Cardiac Biomarkers: Past, Present and Future

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Cardiac BiomarkersPast, Present and Future

• Jeff Sparling, M.D.
• University of Oklahoma Department of Internal
  Medicine

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Outline

• Overview
• History of cardiac clinical biochemistry
• Current techniques
• Markers of Cardiac Necrosis
• Natriuretic Peptides
• Prognostic Markers and Risk Stratification
• Future research and development
• Questions

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History

• 1950s Clinical reports that transaminases
  released from dying myocytes could be detected
  via laboratory testing, aiding in the diagnosis
  of myocardial infarction1
• The race to define clinical markers to aid in the
  diagnosis, prognosis, and risk stratification of
  patients with potential cardiovascular disease
  begins
• 1 Circulation 108250-252

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History

• Initial serum markers included AST, LDH, total CK
  and a-hydroxybutyrate
• These enzymes are all released in varying amounts
  by dying myocytes
• Lack of sensitivity and specificity for cardiac
  muscle necrosis fuels continued research

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History CK and Isoenzymes

• CK known to be released during muscle necrosis
  (including cardiac)
• Quantitative assays were cumbersome and difficult
  to perform
• Total CK designed as a fast, reproducible
  spectrophotometric assay in the late 1960s

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History CK and Isoenzymes

• CK isoenzymes are subsequently described
• MM, MB and BB fractions
• 1970s MB fraction noted to be elevated in and
  highly specific for acute MI1
• 1 Clinical Chemistry 50(11) 2205-2213

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History CK and Isoenzymes

• CKMB now measured via a highly sensitive
  monoclonal antibody assay
• It was felt for a time that quantitative CKMB
  determination could be used to enzymatically
  measure the size of an infarct
• This has been complicated by release of
  additional enzymes during reperfusion

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History CK and Isoenzymes

• As CK-MB assays become more sensitive,
  researchers come to the paradoxical realization
  that it too is not totally cardiac specific
• The MB fraction is determined to be expressed in
  skeletal muscle, particularly during the process
  of muscle regeneration
• The search for cardiac specificity continues
• Clinical Chemistry 50(11) 2205-2213

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History

• Research turns towards isolation of and
  development of assays for sarcomeric proteins
• Myosin light chains were originally isolated and
  then subsequently abandoned because of
  specificity issues

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History Troponin

• Troponin I first described as a biomarker
  specific for AMI in 19871 Troponin T in 19892
• Now the biochemical gold standard for the
  diagnosis of acute myocardial infarction via
  consensus of ESC/ACC
• 1 Am Heart J 113 1333-44
• 2 J Mol Cell Cardiol 21 1349-53

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History

• This work encourages development of other
  clinical assays for diagnosis and prognosis of a
  wide spectrum of cardiac diseases
• Notable examples
• BNP (FDA approved in November 2000 for diagnosis
  of CHF)
• C-reactive protein

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Markers of Cardiac Necrosis
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Markers of Cardiac Necrosis

• Cardiac biomarkers an integral part of the most
  recent joint ACC/ESC consensus statement on the
  definition of acute or recent MI

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Markers of Cardiac Necrosis

• Typical rise and gradual fall (troponin) or more
  rapid rise and fall (CK-MB) of biochemical
  markers of myocardial necrosis with at least (1)
  of the following
• Ischemic symptoms
• Development of pathologic Q waves
• ST segment elevation or depression
• Coronary artery intervention

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Markers of Cardiac Necrosis
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Troponins

• Troponin T (cTnT) and troponin I (cTnI) control
  the calcium-mediated interaction of actin and
  myosin
• cTnI completely specific for the heart
• cTnT released in small amounts by skeletal
  muscles, though clinical assays do not detect
  skeletal TnT

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Troponins

• The preferred biomarker for the diagnosis of
  acute MI
• Measurement carries a Class I recommendation from
  the ACC/AHA task force on diagnosis of AMI
• As with other biomarkers, do not wait on
  measurement of troponins in the setting of ST
  elevation

