Download Imaging the Coronary Arteries

Elizabeth A. Buzney, IV
Gillian Lieberman, MD
July 2002
Imaging the Coronary Arteries
Elizabeth A. Buzney
Harvard Medical School, Year IV
Gillian Lieberman, MD
From http://www.animatedsoftware.com/ascodesc/hartdesc.htm
Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Our Patient, Mr. G.
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68 year-old male
1 year of chest pain with exertion
Pain resolves with 1 nitroglycerin tablet
Denies symptoms of heart failure
Father had MI in 50’s
• Suspect stable angina
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Coronary Artery Imaging
Modalities
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Plane film
Stress EKG
Stress Echocardiogram
Nuclear imaging
Angiography
EBCT (Electron beam CT)
IVUS (Intravascular Ultrasound)
MRA
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Cardiac Imaging Modalities
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Plane film
Stress EKG
Stress Echocardiogram
Nuclear imaging
Angiography
EBCT (Electron beam CT)
IVUS (Intravascular Ultrasound)
MRA
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
First Imaging Modality:
Nuclear Imaging
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Principles of Nuclear Imaging
• Areas of the heart with severe stenosis are always
maximally vasodilated in order to increase
perfusion
• Areas without stenosis are not vasodilated at rest
• When stimulated, normal vessels vasodilate,
stealing blood away from tissue with stenotic
vessels
• Therefore, stenotic areas appear black on perfusion
studies after stress or vasodilation
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Principles of Nuclear Imaging,
Continued
• Since stress causes vasodilation,
vasodilation is often used as a proxy for
stress during nuclear imaging studies
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Choosing a Nuclear Imaging Study
• Exercise or pharmacologic stressor?
• Thallium or Sesta-MIBI?
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Choosing a “Stressor”
• 3 “pharmacologic stressors:” adenosine,
dipyridimole, dobutamine
• Beware: adenosine causes bronchospasm;
avoid in COPD or asthma
Exercise
Dobutamine
Dipyridamole
inhibits breakdown
Inotropy
Adenosine *
Vasodilation
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
The “Best” Stress
Exercise Stress
• Best approximate of
the patient’s expected
realistic physical
stress.
• Higher specificity for
clinically significant
CAD.
• More than just a
physiologic marker.
Pharmacologic Stress
• Best for patients who
cannot exercise
(arthritis, CVA,
amputation, pulm dz,
deconditioning).
• Higher sensitivity for
anatomic CAD in
those unlikely to
perform maximally on
exercise stress.
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Thallium vs. MIBI
Thallium-201
• Potassium analog
• Half-life: 74 hours
• Whole body radiation
dose: 0.20 rads/mCi
Technetium-99m SestaMIBI
• Hydrophilic cation
• Half-life: 6 hours
• Whole body radiation
dose: 0.02 rads/mCi
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Thallium vs. MIBI, continued
Thallium-201
• Uptake depends on
ATPase Æ best measure
of cell viability
Technetium-99m SestaMIBI
• Uptake depends on cell
membranes with intact
electrochemical gradient Æ
only fair measure of viability
• Does not redistribute
• Redistributes over 2-12
hours into all viable cells
• Measures perfusion and • Measures viability only
insofar as cells are perfused
viability independently
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Limitations of Nuclear Imaging
• 10-25% of non-reversible defects found to be
viable upon reperfusion
• Artifact often due to hibernating myocardium
(viable but chronically hypoperfused tissue)
• Hibernating myocardium may be revealed by
thallium reinjection under non-stress conditions
• PET scan best reveals hibernating myocardium:
high glucose uptake relative to perfusion
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Reading Defects on Nuclear
Imaging Studies
• Reversible defect: Ischemia
• Non-reversible defect: Infarct or
hibernating myocardium
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Mr. G’s Stress Test
• Since Mr. G. was able to exercise, he
decided to have an exercise stress
test using a Modified Bruce Protocol
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
What are the Bruce Protocols?
• Treadmill programs where the METS (determined
by grade and mph) change every 3 minutes
Stage
METS
Activity
Modified 1
3
Cooking
Modified 2
4
Light gardening
Modified 3 = Regular 1
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Washing clothes, sex
Regular 2
Regular 3
Regular 4
Regular 5
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10
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Carrying suitcase
Running
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Mr. G’s Stress Test at the BIDMC
Thallium
injection
Imaging Exercise/stress MIBI
Imaging
Stress EKG
injection
at
point
of
From: www.greaterthings.com/Books/ClintonAIDS/
From: www.dis-tenet.com/Procedures/nuclear-cardiology.htm
maximal HR
From: www.perduecreative.com/ fun.html
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Mr. G’s Stress Test
• Exercised 6.5 minutes on a modified Bruce
protocol
• Stress EKG showed 1-2mm EKG changes
inferolaterally
• Had 9/10 chest pain during exercise
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
So How Did Mr. G. Do?
