cardiac markers - aacc
TRANSCRIPT
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Cardiac Markers
Alan H.B. Wu, Ph.D. Professor, Laboratory Medicine, UCSF
Section Chief, Clinical Chemistry, Toxicology, Pharmacogenomics Laboratory, SFGH
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Learning objectives
• Understand the pathophysiology of acute coronary syndromes and heart failure
• Understand how biochemistry of troponin and B-type natriuretic peptides
• Discuss how cardiac troponin the natriuretic peptides are used for diagnosis and risk stratification for ACS and HF
• Understand the role of point-of-care testing for cardiac markers
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Pathophysiology of acute coronary syndromes
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Pathology of Coronary Syndromes
Unstable Angina
Normal
Fatty Streak
Fibrous Plaque
Athero- sclerotic Plaque
Plaque Rupture/ Fissure &
Thrombosis Myocardial Infarction
Clinically Silent Sudden Death
Increasing Age
Stable Angina
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site of plaque rupture non-occlusive thrombi
lipid-rich ‘gruel’
Rupture of a coronary artery
thin fibrous cap
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Pathophysiology of acute coronary syndrome
Uns
tabl
e An
gina
Myo
card
ial
Infa
rctio
n
Plaque Rupture
Intracoronary Thrombus
Reduced Blood Flow
Myocardial Ischemia
Myocardial Necrosis
The Pathophysiologic Continuum of AMI
Asym
ptom
atic
for
CAD
Classical biochemical markers (CK-MB) ECG: St segment elevation
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Biochemical events after AMI
Coronary artery occlusion Myocardial ischemia Anoxia Lack of collateral blood flow Reversible damage Irreversible damage Cell death & tissue necrosis
ATP pump failure Leakage of ions, e.g., potassium Accumulation of metabolites Leakage of metabolites, e.g., lactate Membrane damage Leakage of enzymes, e.g., LDH
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Route of clearance following AMI
Ions Metabolites
Systemic circulation Sl
ow ly
mph
atic
dra
inag
e
Rap
id c
oron
ary
arte
ry
drai
nage
Proteins
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Universal definition of MI: 2007
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Troponins T and I
• Proteins found in thin filament of muscle • Early release due to cytosolic pool • Sustained release due to myofibrils • Cardiac troponin not released from skeletal
muscles. • Very high tissue content.
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cTnI-C-T cTnI-C-T
18 kDa
cTnT
cTnI-C
77 kDa
cTnI
cTnT cTnT free 37 kDa
22kDa
modified from: A. Wu. Clin Chem 98; 44: 1198-1208 + Eur J Clin Chem Biochem 98 A.G. Katrukha. Clin Chem 97; 43: 1379.
cTnC
+ 4 Ca 2+
cytosolic 2- 4%
cytosolic 6- 8%
cTnI
cTnC
cTnI free + sTnC ( ? ) cTnI-sC ( ? )
I C T
I C T
I C T
W. Gerhardt 98
cTnT fragments
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cTnT vs. cTnI
• Equivalent diagnostic utility for AMI and risk stratification • cTnT slightly larger than cTnI (37 vs. 24 kDa) remains
positive after AMI longer. • Abnormal cTnT found more frequently in patients with
chronic renal failure than cTnI due to non-ischemic myocardial damage.
0 1 2 3 4 5 6 10 7
Mul
tipl
es o
f th
e U
RL
100
5
10
15
50
CK-MB Reference interval Myo
Days after Onset
0
cTnT
cTnI
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• Myocardial tissue content • Assays for cTnT and cTnI specific to cardiac injury
• Low normal range enables use of low cutoff concentrations
• Higher myocardial tissue content • CK-MB: 1.4 mg/g wet weight • cTnI: 6.0 mg/g wet weight • cTnT: 10.8 mg/g wet weight
Troponin superior to CK-MB Wu et al. Clin Chim Acta 1999; 284:161-71.
