The reverse flow-metabolism mismatch pattern seen in cardiac PET viability scans is unrelated to underlying degree of coronary stenosis

Abstract

Background: Cardiac PET with N-13 ammonia (NH 3) is frequently used to quantify myocardial blood flow (MBF). Myocardial metabolism is often evaluated with F-18 fluorodeoxyglucose (FDG) in patients with ischemic cardiomyopathy. The interplay between MBF and FDG uptake in areas with a reverse flow-metabolism, or reverse mismatch (RMM), pattern [normal NH 3 / decreased FDG] remains unclear, but such regions have been found to be dysfunctional. The aim of this study was to determine if MBF in areas showing RMM is abnormal in patients with documented coronary artery disease undergoing cardiac PET for the assessment of viability. Methods: PET viability studies of 28 patients (age 62±12 yrs; 22 males) were evaluated. Scans were divided into nine standardized segments. The flow-metabolism pattern in each segment was classified by two experienced readers as normal [normal NH 3/ normal FDG], RMM [normal NH 3 / ↓FDG], hibernating [↓NH 3/ ↑FDG], infarcted [↓NH 3/ ↓FDG] or admixture [inhomogeneous NH 3/ inhomogeneous FDG]. The global MBF within each segment was quantified using a 2-compartment kinetic model. Cardiac catheterization data for all 28 patients were reviewed. Results: A total of 242 cardiac segments were analyzed. The global MBF in 38 normal segments did not differ from that in 82 RMM segments (0.79±0.23 vs. 0.75±0.23 ml/g/min; p = NS). MBF was lower in 63 hibernating (0.65±0.21 ml/g/min), 43 infarcted (0.49±0.18 ml/g/min), and 16 admixture (0.61±0.23 ml/g/min) segments compared with normal regions (p<0.05 for all). No relationship was noted between the severity of coronary stenoses in arteries subtending RMM segments; while 44% of RMM segments were supplied by totally occluded vessels, 40% of RMM segments were supplied by arteries without obstructive lesions. Conclusions: MBF in regions of RMM is not different from MBF in normal regions. The RMM pattern is unrelated to the presence of obstructive coronary stenoses in vessels supplying affected regions, but likely reflects a metabolic derangement in glucose uptake in regions that are viable, but dysfunctional and likely jeopardized.