Threshold values for preserved viability with a noninvasive measurement ofcollateral blood flow during acute myocardial infarction treated by directcoronary angioplasty

Background-Quantitative measures of myocardial perfusion defect severity fr om acute Tc-99m-sestamibi tomographic images (nadir) have correlated closel y with collateral and residual antegrade blood flow during acute myocardial infarction. The purpose of this study was to determine whether a viability threshold could be identified from this measure in patients with acute myo cardial infarction treated in a homogeneous manner with successful reperfus ion therapy. Methods and Results-The study group consisted of 61 patients with acute myo cardial infarction with a risk area of >6% LV treated with primary angiopla sty between 120 and 240 minutes after symptom onset. All patients were inje cted with 20 to 30 mCi of Tc-99m-sestamibi before primary angioplasty and i maged after the procedure. Acute myocardium at risk (MAR) and subsequent in farct size (IS) were quantified by a threshold program. Severity (nadir) fr om the acute image was the lowest ratio of minimal/maximum counts from 5 sh ort-axis slices. Infarct location was anterior in 22 and inferior in 39 pat ients. MAR was 33+/-15% LV and IS was 13+/-15% LV: 23 patients had no infar ction despite MAR similar to those with infarction. Receiver-operator chara cteristic curve analysis identified a nadir value of 0.26 as providing the best separation of patients with and without infarction (sensitivity, 74%; specificity, 74%), This nadir threshold varied by infarct location: anterio r defect, 0.21; inferior defect, 0.31. The sensitivity and specificity for absent infarction for these values were anterior, 69% and 67%, and inferior , 88% and 84%, respectively. Conclusions-In a time frame in which the presence of residual blood flow is important, the severity of the acute Tc-99m-sestamibi defect can be used t o predict whether infarction will develop despite successful reperfusion.