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Troponins
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Troponins

• 4-6 hours to rise post-infarct, similar to CKMB
• 6-9 hours to detect pathologic elevations in all
  patients with infarct
• Elevated levels can persist in blood for weeks
  the cardiac specificity of troponins thus make
  them the ideal marker for retrospective diagnosis
  of infarction

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Troponins

• Elevated serum levels are an independent
  predictor of prognosis, morbidity and mortality
• Meta-analysis of 21 studies involving 20,000
  patients with ACS revealed that those with
  elevated serum troponin had 3x risk of cardiac
  death or reinfarction at 30 days1
• 1 Am J Heart (140) 917

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Troponins GUSTO IV ACS

• Underscored the importance of the degree of
  troponin elevation
• 7000 patients stratified into quartiles based on
  degree of cTnT elevation
• 30-day mortality rate increased from 1.1 to 7.4
  over the first to fourth quartiles

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CK-MB

• High specificity for cardiac tissue
• The preferred marker for cardiac injury for many
  years
• Begins to rise 4-6 hours after infarction but can
  take up to 12 hours to become elevated in all
  patients with infarction
• Elevations return to baseline within 36-48 hours,
  in contrast to troponins

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CK and CK-MB
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CK-MB Shortcomings

• Concomitant skeletal muscle damage can confuse
  the issue of diagnosis
• CPR and defibrillation
• Cardiac and non-cardiac procedures
• Blunt chest trauma
• Cocaine abuse

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CKCK-MB Ratio

• Proposed to improve specificity for use in
  diagnosis of AMI
• Ratios 2.5-5 have been proposed
• Significantly reduces sensitivity in patients
  with both skeletal muscle and cardiac injury
• Also known to be misleading in the setting of
  hypothyroidism, renal failure, and chronic
  skeletal muscle diseases

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CK-MB and Reinfarction

• CK-MB is the marker of choice for diagnosis of
  reinfarction after STEMI, PCI, or CABG because of
  rapid washout
• The ACC/AHA definition of re-infarction includes
  both
• re-elevation of CK-MB
• supporting criteria including ECG changes, pain
  or hemodynamic instability

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Myoglobin

• Heme protein rapidly released from damaged muscle
• Elevations can be seen as early as one hour
  post-infarct
• Much less cardiac specific meant to be used as a
  marker protein for early diagnosis in conjunction
  with troponins

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Markers of Cardiac Necrosis in Chronic Kidney
Disease
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CKD

• CAD is highly prevalent in patients with CKD,
  making interpretation of cardiac markers
  important
• Despite this, interpretation of elevated cardiac
  enzymes in patients with renal failure is often
  confusing at best

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CKD and Elevated Troponins

• Elevations in serum troponin often observed in
  asymptomatic patients with chronic kidney disease
• Even using the most conservative cutoff values, a
  disproportionate number of patients still have
  elevated troponins
• The mechanism for this is unclear

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CKD and Elevated Troponins

• In a 2002 study in Circulation, 733 asymptomatic
  patients with ESRD were evaluated
• Using conservative cutoff values,
• 82 had elevated cTnT
• 6 had elevated cTnI
• Circulation 106 2941

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CKD and Elevated Troponins

• So, are these numbers meaningless, even in a
  patient population that is at such high risk?

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CKD and Elevated Troponins

• They provide important information with regards
  to prognosis
• Serial measurements are still of value in the
  patient with chest pain

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CKD and Elevated Troponins

• Of those 733 asymptomatic patients on HD, 2-year
  mortality rates were 52 in those with cTnI 0.1
  µg/dL
• These data have been corroborated in a number of
  smaller studies in similar populations
• Circulation 106 2941

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CKD and Elevated Troponins

• Serial measurements are helpful in the setting of
  possible ACS
• cTnI appears to be much less likely to be
  associated with false positives in the CKD
  population than cTnT, making it the preferred
  biomarker in this setting

