJ. Morphologic and angiographic features of coronary plaque rupture detected by intravascular ultrasound. J Am Coll Cardiol 2002;40:904e910. 6. Kotani J, Mintz GS, Castagna MT, Pinnow E, Berzingi CO, Bui AB, Pichard AD, Satler LF, Suddath WO, Waksman R, Laird JR Jr, Kent KM, Weissman NJ. Intravascular ultrasound analysis of infarct-related and non-infarct-related arteries in patients who presented with an acute myocardial infarction. Circulation 2003;107:2889e2893. 7. Fujii K, Kobayashi Y, Mintz GS, Takebayashi H, Dangas G, Moussa I, Mehran R, Lansky AJ, Kreps E, Collins M, Colombo A, Stone GW, Leon MB, Moses JW. Intravascular ultrasound assessment of ulcerated ruptured plaques: a comparison of culprit and nonculprit lesions of patients with acute coronary syndromes and lesions in patients without acute coronary syndromes. Circulation 2003;108:2473e2478. 8. Kusama I, Hibi K, Kosuge M, Nozawa N, Ozaki H, Yano H, Sumita S, Tsukahara K, Okuda J, Ebina T, Umemura S, Kimura K. Impact of
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plaque rupture on infarct size in ST-segment elevation anterior acute myocardial infarction. J Am Coll Cardiol 2007;50:1230e1237. Toutouzas K, Karanasos A, Tsiamis E, Riga M, Drakopoulou M, Synetos A, Papanikolaou A, Tsioufis C, Androulakis A, Stefanadi E, Tousoulis D, Stefanadis C. New insights by optical coherence tomography into the differences and similarities of culprit ruptured plaque morphology in non-ST-elevation myocardial infarction and ST-elevation myocardial infarction. Am Heart J 2011;161: 1192e1199. Ino Y, Kubo T, Tanaka A, Kuroi A, Tsujioka H, Ikejima H, Okouchi K, Kashiwagi M, Takarada S, Kitabata H, Tanimoto T, Komukai K, Ishibashi K, Kimura K, Hirata K, Mizukoshi M, Imanishi T, Akasaka T. Difference of culprit lesion morphologies between ST-segment elevation myocardial infarction and non-ST-segment elevation acute coronary syndrome: an optical coherence tomography study. JACC Cardiovasc Interv 2011;4:76e82. Kurisu S, Sato H, Tateishi H, Kawagoe T, Ishihara M, Shimatani Y, Sakai K, Ueda K, Matsuura H. Directional coronary atherectomy for the treatment of acute myocardial infarction. Am Heart J 1997;134: 345e350. McKnight J, Studeny M, Roberts G, Touchon R, Wehner P. Directional coronary atherectomy in acute myocardial infarction. W V Med J 2001;97:109e110. Kolodgie FD, Gold HK, Burke AP, Fowler DR, Kruth HS, Weber DK, Farb A, Guerrero LJ, Hayase M, Kutys R, Narula J, Finn AV, Virmani R. Intraplaquehemorrhage and progression of coronary atheroma. N Engl J Med 2003;349:2316e2325. Khurana R, Simons M, Martin JF, Zachary IC. Role of angiogenesis in cardiovascular disease: a critical appraisal. Circulation 2005;112: 1813e1824. Annex BH, Denning SM, Channon KM, Sketch MH, Stack RS, Morrissey JH, Peters KG. Differential expression of tissue factor protein in directional atherectomy specimens from patients with stable and unstable coronary syndromes. Circulation 1995;91: 619e622. Lee CW, Park CS, Hwang I, Lee H, Park DW, Kang SJ, Lee SW, Kim YH, Park SW, Park SJ. Comparison of ruptured coronary plaques in patients with unstable and stable clinical presentation. J Thromb Thrombolysis 2011;32:150e157.
