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Chapter 18 Flashcards

1
Q

Tracking of radiotracer transit through the blood vessels and the heart starting with the time of radiotracer injection

A

Dynamic imaging

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2
Q

What is the term for the ratio of stress to rest myocardial blood flow?

A

Myocardial flow reserve (MFR)

Normal value =>2.0

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3
Q

Preferred drug for phamacologic stress testing used for dynamic imaging for myocardial blood flow quantitation.

A

vasodilators (preferred)

or dobutamine

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4
Q

First-line preferred test for patients with known or suspected CAD who meet appropriate criteria for a stress imaging test and are unable to complete a diagnostic-level exercise stress imaging study

A

Rest-stress myocardial perfusion PET

Exercise PET does not allow for quantitation of myocardial blood flow.
MPI- shows myocardial blood flow

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5
Q

The ideal radiotracer for MPI should be extracted by the myocardium at a rate that is linearly related to myocardial blood flow. What is the closest to an ideal tracer?

A

15 O-water

Because it is freely diffusible, myocardial perfusion images are difficult to interpret, requiring special corrections or the use of parametric flow maps

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6
Q

FDA-approved SPECT myocardial perfusion tracers (3)

A

99m Tc-sestamibi, 99m Tc-tetrofosmin, and 201 thallium

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7
Q

half-life of 99mTc

A

6 hours

Sestamibi
- passively diffuse into cardiomyocytes at rates proportional to blood flow
- bind to the mitochondria within the first 60 to 90 seconds after injection
-no significant redistribution of 99mTc perfusion tracers and imaging can be delayed for up to several hours
-suitable for exercise or pharmacologic stress testing

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8
Q

half-life of 201Thallium

A

73 hours

-low photon energy
-associated with a higher radiation dose

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9
Q

What SPECT MPI tracer that enters the cardiomyocytes via the Na+/K+ ATPase pump?

A

201Thallium

-circulates to the heart at a rate proportional to blood flow
-washes out of normally perfused and hypoperfused regions at different rates
-poststress 201thallium images are obtained within 10 to 15 minutes after injection
-long t1/2, low photon energy, high radiation dose
-not recommended for perfusion imaging
-mainly used for viability study

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10
Q

TRUE/FALSE
Thallium is not recommended for perfusion imaging.

A

TRUE

instead, it is used for viability assessment at sites without access to other viability tests

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11
Q

Name the 2
PET MPI TRACERS with FDA approval

A

82Rubidium and 13N-ammonia

shorter half-lives
lower radiation dose
13N-ammonia
-passive entry into teh cell
-higher extraction fraction
-shorter positron range

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12
Q

Advantage of PET from SPECT tracers?

A

more suitable for quantifying myocardial blood flow
shorter half-lives
lower radiation dose
rapid clinic throughput

superior extraction characteristics

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13
Q

novel PET perfusion tracer with a half-life of 109 minutes, superior extraction characteristic than rubidium and N-ammonia, superior image resolution than 99m Tc-SPECT MPI

A

18F-flurpiridaz

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14
Q

The only clinically available FDA-approved tracer to image myocardial metabolism is __.

A

18F-FDG

is a glucose analog used to image myocardial glucose metabolism

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15
Q

What is the primary clinical applications of cardiac 18F-FDG PET?
(4)

A

myocardial viability, myocardial and vascular inflammation, and infective endocarditis

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16
Q

What transporter is used by 18 F-FDG to enter the cardiomyocytes through?

A

Glucose transporters (GLUT 1 and 4)

  • ## it is phosphorylated by the enzyme hexokinase and trapped as 18 F-FDG-6-phosphate which cannot be metabolized
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17
Q

What are the causes of increase myocyte glucose uptake, leading to translocation of glucose transporter into the plasma membrane?

A

Insulin, ischemia, and hypoxia

Ischemic and hypoxic cells overexpress GLUTs and preferentially use glucose for their metabolic needs, independent of the substrate or insulin availability.
-Malignant cells and inflammatory cells are also characterized by significantly increased glucose uptake by an insulin-independent mechanism.

