C-reactive protein and clinical instability in carotid artery obstructive disease

Abstracts

CONTEXTO: A atividade inflamatória na aterosclerose vem sendo exaustivamente estudada; entretanto, a relevância da Proteína C Reativa como marcador de instabilidade clínica, na doença obstrutiva de artérias carótidas ainda não encontra-se bem estabelecido OBJETIVO: Identificar se os níveis séricos de proteína C reativa ultra-sensível se associam com a apresentação clínica (estável versus instável) da doença obstrutiva grave das artérias carótidas. MÉTODO: Foram estudados 70 pacientes consecutivos com indicação de endarterectomia de carótida pelos critérios dos ensaios NASCET ou ACST, com diferentes tipos de apresentação clínica: grupo 1- assintomáticos ou com sintomas hemisféricos com mais de 90 dias; grupo 2 - com sintomas hemisféricos com menos de 90 dias. Amostras de sangue de cada paciente foram obtidas por punção venosa periférica; a proteína C reativa ultra-sensível foi dosada por nefelometria e a comparação entre os grupos foi realizada através do teste de t de Student, considerando-se significativo o valor de p < 0,05. RESULTADOS: o quadro clínico neurológico foi considerado estável em 28 (40%) pacientes, enquanto que 42 (60%) dos casos foram considerados instáveis. Os valores de proteína C reativa ultra-sensível foram significativamente maiores nos pacientes clinicamente instáveis, quando comparados aos casos estáveis neurologicamente (1,54±1,7 versus 0,67±0,8 mg/dL, respectivamente; p = 0,006). Não houve diferença nos níveis de proteína C reativa ultra-sensível quando comparados os percentuais de estenose angiográfica. CONCLUSÕES: A constatação de que níveis elevados de proteína C reativa ultra-sensível correlacionam-se com instabilidade da placa de carótidas, possivelmente antevendo eventos clínicos, poderá contribuir para uma redefinição dos critérios de tratamento cirúrgico da doença cerebrovascular.

Proteína C reativa; carótida; aterosclerose; inflamação

ORIGINAL ARTICLE

C-reactive protein and clinical instability in carotid artery obstructive disease

Daniele de Oliveira Silva; Luciano Cabral Albuquerque; Luciane Barreneche Narvaes; Marco Antônio Goldani; Giuliano Chagas Pereira

Hospital São Lucas, Pontifícia Universidade Católica do Rio Grande do Sul (PUCRS), Porto Alegre, RS, Brazil

^{Correspondence}

ABSTRACT

BACKGROUND: Inflammatory activity in atherosclerosis has been exhaustively studied; however, the relevance of C-reactive protein as a marker of clinical instability in carotid artery obstructive disease has not been well established yet.

OBJECTIVE: To identify whether high-sensitivity C-reactive protein serum levels are associated with clinical presentation (stable vs. unstable) of carotid artery severe obstructive disease.

METHODS: Seventy consecutive patients underwent carotid endarterectomy based on NASCET or ACST criteria, and were classified according to clinical presentation: group 1 — asymptomatic or with hemispheric symptoms for more than 90 days; group 2 — with hemispheric symptoms for less than 90 days. Blood samples were collected by peripheral vein puncture; high-sensitivity C-reactive protein was dosed by nephelometry and comparison between groups was performed using Student's t test; p < 0.05 was considered significant.

RESULTS: Neurological clinical status was considered stable in 28 (40%) patients, whereas 42 (60%) cases were considered unstable. High-sensitivity C-reactive protein levels were significantly higher in clinically unstable patients, when compared with neurologically stable cases (1.54±1.7 vs. 0.67±0.8 mg/dL, respectively; p = 0.006). There was no difference in high-sensitivity C-reactive protein levels, when compared with percentages of angiographic stenosis.

CONCLUSIONS: The fact that high levels of high-sensitivity C-reactive protein are associated with unstable carotid plaque, possibly anticipating clinical events, could contribute to redefining indications for cerebrovascular interventions.

Keywords: C-reactive protein, carotid artery, atherosclerosis, inflammation.

Introduction

Atherosclerosis is a chronic process whose progression is predominantly silent, with local and systemic factors interacting to reduce or delay clinical events. In carotid artery obstructive disease, the catastrophic nature of strokes, currently a priority in public health in the developed world, justifies the growing concern about morphological, inflammatory and biochemical characteristics of the atheromatous plaque, which may occasionally identify vulnerable lesions.

Among inflammatory substances associated with atherogenesis, C-reactive protein (CRP) has stood out as the main biomarker of cardiovascular events.^1,2 The association between high CRP levels and cardiovascular prognosis was first demonstrated in acute coronary syndromes (ACS). The association between CRP serum concentration, histological and immunocytologic structure of carotid plaque and presence of neurological symptoms was judiciously investigated by Garcia et al. in 62 patients submitted to carotid endarterectomy (CE).³ Mean CRP was significantly higher in symptomatic cases and in those classified as unstable to histology (p < 0.001). These results corroborate use of CRP as a marker of carotid disease vulnerability.

