Cardiac stress test
From Radipedia
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
