Cardiac stress test

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Under resting conditions, coronary stenosis up to 90% are usually not a/w perfusion abnormality.

Stenosis greater than 70% are significant by angiography, but vary in significance, therefor functional imaging is useful.


Radiopharmaceuticals

Thallium 201

Highest first-pass extraction fraction of any commonly used perfusion tracer, extraction efficiency 90%
K analog tha uses ATPase NA-K pump
Undergoes redistribution - as TI clears from myocardium, it's replaced by circulating TI
Cold defects on early images are due to decreased flow
Ischemic myocardium will fill in on delayed imaging


Tc Sestamibi - Extraction efficiency 60%, diffuses passively into myocardial cells then localizes in mitochondria

Rest - inject 5-8 mCi then wait 30-60 minutes to imgae (allows for hepatic clearance)
Stress - inject 15-24 mCi on treadmill, wait 30-60 minutes to image


Tc Tetrofosmin - Extraction efficiency 50%


Rudidium - Extraction efficiency 60%


Nitrogen 13 Ammonia - Extraction efficiency 70%


Stress Agents

Dipyridamole (Persantine)

Adenosine deaminase inhibitor, potent vasodilator
Side effects include dizzyness, headache, chest pain, flushing, nausea. Can give aminophylline (100-200mg) for severe side effects
Contraindicated in patients with asthma and COPD
Defects indicate a flow reserve deficit


Adenosine

Potenet vasodilator
Very short half life (<10s)
Similar side effects as above, if occur, stop infusion and give supportive case as needed
6 min infusion with radiotracer inhected at 3 min (140 ug/kg/min)
Contraindications: sinus node disease, 2nd for 3rd degree heart block, asthma, COPD
Defects indicate a flow reserve deficit


Dobutamine

Beta agonist that increases myocardial O2 demand by increasing heart rate and contractility
Used when adenosine or dipyridamole are contraindicated (asthma, COPD, caffine)
Half life of 2 minutes, can use beta blocker to counteract side effects.

Special Situations

Left Bundle Branch Block - Dipyridamole or adenosine preferred bause they don't increase HR which can give false positive of septal ischemia