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Natriuretic Peptides
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Natriuretic Peptides

• Present in two forms, atrial (ANP) and brain
  (BNP)
• BNP is used clinically because it exists in a
  much wider range of concentrations in varying
  clinical settings, making it easier to measure

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Natriuretic Peptides

• Both ANP and BNP have diuretic, natriuretic and
  hypotensive effects
• Both inhibit the renin-angiotensin system and
  renal sympathetic activity
• BNP is released from the cardiac ventricles in
  response to volume expansion and wall stress

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BNP Assay

• Approved by the FDA for diagnosis of cardiac
  causes of dysnpea
• Currently measured via a rapid, bedside
  immunofluorescence assay taking 10 minutes
• Especially useful in ruling out heart failure as
  a cause of dyspnea given its excellent negative
  predictive value

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BNP

• Came to market in 2000 based on data from many
  studies, primarily the Breathing Not Properly
  (BNP) study
• Prospective study of 1586 patients presenting to
  the ER with acute dyspnea
• The predictive value of BNP much superior to
  previous standards including radiographic,
  clinical exam, or Framingham Criteria

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Breathing Not Properly

• Important information about BNP from this study
  included
• Reduced the time and resources needed to diagnose
  heart failure
• BNP plasma concentration directly correlated with
  NYHA classification
• Heart failure due to diastolic dysfunction could
  be diagnosed, though not differentiated from
  systolic dysfunction

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Breathing Not ProperlyBNP useful in screening?

• The utility of BNP as a mass screening tool for
  LV dysfunction in asymptomatic persons was
  negligible

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BNP

• BNP has also shown utility as a prognostic marker
  in acute coronary syndrome
• It is associated with increased risk of death at
  10 months as concentration at 40 hours
  post-infarct increased
• Also associated with increased risk for new or
  recurrent MI

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BNP and ACS Risk Assessment

• PRISM 1,791 patients with non-ST elevation ACS1
• NT-proBNP levels that were elevated from baseline
  at 48 and 72 hours associated with higher event
  rates at 30 days
• Patients with negative Troponin T and elevated
  NT-proBNP levels had risk comparable to
  TnT-positive patients
• 1Circulation 110 3206-3212

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BNP and Chronic Kidney Disease

• I should be able to cover this topic completely
  in 1 or 2 slides without causing any controversy,
  right?

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• Wrong.

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Prognostic Markers and Markers of Risk
Stratification
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Prognostic Markers and Markers of Risk
Stratification

• C-reactive protein
• Myeloperoxidase
• Homocysteine
• Glomerular filtration rate

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C-Reactive Protein

• Multiple roles in cardiovascular disease have
  been examined
• Screening for cardiovascular risk in otherwise
  healthy men and women
• Predictive value of CRP levels for disease
  severity in pre-existing CAD
• Prognostic value in ACS

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C-Reactive Protein

• Pentameric structure consisting of five 23-kDa
  identical subunits
• Produced primarily in hepatocytes
• Plasma levels can increase rapidly to 1000x
  baseline levels in response to acute inflammation
  
• Positive acute phase reactant

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C-Reactive Protein

• Binds to multiple ligands, including many found
  in bacterial cell walls
• Once ligand-bound, CRP can
• Activate the classical compliment pathway
• Stimulate phagocytosis
• Bind to immunoglobulin receptors

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C-Reactive ProteinRisk Factor or Risk Marker?