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Detection of minor damage: pre-PCI
Collaterals
Site of stenosis
A
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Detection of minor damage: post-PCI
Side branch occlusion
B
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Troponin after angioplasty Wu et al. Clin Cardiol 1996;19:792
Class -Tn, -MB -Tn, +MB +Tn, -MB +Tn, +MB
Thrombus or Sidebranch occ. NA NA 9 NA
No. Cases 44 (55%) 0 (0%) 13 (16%) 23 (23%)
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CK-MB, myoglobin, and cTnI Eggers et al. Am Heart J 2004;148:574-81.
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Troponin and CK-MB for reinfarction Apple et al. Clin Chem 2005;51:460-3
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Point-of care testing for cardiac markers
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POCT for cardiac markers
• Whole blood platforms. • Quantitative and qualitative assays available • Can significantly reduce assay TAT. • Precision and sensitivity less than central laboratory
platforms
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ACC/AHA Guideline for UA patients Circulation 2000;102:1193-1209
“When a central laboratory is used to measure biochemical cardiac markers, results should be available within 60 minutes and preferably within 30 minutes.”
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Does cardiac POCT reduces TATs?
Study POCT Central lab ∆, ↓ Caragher et al., 2002 38 87 56% Lewandrowski et al. 2003 17 110 85% Collinson, et al. 2004 20 79 75% McCord, et al. 2001 24 71 66% Singer et al. 2005 15 83 85% Mean 23 89 79%
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POC testing for AMI
• STEMI: ECG, no cardiac markers needed • NSTEMI: troponin increased dramatically, POCT
adequate • UA/NSTEMI: variability in performance of POCT
devices.
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Discordances from POC v central lab testing Singh et al. Clin Chim Acta 2009;403:259-60
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0369
12
0369
12
0369
12
OR 4.55; 2.66-7.78
Rapid Troponin I Assay
Outcomes in relation to troponin: assay sensitivity James et al. Int J Cardiol 2004;93:13-20.
% Neg
Death MI Death or MI
56 98 92 130 132 205
Troponin T (0.1 µg/L)
Troponin T (0.01 µg/L)
OR 1.80; 1.30-2.54
1.82; 1.38-2.40
1.64; 1.31-2.06
OR 3.20; 2.22-4.59 2.26; 1.79-2.85
1.47; 1.12-1.93
3.42; 2.57-5.98 4.29; 3.02-6.09
Pos
%
%
41
15
113
139
86
25
136
197
116
36
221
301
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Evolution: troponin cutoff concentrations
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Troponin T cutpoints
LOB
99th percentile =LOD
10% CV limit LOQ
ROC AMI cutoff 0.1
0.03
0.01
cTnT
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NACB Guideline Morrow et al. Clin Chem 2007;53:552-574
• “In the presence of a clinical history suggestive of ACS, the following are considered indicative of myocardial necrosis consistent with MI (Level of Evidence: C):
• Maximal concentration of cardiac troponin exceeding the 99th percentile of values (with optimal precision defined by total CV <10%) for a reference control group on at least 1 occasion during the first 24 h after the clinical event (observation of a rise and/or fall in values is useful in discriminating the timing of injury). “
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Stable angina
no injury no injury
Unstable angina
Myocardial infarction
little to moderate
significant injury
injury
Concentration of cardiac marker
Normal individuals
increasing
Receiver operating characteristic curve derived
Initial strategy prior to ESC/ACC redefinition (ROC)
Strategy based on 10% CV Current ESC/ACC recommendation (99th percentile)
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hsTroponin T for AMI Reichlin et al. NEJM 2009;361:858-67.
Includes next generation hs-cTnT
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hsTnI in ED patients with chest pain
No ischemia
Ischemia?
0
2
4
6
8
10
12
14
16
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 More
pg/ml cTNI
Freq
uenc
y Ischemia?
Non-diagnostic
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Months 0 2 4 6
0.7
0.8
0.9
1.0
Frac
tion
w/o
AM
I or C
ardi
ac D
eath
cTnT=negative
cTnT=positive p<0.05
Cardiac troponin for risk stratification of unstable angina
Ravkilde et al. Scan J Clin Lab Investig 1993;53:677-85.