a Department of Medicine, University of Ulsan, Seoul, Korea; Department of Pathology, School of Medicine, Keimyung University, 194 Dongsan-Dong, Choong-Ku, Daegu, Korea; cDepartment of Pathology, Asan Medical Center, University of Ulsan, Seoul, Korea; and dAsan Institute of Life Science, University of Ulsan, Seoul, Korea. Manuscript received January 15, 2013; revised manuscript received and accepted February 26, 2013. CW Lee and I Hwang contributed equally to this article. Supported by Grant A120045 from the Korean Health Technology R&D Project, Ministry of Health & Welfare, Republic of Korea. See page 72 for disclosure information. *Corresponding author: Tel: 82-2-3010-3150; fax: 82-2-486-5918. E-mail address: [email protected] (S.-J. Park). b
0002-9149/13/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.amjcard.2013.02.050
STEMI and NSTEMI patients. In the present study, we compared IVUS and histologic findings in coronary culprit plaques from patients with STEMI and NSTEMI. Methods Specimens of coronary atherosclerotic plaques from 96 consecutive patients with either STEMI (n ¼ 70) or NSTEMI (n ¼ 26) were obtained from a local biobank that collects atherectomy-derived tissues. Patient demographic and clinical characteristics, and the procedures applied to each patient were prospectively recorded. Patients were considered suitable for directional coronary atherectomy if they had a significant stenotic lesion with a large plaque burden but lacked heavy thrombi in a nontortuous epicardial coronary artery >3 mm in diameter.11,12 Each sample corresponded to a de novo lesion from a single patient. Directional coronary atherectomy was performed with a Flexi-Cut catheter (Abbott Laboratories/Guidant Vascular Interventions, Santa Clara, California) under IVUS guidance. The study protocol was approved by the local Institutional Review Committee, and all patients provided written informed consent. Following intracoronary administration of 0.2 mg nitroglycerin and the guide wire passage, IVUS examinations were performed before directional coronary atherectomy using a motorized transducer pullback system (0.5 mm/sec) www.ajconline.org
Coronary Artery Disease/Culprit Plaque Morphologies in Myocardial Infarction Table 1 Clinical characteristics Characteristics
69
Table 2 Intravascular ultrasound findings STEMI (n ¼ 70)
NSTEMI (n ¼ 26)
p Value
Age (yrs) 55.5 10.5 60.0 8.3 0.051 Male/female 62/8 20/6 0.194 Current smoker 33 (47.1%) 9 (34.6%) 0.272 Diabetes mellitus 13 (18.6%) 5 (19.2%) 0.941 Hypertension 35 (50%) 14 (53.8%) 0.738 Total cholesterol (mg/dl) 194.6 50.4 176.4 27.7 0.084 Triglyceride (mg/dl) 196.1 130.3 129.0 49.2 0.002 HDL cholesterol (mg/dl) 35.2 8.4 39.5 11.3 0.063 Hs-CRP (mg/dl) 4.5 6.0 4.7 5.9 0.912 Multivessel coronary disease 32 (45.7%) 13 (50%) 0.708 Culprit coronary artery 0.057 Left anterior descending 43 (61.4%) 9 (34.6%) Left circumflex 8 (11.4%) 4 (15.4%) Right 19 (27.1%) 13 (50%) TIMI flow grade 3 at baseline* 7 (10%) 16 (61.5%) <0.001 Medications at the time of DCA Aspirin 70 (100%) 26 (100%) 1.0 Clopidogrel 70 (100%) 26 (100%) 1.0 ACEI/ARB 4 (6%) 4 (15%) 0.128 Beta blockers 8 (11%) 8 (31%) 0.024 Calcium antagonists 8 (11%) 7 (27%) 0.063 Statins 19 (27%) 13 (50%) 0.035 ACEI ¼ angiotensin-converting enzyme inhibitor; ARB ¼ angiotensin receptor blocker; DCA ¼ directional coronary atherectomy; hs-CRP ¼ high-sensitivity C-reactive protein; TIMI ¼ thrombolysis in myocardial infarction. * Antegrade TIMI flow grade 3 through the coronary culprit lesion before coronary angioplasty.
