Stress Testing Protocols Flashcards
CBF decreases at rest only once stenosis is >80%
Under hyperemic conditions, see decreased flow in stenosed vessel vs normal at stenosis >50%
Flow disparity is FIRST STEP in ischemic cascade
Sxs is LAST STEP
ST depression is next-to-last step
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To optimize exercise stress, want to achieve at least 6 min exercise (allows max metabolic demand)
<5 METs is associated with signif increase in mortality vs all other METs achieved categories, even over short-term (5 yrs)
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Absolute contraindications for exercise
Unstable angina Decomp CHF BP 200/115 MI within prior 4 DAYS Severe pulmonary HTN Acute myocarditis (or pericarditis) Severe AS --still listed as absolute contraind
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Relative contraindications for exercise
Left main stenosis (not absolute, like severe AS)
Moderate AS
HCM
High grade AVB (can still do it, vs can’t do pharm)
History of significant tachyarrhythmias, even if controlled at present
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When to stop treadmill
Moderate to severe angina Marked dyspnea, fatigue, near-syncope Signs of POOR PERFUSION (cyanosis?) ST depression > 2mm Sustained SVT BP drop > 10 mmHg IF ALSO accompanied by signs of ischemia BP 250/115
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Absolute contraindications for vasodilator stress
History of severe asthma/COPD (steroids, O2 dependent)
Active wheezing
BP <90
HR <40
PO persantine (Aggrenox) within 48 hrs–CANT DO ADENOSINE/REGADENOSON, but can do persantine (high dose overwhelms small amount present at rest)
Caffeine or Theophylline within 12 hrs
High grade AVB or SSS
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Persantine
Inhibits degradation of naturally occurring adenosine so levels increase in extra cellular space–>acts on cell membrane receptors (including vascular smooth muscle cells).
If taking Aggrenox, there’s low level persantine around at rest with accentuated adenosine concentrations at rest.
When give IV adenosine for stress images, don’t get that much higher adenosine levels vs at rest.
But if give IV persantine, you do get much higher adenosine levels
Half life 30-60 minutes
Protocol:
Infusion is for 4 minutes
WAIT 4 MIN after infusion before inject tracer (to allow time for max hyperemia)
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Adenosine
A2 receptor is the one we want (smooth muscle cells)
Half life 2-10 seconds
Protocol: 4-6 min infusion
Inject tracer halfway (3 min)
If combo with exercise, start exercise before adenosine and stop exercise after injection of tracer
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Regadenoson
Dyspnea in 60%
Flushing in 30-40%
Dizziness 25%
Still hits weakly on other A receptors
But almost no effect on receptors causing bronchospasm or AV block–eliminates AVB side effect
Still can get bronchospasm so for boards, same contraindications as adenosine/persantine regarding lung dz
Half life 3-5 min
Can cause seizures
Protocol:
Bolus inject
Then inject tracer 10-20 sec after flush
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Dobutamine contraindications
Similar to exercise
Lists AS and HCM (Absolute with dob?) Large AAA (not contraindication to exercise)
Hemodynamic effects:
SBP rises
DBP falls
Half life–2 minutes
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SPECT protocols–Tc
If do stress-rest, can stop after one image if normal;
But use low dose Tc for stress (bc first image)= poorer quality
Need A.C. if doing stress first (bc need to be see it’s normal)
For rest images, wait 1 hour btw rest injection and imaging–for liver/gut to clear
For stress images, wait 15 min btw stress injection and imaging if EXERCISE;
wait 30-60 min if vasodilator (for liver and bowel tracer to clear)
Always wait 3 HOURS BETWEEN TESTS btw 1st and 2nd images, regardless of which you do first–to allow Tc to decay enough, and clear from myocytes (biological half-life)
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Thallium
Always do only one injection bc it redistributes over time
Stress first–**wait 10 min to image if exercise–clears myocardium fast (redistribution) so if mildly ischemic territory, it may redistribute and fill in if wait more than 10 min to image;
? 15-30 min wait if pharm?
Shorter wait time than Tc bc clears liver and gut much faster (mostly kidney excretion)
Then wait 2.5-4 hrs delay and reimage (allows redistribution, hence rest imaging)
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Interpretation and Reporting
First step = review unprocessed data
Last step = review clinical data and pt history
Steps to looking at images:
1) check orientation (axis)
2) align slices
3) normalize intensity (to myocardium, not to extracardiac tracer)
4) look for defects
5) confirm defect in multiple projections
For CAD territories, for Board exam:
Anterolateral is LCX (not LAD)
Apicolateral is LCX
Inferolateral is LCX (not RCA)
Inferoseptal is RCA
Apical inferior is RCA (not LAD)
Defect severity
Qualitative:
Mild = decrease in counts without wall thinning
Moderate = wall thinning appearance
Severe = defect approaches background activity
Quantitative: 0 = normal 1 = mild reduced counts 2 = moderately reduced counts 3 = severely reduced counts 4 = absent uptake
**Defect size:
Small = <10% of LV, 1-2 segments (17 segment model)
Moderate/medium = 10-20% of LV, 3-4 segments
Large = >20%, 5 or more segments
SSS (summed stress): gives total extent of CAD burden (includes ischemia and scar)
SDS (summed difference): extent of ischemia
When call defect reversible:
Must improve by at least 2 quantitative grades (eg 4 to 2, ie severe to moderate) OR improve to score of 1 (mild), i.e. can go from moderate to mild
If above criteria met, but doesn’t completely normalize, you call it “partially reversible”
Vast majority of study conclusions should be “Normal” or “Abnormal”
Make sure to address the clinical question posed as reason for testing
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Interpretation–gated images
Wall thickening best seen on color
Wall motion best seen on gray scale
(it should thicken and move)
RV size and fxn best seen in gray scale
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