Positron emission tomography in human myocardial ischemia

Positron emission tomography (PET) enables investigations of regional metabolic processes in myocardium on a noninvasive basis. This report deals with clinical studies employing C-11 palmitate and FDG (F-18-2 deoxyglucose). Experimental and clinical results have shown C-11 palmitate to be a well-suited marker for studies of myocardial fatty acid metabolism. Uptake and clearance of C-11 palmitate are proportional to cardiac work and oxygen consumption. In ten patients with coronary artery disease, at rest, there was no difference of C-11 palmitate uptake and clearance between "normal" and "ischemic" myocardium. In contrast, during atrial pacing, in normal myocardium there was a higher increase in C-11 palmitate uptake and more rapid clearance than in ischemic myocardial zones. In the presence of very compromised flow, however, due to diminished appearance of the marker, the activity curves cannot be reliably assessed. FDG is a useful marker for studies of glucose uptake and metabolic activity. In 13 of 15 patients studied two days to 13 weeks after myocardial infarction, in the hypoperfused myocardial zone there was increased FDG uptake. In studies in acute myocardial infarction (40 to 72 hours), zones devoid of FDG uptake subsequently were found to be irreversibly damaged while those with intact FDG uptake at the time of initial investigation were subsequently found to have reversible damage. In 17 patients with coronary artery disease and wall motion impairment, bypass surgery led to improved wall motion in 85% of zones with intact FDG uptake but only in 5% of zones with diminished FDG uptake. On comparison with thallium-201 scintigraphy during exercise, PET demonstrated viable myocardium in 58% or zones with fixed thallium defects while in only 42% was there agreement between the two methods with respect to necrosis. As compared with other diagnostic measures such as EKG, analysis of regional wall motion abnormalities and measurement of regional blood flow, the diagnostic accuracy of PET was clearly superior. New PET equipment in which substantial technological developments have been recently incorporated and new positron-emitting tracers (such as antimyosin antibodies or radioligands) will expand the possibilities for the study of regional myocardial tissue function in humans.