Composition of Carotid Atherosclerotic Plaque Is Associated With Cardiovascular Outcome
A Prognostic Study
Background— Identification of patients at risk for primary and secondary manifestations of atherosclerotic disease progression is based mainly on established risk factors. The atherosclerotic plaque composition is thought to be an important determinant of acute cardiovascular events, but no prospective studies have been performed. The objective of the present study was to investigate whether atherosclerotic plaque composition is associated with the occurrence of future vascular events.
Methods and Results— Atherosclerotic carotid lesions were collected from patients who underwent carotid endarterectomy and were subjected to histological examination. Patients underwent clinical follow-up yearly, up to 3 years after carotid endarterectomy. The primary outcome was defined as the composite of a vascular event (vascular death, nonfatal stroke, nonfatal myocardial infarction) and vascular intervention. The cumulative event rate at 1-, 2-, and 3-year follow-up was expressed by Kaplan–Meier estimates, and Cox proportional hazards regression analyses were performed to assess the independence of histological characteristics from general cardiovascular risk factors. During a mean follow-up of 2.3 years, 196 of 818 patients (24%) reached the primary outcome. Patients whose excised carotid plaque revealed plaque hemorrhage or marked intraplaque vessel formation demonstrated an increased risk of primary outcome (risk difference=30.6% versus 17.2%; hazard ratio [HR] with [95% confidence interval]=1.7 [1.2 to 2.5]; and risk difference=30.0% versus 23.8%; HR=1.4 [1.1 to 1.9], respectively). Macrophage infiltration (HR=1.1 [0.8 to 1.5]), large lipid core (HR=1.1 [0.7 to 1.6]), calcifications (HR=1.1 [0.8 to 1.5]), collagen (HR=0.9 [0.7 to 1.3]), and smooth muscle cell infiltration (HR=1.3 [0.9 to 1.8]) were not associated with clinical outcome. Local plaque hemorrhage and increased intraplaque vessel formation were independently related to clinical outcome and were independent of clinical risk factors and medication use.
Conclusions— The local atherosclerotic plaque composition in patients undergoing carotid endarterectomy is an independent predictor of future cardiovascular events.
Received June 17, 2009; accepted February 16, 2010.
It has been recognized that clinical manifestations of atherosclerotic disease such as myocardial infarction and stroke are caused by acute thrombosis, which is triggered by atherosclerotic plaque instability rather than by gradually progressive luminal narrowing.1–5 Pathology studies revealed that atherosclerotic plaque destabilization is related to specific “vulnerable” plaque characteristics, such as a large lipid core, thin fibrous cap, and marked inflammation.6
Clinical Perspective on p 1950
At present, a reliable method to predict future plaque destabilization and subsequent cardiovascular events is lacking. Systemic circulating markers such as high-sensitivity C-reactive protein have limited predictive value.7 Local atherosclerotic plaque characteristics have not yet been investigated in relation to future cardiovascular events. Evidence originating from previously conducted studies suggesting that vulnerable plaque characteristics portray an increased risk of future cardiovascular events has been mainly cross-sectional. When the potential of plaque imaging is considered, the relation between plaque composition and clinical outcome is of great interest. After identification of predictive plaque markers, noninvasive plaque imaging may be used to identify patients at high risk for future cardiovascular events. Therefore, the present study was performed with the goal of establishing the predictive value of atherosclerotic plaque composition for cardiovascular outcome.
Because atherosclerosis is a systemic disease,8,9 and plaque composition correlates between different arterial segments within individuals,10 we hypothesized that composition of a single atherosclerotic plaque could be predictive of systemic cardiovascular outcome. For this purpose, we included a consecutive cohort of patients undergoing carotid endarterectomy (CEA). In this patient cohort, we related the composition of the plaque excised at baseline to clinical outcome during 3-year follow-up.