This study aims at identifying the association between CRP serum levels and clinical presentation (stable vs. unstable) of carotid artery obstructive disease.

Methods

Patients

From October 2004 to June 2006 at Hospital São Lucas da PUCRS, 70 patients with atheromatous disease of the carotid artery were consecutively assessed. The patients had indication for surgery indicated by their respective assistant physicians, according to the following criteria: symptomatic patients with transient ischemic attack (TIA) or stroke, and carotid bifurcation stenosis estimated by nuclear magnetic resonance (NMR) angiography in at least 50% according to NASCET criteria;⁴ and asymptomatic patients with carotid bifurcation stenosis estimated by NMR in at least 70% according to ACST criteria.⁵ Exclusion criteria were patients with known infectious, inflammatory or autoimmune diseases, and those contraindicated to NMR. Cases of severe peripheral arterial disease (pain at rest, ischemic skin lesions or gangrene) were also excluded, as well as patients with ACS and those submitted to surgical or percutaneous interventions over the past 90 days. The study protocol was approved by the Ethics Committee at our institution and all patients signed a consent term before being included in the study.

Clinical characterization

The patients were classified before the procedure according to presence and evolution time of neurological manifestations, defined by a neurologist (M.F.) who was unaware of NMR data, as well as profile of serum markers. The patients were divided into two groups: (1) asymptomatic or with ipsilateral hemispheric symptoms for more than 90 days; or (2) ipsilateral hemispheric symptoms over the past 90 days.

In the sample of 70 assessed patients, mean age was 66±9 years, and most of the patients were male (66%) and hypertensive (89%); 46% had diabetes mellitus and 27% were active smokers. As to previous heart disease, 26% reported previous history of angina and 19% had suffered a myocardial infarction (AMI) in the past. Previous history of stroke or TIA was observed in 34 and 16% of cases, respectively (Table 1). In the assessment performed by a neurologist blinded to other findings, neurological clinical status was considered stable in 28 (40%) patients; 19 (27%) were asymptomatic and nine (13%) had previous ipsilateral ischemic events, whereas 42 (60%) of cases were considered unstable.

Although having established the criterion to classify the clinically unstable group in up to 90 days, all patients had manifestations up to 45 days of progression. Statins were being used in 69 patients (99%), and 46 (66%) cases were also taking some type of platelet antiaggregating drugs (acetylsalicylic acid, ticlopidine or clopidogrel).

CRP dose

At the operation room, before anesthetic induction, 20 mL of blood were collected from a peripheral vein and immediately sent for processing. CRP dose was performed by Behring CardioPhase nephelometry (Behring^®, Inc., Marburg, Germany), using monoclonal antibody for human CRP, in aliquot of cooled serum, as previously described.⁶ Results were expressed in mg/dL, and values greater than 0.3 were considered high.

Statistical analysis

Continuous variables with normal distribution were expressed as mean ± standard deviation and compared using Student's t test. CRP underwent logarithmic transformation because it did not have normal distribution, and was also compared using Student's t test. Categorical variables are expressed as frequencies and percentages. Two-tailed p < 0.05 was considered statistically significant. Analyses were performed using the statistical package SAS for Windows, version 8.0.

Results

CRP presented mean level of 1.2±1.5 mg/dL. CRP values were essentially identical in different carotid stenosis degrees assessed by nuclear resonance angiography (Figure 1), but they were significantly lower in clinically unstable patients, when compared with neurologically stable cases 1.54±1.7 vs. 0,67±0.8 mg/dL, respectively; p = 0.006 (Figure 2).

Discussion

Carotid bifurcation atheroma is the cause of 20-30% of ischemic strokes, and degree of angiographic stenosis is the predictive factor consensually used to indicate surgical intervention. However, recent evidence has demonstrated that carotid plaque vulnerability has no relationship with the obstructive nature of lesions, but is associated with immunoinflammatory response and structural, molecular and biochemical atheroma disruption.^7,8

Increased serum concentration of interleukins, CRP and other inflammatory markers has been currently proposed as an indication of presence or clinical instability in atherosclerosis, both at a local and systemic level.⁹ Association between high CRP levels and cardiovascular prognosis was first demonstrated in ACS, based on the evidence that high CRP levels were associated with ischemic episodes and worse progression, both early and late.^10,11 In patients after AMI, the CARE study¹² revealed increased risk of recurrent events or death when there are high CRP levels, which is in agreement with other authors.^13,14 In addition, CRP has been pointed in many studies as predictor of sudden death, cerebral infarction or development of lower limb obstructive arterial disease, although having a less powerful effect.^15-17

