Cardiac Biomarkers:

1
Cardiac Biomarkers
2
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

3
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

4
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

5
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

6
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

7
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

8
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

9
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

10
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

11
Markers of Cardiac Necrosis
12
What is Myocardial Infarction?

• Myocardial ischemia results from the reduction of
  coronary blood flow to an extent that leads to
  insufficiency of oxygen supply to myocardial
  tissue
• When this ischemia is prolonged irreversible,
  myocardial cell death necrosis occurs ---this
  is defined as
• myocardial infarction

13
Biochemical Changes in Acute Myocardial
Infarction(mechanism of release of myocardial
markers)

• ischemia to myocardial muscles (with low O2
  supply)
• anaerobic glycolysis
• increased accumulation of Lactate
• decrease in pH
• activate lysosomal enzymes
• disintegration of myocardial proteins
• cell death necrosis

ECG changes
release of intracellular contents to
blood BIOCHEMICAL MARKERS
clinical manifestations (chest pain)
14
Diagnosis of Myocardial Infarction

• SHOULD depend on THREE items
• (as recommended by WHO)
• 1- Clinical Manifestations
• 2- ECG
• 3- Biochemical Markers

15
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

16
Perfect Cardiac Marker

• Early appearance
• Accurate, specific, precise
• Readily available, fast results
• Cost-effective

17
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

18
Markers of Cardiac Necrosis
19
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

20
Troponins
21
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

22
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
• CK-MB is the marker of choice for diagnosis of
  reinfarction after CABG because of rapid washout

23
CK and CK-MB
24
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

25
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

26
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

27
Natriuretic Peptides
28
Natriuretic Peptides

• Present in two forms, atrial (ANP) and brain
  (BNP)
• 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

29
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

30
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

31
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

32
Prognostic Markers and Markers of Risk
Stratification
33
Prognostic Markers and Markers of Risk
Stratification

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

34
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

35
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

36
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

37
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

38
CRP and CV Risk

• Elevated levels predictive of
• Long-term risk of first MI
• Ischemic stroke
• All-cause mortality

39
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

40
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

41
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

42
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

43
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?

44
Glomerular Filtration Rate

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

45
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

46
Glomerular Filtration Rate

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