Athero-Express is an ongoing longitudinal study that includes patients undergoing CEA. The study design has been reported earlier.11 In short, plaques obtained during CEA are collected and processed following a standardized protocol. After the operation, the patients undergo follow-up. All patients undergoing CEA in the participating centers (St Antonius Hospital Nieuwegein and University Medical Center Utrecht) were asked to participate in the study. The medical ethics board of the participating hospitals approved the study, and all participants of the study provided written informed consent. For this study, the inclusion started on April 1, 2002, and ended on March 11, 2008.
All indications for surgery were reviewed by a multidisciplinary vascular team, as described earlier.11 The patients completed questionnaires covering cardiovascular risk factors, medical history, and medication use. Further clinical data were obtained from patient charts. The definitions of hypertension, hypercholesterolemia, and diabetes mellitus were restricted to those cases requiring medical treatment. All patients were examined by a neurologist preoperatively and postoperatively to document cerebrovascular symptom status and to record any new neurological deficits after CEA. Percent stenosis of both carotid arteries was recorded with duplex ultrasound preoperatively following internationally accepted guidelines.12
Preoperatively, patients were started on aspirin, except for patients taking oral anticoagulants for other indications and patients with contraindications to aspirin use. Before exposure of the carotid artery, patients received 5000 U of heparin intravenously. With the use of a standardized carotid endarterectomy technique, the plaque was carefully dissected and removed in toto, without procedure-related complications. Immediately after dissection, the plaque was transferred to the laboratory.
According to a standardized protocol, the plaque was divided in segments of 5-mm thickness along the longitudinal axis. The segment with the greatest plaque burden was subjected to histological examination.11 Semiquantitative estimation of the plaque morphology was performed at ×40 magnification for macrophage infiltration (CD68), smooth muscle cell content (α-actin), amount of collagen (picrosirius red), and calcification (hematoxylin and eosin [H&E]). Histological plaque characteristics were scored as (1) no or minor staining or (2) moderate or heavy staining.11 The criteria for classification were defined as follows: for macrophages: (1) absent or minor CD68 staining with negative or clusters with <10 cells present; (2) moderate or heavy staining, cell clusters with >10 cells present or abundance of positive cells; for smooth muscle cells: (1) no or minor α-actin staining over the entire circumference with absent staining at parts of the circumference of the arterial wall; (2) positive cells along the circumference of the luminal border, with locally at least few scattering cells; for collagen staining: (1) no or minor staining along part of the luminal border of the plaque; (2) moderate or heavy staining along the entire luminal border; and for calcification: (1) no or minor staining along part of the luminal border of the plaque or a few scattered spots within the lesion; (2) moderate or heavy staining along the entire luminal border or evident parts within the lesion. In addition, macrophage infiltration and smooth muscle cell content were scored as the percentage of the total plaque area with the specific staining by using computerized analyses to validate the semiquantitative analyses. Plaque hemorrhage was defined as the composite of plaque bleeding at the luminal side of the plaque as a result of plaque disruption13 and intraplaque hemorrhage, which is observed as a hemorrhage within the tissue of the plaque. Plaque hemorrhage was examined in H&E and fibrin stainings and rated as being absent or present.13,14 Presumed artifacts of surgery such as accumulation of erythrocytes along the border of the specimen were not included in the definition of plaque hemorrhage. Intraplaque vessels were stained with CD34 antibody. Plaque vessel density was determined by the average number of vessels of 3 hot spots within every single plaque. A hot spot was defined as 1 high-power field at ×40 magnification. For vessel quantification, we used a grid (100×100 μm) overlying every hot spot to improve the reproducibility and to avoid counting vessels twice. The vessel density was determined by counting the number of vessels crossed by a bar of the grid within the selected hot spots. Increased vessel density was defined as an average vessel count per hot spot higher than the median (=8) of the cohort. The size of the lipid core was estimated visually as a percentage of total plaque area with the use of H&E and picrosirius red stains, with a division into 3 categories of <10%, 10% to 40% and >40% of the total plaque area, based on the correlation of the lipid core size and plaque stability.15 A panel of the histological plaque characteristics is shown in Figure 1.
