Non-Invasive Cardiac Imaging

Question 1

computed tomography (CT)

• what are the capacities, pros/cons of CT?
• what are its clinical uses?

Answer 1

• pros/cons:
  
  • pros: good for
    
    • cavities
    • lumens
    • calcium
  • cons: does NOT show valves/muscles
    
    • ​thus cannot tell you muscle function
• clinical uses:
  
  • coronary calcium scoring: a means of determining risk of coronary atherosclerosis (“risk strafitication”)
    
    • the idea is that calcifications in/around coronary arteries seen on CT represent degree of calcified atheroma in the arteries, and thus the patients atherosclerosis risk
    • caveats:
      
      • only diagnostic, not interventional
  • coronary virtual angiography: shows lumen of coronary arteries
    
    • caveats:
      
      • only diagnostic, not interventional.
      • requires contrast*

Question 2

Answer 2

Question 3

what imaging modality is used here & what does the image show?

Answer 3

• CT scan
  
  • coronary angiography
  • shows progressively worsening coronary artery disease (lumen gets more stenotic/has more plaques)

Question 4

• discuss the recommendations for CT calcium scoring. for what populations is this testing reasonable, possibly reasonable, and not recommended (has no benefit)?

Answer 4

• Class IIA - reasonable
  
  • for asymptomatic adults wiith intermediate cardiovascular risk (10-20% 10-year risk)
• Class IIB - may be reasonable
  
  • for people at low to intermediate cardiovascular risk (6-10% 10-year risk)
• Class III - no benefit
  
  • for people at low cardiovascular risk (<6% 10 year risk). these pts should NOT undergo calcium scoring

Question 5

for which patients is CT coronary angiography NOT recommended?

Answer 5

• Class III - no benefit
  
  • not recommended as a cardiovascular risk assessment in any asymptomatic patient

Question 6

• nuclear scintograophy
  
  • uses/pros/cons
  • what are the different types?

Answer 6

• pros/cons
  
  • pros: good for stress testing
    
    • can show myocardial viability (in terms of metabolic/perfusion capacity) while patient is active
  • cons: not universally available
• types:
  
  • single photo emessions CT (SPECT)
    
    • Tc⁹⁹/Sestamibi - measures perfusion
  • position emission tomography (PET)
    
    • ¹⁸F-deoxyglucose - measures metabolism
      
      • this is good to look at metabolic status of adjacent sections of cardiac tissue. can be used to dx sarcoid
    • ¹³N-ammonia - measures perfusion

Question 7

what is a multi-gated acuisition scan?

• what does it tell you?
• how is it done?
• what are its clinical uses?

Answer 7

• A Multi-Gated Acquisition Scan (MUGA)
  
  • tells you the heart’s ejection fraction (EF).
    
    • and IV tracer is injected into the bloodstream and fills the heart chambers. the end-diastolic and end-systolic blood volume in the LV are measured to tell you EF
  • clinical uses:
    
    • a reliable test that doesn’t rely heavily on the operator, though it isnt often used anymore
    • has a niche role in oncology: monitors heart function of patient who is doing potentially cardiotoxic chemotherapy

Question 8

cardiac MRI

what are its capacities, clinical uses, pros/cons ect?

Answer 8

• capacities:
  
  • shows muscle
  • shows valves
  • shows pericardium
• clinical uses/pros:
  
  • is the best option for showing valvular function (better than echocardiography)
  • is becoming the gold standard for congestive heart disease, since its shows a greater breadth of anatomy with finer detail
• cons:
  
  • not widely available
  • not great for showing vascular plaque (i.e., not used for coronary artery assessment)

Question 9

when is cardiac MRI not recommended?

Answer 9

• Class III - no benefit
  
  • MRI for detection of vascular plaque is not recommended for cardiovascular risk assessment in asymptomatic adults

Question 10

echocardiography

• what are its clinical uses, capacities pros/cons ect?
• types of echocardiography?