and a commercial scanner (SCIMED/Boston Scientific, Natick, Massachusetts) consisting of a rotating 40-MHz transducer. IVUS measurements were taken by a colleague who was blind to the clinical data. A ruptured plaque was defined as a plaque containing a cavity that communicated with the lumen and that also showed an overlying residual fibrous cap fragment. A thrombus was defined as an intraluminal mass with a layered or lobulated appearance, showing evidence of blood flow (microchannels) within the mass, and demonstrating speckling or scintillation. Using computerized planimetry, the external elastic membrane (EEM) and lumen cross-sectional area (CSA; mm2) were measured in culprit and reference segments. When there was a thrombus in the cavity, the area occupied by the thrombus was included in the cavity area measurement. Cavity length was measured between the proximal and distal edges of the cavity, and the arc of the ruptured cavity was measured from the middle of the lumen. A reference segment was defined as the most normal-appearing cross section within a 5 mm region proximal and distal to the lesion but before any side branch. The remodeling index was calculated as the lesion EEM CSA divided by the mean reference EEM CSA, and the plaque burden was calculated as plaque þ media CSA divided by EEM CSA. Tissue specimens were formalin-fixed and embedded in donor paraffin blocks. Tissue microarrays were produced by reembedding tissues from the preexisting donor paraffin
Variable
STEMI (n ¼ 70)
NSTEMI (n ¼ 26)
p Value
Lesion length (mm) Thrombus Plaque morphology Hyperechoic Mixed Hypoechoic Attenuated plaque Calcium, superficial Plaque rupture Rupture location vs minimal lumen site Proximal Same Distal Proximal reference EEM CSA (mm2) Lumen CSA (mm2) Distal reference segment EEM CSA (mm2) Lumen CSA (mm2) Minimal lumen site EEM CSA (mm2) Lumen CSA (mm2) Plaque burden (%) Remodeling index Rupture site EEM CSA (mm2) Lumen CSA (mm2) Plaque burden (%) Arc of cavity, degree Cavity length (mm) Cavity area (mm2) Remodeling index
26 11 61 (87%)
25 14 21 (81%)
0.715 0.432 0.15
20 13 37 39 47 62
(29%) (19%) (53%) (56%) (67%) (89%)
10 (39%) 8 (31%) 8 (31%) 16 (62%) 22 (85%) 22 (85%)
38 (61%) 3 (5%) 21 (34%)
14 (64%) 4 (18%) 4 (18%)
17.3 5.0 9.5 2.9
16.3 6.0 9.2 4.2
0.145 0.691
10.8 4.0 6.2 2.4
10.7 4.6 6.1 2.5
0.899 0.834
0.608 0.091 0.602 0.090
14.5 1.2 91 1.1
4.3 0.4 4 0.2
14.9 1.3 90 1.1
6.0 0.5 5 0.2
0.742 0.082 0.178 0.251
15.3 3.0 81 69 2.2 1.2 1.1
3.9 1.6 8 28 2.1 1.8 0.2
15.6 3.2 78 52 2.1 1.2 1.1
6.2 1.5 11 20 2.0 1.2 0.3
0.835 0.537 0.171 0.008 0.935 0.949 0.759
blocks into an array on a recipient paraffin block. Sections from the master block were cut with a microtome, mounted on microscope slides, and used for subsequent staining procedures. Standard hematoxylin and eosin staining was performed to determine cellularity and general morphologic features. The area of each plaque was measured with a microscopic image analysis system (Motic Images Advanced 3.2, Motic, Xiamen, China). Plaques were classified as atheromatous (i.e., with necrotic cores and cholesterol clefts, but without connective tissue matrix) or fibrocellular portions. All slides were graded by 2 pathologists (C.-S. Park and I. Hwang) who were blinded to the clinical status of the patient. Discrepancies among their findings were resolved by discussion. Sections of each tissue specimen were stained with monoclonal antibodies (mAbs) against smooth muscle a-actin (1:200, mouse antihuman macrophage antibody clone 1A4; DAKO, Carpinteria, California), CD31 (1:200, mouse antihuman endothelial cell antibody clone WM59; BD Biosciences, Franklin Lakes, New Jersey), and CD68 (1:200, mouse antihuman macrophage antibody clone KP-1; DAKO). Staining was performed with the Envision-Plus Immunostaining Kit and 3,3-diaminobenzidine or 3-amino-9-ethylcarbazole as the chromogen, according to the manufacturer’s instructions
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Figure 1. Representative images of intravascular ultrasound (AeD) and corresponding atherectomy histology (EeJ) in patients with STEMI (A, B, EeG) or NSTEMI (C, D, HeJ). The culprit lesions on IVUS examination show greater rupture in STEMI (A, B) than in NSTEMI (C, D) patients. However, immunohistochemical staining reveals similar positive areas of CD31 (E, H), CD68 (F, I), and smooth muscle a-actin (G, J) in patients with STEMI or NSTEMI. Magnification 400.
