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Core > Nuclear: Cardiac > Flashcards

Nuclear: Cardiac Flashcards

1
Q

What are the most common radiotracers used in myocardial perfusion studies?

A
  • Tc-99m sestamibi
  • Tc-99m Tetrofosmin

Note: Both of these work by passively diffusing into cells and then localizing to mitochondria (they don’t redistribute like thallium, which isn’t used much anymore).

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2
Q

Which is better for myocardial perfusion: sestamibi or tetrofosmin?

A

Tetrofosmin (it is cleared more rapidly from the liver, decreasing the chance of hepatic uptake artifact)

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3
Q

How long after injection should myocardial perfusion scans be done?

A

30-90 min after injecting Tetrofosmin or Sestamibi (allowing for clearance of background)

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4
Q

How bad must coronary artery stenosis be for it to be visible on myocardial perfusion scanning?

A

Non-stress: 90%
Stress: 50%

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5
Q

How long before a myocardial perfusion scan should a pt be NPO

A

NPO for 4 hours prior to the exam (to reduce GI blood flow)

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6
Q

Which medications should be stopped prior to myocardial perfusion scan (if possible)?

A
  • Beta blockers
  • Calcium channel blockers
  • Long acting nitrates

Note: These medications mess with the sensitivity of the stress portion of the scan.

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7
Q

What medication is used for the stress portion of a myocardial perfusion scan (if unable to do the treadmill)?

A

Regadenoson (a specific adenosine receptor agonist that acts as a coronary vasodilator) or dobutamine

Note: Regadenoson is more specific (has less bronchospasm) than adenosine or dipyridamole, which used to be used.

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8
Q

Why is it important to know a pt has a left bundle branch block prior to a myocardial perfusion scan?

A

LBBB can cause a false positive reversible perfusion defect at the septum (anteroseptal region), which is more common with some stress agents

Note: This is probably due to irregular relaxation during diastolic coronary filling.

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9
Q

Should dobutamine be used for the stress portion of a myocardial perfusion scan in a pt with a left bundle branch block?

A

No, you should use a coronary vasodilator (regadenoson, adenosine, or dipyridamole)

Note: Dobutamine causes more false positives in these pts (because it increases the heart rate more, which causes more septal irregularities in LBBB).

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10
Q

Fixed defect (on stress and rest) on a myocardial perfusion scan…

A

Scar from old infarction

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11
Q

Reversible defect (seen on stress, better on rest) on a myocardial perfusion scan…

A

Ischemia

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12
Q

Fixed defect with reversible defect around it on a myocardial perfusion scan…

A

Infarction with peri-infarct ischemia

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13
Q

Left ventricular cavity appears larger on stress than on rest on a myocardial perfusion scan…

A

Think transient ischemic dilatation (from diffuse subendocardial hypo perfusion)

Note: This is associated with high risk disease (left main or 3 vessel disease).

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14
Q

Fixed dilatation of the left ventricular cavity on stress and rest on a myocardial perfusion scan…

A

Dilated cardiomyopathy

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15
Q

Right ventricular activity similar to the left ventricle during the rest portion of a myocardial perfusion scan…

A

Think right ventricular hypertrophy

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16
Q

Lots of bowel/liver activity on a myocardial perfusion scan…

A

Pt isn’t stressed (exercise or medication) enough to shift blood flow from the bowel/liver to the heart

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17
Q

Normal perfusion but poor contractility on a myocardial perfusion scan that improves after a few weeks…

A

Think stunned myocardium

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18
Q

Fixed defect (rest and stress) on myocardial perfusion imaging, but avid FDG uptake…

A

Hibernating myocardium

Note: This is a chronic process resulting from severe CAD and chronic hypoperfusion (myocardial tissue is alive but conserving energy by not contracting because it doesn’t have enough blood supply).

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19
Q

Fixed defect on myocardial perfusion imaging and hot on thallium imaging…

A

Hibernating myocardium

Note: Myocardial tissue is alive (able to take up thallium via Na/K ATPase) but is not contracting to conserving energy because it doesn’t have enough blood supply.

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20
Q

What nuclear imaging study can be done to estimate left ventricular ejection fraction?

A

MUGA (multigated acquisition scan)

Note: This is basically a nuclear angiogram using Tc-99m RBCs. It is more accurate than myocardial perfusion imaging for estimating LVEF.