• 6.5 min on modified Bruce – washing clothes
• Achieved only 74% of maximal heart rate
• Should achieve 80-85% maximal heart rate for
a good stress test
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Reading Nuclear Imaging Scans
RV
LV
Base
Apex
Short axis
Vertical;
Oblique
sagittal
Apex
Base
From http://brighamrad.harvard.edu/education/
online/Cardiac/anatomic-orient.html
Horizontal;
Oblique
transaxial
From Braunwald: Heart Disease: Cardiovascular
Medicine, 6th ed., 2001, Fig. 9-6
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Coronary Artery Territories on
Nuclear Imaging
From http://brighamrad.harvard.edu/education/
online/Cardiac/coronary-artery-territory.html
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Mr. G’s MIBI
Moderate reversible anterior defect
Severe reversible
apical defect
From BIDMC PACS
From http://brighamrad.harvard.edu/education/
online/Cardiac/anatomic-orient.html
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Another example: Patient II
Severe reversible defect in inferior region
From http://brighamrad.harvard.edu/education/
online/Cardiac/coronary-artery-territory.html
From BIDMC PACS
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Last example: Patient III
Severe reversible defect in lateral region
From http://brighamrad.harvard.edu/education/
online/Cardiac/coronary-artery-territory.html
From BIDMC PACS
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
And patient III after CABG…
Lateral defect has partially resolved!
From BIDMC PACS
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Back to Mr. G…
• Anterior and apical defects: LAD region
stenoses
• Reversibility suggests ischemia
• These regions are still viable and might
benefit from cardiac catheterization
Mr. G. goes to cardiac catherization!
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Second Imaging Modality:
Cardiac Catheterization
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Indications for
Cardiac Catheterization
• Gold standard for identification of CAD
when noninvasive imaging modalities
are equivocal
• Assessment of disease extent for
interventional therapy (angioplasty or
surgery)
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Risks for Coronary Catheterization
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Rare (<0.1%) risk of MI, CVA or death
Risk increased if: emergency, acute MI, unstable
Allergic reactions (0.37%)
Arrhythmia (0.38%)
Vascular occlusion (0.43%)
Contrast medium-induced renal failure (3-7%)
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Mr. G’s Coronary Catheterization
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Fasting
Conscious sedation
5000U IV Heparin
Percutaneous catheter into R femoral artery,
advanced under fluoroscopy
• Iodine-containing radio-opaque dye injected
into coronary arteries
• Digital acquisition of x-ray images
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Mr. G.’s Catheterization Results
• 99% stenosis of proximal LAD and first
diagonal branch
• 80% stenosis of RCA
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Mr. G’s catheterization:
Left main artery disease
Left main
Circumflex
Diagonal
Defects
Catheter
LAD
From BIDMC Coronary Catheterization Lab
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Mr. G’s catheterization:
Intermediate step in repair
LAD has been stented,
but diagonal has been
completely occluded
in the process
From BIDMC Coronary Catheterization Lab
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Mr. G’s catheterization:
Left main repair completed
Stent has been placed in diagonal
From BIDMC Coronary Catheterization Lab
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Mr. G’s catheterization:
Right coronary artery repair
From BIDMC
Coronary
Catheterization Lab
RCA defect …here corrected with stent
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Coronary Angiography vs. IVUS:
Angiographic underestimation of disease
Catheter
Atheroma
Lumen
Adapted from Nissen SE, Yock P. Circulation.2001; 103:604-616
Courtesy of Dr. Clouse, BIDMC
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Third Imaging Modality:
EBCT (Electron-Beam CT)
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
What Is EBCT?
• Also known as Ultrafast CT (UFCT)
• Electron stream is aimed onto tungsten
rings which focus the electrons to generate
xrays
• Moving xray tube is eliminated
• Entire heart imaged in one breathhold Æ
eliminates blurring
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
How Can EBCT Image the
Coronary Arteries?