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Risk stratification vs. cutoff Morrow et al. JAMA 2001;286:2405-12.
181 patients out of 1821 missed when raising the cutoff to the 10% CV.
% D
eath
, AM
I
0
1
2
3
4
5
6
7
8
99th 10% CV AMI
cTnI +ve cTnI -ve
Relative cutoff concentrations
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Troponin elevations without ischemia Wu et al. Clin Chem 2007;53:2086-96
• Trauma, burns • Congestive heart failure • Aortic valve disease and hypertrophic obstructive cardiomyopathy • Hypertension and hypotension • Postoperative noncardiac surgery patients and PCI • Renal failure • Critically ill patients (diabetes, respiratory failure, GI bleed, sepsis) • Drug toxicity (adriamycin, 5-fluorouracil, herceptin, snake venoms) • Hypothyroidism • Abnormalities in coronary vasomotion, including coronary vasospasm • Apical ballooning syndrome • Inflammatory diseases (e.g., myocarditis, parvovirus, Kawasaki disease) • Pulmonary emboli, severe pulmonary hypertension • Infiltrative diseases (e.g., amyloidosis, hemochromatosis, scleroderma) • Acute neurological disease, (e.g., CVA, subarachnoid bleeds) • Rhabdomyolysis with cardiac injury • Transplant vasculopathy • Vital exhaustion
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AMI rule out algorithm Hamm et al. Eur Heart J. 2011;32:2999-3054
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Summary for troponin
• Key element in re-definition of AMI • Important for risk stratification for short-term adverse
cardiac events • Little difference in cTnT vs. cTnI • Use of the 99th percentile optimizes detection of minor
myocardial damage high risk • CK-MB and myoglobin redundant today
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Natriuretic peptides
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Congestive heart failure
A condition where the heart is unable to supply the body with enough oxygen-rich blood to accommodate the body’s needs during exercise and at rest. As a result of decreased function body fluids may build up in the lungs and limbs. •
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Healthy
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Heart failure
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Natriuretic peptides
• The natriuretic peptides are a family of 3 related forms.
• They are increased in CHF due to enhanced atrial & ventricular synthesis.
• ANP: 28-aa peptide found in the atrium of the heart
• BNP: 32-aa peptide found in the brain and ventricles of the heart
• CNP: 22 aa peptide found in the brain and CNS • Urodilatin: 32 aa peptide, is the renal form of ANP
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Architectural Changes of the Failing Heart
Ischemic Normal
Hypertension Dilated Cardiomyopathy
Decreased Blood Output
Spherical shape not energetically efficient.
Elliptical shape is energetically efficient.
BNP released w/ wall stretching
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Natriuretic peptides and vasopressin: counterbalance
Hypertension
BNP, ANP
Hypotension
•Vasodilatation
•Natriuresis/diuresis
•Vasoconstriction •Salt/water retention •Increase heart rate/ contractility
Renin, aldosterone
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Release of BNP from Cardiac Myocytes Mair et al. Clin Chem Lab Med 39:571-88.
Roche, Dade, DPC, Ortho Abbott, Bayer, Biosite (Beckman)
Blood
Cardiomyocyte
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NT-ProBNP vs. BNP
• For CHF patients, no difference in performance between BNP and NT-ProBNP.
• T½: BNP-20 min, NT-ProBNP: 90 min (sheep). • Cannot use BNP to monitor endogenous BNP levels
during nesiritide therapy. • NT-Pro BNP has a longer in vitro sample stability (72 h)
than BNP (4 h).
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BNP in apparently healthy individuals
0
10
20
30
40
50
60
70
<45 45-54 55-64 65-74 >75
male female
Age (years)
BN
P (
pg/m
l)
Median values
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BNP vs. NYHA Classification Wieczorek S, Wu A. Am Heart J 2002 144:834-9.
