Baseline/postnitrate tetrofosmin SPECT for myocardial viability assessment in patients with postischemic severe left ventricular dysfunction: New evidence from MRI

The aim of this study was to compare ^99mTc-tetrofosm in SPECT with contrast-enhanced MRI (ceMRI), a new direct sign of myocardial fibrosis. Methods: We studied 21 patients (age, 60 ± 11 y; 19 male) with previous myocardial infarction and severe left ventricular dysfunction (ceMRI EF, 29% ± 6%). All patients underwent resting and postnitrate (intravenous isosorbide dinitrate) ^99mTc-tetrofosmin gated SPECT as well as ceMRI. Scintigraphic analysis was performed using quantitative perfusion SPECT (QPS), providing the percentage radiotracer uptake and defect severity in a 20-segment model. Hyperenhancement was defined by the increase of ceMRI signal intensity 20 min after intravenous injection of gadolinium-diethylenetriaminepentaacetic acid and its regional extension as the percentage of the total segment area. Results: In ceMRI dysfunctional segments, the correlation between the extent of hyperenhancement and both ^99mTc-tetrofosmin uptake and defect severity was significantly better after nitrate administration rather than at rest (P <0.0001). Using a ceMRI cutoff below 40%, 102 of 196 (52%) segments were viable, whereas 94 (48%) segments were not viable. According to receiver-operating characteristic curve analysis, diagnostic accuracies were higher for postnitrate ^99mTc-tetrofosmin uptake as well as perfusion defect severity than using resting data (0.84 vs. 0.71, P <0.001; 0.89 vs. 0.76, P <0.001, respectively). Conclusion: After nitrate administration, ^93mTc-tetrofosmin uptake and perfusion defect severity were closely related to ceMRI, demonstrating, in vivo, the existence of an inverse correlation between the transmural distribution of fibrosis and tracer delivery to the myocardium.