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18
Q

TRUE/FALSE
Ischemic and hypoxic cells preferentially use glucose for their metabolic needs, independent of the substrate or insulin availability.

A

TRUE

Malignant cells and inflammatory cells are also characterized by significantly increased glucose uptake by an insulin-independent mechanism

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19
Q

Dietary preparation to image myocardial viability?

A

Glucose load with IV insulin

Ischemic and hypoxic cells preferentially use glucose

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20
Q

Dietary preparation to image cardiovascular inflammatory conditions (sarcoidosis, infective endocarditis, and vasculitis)?

A

Low-carbohydrate, high-fat diet followed by prolonged fasting

Malignant cells and inflammatory cells are also characterized by significantly increased glucose uptake by an insulin-independent mechanism.

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21
Q

Main difference of Tc and Thallium in the mechanism of myocardial entry?

A

Tc-passive binding to the mitochondria
Thallium- active (Na+/K+ ATPase pump)

Tc-shorter half-life (6 hours), no significant redistribution, hence imaging can be delayed for up to several hours
-suitable for exercise or pharmacologic stress testing
Thallium- longer half-life (73 hours), different rates of wash-out with normal and ischemic cells
-good for viability study

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22
Q

What is the normal coronary blood flow at rest?

A

0.7 to 1 mL/min

-can increase three- to fivefold during maximal vasodilation
-remains constant over a wide range of coronary perfusion pressures

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23
Q

Coronary blood flow remains constant over a wide range of perfusion pressures until?

A

The presence of very severe upstream coronary stenosis (>90% luminal narrowing)

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24
Q

What is the earliest event in the ischemic cascade?