The histological examinations were performed carefully on a regular basis after processing of the tissue by 2 independent observers, who were blinded for clinical outcome. The histological examination showed good to excellent intraobserver and interobserver reproducibility on the different items (κ=0.6 to 0.9).16 In addition, the stainings for macrophages and smooth muscle cells were scored quantitatively with the use of computer-based analyses. The semiquantitative and quantitative scorings revealed an excellent correlation.16
Follow-Up and Outcome
Definition of Outcome
The primary outcome was defined as any vascular event or vascular intervention.11 This composite end point included any death of presumed vascular origin (fatal stroke, fatal myocardial infarction, sudden death, other vascular death), nonfatal stroke, nonfatal myocardial infarction, and any arterial vascular intervention that had not already been planned at the time of inclusion (eg, carotid surgery or angioplasty/stenting, coronary bypass, percutaneous coronary intervention, peripheral vascular surgery or angioplasty/stenting). For additional subgroup analyses, the primary outcome was divided into the outcome events for separate vascular territories: stroke, coronary event (myocardial infarction or coronary intervention), peripheral vascular intervention (all vascular interventions except coronary interventions), and nonstroke vascular event (primary end point except stroke). Perioperative events were defined as outcome events occurring ≤30 days after surgery.
After CEA, all patients underwent clinical follow-up. First, all perioperative adverse events were recorded from the patient charts. At 1, 2, and 3 years after the operation, patients received a questionnaire inquiring whether patients had experienced any vascular event or had been hospitalized in the past year. If any of these was answered positively, further research was performed to investigate the potential outcome of the event. Following a standard scheme, discharge letters and, if needed, laboratory measurements and results of additional studies such as ECGs or imaging studies were collected from the institution where the event occurred. If patients did not respond to the follow-up questionnaire, the general practitioner was contacted. For each potential outcome event, all available information was assessed by 2 members of the outcome assessment committee. If the 2 members disagreed in regard to whether the criteria for the outcome event were met, a third opinion was requested.
Statistics and Data Analysis
SPSS 15.0 was used for all analyses (SPSS Inc, Chicago, Ill). Kaplan–Meier survival analysis was used to obtain cumulative event rates. The survival curves were compared between the 2 groups (no/minor versus moderate/heavy staining) for each plaque characteristic or between absent versus present for plaque hemorrhage. The Kaplan–Meier estimate of cumulative event rate at 1, 2, and 3 years after CEA and the corresponding risk difference according to plaque characteristics at baseline were calculated. Single predictor analyses were used to obtain the hazard ratio (HR) with 95% confidence interval (CI). Additionally, we related perioperative events, defined as primary outcome within 30 days after the index procedure, to baseline plaque characteristics in 2×2 tables with the χ2 test to assess statistically significant associations. In a more detailed analysis, plaque characteristics were also studied in relation to vascular outcomes in the different vascular territories. To adjust for potential confounders, we performed single predictor analyses to assess the HR for each clinical determinant separately in relation to clinical outcome. Potential confounders showing statistically significant association (P<0.05) at baseline or with primary outcome were included in a multivariable Cox proportional hazards model, with backward elimination of nonsignificant variables based on the likelihood ratio, with P<0.10 used as the cutoff value. Determinants with P<0.05 or a 95% CI not including 1 were regarded as statistically significant. The authors had full access to and take full responsibility for the integrity of the data. All authors have read and agree to the manuscript as written.
In total, 892 patients underwent CEA during the study period, of which 826 participated. Eight patients were lost to follow-up, resulting in a study cohort of 818 patients (Figure 2). During mean follow-up of 2.3 years (SD=1.2, maximum=4.7), 196 patients (24%) reached the primary outcome. The baseline characteristics are given in Table 1. Examination of the presence of plaque hemorrhage and vessel density in relation to baseline characteristics revealed significant associations with gender, hypertension, history of vascular intervention, bilateral stenosis, and statin and dipyridamole use. In addition, aspirin use did not reveal an association between plaque characteristics and was not related to outcome during follow-up (Table Ia in the online-only Data Supplement).