Previous studies have tried to demonstrate the correlation between increased CRP levels and presence and instability of cerebrovascular disease.. The role of CRP in predicting events was studied in a cohort study by Framingham, who correlated incidence of the first TIA episode or stroke with CRP serum quartiles. Throughout 14 years, upper quartile doubled the relative risk of outcomes in men and tripled it in women, independent of age, although there was predominance of elderly individuals in the sample (mean 70 years).¹⁶ Wang et al. demonstrated that development of plaques in the internal carotid artery, independent of clinical disease, was also significantly higher in CRP upper quartile.¹⁸ The association between CRP, carotid intima-media thickness and risk of stroke was prospectively assessed in 5,417 elderly patients by the Cardiovascular Health Study.¹⁹ There was a strong positive correlation between CRP levels and stroke in the highest thickening tertile (p < 0.02), which had already been demonstrated by Magyar et al. in a study of younger individuals.²⁰ It has also been suggested that increased CRP can be an independent predictor of death and recurrent events after the first episode of stroke.^21,22

The association between CRP, interleukin-6 and silent cerebral infarction was prospectively assessed in 194 patients with no signs of carotid and coronary disease or peripheral arteriopathy over a 10-year period. In 40 cases of small silent cerebral infarction, documented by brain magnetic resonance, CRP and IL-6 levels were significantly higher, suggesting a pro-inflammatory action of those mediators in intracranial arteries.²³

In the clinical setting, a systematic review conducted by the American Heart Association indicated the recommendations about using several inflammatory markers in atherosclerosis. As to CRP, it was concluded that its use cannot be justified as an independent predictor of events in the general population, but as an adjuvant in people with estimated risk of heart disease between 10-20% in 10 years.²⁴ However, extrapolation of such recommendations concerning cerebrovascular diseases showed that there is insufficient evidence for a CRP systematic use in primary prevention of strokes. In addition, a recent analysis of a subgroup of 6,430 patients from the Rotterdam Study demonstrated that CRP levels cannot predict individual risk of stroke yet.²⁵ For secondary prevention, there is prognostic value when associated with other factors, and its role as determinant of therapeutic decisions has not been established.²⁶

In this study, we assessed the behavior of CRP levels in patients submitted to CE. We defined clinical instability as patients with TIA or stroke occurred in up to 90 days of progression, with the aim of restricting this group to events directly associated with carotid plaque vulnerability. Patients with signs of unstable atherosclerotic disease in other arterial sites, such as coronary arteries or lower limbs, were also excluded from the analyses. Our results confirm the previously proposed relationship between high CRP levels and clinical instability. Similarly, Garcia et al. investigated the association between CRP serum concentration, histological and immunocytologic structure of the carotid artery plaque. Mean CRP was significantly higher in symptomatic cases, independent of evolution time of manifestations, and in those classified as unstable at microscopy, also showing a positive correlation with infiltration of macrophages and T lymphocytes in the plaque.³ We verified that current indication for carotid intervention, which especially considers stenosis percentage, does not seem to be the most accurate for clinical decision. The finding that high CRP levels can indicate carotid plaque instability can contribute to modification in current intervention criteria in cerebrovascular disease.

References

Manuscript received November 30, 2006, accepted March 8, 2007.