A

perfusion defect

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25
Cause of ischemic ST depression during vasodilator stress testing?
coronary steal ## Footnote -vasodilator stress does not increase oxygen demand -the diseased and non-diseased territories manifest differential hyperemic responses due to differences in resting microvascular dilation
26
In what instance is balanced ischemia observed?
Severe multi-vessel obstructive CAD ## Footnote -coronary blood flow is reduced in all vascular territories -results to apparently normal appearing relative myocardial perfusion image
27
What is the next diagnostic test after finding of a balanced ischemia?
coronary angiography (high-risk) coronary CTA (without high-risk features) ## Footnote invasive for patients with high-risk stress features or symptoms
28
Maximal exercise definition
ability to achieve an exercise heart rate of at least 85% of age-predicted maximal heart rate (220-age) ## Footnote To evaluate anginal symptoms in patients without documented prior CAD, maximal heart rate is desired.
29
What is the minimum workload to evaluate anginal symptoms on maximal medical therapy in patients with known prior CAD?
at least 5 metabolic equivalents (METS) | regardless of the heart rate
30
When stress test is converted to vasodilator test, what medication is well-suited?
Regadenoson ## Footnote a non–weight-based fixed dose stress agent
31
Three most commonly used vasodilator stress agents
Adenosine, dipyridamole, and regadenoson
31
Match the Adenosine receptor to its function: 1. A1 2. A 2A 3. A3 4. A2B A. coronary vasodilation B. heart block C. wheezing D. peripheral vasodilation
A1-heart block A 2A- coronary vasodilation A2B- wheezing A3 -peripheral vasodilation ## Footnote >vasodilator agents cause splanchnic hyperemia and intense radiotracer uptake in the liver that may scatter into the inferior wall of the left ventricle >low-level treadmill exercise has been shown to improve heart to liver ratio
32
A vasodilator agent that is specific A 2A receptor agonist
Regadenoson ## Footnote A 2A- coronary vasodilation -avoid the side effects of the nonspecific vasodilators
33
Contraindications for vasodilator agents (4)
active wheezing, high-grade atrioventricular (AV) block without a functioning pacemaker, systolic blood pressure (BP) <90 mm Hg, and any contraindications for stress testing (acute MI, unstable angina, aortic dissection, acute pulmonary embolism).
34
Contraindication to Regadenoson (2)
History of seizure Structural brain injury (ischemic or hemorrhagic stroke or brain tumors)
35
How to administer vasodilator agents?
Administered over 4 minutes: adenosine (140 mcg/kg/min) dipyridamole (0.56 mg/kg) Regadenoson is a fixed-dose rapid IV bolus over 10 seconds (0.4 mg/5 mL prefilled solution administered as a rapid bolus over 10 seconds)
36
Side effects of vasodilator agents:
symptoms of hyperemia in about 50% of patients urge to breathe deeply chest tightness headache flushing 10 to 20 beat increase in heart rate 10-mm Hg decrease in systolic BP ## Footnote side effects occur acutely with adenosine but are typically short-lived (due to the 3-second half-life of adenosine), terminate when the infusion is completed.
37
Competitive antagonists of the adenosine receptors
Methylxanthines ## Footnote >can reverse the vasodilatory effects of vasodilator agents >should be hold for at least 12 hours before vasodilator stress
38
Antidote for side effects of vasodilator stress agents
IV aminophylline (1 to 2 mg/kg slow push over 1 to 2 minutes)
39
TRUE/FALSE Vasodilator stress has been shown to be safe for evaluation of myocardial ischemia within 24 to 48 hours after presentation with ACS or uncomplicated MI.
TRUE
40
TRUE/FALSE Dobutamine plus atropine stress testing with maximal heart rate response has been shown to increase myocardial blood flow equivalently to vasodilator stress
TRUE
41
Contraindication for atropine (2)
angle closure glaucoma prostatism
42
True of preparation for Nuclear Cardiology Testing Stress Testing? A. 4 to 6 hour fast before a stress test B. no smoking for 6 hours C. Caffeine intake (including caffeine-containing medications) should be withheld for 12 hours D. theophylline-containing medications and oral dipyridamole are withheld for 48 hours before testing E. Patients without known CAD are ideally tested by withholding their beta blockers and antianginal medications for 12 hours before testing F. all of the above
F ## Footnote Known CAD are generally tested on their anti-ischemic therapy Patients on dialysis are typically scheduled for their test on the day after dialysis.
43
Preparation for 18 F-FDG testing: for viability for Inflammation/Infection
for viability- 6-hour fast for Inflammation/Infection- high-fat, low to zero carbohydrate diet for at least two large meals 24 hours before the test followed by overnight fast (8 to 12 hour fast) ## Footnote no specific dietary preparation for amyloidosis
44
How may segments does a large defect size has in a myocardial perfusion scan?
45
Common normal variants in: SPECT or PET/MPI
SPECT or PET/MPI--apical thinning (a fixed perfusion defect in the apical inferior wall or septum with normal wall motion) 13 N-ammonia PET/CT- fixed basal lateral perfusion defect with normal wall motion