Plaque hemorrhage was associated with decreased smooth muscle cell content and increased lipid core size, and increased vessel density was positively associated with macrophage infiltration and smooth muscle cell content at baseline (Table Ib in the online-only Data Supplement). Plaque hemorrhage was observed in 69.9% (107/153) of the asymptomatic patients, which was increased in the number of patients who suffered from transient ischemic attack (71.4%, 342/479) and stroke (76.3%, 142/186). Increased vessel density in relation to clinical presentation did not reveal differences between asymptomatic patients (50.0%, 73/146) and patients who suffered from transient ischemic attack (49.4%, 229/464) or stroke (50.8%, 95/185) (Table Ia in the online-only Data Supplement).
Examination of the CEA specimens in relation to the clinical follow-up revealed that macrophage infiltration and lipid core size in the dissected carotid plaque showed no association with the primary outcome (Figure 3⇓ and Table 2). Confirming earlier observations,17 lipid core size was associated with perioperative events: 41/644 (6.4%) for lipid core ≥10% versus 4/174 (2.3%) for lipid core <10% of plaque area (relative risk=2.8; 95% CI, 1.1 to 7.6). Smooth muscle cell and macrophage infiltration, collagen content, and extent of calcifications in the plaque were not associated with the primary outcome or perioperative events (Table 2).
The presence of plaque hemorrhage was related to a higher event rate during follow-up. The Kaplan–Meier estimate of 3-year risk was 30.6% in patients whose plaque revealed the presence of plaque hemorrhage at baseline versus 17.2% in patients with a plaque not having any plaque hemorrhage (HR=1.7; 95% CI, 1.2 to 2.5). The risk difference was not due to difference in perioperative events (n=45): 10/227 (4.4%) versus 35/591 (5.9%; risk difference =+1.5%; 95% CI, −1.8% to +4.8%) and increased with time, at +3.8% at 1 year, +7.7% at 2 years, and +13.4% at 3 years. When perioperative events were excluded from the analysis, the relation between plaque hemorrhage and the primary outcome remained intact; the Kaplan–Meier estimate of cumulative event rate was 14.3% (no plaque hemorrhage) versus 25.7% (plaque hemorrhage; HR=1.7; 95% CI, 1.2 to 2.6). Thirty-five patients with plaque hemorrhage reached a primary perioperative end point versus 10 without plaque hemorrhage (Table II in the online-only Data Supplement). Six patients with plaque hemorrhage died within 30 days after CEA versus 1 without plaque hemorrhage. Additionally, we performed analyses of plaque hemorrhage at baseline versus outcome in the different vascular territories: stroke, coronary events, peripheral interventions, and nonstroke vascular events. Table III in the online-only Data Supplement shows that the positive association between plaque hemorrhage and clinical outcome was observed for events originating from the different individual vascular territories.
Increased plaque vessel density was also related to a higher event rate during follow-up. The 3-year risk was 30% in patients with a plaque demonstrating increased vessel density compared with 23.8% in patients with a plaque demonstrating vessel density below the median of the group (HR=1.4; 95% CI, 1.1 to 1.9). Increased plaque vessel density was associated with increased occurrence of perioperative events: 28/396 (7.1%) versus 15/399 (3.8%; risk difference=+3.3%; 95% CI, +0.2% to +5.5%); rates were +7.8% at 1 year, +5.9% at 2 years, and +6.2% at 3 years. Because the risk difference was predominantly established early after CEA and did not increase significantly over time, we assumed that the clinical outcome was related to the event rate within 30 days after surgery. Twenty-eight patients with increased plaque vessel density reached a perioperative end point in comparison with 15 patients with decreased plaque vessel density (Table II in the online-only Data Supplement). Four patients with increased plaque vessel density died versus 3 with decreased plaque vessel density. An evident difference in perioperative cerebral events was observed in favor of patients with decreased vessel density. Additional analyzes confirmed these observations and revealed that vessel density was not associated with outcome when perioperative events were excluded (HR=1.2; 95% CI, 0.9 to 1.7). In addition, increased vessel density was not associated with clinical outcome in different vascular regions, except stroke (HR=2.0; 95% CI, 1.2 to 3.4).
