© Copyright 2009 by the American Association for Clinical Chemistry

Plasma Myeloperoxidase Predicts Incident CardiovascularRisks in Stable Patients Undergoing Medical Managementfor Coronary Artery Disease

W.H.W. Tang, Y. Wu, S.J. Nicholls, and S.L. Hazen

January 2011

http://www.clinchem.org/cgi/reprint/57/1/33

© Copyright 2011 by the American Association for Clinical Chemistry

Journal ClubJournal Club

© Copyright 2009 by the American Association for Clinical Chemistry

IntroductionIntroduction

Atherosclerotic coronary artery disease (CAD)Medical management common in stable CAD• COURAGE trial showed equivalent outcomes when managed

either with aggressive medical management versus revascularization.

Risk stratification for aggressive managementBiomarker identification of high-risk individuals

• JUPITER trial showed early statin therapy in patients with increased high-sensitivity C-reactive protein (hsCRP) leads to improved outcomes.

© Copyright 2009 by the American Association for Clinical Chemistry

Introduction (con’t)Introduction (con’t)

Myeloperoxidase (MPO)Potential marker of plaque vulnerability• Hemoprotein enzyme stored within neutrophils, monocytes,

and certain tissue macrophages.

• Released during leukocyte activation.

• Produces hypochlorous acid as part of the innate host defense.

• Enriched in atherosclerotic plaque and culprit lesions.

• Prognostic value seen in setting of acute coronary syndrome.

Study Objective• To examine the potential for plasma MPO concentrations to

identify who may be at heightened long-term risk among stable CAD patients in the setting of aggressive medical therapy.

© Copyright 2009 by the American Association for Clinical Chemistry

QuestionsQuestions

What is an appropriate patient population to test the clinical utility of a biomarker for risk stratification?

How do you test a specific biomarker in the setting of existing clinical practice strategies of clinical and biochemical risk stratification?

© Copyright 2009 by the American Association for Clinical Chemistry

Materials and MethodsMaterials and MethodsStudy Population

Cleveland Clinic GeneBank study• Prospective cohort from 2001-6.• Stable individuals undergoing either cardiac catheterization or

coronary computed tomography angiography for evaluation.• Current study included 2,460 consecutive individuals without

evidence of myocardial infarction (cardiac troponin I <0.03 g/L) with significant CAD (50% stenosis at any coronary artery).

• Excluded patients with revascularization within 30 days before or after procedure.

Endpoint: Major Adverse Cardiovascular Event (MACE)• Death, non-fatal myocardial infarction, non-fatal

cerebrovascular accident over ensuing 3 years.

© Copyright 2009 by the American Association for Clinical Chemistry

Materials and Methods (con’t)Materials and Methods (con’t)

Plasma MPO AssayAbbott Architect ci8200• Analyzed venous blood samples collected in EDTA tubes

stored at -80F• Chemiluminescent automated immunoassay using MPO-

specific monoclonal antibodies in a 2-step sandwich format• Dynamic range of 0–10,000 pmol/L• Limit of detection <20.0 pmol/L• Functional sensitivity of < 50.0 pmol/L• Total CV 20%

© Copyright 2009 by the American Association for Clinical Chemistry

Materials and Methods (con’t)Materials and Methods (con’t)Statistical Analysis

• Between group comparison with student t-test or Wilcoxon rank-sum test for continuous variables, χ2 test for categorical variables.

• Cochran-Armitage test for trend analyses across quartiles• ROC curve analyses and 5-fold cross validation to determine

optimal MPO cut-off. • Kaplan-Meier survival analysis with log-rank test according to

MPO and MPO/hsCRP cut-off values.• Cox proportional hazard regression analysis with covariates

including traditional risk factors, hsCRP, and creatinine clearance.

• Pencina method for reclassification analysis, using ratio of 6:3:1 categorization due to non-parametric distribution of MPO.

• Performed using R 2.8.0, p<0.05 as statistical significance.

© Copyright 2009 by the American Association for Clinical Chemistry

QuestionsQuestions

What are the statistical analyses that can provide the best bedside clinical relevance for a clinical test?

What are the strengths and limitations of a single cut-off value for a clinical test for the purpose of risk stratification?

What are the strengths and limitations of novel statistical analyses for biomarkers?

© Copyright 2009 by the American Association for Clinical Chemistry

ResultsResults

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ResultsResults

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ResultsResults

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ResultsResults

© Copyright 2009 by the American Association for Clinical Chemistry

ResultsResults

© Copyright 2009 by the American Association for Clinical Chemistry

Results (con’t)Results (con’t)

Correlation Analyses• Weak correlation between MPO and hsCRP (r = 0.186;

p<0.0001)

Novel Statistical Analyses• Area under ROC curve (AUC) was 67%• Integrated discrimination improvement (IDI) of 10% (p<0.001)• Event-specific net reclassification (NRI) of 6% (p=0.022)

© Copyright 2009 by the American Association for Clinical Chemistry

DiscussionDiscussion

Conclusions1. Plasma MPO concentration provide independent prognostic value

for the prediction of long-term incident major adverse cardiovascular events in a stable, medically managed patient population with coronary artery disease.

2. In individuals with increased hsCRP concentrations, we observed lower risk of incident MACEs when concomitant MPO concentrations were lower versus when MPO concentrations were higher.

© Copyright 2009 by the American Association for Clinical Chemistry

Discussion (con’t)Discussion (con’t)

Take-Home Messages:

• Different biomarkers may provide distinctive insights into underlying pathophysiology.

• Identification of intermediate risk patients may provide useful clinical insights into individual disease states.

• Clinical significance of a specific biomarker requires appropriate clinical interpretation of patient populations being studied, with the support of rigorous statistical justification.

• Standard statistical analyses techniques provide quantification of incremental risk, but are difficult to apply in clinical setting.