Quantification of limited augmentation of myocardial Tc-99m-tetrofosmin uptake at exercise in stable coronary artery disease

We evaluated the diagnostic accuracy of a new method for quantitative analysis of myocardial perfusion at exercise using Tc-99m-tetrofosmin tomographic imaging. Tc-99m-tetrofosmin imaging of an exercise-rest sequence was performed in 30 patients with coronary artery disease (CAD) and eight age-matched control subjects. The exercise-induced myocardial count increase was calculated as the relative value (per cent increase ratio, %IR) to that at rest by correcting for physical decay for Tc-99m and injected doses and by a subtraction technique. Exercise and rest Tc-99m-tetrofosmin images were assessed visually and quantitatively using the per cent peak count and %IR of the myocardial count at exercise. Segments with significant coronary stenosis (diameter stenosis = 75% or more) showed a significantly lower %IR than did those without significant coronary stenosis in the CAD patients (37 +/- 19% vs 63 +/- 21%, P<0.05). The diagnostic efficacy of visual analysis for detecting coronary stenosis was as follows: sensitivity, 58.1% and specificity, 81.4%. When %IR=37% was used for detecting significant coronary stenosis, sensitivity and specificity increased to 74.2% and 93.2%, respectively. Furthermore, the quantitative analysis significantly (P=0.04) improved the overall diagnostic accuracy from 73.3% to 86.7% compared to that of visual assessment. Thus, augmentation of myocardial Tc-99m-tetrofosmin uptake at exercise is blunted in the myocardium with significant coronary stenosis. The calculation of myocardial count increase at exercise relative to that at rest can improve the diagnostic value of Tc-99m-tetrofosmin SPECT imaging and may contribute to more accurate quantification of myocardial ischaemia and impaired tracer uptake in coronary artery disease. ((C) 2001 Lippincott Williams & Wilkins).