• Noninvasive coronary angiography
• Assessment of myocardial perfusion
• Calcium deposit detection
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
EBCT Coronary Angiography
• Uses intravenous contrast
• Sensitivity of 77-82% and specificity of
92% for detecting luminal stenoses of >50%
• Limitations: - inadequate image quality
- requires breathold
- requires contrast
• Still undergoing refinement
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
EBCT Coronary Angiography
Patient IV
LAD Imaging
Soft plaque
within LAD
3D reconstruction
Pulm.
trunk
LCX
Aorta
Obtuse
Marginal 1
LV
LA
Courtesy of Dr. Clouse, BIDMC
LAD
LV
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
EBCT Calcium Detection
• Highly controversial means of visualizing
calcium within the coronary arteries
• Non-contrast CT
• Not covered by insurance
• $400.00 at BIDMC
• Patients are given a calcium score: estimate
of total artery calcification by volume and
by arterial location (age/sex –related)
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Coronary Artery Calcification
Patient V
RV
RCA
RA
AA
LV
LA
LAD
DA
From BIDMC PACS
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Examples of Coronary Artery Scans
Patient VI
No calcification
Patient VII
Patient VIII
Moderate calcification Significant calcification
Images courtesy of HeartScan San Francisco
Courtesy of Dr. Clouse, BIDMC
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Coronary Calcification Detection
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Advantages
150,000 Americans/yr die
from first MI
All other tests designed to
detect disease when patient
is symptomatic (70-90%
lumenal stenosis)
EBCT detects calcification
with 20% lumenal stenosis
Coronary Ca++ more Se and
Sp than cholesterol for
CAD death prediction
Questions
• Yes, 90% of plaques
contain Ca++,BUT does calcification predict clinically
significant plaques?
• Yes, EBCT detects plaques
that do not impede flow,
BUT do these plaques
provide significant risk?
• Does “plaque burden” add
to Framingham risk score
(CAD prediction)?
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Current recommendations for EBCT
• Negative EBCT: Good predictor for clean coronaries
• Positive EBCT:
– 85% Se and 49% Sp for diagnosis of angiographic CAD
(vs. 85% and 91% for MIBI)
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– Greater Ca = greater likelihood of occlusive CAD
– BUT no 1:1 relationship
– AND findings may not be site specific
– Total calcium underestimates total plaque burden
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– High Ca score may mean high MI risk in 2-5yrs
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
References
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Arad Y, Spadaro LA, Goodman K, Lledo-Perez A, Sherman S, Lerner G, Guerci AD. Predictive value of EBCT
of the coronary arteries: 19-month follow-up of 1173 asymptomatic subjects. Circulation 1996; 93: 1951-53.
Braunwald E, editor-in-chief, Zipes DP, Libby P. Heart Disease: A Textbook of Cardiovascular Medicine, 6th ed.
W. B. Saunders Company: Philadelphia, 2001.
Cerqueira MD and Lawrence A. Nuclear cardiology update. Radiologic Clinics of North America 2001; 39: 931946.
Donohoe KJ and Van den Abbeele AD. Teaching Atlas of Nuclear Medicine. Thieme Medical Publishers: New
York, 2000.
He ZX, Hedrick TD, Pratt CM, Verani MS, Aquino V, Roberts R, Mahmarian JJ. Severity of coronary artery
calcification by EBCT predicts silent myocardial ischemia. Circulation 2000; 101: 244-251.
Mazur W, Nagueh SF. Myocardial viability: recent developments in detection and clinical significance. Current
Opinion in Cardiology 2001; 16: 277-81.
O'Rourke RA, Brundage BH, Froelicher VF, Greenland P, Grundy SM, Hachamovitch R, Pohost GM, Shaw LJ,
Weintraub WS, Winters WL Jr, Forrester JS, Douglas PS, Faxon DP, Fisher JD, Gregoratos G, Hochman JS,
Hutter AM Jr, Kaul S, Wolk MJ. American College of Cardiology/American Heart Association Expert
Consensus document on electron-beam computed tomography for the diagnosis and prognosis of coronary artery
disease. Circulation 2000; 102: 126-40.
San Roman JA, Vilacota I, Castillo JA, Rollan MJ, Hernandez M, Peral V, Garcimartin I, de la Torre MM,
Fernandez-Aviles F. Selection of the optimal stress test for the diagnosis of coronary artery disease. Heart 1998;
80: 370-376.
Schelbert HR. 18F-deoxyglucose and the assessment of myocardial viability. Seminars in Nuclear Medicine 2002;
32: 60-69.
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Elizabeth A. Buzney, IV
Gillian Lieberman, MD
Acknowledgements
Dan Saurborn, MD
Melvin Clouse, MD
Kevin Donohoe, MD
Thomas Tu, MD
Sven Paulin, MD
Bertrand d’Othee, MD
Eric Niendorf, MD
Gillian Lieberman, MD
Pamela Lepkowski
Larry Barbaras and Cara
Lyn D’amour
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