• CRP previously known to be a marker of high risk
  in cardiovascular disease
• More recent data may implicate CRP as an actual
  mediator of atherogenesis
• Multiple hypotheses for the mechanism of
  CRP-mediated atherogenesis
• Endothelial dysfunction via ? NO synthesis
• ?LDL deposition in plaque by CRP-stimulated
  macrophages

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CRP and CV Risk

• Elevated levels predictive of
• Long-term risk of first MI
• Ischemic stroke
• PVD
• All-cause mortality
• This relationship persists even when data is
  adjusted for classic CV risk factors (age,
  tobacco, lipid levels, DM, and HTN)

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Limitations to CRP in Screening

• Low specificity
• What do you do with an elevated CRP?
• No evidence that lowering CRP levels decreases CV
  risk
• Some medications (statins and TZDs) do lower CRP
  levels unclear what the implication is

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CRP and Existing CAD

• Unclear of the role of CRP in stable CAD acute
  phase response not present in stable angina
• Predictive of worse short- and long-term
  prognosis in non-ST elevation ACS
• Possibly some correlation with poor outcomes
  post-CABG and post-PCI

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CRP ACC/AHA Recommendations

• Not useful as a public health measure screening
  the entire adult population should be avoided
• It is considered the inflammatory marker most
  useful in clinical practice
• Useful in guiding further evaluation in
  intermediate risk patients (10-20 risk of
  significant CAD in 10 years)

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CRP ACC/AHA Recommendations

• Should not determine the application of secondary
  prevention measures
• Serial measurements should not be used to gauge
  efficacy of treatment
• Measure hs-CRP serum levels in an outpatient
  setting twice (at least two weeks apart) and
  average the two levels

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Myeloperoxidase

• Released by activated leukocytes at elevated
  levels in vulnerable plaques
• Predicts cardiac risk independently of other
  markers of inflammation
• May be useful in triage of ACS (levels elevate in
  the 1st two hours)
• Also identifies patients at increased risk of CV
  event in the 6 months following a negative
  troponin
• NEJM 349 1595-1604

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Homocysteine

• Intermediary amino acid formed by the conversion
  of methionine to cysteine
• Moderate hyperhomocysteinemia occurs in 5-7 of
  the population
• Recognized as an independent risk factor for the
  development of atherosclerotic vascular disease
  and venous thrombosis
• Can result from genetic defects, drugs, vitamin
  deficiencies, or smoking

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Homocysteine

• Homocysteine implicated directly in vascular
  injury including
• Intimal thickening
• Disruption of elastic lamina
• Smooth muscle hypertrophy
• Platelet aggregation
• Vascular injury induced by leukocyte recruitment,
  foam cell formation, and inhibition of NO
  synthesis

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Homocysteine

• Elevated levels appear to be an independent risk
  factor, though less important than the classic CV
  risk factors
• Screening recommended in patients with premature
  CV disease (or unexplained DVT) and absence of
  other risk factors
• Treatment includes supplementation with folate,
  B6 and B12

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Glomerular Filtration Rate

• The relationship between chronic kidney disease
  and cardiovascular risk is longstanding
• Is this the result of multiple comorbid
  conditions (such as diabetes and hypertension),
  or is there an independent relationship?

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Glomerular Filtration Rate

• Recent studies have sought to identify whether
  creatinine clearance itself is inversely related
  to increased cardiovascular risk, independent of
  comorbid conditions

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Glomerular Filtration Rate

• Go, et al performed a cohort analysis of 1.12
  million adults in California with CKD that were
  not yet dialysis-dependent
• Their hypothesis was that GFR was an independent
  predictor of cardiovascular morbidity and
  mortality
• They noted a strong independent association
  between the two
• NEJM 351 1296-1305

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Glomerular Filtration Rate
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Glomerular Filtration Rate

• Reduced GFR has been associated with
• Increased inflammatory factors
• Abnormal lipoprotein levels
• Elevated plasma homocysteine
• Anemia
• Arterial stiffness
• Endothelial dysfunction

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So much information!

• What does it all mean?!?

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The Future of Cardiac Biomarkers

• Many experts are advocating the move towards a
  multimarker strategy for the purposes of
  diagnosis, prognosis, and treatment design
• As the pathophysiology of ACS is heterogeneous,
  so must be the diagnostic strategies

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Circulation 108 250-252
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2005 OKC Heart Walk

• Please donate! This years walk is April 30,
  2005
• Contact Jeff, Beau, Soni, or Ross for details
• Any amount helps!

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Any Questions?