Background. Positron emission tomography (PET) flow/metabolic mismatch is considered the nuclear medicine gold standard for the assessment of myocardial viability. The aim of this study was to investigate whether baseline/nitrate technetium 99m tetrofosmin single photon emission computed tomography (SPECT) mismatch may provide equivalent clinical information. Methods and Results. We studied 23 patients (aged 62 10 years, 19 men) with previous myocardial infarction (16 anterior, 4 inferior, and 3 anterior plus inferior) and postischemic heart failure (gated SPECT [G-SPECT] ejection fraction, 26% +/- 8%). All patients underwent Tc-99m tetrofosmin G-SPECT at rest and after nitrates (intravenous isosorbide dinitrate, 0.2 mg/mL, 10 mL/h) as well as a fluorine 18 fluoro-2-deoxy-D-glucose (FDG) PET scan. Regional wall motion analysis was performed with quantitative G-SPECT (QGS). Myocardial dysfunction was defined as a regional QGS score of 2 or greater. Regional perfusion was assessed by quantitative perfusion score (QPS) providing percent Tc-99m tetrofosmin uptake in a 20-segment model. Semiquantitative analysis of FDG uptake was performed by use of polar maps generated by Siemens ECAT HR + software. In areas with a perfusion rate lower than 80%, PET viability was identified by a normalized FDG percent uptake/baseline Tc-99m tetrofosmin percent uptake ratio greater than 1.2. We analyzed 460 segments; 298 (64%) were dysfunctional by QGS analysis. Of these, 170 were viable by PET imaging whereas 128 were nonviable. Regional Tc-99m tetrofosmin uptake was higher in viable than in nonviable segments both at rest (60% +/- 24% vs 42% +/- 12%, P <.01) and after nitrates (67% +/- 20% vs 41% +/- 18%, P <.01). According to receiver operating characteristic curve analysis, a cutoff value of 63% for resting as well as post-nitrate G-SPECT provided the highest diagnostic accuracy for the detection of myocardial viability (67% and 72% at rest and after nitrates, respectively). When the same algorithm used for the comparison with PET (normalized nitrate percent uptake/ baseline percent uptake) was applied to G-SPECT, we obtained the highest agreement with PET (accuracy, 93%; sensitivity, 95%; specificity, 92%). Conclusions. In patients with severe left ventricular dysfunction, perfusion data alone, both at rest and after nitrates, do not allow an accurate estimate of myocardial viability. In dysfunctioning segments, the analysis of rest/post-nitrate Tc-99m tetrofosmin mismatch provides results similar to those obtained by PET flow/metabolic mismatch.
