Cardiac Evaluation

Stockton MRI & Molecular Imaging

• PET-CT: Myocardial Viability Evaluation
• Cardiac MUGA

PET-CT MYOCARDIAL VIABILITY Evaluation

INDICATION

A myocardial FDG PET-CT scan is used to distinguish between scar and dysfunctional but viable myocardial tissue, particularly helpful in deciding management and revascularization therapy in patients with ischemic cardiomyopathy and left ventricular dysfunction.3 Myocardial viability is evaluated by using fluorine-18 2-fluoro-2-deoxyglucose (FDG), a radiolabelled glucose (analog) tracer, to image the distribution of glucose uptake in the left ventricular myocardium as an indicator of regional metabolic activity. See "What is PET-CT?" and "What is FDG?" for more information.

EXAMPLE

A 65 year old male patient with coronary artery disease, dilated cardiomyopathy, CHF with an LVEF < 20% was being considered for possible revascularization. A resting myocardial perfusion scan was followed by a PET-CT myocardial viability scan. Although perfusion of the inferior left ventricular myocardial wall was notably decreased (figure 1), the inferior wall remained viable (figure 2). Apical wall decreased perfusion also showed partial viability.

	Figure 1. Resting myocardial perfusion (Tc-99m sestamibi): Selected images of the left ventricular myocardium show decreased perfusion throughout the inferior wall and apex.	Figure 2: Myocardial metabolic imaging (FDG PET-CT): Corresponding images of the left ventricular myocardium show notable preserved metabolic activity in the inferior wall, also partially in the apex.

ACCURACY

A literature review of FDG PET in the assessment of viable myocardium examined 11 studies published between 1986 and 2000 (NEJM, J Am Coll Cardiol, Am Heart J, Am J Cardiol, Circulation, Eur J Nucl Med).3 All studies used overall cardiac functional improvement post revascularization as the gold standard for comparison with the FDG-PET findings. With a total of 432 patients, the overall multi-study average statistics were as follows:

• sensitivity 89%,
• specificity 73%,
• positive predictive value 74%,
• negative predictive value 86%,
• accuracy 89%.

MEDICARE

According to the Medicare National Coverage Determinations Manual: "Medicare covers FDG PET for the determination of myocardial viability as a primary or initial diagnostic study prior to revascularization."4

PATIENT PREPARATION and PROCEDURE

• FASTING STATE: NPO (except water, medications) for at least 4-6 hours prior to arrival is very important. We will administer intravenous dextrose loading and/or insulin in order to promote glucose substrate use in myocardial oxidative metabolism. This will be followed by close monitoring of blood glucose levels in order to determine the appropriate time to inject intravenous FDG.
• DIABETIC PATIENTS: Elevated glucose levels in an uncontrolled diabetic patient can significantly reduce the optimal quality of the test; therefore, establishing better diabetes control is highly recommended prior to undergoing this procedure.
• DURATION: The entire procedure will last approximately 3 hours, including injections and uptake times, the resting nuclear myocardial perfusion scan (20 min), and the PET-CT myocardial viability scan (25 min).
• See also What should I expect on the day of my PET-CT scan? and Patient Preparation for a PET-CT scan.

REFERENCES

1. Bacharach et al. American Society of Nuclear Cardiology Practice Guidelines. J Nucl Cardio, Vol.10 No.5, Sept/Oct 2003.
2. Clark et al. Nuclear Cardiology in Clinical Practice. Q J Nucl Med Mol Imaging, 2005;49:43-58.
3. Gambhir et al. A Tabulated Summary of the FDG PET Literature. J Nucl Med, Vol. 42, No. 5, May 2001.
4. Medicare National Coverage Determinations Manual…PDF
5. Streeter et al. Clinical glucose loading protocol for F-18 FDG myocardial viability imaging. Molec Imaging Biol 2002; 4:192.
6. Takalkar et al. PET in Cardiology. Radiol Clin N Am 43 (2005) 107 - 119.