Bw's ch. 16 nuclear cardiology part 4
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Transcript of Bw's ch. 16 nuclear cardiology part 4
Tagenarayan Niwaz
January 23, 2015
Two major goals of testing:
Diagnosis
Absence or presence of CAD
Prognosis
Determine long-term prognosis or the
risk for an adverse outcome over time
The performance characteristics of
radionuclide imaging for diagnosis
often are based on an angiographic
definition of stenosis of ≥50 or 70%
stenosis in epicardial vessel
CAD - more complex process
Plaque progression/growth
Stable unstable plaque transition
Exertional angina/potential for ACS
With evolution of preventive measures, testing
has shifted toward assessment of CV risk
and predicting future events
Risk stratification and assessment of prognosis
by noninvasive imaging –
reducing risk of MI and cardiac death
optimizing the selection of patients for
revascularization vs medical therapies
Goal is to detect patients at risk for:
1. “Hard” cardiac events
Nonfatal MI, cardiac death, all-cause
mortality
2. “Soft” cardiac events
Revascularization, hospital admission for
unstable angina or CHF
More common than hard events
Low risk - <1% per year risk of hard cardiac
events
Least likely to benefit from revascularization strategy
Benefit from medical therapy, risk factor modification
Intermediate risk - 1% to 3% per year risk
High risk - >3% per year risk
Most likely to benefit from revascularization strategy
Extent of perfusion abnormality by stress MPI - important relationship with subsequent likelihood of an adverse natural history outcome. A = small defect. B = large defect
Incremental Prognostic Value N = 2,200 patientsMPI Further risk stratification
Revascularization better if >10% of ischemic myocardium involved
N= 10,000 patients with suspected CAD studied by stress MPI
Normal study - hard event rate (i.e., rate of
cardiac death or nonfatal MI) occurring during
an average follow-up period of 2 years is
0.7% per year
Low-risk outcome after a normal MPI study extends
approximately 2 years after testing
Higher risk in pts w/ prev risk factors (DM, smoking)
Seen with a board spectrum of isotopes, protocols,
and stressors
If CAD is present by CATH w/ stable
symptom complex, a normal stress MPI
study result is associated with a low-risk
outcome (Approx 0.9% per year)
Why normal MPI?
Preserved endothelial function, allowing
appropriate flow-mediated vasodilation during
stress, reduced impact stenosis on downstream
myocardial perfusion
Preserved endothelial function - less
susceptible to plaque fissuring or rupture
Another mechanism may involve the presence
of collateral circulation, allowing normal
stress perfusion in the setting of a stenosis,
and protecting against infarction should the
stenosis become completely occluded
PET or SPECT assessment - improvement in
stress perfusion after statin therapy
No change in degree of luminal stenosis but due to
statin-mediated improvement in endothelial
function
Changes in perfusion – define patients that can
gain benefit from statin therapy in terms of
vascular stability
Long term follow up needed
Extent Of IschemiaAfter Statin
Angiography - gold standard to detect CAD
Accuracy of noninvasive testing is based upon:
Sensitivity
Percentage of true-positive test results among those with
CAD as defined by angiography
Specificity
Percentage of true-negative test results among subjects
without CAD
Coronary atherosclerosis - complex disease process Involving the coronary arteries diffusely and not
focally
Underlying disease still present
Whether a discrete stenotic lesion seen at rest during Cath results in a perfusion abnormality during stress 1. Dependent on the percentage degree of stenosis
2. Dilatory or constrictor response of the vessel during stress (mediated by endothelial function)
3. Presence or absence of collaterals
Epicardial vessel with 70% stenosis but preserved
endothelial function and collateral supply may have a
normal stress MPI
False-negative finding b/c CAD exist, reduced MPI
sensitivity
MPI data - correct physiologic information with
adequet blood flow reserve despite coronary
stenosis
This example illustrates the limitation of using
angiography as a gold standard in evaluation of a
physiologic modality
Isolated septal reversible perfusion defects Due to flow between the LAD and LCx territories 2/2
to delayed relaxation of the septum in LBBB leading to reduced coronary flow reserve in early diastole
See in pts w/ LBBB w/o stenosis of the LAD
Decrease specificity and predictive value of a septal perfusion defect with LBBB
Apical or anterior involvement in septal perfusion defects increases the specificity for CAD
Septal defect in LBBB – seen w/ high heart rates pharmacologic stress improves specificity
Asymmetric septal hypertrophy – seen in HCM,
appearance of greater amount tracer uptake in the