(DAKO). Briefly, samples were incubated with primary antibodies (diluted in antibody diluent, DAKO) for 1 hour, washed twice (5 min each) with Tris-buffered saline/Tween20, incubated with secondary antibodies conjugated with horseradish peroxidase (HRP)-labeled polymer (DAKO) for 1 hour, and washed again. As negative controls, adjacent sections were stained with species- and isotype-matched irrelevant antibodies, including normal rabbit immunoglobulin G (Abcam, Cambridge, UK). The immunopositive area was calculated as the ratio of the area of positively stained regions to the total plaque area. Continuous variables are expressed as means SD or medians with interquartile ranges. Categorical variables are expressed as frequencies. Continuous variables were compared by Student t tests or Mann-Whitney U tests, and
categorical variables were analyzed using the chi-squared test. Statistical significance was defined as a 2-sided p value <0.05. Results Clinical characteristics were largely similar between the 2 groups, except lipid profiles and medications (Table 1). The median age was 57 years; 18.8% of the patients had diabetes mellitus, and 51.0% had hypertension. The median time from onset of chest pain to angioplasty was 4 hours for STEMI (n ¼ 70) and 48 hours for NSTEMI (n ¼ 26). Normal antegrade flow before angioplasty was less frequently observed in patients with STEMI than in patients with NSTEMI. At the time of the index procedure, beta
Coronary Artery Disease/Culprit Plaque Morphologies in Myocardial Infarction Table 3 Histological findings Variable
STEMI (n ¼ 70)
NSTEMI (n ¼ 26)
Histology Atheroma 18.3 (0.1e42) 20.3 (0.2e43.1) Fibrocellular area 55.1 (31.6e85.5) 70.9 (45.2e86.1) Thrombus 1.7 (0e13.6) 0.9 (0e5.6) Calcium 0 (0e0.1) 0 (0e0.1) 391 (240e648) Total plaque area (mm2) 346 (250e528) Immunohistochemistry CD31 1.1 (0.4e3.4) 0.7 (0.3e3.5) CD68 9.1 (1.1e21.6) 5.7 (1.3e10.4) 3.0 (1.7e5.7) 3.5 (1.2e7.7) Smooth muscle a-actin
p Value 0.240 0.327 0.474 0.404 0.307 0.471 0.550 0.993
Data are expressed as percent-positive areas (immunostained area/total plaque area 100), and as median values with interquartile ranges.
blockers and statins were less frequently used in patients with STEMI than in those with NSTEMI. IVUS data are shown in Table 2. A thrombus was observed in 87.1% of patients with STEMI, compared with 80.8% of patients with NSTEMI (p ¼ 0.432). Plaque rupture was more commonly observed at the proximal side of the minimal lumen site. Proximal and distal reference measurements were similar in the 2 groups. Likewise, there were no significant differences in EEM CSA, lumen CSA, calcification, plaque burden, or remodelling index at the rupture and minimal lumen sites, and the ruptured cavity area was similar in the 2 groups. However, the arc of the ruptured cavity was significantly greater in patients with STEMI than in those with NSTEMI (69.4 27.9 vs 51.8 20.0 , respectively, p ¼ 0.008). Representative cases of plaque rupture and corresponding histopathology are shown in Figure 1. Histological findings are summarized in Table 3. The proportion of atheroma, fibrocellular, and thrombus areas was not different between the 2 groups. The relative areas immunopositive for CD31 (1.1 [0.4e3.4] vs 0.7 [0.3e3.5], p ¼ 0.471), and CD68 (9.1 [1.1e21.6] vs 5.7 [1.3e10.4], p ¼ 0.550) were similar between the 2 groups. Likewise, the proportion of areas immunopositive for smooth muscle a-actin was not different between the 2 groups. Discussion This study showed that coronary culprit lesions in patients with STEMI had a lesser normal antegrade flow before angioplasty and a larger plaque rupture than those with NSTEMI. Unlike angiographic and IVUS findings, histologic features including CD31- and CD68-immunopositive areas were not different between STEMI and NSTEMI patients; therefore, other factors may be responsible for the types of acute myocardial infarction after plaque rupture. Plaque rupture occurs during the course of atherosclerosis, but only a few patients with ruptured plaques may develop acute myocardial infarction. In autopsy studies, plaque rupture is present in w70% of individuals who died after acute myocardial infarction, with the remaining w30% of deaths associated with plaque erosion or calcified nodules.1e3 However, it remains uncertain why some plaque ruptures trigger STEMI, whereas others trigger NSTEMI.