To investigate potential confounding factors and to assess independence of the 2 histological determinants, we adjusted the relation between plaque hemorrhage and vessel density with clinical outcome for potential confounding factors. In our patient group, parameters that were significantly related to plaque hemorrhage and vessel density at baseline (gender, previous vascular intervention, bilateral carotid stenosis, hypertension, statin and dipyridamole use, and C-reactive protein and high-density lipoprotein levels) (Tables Ia and IV in the online-only Data Supplement) or those that were associated with clinical outcome were included in the multivariate model to determine the adjusted HRs for both histological characteristics: previous myocardial infarction and aspirin and oral anticoagulant use. The adjusted HRs for plaque hemorrhage and vessel density were 2.2 (95% CI, 1.3 to 3.9) and 1.5 (95% CI, 1.1 to 2.1), respectively. The predictive value of plaque hemorrhage and increased vessel density was independent of high-sensitivity C-reactive protein plasma levels, which were not associated with adverse secondary cardiovascular outcome (Table 3).
Athero-Express is the first study to relate the composition of locally dissected plaques to clinical follow-up. In this longitudinal study, we found that plaque hemorrhage and increased vessel density in a single carotid artery plaque is predictive of systemic cardiovascular outcome. The association of plaque hemorrhage and intraplaque vessel density with clinical outcome could not be explained by traditional risk factors or other potential confounders.
The relation between plaque composition and clinical outcome has several implications. There remains a pressing need for diagnostic tools to identify vulnerable patients at high risk for future cardiovascular events.18 Epidemiological approaches that link systemic markers to outcome, such as C-reactive protein,7 have yielded limited predictive value thus far, and clinical application is lacking. Therefore, research focus has shifted to identify more specific markers of cardiovascular vulnerability. When results from autopsy series are considered,19 the presence of characteristics such as large lipid core and marked inflammation, the so-called vulnerable plaque characteristics, is thought to portray an increased risk of plaque rupture and thus clinical events. However, longitudinal imaging studies that are obligatory for validation of this concept for risk prediction are lacking.
In the present study, we followed a different approach. We assumed that plaque characteristics may show similarities among vascular territories. Subsequently, we related local histological plaque characteristics to all clinical events due to progression of atherosclerotic disease.
We show that macrophage infiltration and large lipid core in local plaques, which are considered hallmark features of the vulnerable plaque, are not predictive of systemic cardiovascular outcome. In contrast, local plaque hemorrhage was shown to be an independent predictor of outcome. Because the endarterectomy specimens are frequently fragmented, it is difficult to determine the exact source of plaque hemorrhage. We defined plaque hemorrhage as the combination of plaque bleeding at the luminal site due to plaque disruption, as discussed by Schwartz et al,13 and intraplaque hemorrhage as a result of defective intraplaque vessels. In addition, in the early 1980s, Barger et al20 suggested that atherosclerotic coronary arteries are associated with increased presence of vasa vasorum, and because we know that plaque neovascularization is strongly associated with plaque progression and is likely the primary source of plaque hemorrhages, we quantified plaque vessel formation as a potential predictive determinant for cardiovascular outcome.21
The outcome of the present study can be applied clinically in different ways. The predictive value of plaque hemorrhage and intraplaque vessel density could enable early identification of the vulnerable patient and provides opportunities for prognostic imaging modalities. Plaque hemorrhage and intimal vessel density could serve as targets for plaque imaging, with the objective of serving as biomarker for future cardiovascular events. Local carotid hemorrhage detection and plaque vascularization could serve as surrogate end points in clinical studies to examine disease progression or drug efficacy. With the use of magnetic resonance direct plaque hemorrhage imaging, visualization of plaque hemorrhage is feasible.22 A pilot study has already suggested that magnetic resonance imaging–detected plaque hemorrhage was associated with adverse clinical events during follow-up.23 Furthermore, histopathological examination of atherosclerotic plaques excised during surgical interventions is not common practice. This study and our previous report24 clearly demonstrate that thrombotic, inflammatory, and lipid components and vessel density hold prognostic value for future cardiovascular events or restenosis development and therefore strengthen the idea that pathological examination of dissected plaques should be executed after surgery because it provides important prognostic information.
