Download Nuclear Cardiology

V. R. Dabbagh , M.D.
Associate Professor
DSNMC
NMRC; MUMS
www.DSNMC.ir
No:1/4; Mollasadra 11; Mollasadra Blvd; Mashhad; IRAN
Tel:+98(51) 38411524; +98(51)38472927
Nuclear Cardiology
&
Hibernating
Some
differences
with other
modalities
Medical vs.
Revascularization
management
Nuclear
Medicine
Procedures
Hibernating myocardium
Persistently impaired function at rest
(wall motion and thickening )
&
Reduced coronary blood flow.
Hibernating myocardium
Moderate to severe LV dysfunction:
Morbidity and mortality :
Revascularization???
The important clinical issue
Viable myocardium identified
and revascularized:
Improvement in
LV function and survival
Meta-Analysis
3088 Pts
Viability Assessment
 Dobutamine echocardiography;
 Contractile reserve
 Myocardial Perfusion SPECT
 Gated Myocardial Perfusion SPECT
 PET
Nuclear Medicine Techniques
 Gated myocardial perfusion SPECT

Tl201 Imaging:




Stress---3-h re-distribution
Stress--------24h re-distribution
Stress----- Re-injection: The best Protocol: assessment of both stressinduced ischemia and viability
Rest------- re-distribution: Only assessment of Viability
 Tc99m-Sestamibi Imaging
 PET

18F-FDG-PET
(FDG-blood flow mismatch)
Myocardial Perfusion SPECT & Viability
 Viable:
 Membrane integrity
 Electromechanical gradients across sarcolemma
In theory imaging agents that reflect regional
myocardial BF and membrane integrity
should provide good information regarding
tissue viability.
Modifications in 201Tl Imaging protocols
 Late Tl-201 Redistribution Imaging
-
Redistribution is a continual process
22%-54% of irreversible defects at 3-4-hr after stress show
reversibility at 24-hr
 Tl-201 Re-injection Imaging
 Greater accuracy for detection of viability
Stress
induced
Ischemia
and
hinbernation
Modifications in 201Tl Imaging protocols
 Rest-Redistribution Tl-201 imaging
 Only for assessment of viability of the regions with
systolic dysfunction
 Accurate viability data:
 NPV>90%
 Defect
 Reversibility: better predictor
 Level of Tl-201 activity: Mild persistent defect
 No assessment of stress-induced ischemia
Tl-201: Rest Redistribution
Tl-201 vs FDG PET
 Bonow and coworkers:
Tl 201 reinjection imaging has an 88%
concordance with 18FDG PET imaging.
Tc99m-Sestamibi Imaging
 No redistribution after its initial uptake
 Underestimates of viability in chronic CAD and LV
dysfunction
 Excellent as a perfusion agent for assessment of inducible
ischemia
 Useful for viability: quantitative analysis of Tc99m-MIBI
uptake at rest

Enhance the Use of
Tc-99m Sestamibi as a Viability Agent
1- Nitrates: improve collateral blood flow to hypoperfused
areas
 Meta-analysis: nitrate-enhanced sestamibi imaging : a
sensitivity of 86% and a specificity of 83% in predicting
myocardial viability.
2- ECG-Gated SPECT: Concomitant assessment of
ventricular function
3- A novel approach: acquiring ECG-gated SPECT images at


baseline and
during low dose dobutamine infusion
 looking not only at tracer uptake, but also at changes in wall
motion to assess contractile reserve.
Gated SPECT
Viability assessment
Levin et al. showed
Gated SPECT
Increase
sensitivity and overall accuracy of
viability detection compared to the SPECT
18F-FDG
Imaging
 In viable myocardium:
 Metabolic substrate: greater glucose use rather than use
of fatty acids or lactate
 FDG-PET ----- Blood Flow Imaging

Mismatched defect
 Accurate marker
Perfusion
agent
FDG
Metabolism – Hibernation
Perfusion (99mTc-MIBI-SPECT)
Apical
Medial
Basal
Glucose Metabolismus (18F-FDG-PET)
Apical
Medial
Basal
Perfusion-Metabolism-Mismatch
45
40
Mortality (%)
35
30
25
medical
interventional
20
15
10
5
0
mismatch
no mismatch
Di Carli et al., Am J Cardiol 1993
PET Metabolic Imaging:
Assessment of viability
•
Extent and magnitude of the FDG-blood flow mismatch
 predict the magnitude of recovery in global LV function
after revascularization
Normal myocardium
Perfusion
agent
FDG
Hibernating Myocardium
Defect
Perfusion
agent
FDG
Infarcted Myocardium
Defect
Defect
Perfusion
agent
FDG
Viability assessment
 Heart transplant centers: often use PET to determine those
patients in whom coronary artery bypass grafting can be
performed rather than transplantation.
30 to 50% of patients referred for transplantation have
hibernating myocardium based on PET.
These patients do well when revascularized.
Viability assessment
 Haas and coworkers:
 Patients sent to surgery with no viability assessment:
significantly worsened postoperative course,
including a lower 12-month survival rate,
79% versus 97%
Hibernating myocardium
Nuclear Techniques
CAD:
Nuclear imaging appears to
require fewer viable cells for
detection
Higher sensitivity but a
lower specificity than stress
echocardiography for
predicting postrevascularization
improvement of ventricular
function.
Because the gold
standard in the papers
was improvement of LV
function after
revascularization
LV functional
improvement may
not always be
necessary for clinical
improvement
Stress Echo
 There may be a critical mass of myocardium: detect viability in:
 Stress echocardiography
 Functional improvement after revascularization.
 More histologically viable cells : for a segment to exhibit viability
as compared to the NM techniques.
 Segments with 25% viable myocytes showed evidence of viability with:


Stress echo in only 19% of cases,
FDG PET or Tl-201 SPECT in more than 33%of cases
 Radionuclide imaging techniques:
 Require fewer viable cells to show viability, which in many
cases may be insufficient to, at least initially, show functional
improvement after revascularization.
Viability assessment
 The principal goal of myocardial viability
assessment:
 Identify patients whose symptoms and natural
history may improve after revascularization.
Prognostic Implications of FDG PET
Myocardial Imaging
 Up to 50% with perfusion-metabolic mismatch defects:
a cardiac event in 12 months in the absence of
intervention
 The greater the number of mismatched segments, the
greater the risk for subsequent cardiac event
 Predictive after Revascularization:
 For improvement in heart failure symptoms
 Significant improvement in survival
Nuclear Medcine Techniques
 Preservation of the small areas viability detected by perfusion
imaging techniques may improve clinical outcome by
Stabilizing the electrical milieu & preventing lethal
arrhythmias
Preventing a subsequent MI
Improving symptoms and functional capacity through
prevention of deleterious myocardial dilation and
remodeling.
????????
The extent of viability needed for a patient to benefit
from revascularization is unclear and may vary in different
clinical circumstances.
It is not clear that improvement of ventricular function,
regional or global, is necessary :for patient benefit.