hypertrophied septum relative to the lateral wall
Lateral wall perfusion defect
Asymptomatic patients with HCM – can have inducible,
reversible perfusion abnormalities in the absence of
CAD, typically involving the septum
Possibly related to microvascular abnormalities
Unfavorable prognosis
Apex consistent with infarctionHypertrophied septum
Silent Ischemia In The Anterior, Lateral, And Inferior Wall in HCM
MPI perfusion abnormalities – can develop in
patients with pressure overload LVH related
to either hypertension or aortic stenosis
In the absence of CAD – may represent regional
myocardial ischemia based on abnormal
microcirculation and limited vasodilator reserve
Accuracy of MPI w/ LVH to detect CAD = to pts
without LVH
ACC/AHA Guidelines: Class I indication for CAD
detection when LVH present
Abnormalities MPI - common in
patients with dilated
cardiomyopathy despite normal
epicardial coronary arteries
Likely a result of abnormal coronary
flow reserve
Worse prognosis, even in the absence
of CAD
LV systolic dysfunction – MPI help
distinguishing those w/ cardiomyopathy due to
CAD (potentially reversible LV dysfunction) vs
those with Idiopathic, Non Ischemic Dilated
Cardiomyopathy
Normal MPI usually excludes CAD as the cause
of the cardiomyopathy
Abnormal MPI usually associated with CAD
rather than with Non Ischemic Dilated
Cardiomyopathy
• MPI Stress/Rest in a patient with LV Dysfunction – low likelihood of CAD
Abnormalities in myocardial perfusion detected by SPECT MPI have been demonstrated in patients with coronary endothelial dysfunction w/o “significant” epicardial stenosis
These findings represent true abnormalities in coronary flow reserve Improvement in perfusion on follow-up MPI after
treatment with medical therapies directed at improving endothelial function
Data from Cardiac MRI - demonstrating blunted subendocardial coronary flow reserve in patients with angina and normal coronary arteries
2003 ACC/AHA/ASNC Radionuclide Imaging
Guidelines Sensitivity and Specificity
Metanalysis - 33 studies; 4,480 patients w/ exercise
SPECT imaging
Sensitivity to detect CAD is 87% (range, 71% to
97%)
Specificity to rule out CAD is 73% (range, 36% to
100%)
Limited incorporation of ECG-gated SPECT imaging
of regional function or attenuation correction
Enhanced specificity
201Tl (thallium) vs 99mTc-sestamibi - no
significant improvement in sensitivity or
specificity
Exception - improved specificity in women
with 99mTc-sestamibi vs 201Tl
99mTc-based agents - greater photon
energy,
Better for obese patients and those with large
breasts
Higher-quality gated images
Intraobserver and Interobserver variability
in the visual analysis of myocardial
perfusion images can occur
Quantitative analysis of MPI
Developed to reduce the variability in reading
by
“Objectifying” image analysis by comparing
regional uptake values against a database of
normal values
Emory Toolbox,1 Cedars QPS,60 and 4D-
MSPECT
Compared:
4DMSPECT (4DM), Emory Cardiac Toolbox (ECTb),
and Cedars Quantitative Perfusion SPECT (QPS)
N= 1,052 consecutive pts w/ 2-day stress/rest
99mTc-sestamibi MPS studies
Reference classifications - three physicians, w/
> 25 years of experience in nuclear cardiology
Conclusion: 4D-MSPECT showing the best
performance and Emory Toolbox,1 the worst
Large apical reversible defect
Sensitivity and Specificity of vasodilator
pharmacologic stress combined with MPI
for the detection of CAD
Similar to exercise stress
Lexiscan MPI = Treadmill MPI
2003 ACC/AHA/ASNC Radionuclide
Imaging Guidelines
2,465 Patients and 17 studies
Sensitivity of 89% and specificity of 75%
Dobutamine Stress- similar to
pharmacologic and exercise stress
modalities for the detection of CAD
Downsides: Maximal coronary flow reserve is
not achieved as often as with vasodilator
stressors and side effects
Hence, dobutamine recommended only when
adenosine, dipyridamole, or regadenoson is
contraindicated
Reactive airways disease
Sensitivity of MPI highest when the
highest possible level of oxygen demand
is achieved to stimulate the greatest
coronary flow reserve
For exercise ECG testing - sensitivity
decrease if maximum predicted heart
<85% not achieved
If unable to reach goal, convert to
pharmacologic test
Perfusion changes occur at lower degrees of
supply-demand mismatch vs EKG changes
Sensitivity of MPI to detect CAD seen maintained at
lower workloads
Pts with CAD - stressed with MPI at a maximal
workload and then again at submaximal workload
No difference in sensitivity between the maximal and
the submaximal tests
Extent and severity of reversible perfusion defects were
diminished at submaximal compared with maximal
workloads
Exercise is the preferred stressor
Allows for association of symptoms
with perfusion abnormalities
Incorporation of validated stress test
criteria
Duke Treadmill Score, heart rate reserve,
or heart rate recovery with the MPI data