Several findings support our hypothesis that the composition of a single atherosclerotic plaque could hold predictive value for systemic cardiovascular outcome. Atherosclerosis is a systemic disease,8,9 and the plaque composition correlates between different vascular beds, in both coronary and peripheral arteries.10 The results of this longitudinal study confirm earlier hypotheses raised by cross-sectional studies that suggest that plaque hemorrhage is an important source of progression of atherosclerotic disease.25 Although unproven, a tendency for systemic intraplaque bleeding would explain the association between local (intra)plaque hemorrhage and clinical outcome in our study. Furthermore, plaque hemorrhages can also cause severe disruption of plaque integrity and thereby accelerate thrombosis with associated clinical events.26 Our observations support the current idea that plaque hemorrhage may be an important determinant of plaque growth and disease progression. The finding that increased plaque vessel density is associated with worse cardiovascular outcome is in agreement with the observation that plaque hemorrhage is an independent predictor because neovessels may serve as the primary source of intraplaque hemorrhages. The presence of plague hemorrhage and vessel density were significantly correlated; however, further research is needed to elaborate on this subject. In addition, statin use was also independently associated with clinical outcome. However, we believe that we may not draw inferences relative to statin use and clinical outcome because statins are prescribed to those patients at higher risk and with more previous events.
To our knowledge, no studies investigating plaque histology in relation to clinical outcome have been conducted previously. Most imaging studies, however, focus on local plaque composition to predict local outcome (eg, the composition of coronary plaques in relation to future myocardial infarction in the corresponding territory). The Integrated Biomarker and Imaging Study (IBIS) performed intravascular ultrasound and intravascular ultrasound–based elastography and correlated the baseline findings to 6-month follow-up.27 After 6 months of follow-up, no difference in intravascular ultrasound–detected lumen and plaque dimensions was found in the coronary system, probably because of limited patient number and limited follow-up duration. More advanced plaque imaging techniques and improvement of current techniques, such as high-resolution magnetic resonance imaging, as well as large-scale follow-up studies with plaque imaging are needed to help to characterize plaques in vivo and thus enable the evaluation of the natural history of plaque progression toward instability and associated clinical manifestations noninvasively.28
Our study has some potential weaknesses. As mentioned previously, the carotid plaque was excised, and therefore, by definition, we could not link the carotid plaque composition to local clinical outcome (ie, stroke) or local plaque progression. Patients who had bilateral stenoses and who were operated on the contralateral side (n=23; 2.8%) were included as different samples, and follow-up was scored for both. Because this is a minority of the study population, we believe that this has not influenced the outcome of the study. The present study also has unique strengths. It encompasses the largest cohort of patients presented thus far whose carotid plaque was examined with the use of the gold standard of histology. Second, the plaque histology was linked to clinical follow-up, which has been lacking in studies conducted thus far. Because the assessments of the plaque hemorrhages revealed signs of organization, which indicates that the plaque hemorrhage was not an artifact due to surgical dissection, we assume that the predictive value is not due to artifacts caused by dissection of the plaque.
In conclusion, this is the first study investigating the histological composition of local atherosclerotic plaques in relation to clinical outcome in a longitudinal study. We report that the presence of plaque hemorrhage and increased vessel density in the CEA specimen are independently associated with increased risk of future cardiovascular events. The outcome provides unique clinical opportunities for prediction of secondary events in the vulnerable patient as well as guidance for new diagnostic imaging modalities.