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IVUS studies have shown that ruptured plaques in culprit lesions of acute coronary syndrome have smaller lumens, greater plaque burdens, and more thrombus than in stable angina.5e7 In this study, the arc of the ruptured cavity, but not the area of the ruptured cavity, was larger in patients with STEMI than in those with NSTEMI. These findings indicate a bigger tear of the culprit plaques in STEMI patients compared with NSTEMI patients because lumen and vessel sizes at the sites of plaque rupture were similar between the 2 groups. High-resolution optical coherence tomography revealed that patients with STEMI have greater plaque disruption and smaller minimal lumen area than those with NSTEMI.8e10 Furthermore, a ruptured plaque with the aperture open-wide against the direction of coronary flow was more often seen in STEMI, indicating that the morphology of the culprit lesions may affect clinical presentation after plaque rupture.10 However, aspiration thrombectomy is usually required to visualize the culprit plaques before optical coherence tomography examination, which can damage the fibrous cap with artificial plaque rupture and make it difficult to interpret their findings. Plaques vulnerable to rupture are commonly composed of a thin fibrous cap with higher macrophage infiltration and a large lipid core, indicating that inflammation drives the rupture of the coronary culprit plaques.1e3 In addition, coronary atherosclerotic plaques prone to rupture contain a large amount of red blood cells caused by the hemorrhage of blood vessels into the plaque,13,14 supporting the notion that neovascularization also contributes to the growth of atherosclerotic lesions and is a key factor in plaque destabilization leading to rupture. However, few data are available on in vivo histologic comparisons between STEMI and NSTEMI. In the present study, CD31 (endothelial cell marker)- and CD68 (macrophage marker)-immunostaining areas in coronary culprit plaques were not different between STEMI and NSTEMI patients; therefore, factors other than angiogenesis and inflammation seem to be responsible for the development of either STEMI or NSTEMI after plaque rupture. Ruptured plaques in patients with acute coronary syndrome have stronger tissue factor expression than those in patients with stable angina,15,16 and clinical manifestations may depend on the extent and severity of thrombus formation and the degree of collateral flow to the jeopardized myocardium. In our study, the culprit lesions had total occlusion and severe plaque rupture more frequently in patients with STEMI than in those with NSTEMI. Therefore, it seems likely that a greater plaque rupture exposes more thrombogenic parts of the atherosclerotic plaque, leading to total occlusion of the coronary culprit lesion with STEMI. Study limitations should be noted. First, atherectomy tissues were extracted from selected lesions in large vessels, because calcified, tortuous, or small vessels are not suitable for directional coronary atherectomy. It may not be possible to generalize our findings to lesions at sites other than large vessels. Second, systemic blood factors that increase thrombogenicity around ruptured plaques were not measured. Third, the site of IVUS evaluation and section of tissue specimen may not have been at the same location. Finally, the relatively low resolution of IVUS precludes
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a detailed assessment of the ruptured plaque, including fibrous cap thickness.
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Disclosures The authors have no conflicts of interest to disclose. 1. Falk E, Shah PK, Fuster V. Coronary plaque disruption. Circulation 1995;92:657e671. 2. van der Wal AC, Becker AE, van der Loos CM, Das PK. Site of intimal rupture or erosion of thrombosed coronary atherosclerotic plaques is characterized by an inflammatory process irrespective of the dominant plaque morphology. Circulation 1994;89:36e44. 3. Libby P. Inflammation in atherosclerosis. Nature 2002;420:868e874. 4. García-García C, Subirana I, Sala J, Bruguera J, Sanz G, Valle V, Arós F, Fiol M, Molina L, Serra J, Marrugat J, Elosua R. Long-term prognosis of first myocardial infarction according to the electrocardiographic pattern (ST elevation myocardial infarction, non-ST elevation myocardial infarction and non-classified myocardial infarction) and revascularization procedures. Am J Cardiol 2011;108:1061e1067. 5. Maehara A, Mintz GS, Bui AB, Walter OR, Castagna MT, Canos D, Pichard AD, Satler LF, Waksman R, Suddath WO, Laird JR Jr, Kent KM, Weissman NJ. Morphologic and angiographic features of coronary plaque rupture detected by intravascular ultrasound. J Am Coll Cardiol 2002;40:904e910. 6. Kotani J, Mintz GS, Castagna MT, Pinnow E, Berzingi CO, Bui AB, Pichard AD, Satler LF, Suddath WO, Waksman R, Laird JR Jr, Kent KM, Weissman NJ. Intravascular ultrasound analysis of infarct-related and non-infarct-related arteries in patients who presented with an acute myocardial infarction. Circulation 2003;107:2889e2893. 7. Fujii K, Kobayashi Y, Mintz GS, Takebayashi H, Dangas G, Moussa I, Mehran R, Lansky AJ, Kreps E, Collins M, Colombo A, Stone GW, Leon MB, Moses JW. Intravascular ultrasound assessment of ulcerated ruptured plaques: a comparison of culprit and nonculprit lesions of patients with acute coronary syndromes and lesions in patients without acute coronary syndromes. Circulation 2003;108:2473e2478. 8. Kusama I, Hibi K, Kosuge M, Nozawa N, Ozaki H, Yano H, Sumita S, Tsukahara K, Okuda J, Ebina T, Umemura S, Kimura K. Impact of
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