Assessment of myocardial viability by use of 11C-acetate and positron emission tomography : Threshold criteria of reversible dysfunction

Dual positron emission tomography (PET) imaging with a perfusion tracer and 18F-fluorodeoxyglucose (FDG) can detect myocardial viability. This approach may be replaced by a single 11C-acetate study, which enables quantification of both regional blood flow and oxidative metabolism. The significance of acetate-derived indexes for myocardial viability is examined. Thirty postinfarct patients with akinetic ventricular segments, a mean ejection fraction of 42 +/- 11%, and high-grade coronary obstructions were studied with serial 11C-acetate PET scanning before and 7 +/- 5 months after coronary revascularization. Acetate PET was tested against FDG and serial assessments of segmental wall motion. Sixty of 155 severely dysfunctional LV segments improved postoperatively, and regional blood flow increased. Flow estimates after revascularization suggested little fibrosis in reversible segments. At baseline, blood flows differed between normal myocardium, reversible dysfunction, and irreversible dysfunction (1.04 +/- 0.27, 0.73 +/- 0.18, and 0.43 +/- 0.18 mL.min-1.g-1, respectively; P < .001). Oxidative metabolic rates were reduced only in irreversibly injured LV segments. Multivariate analysis identified the acetate perfusion index as the only independent predictor of postoperative recovery. Its predictive accuracy was similar to that of FDG imaging but superior to indexes of flow-metabolic mismatch or oxidative metabolism. After myocardial infarction, quantitative indexes of perfusion and oxidative metabolism from acetate PET indicate a critical threshold beyond which tissue is irreversibly injured. Findings support the use of blood flow as a marker of myocardial viability in chronic postinfarct patients with modestly reduced ejection fractions.