Sources of Funding
This work was supported by the European Union (grant EU OIF21773). This study was funded by the University Medical Center of Utrecht and the Interuniversity Cardiology Institute of the Netherlands. The University Medical Center of Utrecht and the Interuniversity Cardiology Institute of the Netherlands had no role in the design and conduct of the study; in the collection, analysis, and interpretation of the data; or in the preparation or approval of the manuscript.
The concept of the predictive value of local plaque markers in relation to clinical outcome has been incorporated in a start-up company, Cavadis. Drs Pasterkamp, Moll, van der Spek, and de Kleijn are cofounders of Cavadis B.V. The remaining authors report no conflicts.
Davies MJ. The pathophysiology of acute coronary syndromes. Heart. 2000; 83: 361–366.
Falk E, Shah PK, Fuster V. Coronary plaque disruption. Circulation. 1995; 92: 657–671.
Lee RT, Libby P. The unstable atheroma. Arterioscler Thromb Vasc Biol. 1997; 17: 1859–1867.
Schaar JA, Muller JE, Falk E, Virmani R, Fuster V, Serruys PW, Colombo A, Stefanadis C, Ward CS, Moreno PR, Maseri A, van der Steen AF. Terminology for high-risk and vulnerable coronary artery plaques: report of a meeting on the vulnerable plaque, June 17 and 18, 2003, Santorini, Greece. Eur Heart J. 2004; 25: 1077–1082.
Verhoeven BA, Velema E, Schoneveld AH, de Vries JP, de Bruin P, Seldenrijk CA, de Kleijn DP, Busser E, van der GY, Moll F, Pasterkamp G. Athero-express: differential atherosclerotic plaque expression of mRNA and protein in relation to cardiovascular events and patient characteristics: rationale and design. Eur J Epidemiol. 2004; 19: 1127–1133.
Grant EG, Benson CB, Moneta GL, Alexandrov AV, Baker JD, Bluth EI, Carroll BA, Eliasziw M, Gocke J, Hertzberg BS, Katanick S, Needleman L, Pellerito J, Polak JF, Rholl KS, Wooster DL, Zierler RE. Carotid artery stenosis: gray-scale and Doppler US diagnosis: Society of Radiologists in Ultrasound Consensus Conference. Radiology. 2003; 229: 340–346.
Schwartz SM, Galis ZS, Rosenfeld ME, Falk E. Plaque rupture in humans and mice. Arterioscler Thromb Vasc Biol. 2007; 27: 705–713.
Davies MJ, Richardson PD, Woolf N, Katz DR, Mann J. Risk of thrombosis in human atherosclerotic plaques: role of extracellular lipid, macrophage, and smooth muscle cell content. Br Heart J. 1993; 69: 377–381.
Verhoeven BA, de Vries JP, Pasterkamp G, Ackerstaff RG, Schoneveld AH, Velema E, de Kleijn DP, Moll FL. Carotid atherosclerotic plaque characteristics are associated with microembolization during carotid endarterectomy and procedural outcome. Stroke. 2005; 36: 1735–1740.
Naghavi M, Libby P, Falk E, Casscells SW, Litovsky S, Rumberger J, Badimon JJ, Stefanadis C, Moreno P, Pasterkamp G, Fayad Z, Stone PH, Waxman S, Raggi P, Madjid M, Zarrabi A, Burke A, Yuan C, Fitzgerald PJ, Siscovick DS, De Korte CL, Aikawa M, Juhani Airaksinen KE, Assmann G, Becker CR, Chesebro JH, Farb A, Galis ZS, Jackson C, Jang IK, Koenig W, Lodder RA, March K, Demirovic J, Navab M, Priori SG, Rekhter MD, Bahr R, Grundy SM, Mehran R, Colombo A, Boerwinkle E, Ballantyne C, Insull W Jr, Schwartz RS, Vogel R, Serruys PW, Hansson GK, Faxon DP, Kaul S, Drexler H, Greenland P, Muller JE, Virmani R, Ridker PM, Zipes DP, Shah PK, Willerson JT. From vulnerable plaque to vulnerable patient: a call for new definitions and risk assessment strategies, part I. Circulation. 2003; 108: 1664–1672.