Answer 10

• capacities
  
  • valve function assessment
    
    • ​recall that its the standard for determining degree of stenosis/regurgitation in mitral stenosis/regurgitation
    • note that cardiac MRI might be better
  • shows pressure gradients across valves
  • doppler flow
• cons:
  
  • doesn’t tell you myocardial viability (need SPECT for that)
  • doesn’t show coronary arteries (use CT angiography for that)
• types of echocardiography:
  
  • TTE - cheap, quick, available everywhere
  • TEE - requires sedation

Question 11

• what are the major “stress methods” for assessing cardiovascular function?
  
  • how are they done and what purpose do they serve?
  • under which circumstances is each test ideal?

Answer 11

• “stress methods” are done to induce stress - i.e., increase oxygen demand - of the cardiac tissue so that the capacity of coronary blood flow can be assessed (can look for coronary artery disease)
  
  • exercise
    
    • how its done:
      
      • w/ a treadmill.
      • pt does “bruce protocol” - speed/incline of treadmill is intermittently increased, for a max of 30 minutes
    • when its used:
      
      • this is the #1 stress test choice if pt can walk.
      • use an alternate test if pt cannot walk (uses walker, crushing chest pain when walking, ect)
  • vasodilators: lexiscan, adenosine, dipyridamole
    
    • how its done:
      
      • vasodilators will induce dilation in healthy coronary arteries but not diseased ones. if pt has CAD, all blood flow will get redirected to the other arteries, and certain cardiac tissue will be hypoperfused
    • when its done:
      
      • if exercise contraindicated
      • or, if pt is a low risk for CAD: give dilators & assess w/ ECHO
      • can be used for any pt, just need IV access
  • ionotropes: dobutamine
    
    • ​how its done:
      
      • dobutamine is both ionotropic/chronotropic, increasing contractility/HR. this increases O2 demand
    • when its done
      
      • like vasodilators, 2nd choice to exercise.
      • is contraindicated in patients with critical aortic valve disease

Question 12

discuss the imaging methods used to interpret the way that the heart responses to induced stress.

• how does each method work?
• how should you decide which test to use?

Answer 12

• the following methods are in order from most to least specific (and from least to most sensitive). as a general rule: you opt for lower sensitivity with lower suspicion of CAD, and higher sensitivity with higher suspiscion of CAD.
  
  • EKG
    
    • look for ST changes, which indicate ischemia.
    • EKG must be interpretable.
      
      • for example, cant used this method in pt w/a bundle banch block, as their ST segment won’t be visible
    • most specific, least sensitive: opt for this test with low suspicion of CAD.
      
      • ex: 21 yr old with mild chest pain & no family hx of CAD ​
  • ECHO
    
    • ​look for differences in kinetic activity in adjacent cardiac segments. a relatively hypokinetic/akinetic cardiac segment indicates hypoperfusion (ischemia) in this area
  • MUGA
    
    • ​look at ejection fraction. a lower EF may indicate hypoperfusion/ischemia
  • SPECT
    
    • ​this method tells you the viability of cardiac tissue (tells level of perfusion/metabolism). low viability indicates ischeima
    • most sensitive, least specific: order this test with a high suscpicion of CAD
      
      • ex: an older patient with hx of previous coronary of revascularization

Question 13

what is a contraindication to all stress testing?

Answer 13

if they have an unstable disease somewhere else
eg: bleed in the brain, dissected aorta - fix those things first instead of doing a stess test.

Question 14

outline the process of deciding what stress tests/imaging methods to choose in the assessment of CAD

Answer 14

• when to not do any stress testing:
  
  • if they are immediate/high risk for CAD - don’t do stress testing, just take them to the cath lab and fix it.
  • if stress testing is contraindicated: - if they have an unstable disease somewhere else

MPI = SPECT test.

previous coronary vascularization: would mean having a catheter, or a stent put in

baseline EKG is uninterpretable: example would be a bundle branch block, cant see ST segment in this person. do an echo instead.

Question 15

what are the vasodilators used to induce stress testing?

Answer 15

Lexiscan

Adenosine - use if pt is over 150 kg

Dipyridamole