21
Q

Regional wall motion abnormality on a resting MUGA study…

A
  • Infarction (usually)
  • Stunned myocardium
  • Hibernating myocardium
22
Q

Common causes of an artifactually lowered LVEF on a MUGA study

A

Poor left anterior oblique view (you should be able to see a region of photopenia representing the ventricular septum)

Note: If the left ventricle is overlapping the right ventricle or left atrium, the LVEF will be artifactual lowered.

23
Q

Common causes of an artifactually elevated LVEF on a MUGA study

A

Poor background region of interest

Note: If the background region of interest is placed over the spleen, this will cause oversubtraction of background and artifactually increase the LVEF.

24
Q

What view is used to estimate LVEF on a MUGA study?

A

Left anterior oblique (the best view to visualize the inter ventricular septum)

Note: You can tell positioning is good if you can identify the photopenic ventricular septum.

25
Q

What is abnormal about this MUGA study?

A

Photopenic halo (large pericardial effusion)

26
Q

Rubidium-82

A

A potassium analog that acts similar to thallium-201 (both are taken up by the Na/K pump) and can act as a viability radiotracer

Note: Rarely used because it is expensive and has a very short half life (75 seconds).

27
Q

What are the two radiotracers made by a generator?

A
  • Tc-99m
  • Rubidium
28
Q

Blue vascular territory

A

Left anterior descending artery

Note: The LAD supplies the ventricular apex.

29
Q

Yellow vascular territory

A

Right coronary artery

30
Q

Purple vascular territory

A

Left circumflex artery

31
Q

Arrow

A

Breast-attenuation artifact (decreased activity in the anterior wall, can also affect septal and lateral walls)

Note: Confirm this by ensuring there are no ECG changes or wall motion abnormalities. If you aren’t sure, repeat in the prone position.

32
Q

How can you confirm that decreased activity in the anterior wall on myocardial perfusion imaging is due to breast-attenuation artifact and not true ischemia?

A

If there are no ECG changes or wall motion abnormalities, you can call it artifact.

If you aren’t sure, repeat the study in the prone position.

33
Q

What went wrong?

A

The pt moved during the study (the left ventricle is offset between frames)

34
Q

What went wrong on this myocardial perfusion scan?

A

ECG gating issue

Note: This is the “flickering artifact” (numerous scattered bright pixels).

35
Q

What went wrong?

A

Breast-attenuation artifact

36
Q

What is causing the apparent perfusion defect in the inferior wall in this male pt?

A

Left hemidiaphragm motion

Note: This is not significant using the appropriate male database, but appears significant if the female database is used.

37
Q

What is suboptimal about this myocardial perfusion scan?

A

There is a lot of sub diaphragmatic activity (in the liver/bowel)

Note: You can have the pt exercise a little to shift blood flow from the liver/bowel to the heart.

38
Q

What should you do if there is respiratory motion artifact on a myocardial perfusion scan?

A

Repeat the study immediately

Note: You don’t have to give more radiotracer because it should remain fixed for 2 hours.

39
Q

What is the cause of this septal perfusion defect?

A

Artifact from a left bundle branch block

40
Q

Where is there often an artifactual perfusion defect in pts with a left bundle branch block?

A

Fixed septal defect that spares the apex

41
Q

What often causes artifactually decreased myocardial perfusion due to increased perfusion of the ventricular septum?

A

Hypertrophic cardiomyopathy

Note: Wall motion should be normal.

42
Q

MOA for dipyridamole

A

Inhibition of the breakdown of adenosine (allowing adenosine, a potent vasodilator, to accumulate)

Note: Less significant side effects than adenosine.

43
Q

What is the most significant possible side effect of adenosine?

A

AV block

Note: Fortunately adenosine has a short half-life, so the AV block will only be temporary.

44
Q

MOA for dobutamine

A

Beta 1 agonist (increases heart rate and myocardial contraction)

45
Q

What medication is best to use for myocardial stress testing in pts who have had caffeine within the past 12 hours?

A

Dobutamine (unless pt is on a beta blocker)

Note: You cannot use regadenoson, adenosine, or dipyridamole if the pt has had caffeine recently.

46
Q

Which pharmacological stress agent cannot be used if the pt is on a beta blocker?

A

Dobutamine (a beta 1 agonist)

47
Q

Which pharmacological stress agent is best for pts with COPD or asthma?

A

Dobutamine (beta 1 agonist)

48
Q

Which pharmacological stress agent should be avoided in pts with a left bundle branch block?

A

Dobutamine (increased heart rate makes LBBB artifacts worse)

49
Q

What is the antidote for adenosine (if needed due to AV block)

A

Aminophylline

Note: The half life is even shorter than that for adenosine, so make sure to continue close monitoring of the pt.

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