PET And Viability Flashcards
Peak stress EF with PET
(Short half life of tracers so have to image right away, and no need wait for clearance from extracardiac sites)
PET better TEMPORAL (as well as spatial) resolution
Better diagnostic vs SPECT:
Sensitivity 90%
Specificity 89%
About the same prognostic vs SPECT
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Coronary flow reserve with PET gives good prognostic info (correlates with CV mortality)
CFR = stress CBF/ rest CBF
Reason you can quantify absolute CBF is bc you have such accurate attenuation correction
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PET indications
Equivocal SPECT
Need pharm stress (can’t exercise, LBBB/paced)
Identical AUC
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A.C.
Used with every PET scan
Transmission source is CT or radionuclide
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When assess viability?
Low EF
Ischemic CMP
No angina (if +angina, at least some is viable!–you revascularize)
No ischemia (if + ischemia, means rest is normal perfusion–it’s viable!)
Appropriateness say you can go straight to Cath or do noninvasive ischemia testing for new systolic CHF
Regional fixed defects not always CAD!!, just means “fibrosis”–
myocarditis, sarcoid
In CHF pts:
NPV of NORMAL MPI is HIGH
PPV of ABNORMAL MPI (for ischemic CMP basis) is LOW
Ischemia is BEST predictor that hypocontractile myocardium will recover after revasc
Corollary: sometimes with ISCHEMIC CMP, still have NORMAL REST PERFUSION (repetitive stunning > hibernating?)
And with NONISCHEMIC CMP, often have NORMAL perfusion in hypocontractile segments (depends how much fibrosis is present there)
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Contractile function (i.e. loss of contractile reserve) is LAST to go in hibernation (metabolism changes occur much earlier)
So if only use dobut echo to assess viability, a positive response is very SPECIFIC but not sensitive (misses areas where metabolism is off but not yet hypocontractile)
Whereas metabolism imaging high sensitivity (>90%), not great specificity (65%)
Can use tracer uptake in hypocontractile region to predict viability (if >60% peak tracer activity in myocardium)–? can you skip FDG or dobut echo …doubt bc still some not viable)…“a useful guide”
If <40%, likely not viable
If combine quant uptake on SPECT with dobut contractile reserve, get good accuracy to predict recovery
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Thallium redistribution
Stress, then rest images
About 50% fixed defects at 4 hrs on standard stress-redistribution imaging will fill in (“viable”) if reinject Thall prior to 4 HR images
(Wait 10 min after reinject before imaging the 4 HR redistribution images)
About 25% not filled in at 24 hrs still viable by FDG
Thall less sensitive than FDG PET
As opposed to stress-rest Thall for ischemia, for viability you REINJECT Thall (1 mCi, bs 3-4 mCi for stress) prior to the 4 HR redistribution imaging (to increase concentration in blood pool, and incr gradient blood-to-myocardium, to enhance fill-in where possible to happen (i.e. Where viable)
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Shift from FA to glucose metabolism in chronically ischemic (viable) myocytes
Hypoxia inhibits B-ox of FAs in myocyte cell
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Studies showing prediction of viability testing
Meta-analysis of retrospective/observational:
Death AND MI better with revasc vs meds in viable group;
In non-viable pts, NO statistical difference btw Tx approaches (TREND numerically toward higher death AND higher MI if revasc the non-viable group)
Suggests threshold of total viable >10% of total myocardium
No RCTs show outcomes benefit
(STICH only used Thall or dobut echo, compared outcomes of revasc vs meds based on viability presence (in substudy))
(PARR-2 compared outcomes among those in standard decision making arm vs FDG PET-guided arm;
negative in intention to treat analysis; but if looked at those pts actually treated based on viability results, CV outcomes better with revasc in that group)
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Factors that seem to modify ability of +viability test result to predict recovery of function (or CV outcomes?)
More remodeled (hi LVESV)–best outcome in viable with no LV dilation;
Extensive amount of scar (eg on CMR but also size of scar on perfusion images of the FDG PET has shown to predict recovery of function)
Lower baseline LVEF less likely to recover
Time to revasc (shorter duration of hibernation shows better outcomes for viable segments in some studies)
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