Comparative study of rest technetium-99m sestamibi SPET and low-dose dobutamine stress echocardiography for the early assessment of myocardial viability after acute myocardial infarction: Importance of the severity of the infarct-related stenosis

Rest technetium-99m sestamibi single-photon emission tomography (SPET) has been shown to underestimate viability in some patients with chronic ischaemic myocardial dysfunction. The present study was designed to appraise the value of Tc-99m-sestamibi as a viability tracer in patients with a recent myocardial infarction and to determine factors that might influence its accuracy in assessing infarct size, Therefore, rest Tc-99m-sestamibi SPET, low-dose dobutamines stress echocardiography and quantitative coronary angiography were performed in 51 patients with a recent myocardial infarction. Perfusion activity and regional wall motion were scored semi-quantitatively using the same segmental division of tile left ventricle, Assessment of Tc-99m-sestamibi uptake as a marker of viability was performed by comparing a binary uptake score (viable=>50% vs necrotic =less than or equal to 50% of the maximal tracer activity) with a binary wall motion classification during low-dose dobutamine infusion (viable=normal/hypokinetic vs necrotic=akinetic/dyskinetic). Infarct size, expressed as the number of segments With evidence of necrotic tissue, was significantly greater in the scintigraphic study than in the echocardiographic study (2.8+/-1.5 vs 2.2+/-1.3, P=0.006), This overestimation of infarct size by by Tc-99m-sestamibi was present only in patients with a severe infarct-related stenosis (% diameter stenosis greater than or equal to 65%-100%) and particularly those with ''late'' reperfusion therapy (time delay greater than or equal to 180 min), in patients without a severe infarct-related stenosis. Tc-99m-sestamibi was able to accurately distinguish viable from necrotic segments. Thus, rest Tc-99m-sestamibi scintigraphy early after acute myocardial infarction may underestimate residual viability within the infarct region, particularly in patients with low flow state coronary anatomy, as a result of a severe infarct-related stenosis and/or late reperfusion therapy.