Myocardial Perfusion Scintigraphy

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Contents 1 Indications 2 Contraindications 3 Procedure 4 More General Terms 5 Additional Terms 6 References

Indications

• ECG stress testing for patients with suspected coronary artery disease

• failed treadmill testing
• cannot undergo treadmill testing
• baseline ECG that renders treadmill testing inappropriate
• yearly testing not unreasonable in high-risk patients [6]

• triage in patients presenting to the emergency room with chest pain & ECG without evidence of acute myocardial ischemia (non- ST segment elevation myocardial infarction, NSTEMI)
  

• prognostic value similar to dobutamine stress echocardiography [4]

Contraindications

• baseline second degree heart block is a contraindication to use of adenosine

Procedure

• 
  

• Perfusion imaging agents include:

• Tl[201]
• Tc[99]sestamibi
• Tc[99]teboroxime
• Tc[99]tetrofosmin
  

• A resting image of myocardial uptake of Tl[201] administered in the form of thallous chloride is compared with a post vasodilation uptake of Tc[99] in the form of sestamibi. Vasodilation* may be induced by:

• exercise
• persantine
• adenosine
• dobutamine# [5]
  

• * A 3-5 fold increase in blood flow normally occurs.
• # beta-blocker must be held prior to the test
  
• 3 mCi of Tl[201] in the form of thallous chloride is administered IV. Cardiac muscle has an extraction efficiency of 80-90% for Tl+. Approximately 4% of administered Tl+ is taken up by the myocardium. Myocardial uptake is dependent upon blood flow. A redistribution occurs reflecting the local K+ pool (i.e. viable myocardium). Redistribution appears to be complete in 3-5 hours. Therefore imaging should be begun within 5 minutes of Tl[201] injection.
  
• Emitted radiation is sensed with an Anger type gamma counter with either medium or high resolution collimators. Images are obtained from the anterior & at least other projections 40 & 70 degrees so that all cardiac segments are well visualized.
  
• Persantine 0.57 mg/kg is injected IV over 4 minutes. At 7 minutes, 25 mCi of Tc[99]-labeled sestamibi is injected. Sestamibi is extracted less efficiently than Tl+ & almost no redistribution occurs. This permits a larger time window between isotope injection & imaging for uptake with vasodilation.
  
• With vasodilation, normal arteries vasodilate, but stenotic vessels do not. Nitroglycerin should be avoided as it will dilate stenotic vessels as well.
  
• Resting images may be then compared with images after vasodilation. Three different perpendicular views including short axis, & two long axes views are obtained. A comparison is made of the resting & vasodilation images in order to identify regions of inviable myocardium & regions of myocardium at risk for ischemia during stress.
  
• False positive results may be obtained in patients with left bundle branch block & severe left ventricular hypertrophy.

More General Terms

• ECG stress testing
• scintigraphy (radionuclide test)

Additional Terms

• dipyridamole (Persantine)
• radionuclide ventriculography (RVG, MUGA)
• sestamibi (Cardiolite)
• single photon emission computed tomography (SPECT)
• teboroxime
• tetrofosmin (Myoview)
• Tl+

References

1. The Guide to Cardiology, 3rd edition, RA Kloner (editor), LeJacq communications, Greenwich Connecticut, 1995
2. Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 86
3. Journal Watch 23(3):24, 2003 Udelson JE et al Myocardial perfusion imaging for evaluation and triage of patients with suspected acute cardiac ischemia: a randomized controlled trial. JAMA 288:2693, 2002 PMID: &dopt=Abstract
4. Journal Watch 24(16):126, 2004
   - Schinkel AF et al Long-term prognostic value of dobutamine stress echocardiography compared with myocardial perfusion scanning in patients unable to perform exercise tests. Am J Med. 2004 Jul 1;117(1):1-9. PMID: [1]
   - Marwick TH. Does the extent of malperfusion or ischemia on stress testing predict future cardiac events? Am J Med. 2004 Jul 1;117(1):58-9. No abstract available. PMID: [2]
5. Medical Knowledge Self Assessment Program (MKSAP) 15, American College of Physicians, Philadelphia 2009
6. Veterans Administration
7. National Guideline Clearinghouse
   - ACC/AHA/ASNC guidelines for the clinical use of cardiac radionuclide imaging: A report of the American College of Cardiology/American Heart Association Task Force on practice guidelines (ACC/AHA/ASNC Committee to revise the 1995 guidelines for the clinical use of cardiac radionuclide imaging). ngc-guideline: [3]

myocardial perfusion & viability scintigraphy