0 200 400 600 800
1000 1200
Control I II III IV
BN
P (p
g/m
L)
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Survival and the 6-min walk test (EF<45%) Roul et al. Am Heart J 1998;136:449-57.
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6-min walk test Wieczorek, Wu, et al. Clin Chim Acta 2003;328:87-90.
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“Breathing Not Properly” Study Maisel, Wu et al. NEJM 2002;347:161-7.
• 1586 patients presenting to the ED with shortness of breath
• Data recorded: history, physical exam, lab tests
• Initial assessment by ED physicians • Followup assessment: 2 cardiologists with
access to all tests (echos), hospital course, response to treatment, etc.
• BNP measured
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BNP in Patients Without CHF, Baseline LV Dysfunction and CHF
non-cardiac cause
0 200 400 600 800
1000 1200 1400
BN
P (
pg/m
l)
Non-CHF CHF Known LV dysfunction not acute
n = 770 n = 744
n = 72
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BNP vs. BMI in patients with CHF Daniels, Wu, et al. Am Heart J 2006;151:999-1005
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BNP in renal disease McCullough, Wu et al. Am J Kid Dis 2003; 41:571-9
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Log BNP (pmol/l)
LVEF
(%
)
0
20
40
60
80
100
0 1.0 3.0
y=-0.7, p<0.001
BNP vs. EF by echocardiography Davis et al. Lancet 1994;343:440-4.
Systolic HF
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BNP in diastolic HF Maisel, Wu et al. J Am Coll Cardiol 2003;410:2010-17.
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0
BNP after CHF (EF<45%) Tsutamoto et al. Circulation 1997;96:509.
100
75
50
25
10 20 30 40 50 60 Months
BNP>73 pg/ml
p<0.001
Cu
mu
lati
ve s
urv
ival
0
BNP <73 pg/ml
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ESC Heart failure guideline
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HF case reports
• Three patients present at different times to the ED with dysnea. They are all males, aged 50-55 y and a 3-5 y hx of heart failure.
• BNP is tested daily until discharge (not recommended practice).
• Each patient is followed over the next 180 days for recurrent HF death or re-hospitalization.
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Which of these patients has a better prognosis upon discharge?
100300500700900
11001300150017001900
Day 1 Day 2 Day 3 Day 4 Day 5 Day 6
Patient 1 Patient 2 Patient 3
BNP Serial Testing High baseline,
greatest change
Lowest Pre- discharge
BNP
Lowest Baseline
BNP Level
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Heart failure outcomes Logeart et al. J Am Coll Cardiol 2004;43:635-641
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Summary for BNP/NT-proBNP
• Widely used for diagnosis of HF in ED • Important for risk stratification for short-term adverse
cardiac events • Little difference in BNP vs. NT-proBNP • Utility for screening asymptomatic patients to be
determined • Utility for therapeutic monitoring of decompensated HF
established • Utility for outpatient therapeutic monitoring to be
determined
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Self-assessment questions
Which of the following is the recommended strategy for cutoff assignments for troponin? A. 95th percentile of healthy population B. 99th percentile of healthy population C. Value at the assay’s 10% CV D. Receiver operating characteristic curve-derived cutoff E. B and C. Answer: The ACC/AHA Task Force has recommended the 99th percentile for assays that have a 10% CV or less
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Self-assessment questions
Which of the following does not increase the level of BNP/NT-proBNP in a patient population who is asymptomatic for heart disease? A. Renal insufficiency B. Female gender C. Subject age D. Body mass index E. None of the above Answer: D. Obesity decreases BNP/NT-proBNP.
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Self-assessment questions
Which is FALSE regarding point-of-care testing for troponin? A. Current POC assays are less sensitive than the central
lab. B. Turnaround times are improved with POC. C. Clinical studies have demonstrated improved clinical
outcomes with use of POC testing D. POC test results are not standardized with central lab
results. E. POC test results can be used for risk stratification
Answer: C. No such clinical trial has shown a clinical advantage of POCT.