Citations

Background —Quantitative measures of myocardial perfusion defect severity from acute 99m Tc-sestamibi tomographic images (nadir) have correlated closely 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 myocardial infarction treated in a homogeneous manner with successful reperfusion therapy. Methods and Results —The study group consisted of 61 patients with acute myocardial infarction with a risk area of >6% LV treated with primary angioplasty between 120 and 240 minutes after symptom onset. All patients were injected with 20 to 30 mCi of 99m Tc-sestamibi before primary angioplasty and imaged after the procedure. Acute myocardium at risk (MAR) and subsequent infarct size (IS) were quantified by a threshold program. Severity (nadir) from the acute image was the lowest ratio of minimal/maximum counts from 5 short-axis slices. Infarct location was anterior in 22 and inferior in 39 patients. MAR was 33±15% LV and IS was 13±15% LV: 23 patients had no infarction despite MAR similar to those with infarction. Receiver-operator characteristic 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: anterior 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 99m Tc-sestamibi defect can be used to predict whether infarction will develop despite successful reperfusion.

BACKGROUND Because acute exercise increases systemic catecholamines, we sought to determine whether exercise training would alter daily or exercise-related catecholamine release and inactivation. METHODS AND RESULTS In 24-hour urine collections, catecholamines and metabolites provided indexes of overall oxidative deamination, sulfation, and O-methylation. Plasma catecholamines, the sulfoconjugates of each, and chromogranin-A were determined at rest and during exercise in 10 well-trained male subjects and nine minimally trained male subjects (maximal oxygen uptake 55.2 and 42.5 ml/kg/min, respectively), and levels of activities of catechol-O-methyltransferase (COMT), monoamine oxidase B (MAO-B), and thermolabile phenolsulfotransferase (TL-PST) were also determined. Plasma-free catecholamines showed minimal differences between the two groups at submaximal exercise (4 minutes) but large differences at maximal exercise, reflecting the different exercise levels attained. Inactivation of plasma catecholamines by sulfation across rest and exercise tended to be greater in the well-trained group, with small increases in both plasma sulfoconjugated dopamine and sulfoconjugated norepinephrine. In the well-trained group, urinary metabolites demonstrated trends toward increased dopamine release (p less than 0.07) and small increases in the daily release of epinephrine and its sulfoconjugated metabolites. Indexes of deamination, sulfoconjugation, and O-methylation, with the exception of a reduced deamination of dopamine and the activities of COMT, MAO-B, and TL-PST were not different in the two groups. CONCLUSIONS Despite considerable differences in the exercise activities per week between well-trained and minimally trained individuals, there were minimal differences in the release and metabolism of catecholamines at rest or during exercise.

99mTc-hexakis-2-methoxy-2-methylpropyl-isonitrile (Tc-Sestamibi), a new myocardial perfusion radiopharmaceutical, was injected intravenously in 11 patients within 4 hours of the onset of acute myocardial infarction before treatment with intravenous tissue-type plasminogen activator and 6-14 days later. Five patients with acute myocardial infarction who did not receive intravenous thrombolytic therapy underwent a similar injection of radiopharmaceutical. The absence of redistribution of Tc-Sestamibi permitted imaging with single-photon emission computed tomography up to 6 hours after intravenous injection to assess the distribution of myocardial perfusion at the time of administration. The region of hypoperfused myocardium on the initial images varied widely from 9% to 68% of the left ventricle and was significantly greater in anterior than in inferior infarcts (p less than 0.01). The region of hypoperfused myocardium on the final images varied widely from 0% to 63% of the left ventricle and was also greater in anterior infarcts (p less than 0.01). The final hypoperfused region correlated (r = -0.82) with the late resting ejection fraction and with the late regional wall motion score in the infarct segment for both anterior (r = -0.74) and inferior (r = -0.97) infarcts. There was a significant decrease (-13 +/- 11%, p less than 0.003) in the extent of hypoperfused myocardium between the initial and final studies in the patients who received thrombolytic therapy compared with an insignificant increase (4 +/- 6%, p greater than 0.5) in the patients who did not receive thrombolytic therapy. Tomographic imaging with Tc-Sestamibi permits determination of the amount of hypoperfused myocardium "at risk" in acute myocardial infarction. The change in myocardial perfusion determined by Tc-Sestamibi before and after therapy in acute myocardial infarction is a promising tool for assessing treatment.