Functional evaluation of myocardial viability by Tc-99m tetrofosmin gated SPECT - A quantitative comparison with F-18 fluorodeoxyglucose positron emission CT (F-18 FDG PET)

To validate functional analysis of gated SPECT in detecting myocardial viab ility, seventeen patients (male 15, female 2, mean age 58) with angiographi cally proven chronic ischemic heart disease (RCA 6, LAD 10, LCX 1) and eigh t normal volunteers tall male) were studied. All patients underwent F-18 FD G PET and Tc-99m tetrofosmin (TF) gated SPECT within a week. After being di splayed in a polar map, myocardial perfusion was regionally determined by t he mean count in 9 segments at end diastole (ED) and end systole (ES) in ga ted SPECT. Systolic function was determined by the count increase ratio fro m ED to ES (WTI: ES - ED/ED). Glucose metabolism was assessed by F-18 FDG P ET in the segments correspondent to those defined for SPECT. TF %uptake of < 60% was defined as hypoperfusion, and FDG %uptake of < 50% was defined as reduced glucose metabolism. Results: The myocardial segments were classifi ed into 3 categories: "normal" perfusion (n = 85), "mismatch" (reduced perf usion with reserved FDG uptake, n = 25) and "matched" reduced perfusion and metabolic reduction (n = 26). Mean WTI in "mismatch" segment was 0.38 +/- 0.21, and was significantly greater than that in "matched reduced" segments , 0.15 +/- 0.20 (p < 0.001). It was also greater than that in "normal" segm ents, 0.27 +/- 0.16. Regression analysis showed that association between WT I and FDG %uptake was significant (r = 0.57, p < 0.0005) for the ischemic s egments ("mismatch" + "matched", n - 51), but the association was weak for the entire segments although it was statistically significant (r = 0.26, p = 0.02, n = 136). Conclusion: For the segments determined as infarct by per fusion image, systolic functional analysis by gated SPECT is helpful in dif ferentiation of a viable myocardial region or artifact horn a scar. Neverth eless, further clinical and technical assessment is required for ECG gating to eliminate overestimation of viability and to warrant clinical use.