Myocardial Perfusion

cardiac output

volume of blood pumped by either ventricle in 1 minute

average male CO

5.6 L/min

average female CO

4.9 L/min

cardiac output formula

CO = SV x HR

SV = systemic volume
HR = heart rate

normal end diastolic volume (EDV)

120 mL

What part of the heart moves the least?

apex

What part of the heart moves the most?

anterior wall

What happens to the septum during a contraction?

thickens and moves toward the left ventricle

akinetic

no wall movement, absent

hypokinetic

diminished movement

dyskinetic

opposite movement, pumping the wrong way, caused by cardiac aneurysm

Arterial narrowing above what percent is clinically significant?

50%

Arterial narrowing above what percent will be seen on a stress test only?

70%

Arterial narrowing above what percent will be seen on a stress test and rest test?

90%

infarct

areas of necrotic myocardium, AKA “fixed defects”

ischemia

diminished blood supply due to narrowing or blockages of coronary arteries, AKA “reversible defects”

Areas of decreased uptake on both stress and rest images are indicative of __

infarct

Areas of decreased uptake on only stress images are indicative of __

ischemia

common causes of increased attenuation

diaphragm and breast tissue

common causes of increased uptake

gut, liver, gallbladder counts

What are the three radiopharmaceuticals used for myocardial perfusion?

201-Thallous Chloride, Tc-99m Tetrofosmin, Tc-99m Sestamibi

Which radiopharmaceutical has to be boiled?

sestamibi

Tl-201

potassium analog that accumulates in viable myocardium, distribution correlates with blood flow

Tl-201 method of localization

active transport via Na+/K+ pump

Tl-201 production

cyclotron

Tl-201 half life

73.1 hours

Tl-201 energy range

68-80 keV (x-rays)

Tl-201 dose

2-5 mCi (ONE dose)

Tl-201 protocol

• patient achieves 85% MPHR, then is injected with Tl-201

• 10 minute wait

• stress images are taken

• 3-4 hour wait (clear liquids only)

• rest images are taken

redistribution

the tracer is cleared from normally perfused myocardium and recirculates in the blood stream where it can re-enter the heart muscle

Why would we reinject Tl-201?

amount of thallium present in bloodstream not sufficient

Tl-201 reinjection techniques

• immediately after stress images, image rest 4 hours later

• immediately after stress images, image rest 1 hours later

• take rest images, if not of high quality reinject Tl-201, image rest 24 hours later

Tc-99m Sestamibi

accumulates in viable myocardium in mitochondria

Tc-99m Sestamibi method of localization

passive diffusion

Tc-99m Sestamibi half life

6 hours

Tc-99m Sestamibi dose (1 day)

1st dose: 8-10 mCi
2nd dose: 24-30 mCi

Tc-99m Sestamibi dose (2 day)

1st dose: 30-40 mCi
2st dose: 30-40 mCi

Tc-99m Tetrofosmin advantages over Sestamibi

• longer shelf life (12 hours)

• no gut uptake

• can scan sooner after injection

• no boiling

Tc-99m Tetrofosmin

accumulates in myocardium in proportion to blood flow; binds to myocytes

Tc-99m Tetrofosmin method of localization

passive diffusion

Tc-99m Tetrofosmin dose (1 day)

1st dose: 8-10 mCi
2nd dose: 24-30 mCi

Tc-99m Tetrofosmin dose (2 day)

1st dose: 30-40 mCi
2st dose: 30-40 mCi

indications for myocardial perfusion

• detect ischemia

• detect CAD (coronary artery disease)

• determine extent of damage after MI (myocardial infarction)

• follow-up after procedures

  • CABG (coronary artery bypass graft)

  • PTCA (percutaneous transluminal coronary angioplasty)

  • stent placement

• evaluation of chest pain, shortness of breath, palpitations

• evaluation of elevated cardiac enzymes

  • CPK (creatinine phosphokinase)

  • LDH (lactose dehydrogenase)

  • Troponin

  • Myoglobin

CABG

coronary artery bypass graft

PTCA

percutaneous transluminal coronary angioplasty

cardiac enzymes

• CPK (creatinine phosphokinase)

• LDH (lactose dehydrogenase)

• Troponin

• Myoglobin

contraindications for myocardial perfusion

• MI within 2-4 days

• caffeine 12-24 hours before

• extremely high blood pressure

• severe arrhythmias

• severe aortic or mitral stenosis

• beta blockers

patient positioning

supine with left arm raised

normal variants

• breast attenuation

• diaphragm attenuation

• respiratory motion

• apical thinning

• left arm attenuation if not raised

test to detect myocardial viability

resting thallium; patient injected 2-5 mCi, 15 min wait, images, 4 hour wait, images

stunned myocardium

myocardium with normal regional perfusion but abnormal contraction

stunned myocardium process

short term, total reduction of coronary blood flow, reestablishment of coronary blood flow (results in left ventricle dysfunction)

hibernating myocardium

chronically ischemic myocardium with decreased blood flow and decreased contractility

hibernating myocardium process

chronic but potentially reversible ischemic dysfunction due to a stenosed coronary artery

bullseye quantification

each short axis slice is divided into 5 pieces and maximum counts computed; displayed as a bullseye with apex as center, septum on left, lateral wall on right, anterior wall above, and inferior wall below

gated myocardial perfusion

EKG hookup, R wave triggers data collection, for each SPECT slice the cardiac cycle is divided into 8 bins, bins added together to make a movie “cine”

gated myocardial perfusion allows us to calculate an __

ejection fraction

normal ejection fraction left ventricle

>45%

normal ejection fraction right ventricle

>40%