Virmani R, Kolodgie FD, Burke AP, Farb A, Schwartz SM. Lessons from sudden coronary death: a comprehensive morphological classification scheme for atherosclerotic lesions. Arterioscler Thromb Vasc Biol. 2000; 20: 1262–1275.
Virmani R, Kolodgie FD, Burke AP, Finn AV, Gold HK, Tulenko TN, Wrenn SP, Narula J. Atherosclerotic plaque progression and vulnerability to rupture: angiogenesis as a source of intraplaque hemorrhage. Arterioscler Thromb Vasc Biol. 2005; 25: 2054–2061.
Moody AR, Murphy RE, Morgan PS, Martel AL, Delay GS, Allder S, MacSweeney ST, Tennant WG, Gladman J, Lowe J, Hunt BJ. Characterization of complicated carotid plaque with magnetic resonance direct thrombus imaging in patients with cerebral ischemia. Circulation. 2003; 107: 3047–3052.
Takaya N, Yuan C, Chu B, Saam T, Underhill H, Cai J, Tran N, Polissar NL, Isaac C, Ferguson MS, Garden GA, Cramer SC, Maravilla KR, Hashimoto B, Hatsukami TS. Association between carotid plaque characteristics and subsequent ischemic cerebrovascular events: a prospective assessment with MRI: initial results. Stroke. 2006; 37: 818–823.
van Mieghem CA, McFadden EP, de Feyter PJ, Bruining N, Schaar JA, Mollet NR, Cademartiri F, Goedhart D, de Winter S, Granillo GR, Valgimigli M, Mastik F, van der Steen AF, van der Giessen WJ, Sianos G, Backx B, Morel MA, van Es GA, Zalewski A, Serruys PW. Noninvasive detection of subclinical coronary atherosclerosis coupled with assessment of changes in plaque characteristics using novel invasive imaging modalities: the Integrated Biomarker and Imaging Study (IBIS). J Am Coll Cardiol. 2006; 47: 1134–1142.
Postmortem studies have revealed plaque characteristics that are associated with clinical cardiovascular events. However, the prognostic value of the vulnerable plaque characteristics for the development of a cardiovascular event is unknown because prospective studies are lacking. Atherosclerosis is considered a systemic disease. Currently, most research focuses on the local plaque characteristics as a determinant of future plaque thrombosis. In this study, we followed a different concept. We assumed that local atherosclerotic lesions hold cellular and molecular information that reflects the stability of atherosclerotic lesions in all other vascular territories. Therefore, we performed a prospective study investigating whether the morphology of the local atherosclerotic carotid plaque enables identification of patients who are at increased risk to suffer from a cardiovascular event within 3 years after carotid endarterectomy. This innovative approach would facilitate risk stratification for systemic cardiovascular events in patients after carotid endarterectomy. In addition, plaque characteristics may serve as imaging targets for diagnostic applications. In the present study, we show for the first time that plaque hemorrhage and increased vessel density in a local atherosclerotic lesion are associated with increased risk for cardiovascular events. This study shows that local vascular plaque tissue that is dissected during vascular surgery procedures holds prognostic information. In addition, this study supports the concept that plaque revascularization and intraplaque bleeding are a hallmark of the progression of the disease. Following this concept, molecular local plaque studies could be considered that reveal targets for individual risk stratification, imaging applications, and pharmaceutical interventions to prevent acute clinical manifestations of atherosclerotic disease.
↵*The first 2 authors contributed equally to this work.
The online-only Data Supplement is available with this article at http://circ.ahajournals.org/cgi/content/full/CIRCULATIONAHA.109.887497/DC1.