• 1. Jialal I, Devaraj S, Venugopal SK. C-reactive protein: risk marker or mediator in atherosclerosis? Hypertension. 2004;44:6-11.
• 2. Koenig W. Predicting risk and treatment benefit in atherosclerosis: the role of C-reactive protein. Int J Cardiol. 2005;98:199-206.
• 3. Alvarez Garcia B, Ruiz C, Chacon P, Sabin JA, Matas M. High-sensitivity C-reactive protein in high-grade carotid stenosis: risk marker for unstable carotid plaque. J Vasc Surg. 2003;38:1018-24.
• 4. Barnett HJ, Taylor DW, Eliasziw M, et al. Benefit of carotid endarterectomy in patients with symptomatic moderate or severe stenosis. North American Symptomatic Carotid Endarterectomy Trial Collaborators. N Engl J Med. 1998;339:1415-25.
• 5. Halliday A, Mansfield A, Marro J, et al. Prevention of disabling and fatal strokes by successful carotid endarterectomy in patients without recent neurological symptoms: randomized controlled trial. Lancet. 2004;363:1491-502.
• 6. Whicher JT, Ritchie RF, Johnson AM, et al. New international reference preparation for proteins in human serum (RPPHS). Clin Chem. 1994;40:934-8.
• 7. Fuster V, Moreno PR, Fayad ZA, Corti R, Badimon JJ. Atherothrombosis and high-risk plaque: part I: evolving concepts. J Am Coll Cardiol. 2005;46:937-54.
• 8. Rohde LE, Lee RT. Pathophysiology of atherosclerotic plaque development and rupture: an overview. Semin Vasc Med. 2003;3:347-54.
• 9. Ballantyne CM, Nambi V. Markers of inflammation and their clinical significance. Atheroscler Suppl. 2005;6:21-9.
• 10. Morrow DA, Rifai N, Antman EM, et al. C-reactive protein is a potent predictor of mortality independently of and in combination with troponin T in acute coronary syndromes: a TIMI 11A substudy. Thrombolysis in Myocardial Infarction. J Am Coll Cardiol. 1998;31:1460-5.
• 11. Heeschen C, Hamm CW, Bruemmer J, Simoons ML. Predictive value of C-reactive protein and troponin T in patients with unstable angina: a comparative analysis. CAPTURE investigators. Chimeric c7E3 AntiPlatelet Therapy in Unstable angina REfractory to standard treatment trial. J Am Coll Cardiol. 2000;35:1535-42.
• 12. Ridker PM, Rifai N, Pfeffer MA, et al. Inflammation, pravastatin, and the risk of coronary events after myocardial infarction in patients with average cholesterol levels. Cholesterol and Recurrent Events (CARE) Investigators. Circulation. 1998;98:839-44.
• 13. Retterstol L, Eikvar L, Bohn M, Bakken A, Erikssen J, Berg K. C-reactive protein predicts death in patients with previous premature myocardial infarction a 10 year follow-up study. Atherosclerosis. 2002;160:433-40.
• 14. Tomoda H, Aoki N. Prognostic value of C-reactive protein levels within six hours after the onset of acute myocardial infarction. Am Heart J. 2000;140:324-8.
• 15. Albert CM, Ma J, Rifai N, Stampfer MJ, Ridker PM. Prospective study of C-reactive protein, homocysteine and plasma lipid levels as predictors of sudden cardiac death. Circulation. 2002;105:2595-9.
• 16. Rost NS, Wolf PA, Kase CS, et al. Plasma concentration of C-reactive protein and risk of ischemic stroke and transient ischemic attack: the Framingham study. Stroke. 2001;32:2575-9.
• 17. Ridker PM, Cushman M, Stampfer MJ, Tracy RP, Hennekens CH. Plasma concentration of C-reactive protein and risk of developing peripheral vascular disease. Circulation. 1998;97:425-8.
• 18. Wang TJ, Nam BH, Wilson PW, et al. Association of C-reactive protein with carotid atherosclerosis in men and women: the Framingham Heart Study. Arterioscler Thromb Vasc Biol. 2002;22:1662-7.
• 19. Cao JJ, Thach C, Manolio TA, et al. C-reactive protein, carotid intima-media thickness, and incidence of ischemic stroke in the elderly: the Cardiovascular Health Study. Circulation. 2003;108:166-70.
• 20. Magyar MT, Szikszai Z, Balla J, et al. Early-onset carotid atherosclerosis in associated with increased intima-media thickness and elevated serum levels of inflammatory markers. Stroke. 2003;34:58-63.
• 21. Kocer A, Canbulat C, Gozke E, Ilhan A. C-reactive protein is an indicator for fatal outcomes in first-time stroke patients. Med Sci Monit. 2005;11:CR540-4.
• 22. Arenillas JF, Alvarez-Sabin J, Molina CA, et al. C-reactive protein predicts further ischemic events in first-ever transient ischemic attack or stroke patients with intracranial large-artery occlusive disease. Stroke. 2003;34:2463-8.
• 23. Hoshi T, Kitagawa K, Yamagami H, Furukado S, Hougaku H, Hori M. Relations of serum high-sensitivity C-reactive protein and interleukin-6 levels with silent brain infarction. Stroke. 2005;36:768-72.
• 24. Pearson TA, Mensah GA, Alexander RW, et al. Markers of inflammation and cardiovascular disease: application to clinical and public health practice. A statement for healthcare professionals from the Centers for Disease Control and Prevention and the American Heart Association. Circulation. 2003;107:499-511.
• 25. Bos MJ, Schipper CM, Koudstaal PJ, Witteman JC, Hofman A, Breteler MM. High serum C-reactive protein level is not an independent predictor for stroke: the Study. Circulation. 2006;114:1591-8.
• 26. Di Napoli M, Schwaninger M, Cappelli R, et al. Evaluation of C-reactive protein measurement for assessing the risk and prognosis in ischemic stroke: a statement for health care professionals from the CRP Pooling Project Members. Stroke. 2005;36:1316-29.

Publication Dates

• Publication in this collection
  20 Sept 2007
• Date of issue
  June 2007

History

• Received
  30 Nov 2006
• Accepted
  08 Mar 2007