46
Differential diagnosis of a fixed perfusion defect (2)
>artifact (if wall motion is normal) >real defect (if wall motion is abnormal)
47
High-Risk Features in MPI (5)
>Large single or multiterritorial fixed and/or reversible myocardial perfusion defects involving >15% of the LV mass >Transient ischemic dilation of the left ventricle >Stress-induced myocardial stunning with a drop in LVEF poststress >Transient RV tracer uptake >Increased pulmonary tracer uptake
48
High-Risk Features in Stress Test (7)
Significant (>3 mm) ST-segment depression Prolonged ST-segment depression ST depression at low workload Multilead ST depression ST-segment elevation (>1 mm) Hypotension (>10 mm Hg) with exercise Sustained ventricular tachycardia
49
Interpret the defects:
1. Hibernation (mismatch) 2. Scar (match) 3. Nontransmural scar (partial mismatch) ## Footnote myocardial perfusion defects during stress develop downstream to an epicardial stenosis with ≥50% to 70% luminal narrowing
50
Interpret the defects:
1. Normal 2. Nonspecific 3.Focal myocardial inflammation 4.Focal myocardial inflammation 5.Fibrosis
51
TRUE/FALSE Among high-risk population (eg. DM), a preserved MFR by PET identifies truly low-risk individuals.
TRUE ## Footnote >absolute quantification of myocardial blood flow and flow reserve by PET (an integrated marker of epicardial stenosis, diffuse atherosclerosis, and microvascular dysfunction) is a definite advantage in higher-risk patients >severely reduced global MFR is associated with a higher risk of death than in the setting of relatively preserved MFR >the risk associated with a normal radionuclide MPI has not necessarily been low (<1%) in higher risk cohorts >similar findings with CKD patients
52
Prognostication from Stress MPI: 1. fixed perfusion defects (and the presence of often associated LV dilatation and reduced LV function) 2. reversible or ischemic defects 3. presence of LV dilatation and/or reduced LVEF
1. associated with a greater risk of cardiac death 2. more closely associated with the occurrence of nonfatal MI 3. further increases clinical risk across all levels of myocardial perfusion abnormalities ## Footnote normal study is sufficiently low that referral to revascularization will not further improve patient outcomes
53
PET viability interpretation as to peak activity: Viable Non-viable for further evaluation
>60% peak activity of perfusion tracer-considered viable <40% peak activity - nonviable 40% to 60% of peak activity - further evaluation for myocardial viability
54
TRUE/FALSE Radionuclide MPI is appropriate in symptomatic patients with suspected CAD.
TRUE ## Footnote EVINCI and PACIFIC studies >MFR >2.0 is associated with a >97% negative predictive value for ruling out high-risk angiographic CAD >younger patients coronary CT angiography may be an excellent choice to screen for CAD- Class I in NSTEMI with low risk profile
55
Location of the following attenuation artifacts: Women- breast Men- diaphragm muscle
Women- anterior wall Men- inferior wall ## Footnote Most attenuation artifacts typically result in fixed defects
56
TRUE/FALSE Quantitative PET imaging is considered the most accurate and reproducible noninvasive technique for symptomatic patients without angiographic obstructive CAD.
TRUE ## Footnote coronary microvascular dysfunction (CMD)
57
most accurate and reproducible noninvasive technique for interrogation of coronary microvascular function
quantitative PET imaging
58
Interrogation of coronary microvascular function is necessary to establish the diagnosis of ____.
coronary microvascular dysfunction (CMD)
59
True of microvascular coronary dysfunction? A. coronary flow reserve <2 B. affects <50% of men and women presenting with ischemic symptoms C. does not affect clinical risk D. A and B
A ## Footnote >affects >50% of men and women presenting with ischemic symptoms >a marker of increased clinical risk >severity of CMD is similar in men and women
60
Appropriate test for Patients with Known Stable Coronary Artery Disease
Radionuclide MPI
61
Appropriate test for for diagnosis of ischemia and risk stratification among Patients with Prior PCI and Recurrent Symptoms
Radionuclide MPI ## Footnote provides localization and quantification of myocardial ischemia >stress test should be done when feasible (good prognostic value)
62
Appropriate test for suspected ACS patients with Nondiagnostic Electrocardiogram and Troponin Elevation
quantitative stress PET perfusion imaging ## Footnote >in intermediate-high risk patients with low-level elevation of cardiac troponin
62
Patients with Recent Myocardial Infarction Evaluated for Potential Staged PCI
Stress radionuclide imaging
63
Patients with Prior Myocardial Infarction and Ventricular Arrhythmias
SPECT or PET imaging
64
Patients with Chronic Total Coronary Artery Occlusion
Radionuclide perfusion imaging
65
Patients with Cardiac Allograft Vasculopathy
cardiac PET ## Footnote -measured myocardial blood flow is a sensitive tool with high diagnostic value >cardiac allograft vasculopathy remains a leading cause of mortality and retransplantation in these individuals >patients with PET-defined vasculopathy are at significantly higher risk of mortality
66

Braunwalds (34 decks)

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