Applications in Cardiology

PET has demonstrated excellent utility for measuring myocardial blood flow and perfusion and for detecting Coronary Artery Disease (CAD). The high-energy emissions of PET tracers produce high-quality images even in obese patients.

Determining whether there is viable myocardium in an area of prior infarction is a very common clinical challenge - one which may determine whether or not a patient requires invasive intervention.

PET has demonstrated excellent utility for this application. An FDG study showing a "mismatch" - i.e., increased glucose utilization in areas of decreased blood flow - may indicate viable myocardium that is likely to respond to revascularization.

Approximately 20% of CAD patients will not benefit from this surgery, however. These are patients showing a "match," in which the myocardial tissue in an area of prior infarction does not show significant glucose consumption in areas of decreased blood flow. This is consistent with the presence of scar tissue and the lack of viable myocardial cells in the region of interest.

In these cases, PET can provide important information for determining which patients will most likely benefit from expensive and highly invasive procedures - and which will not.

In PET images, blocked vessels demonstrate as areas of decreased regional myocardial flow or perfusion. The short half-lives of PET tracers allow sequential rest-stress studies within a short time frame. At rest, regional myocardial perfusion may be maintained despite relatively severe stenosis; however, under stress, coronary arteries with over 50% stenosis exhibit diminished capacity to increase blood flow compared with normal coronary arteries.

However, approximately 20% of CAD patients will not benefit from this surgery. These are patients in whom myocardial tissue in an area of prior infarction does not show significant glucose consumption in areas of decreased blood flow (in PET language, a "match"). This is consistent with the presence of scar tissue and the lack of viable myocardial cells in the region of interest. PET can provide important information for patient selection and to help physicians determine which patients will most likely benefit from expensive and highly invasive procedures, and which will not.

Clinical Example:

January 1994: Normal myocardial perfusion examination.

November 1994: Equivocal myocardial perfusion examination.

December 1994: Unequivocal PET. Stress induced regional hypoperfusion of the lateral wall.

PET result used to avoid SPECT false-positive (and unnecessary catheterization) or false-negative (reduced Quality-Adjusted Life Years). PTCA was performed. Post revascularization scan was nearly normal. Patient has been symptom free since revascularization.

Clinical Example:

64-year-old male. Increasing episodes of angina on exertion and periodic nocturnal angina, responsive to nitroglycerine. Referred for PET exam to identify potentially salvageable segments of the myocardium.

Matching segment of low perfusion and low FDG uptake in the anterior wall. Low perfusion, but significant FDG uptake in segment of free wall. Based on results of PET study, further investigation and possible invasive instruction is indicated in an attempt to improve the blood supply to the ischemic myocardial tissue.