Relation of myocardial perfusion at rest and during pharmacologic stress to the PET patterns of tissue viability in patients with severe left ventricular dysfunction

Background. Stress perfusion imaging can assess effectively the amount of j eopardized myocardium, but its use for identifying underperfused but viable myocardium has yielded variable results, We evaluated the relation between measurements of myocardial perfusion at rest and during pharmacologic stre ss and the patterns of tissue viability as determined by positron emission tomographic (PET) imaging. Methods and Results, We studied 33 patients with coronary artery disease an d left ventricular (LV) dysfunction (LV ejection fraction, 30% +/- 8%), PET imaging was used to evaluate regional myocardial perfusion at rest and dur ing pharmacologic stress with [N-13]-ammonia as a flow tracer, and to delin eate patterns of tissue viability (ie, perfusion-metabolism mismatch or mat ch) using [F-18]-deoxyglucose (FDG), We analyzed 429 myocardial regions, of which 229 were dysfunctional at rest. Of these, 30 had normal perfusion an d 199 were hypoperfused, A severe resting defect (deficit >40% below normal ) predicted lack of significant tissue viability; 31 of 35 regions (89%) ha d a PET match pattern denoting transmural fibrosis, Although regions with m ild or moderate resting defects (deficit <40% below normal) showed evidence of metabolic activity, perfusion measurements alone failed to identify reg ions with PET mismatch (reflecting hibernating myocardium), Reversible stre ss defects were observed with slightly higher frequency in regions with a P ET mismatch (10 of 37) than in those with a PET match (36 of 162) pattern o f viability, A reversible stress defect was a specific (78%) marker, but wa s a relatively insensitive marker (27%) of viable myocardium as defined by the PET mismatch pattern, Conclusions. In patients,vith LV dysfunction, the severity of regional cont ractile abnormalities correlates with the severity of flow deficit at rest, Severe reductions in resting blood flow in these dysfunctional regions ide ntify predominantly nonviable myocardium that is unlikely to have improved function after revascularization. Although dysfunctional myocardium with mi ld to moderate flow reductions contains variable amounts of viable tissue ( as assessed by FDG uptake), flow measurements alone do not distinguish betw een regions with PET mismatch (potentially reversible dysfunction) and PET match (irreversible dysfunction), The presence of an irreversible defect on stress imaging is a relatively specific (78%) marker of PET match, whereas a reversible stress defect is a rather insensitive (27%) marker of viabili ty, as defined by the PET mismatch pattern.