Comparison of Nitrate-augmented resting gated 99mTc-Sestamibi imaging with Low Dose Dobutamine SPECT for the detection of Myocardial Viability

Background: Dobutamine Echocardiography and Radionuclide imaging with Tl-201 and Technetium agents are two of the most established techniques available for the detection of viable myocardium. The purpose of this study was to evaluate the utility of Low dose Dobutamine gated Myocardial SPECT in identifying additional areas of dysfunctional, but viable myocardium when compared to nitrate-augmented rest gated SPECT with SestaMIBI. Materials and Methods: 20 patients (19 males and 1 female, with an age range of 40- 65 yrs and a mean of 52.75yrs) all with history of MI or severe LV dysfunction were included in this study. Patients with LBBB, recent revascularisation, arrhythmias etc were excluded from the study. A routine stress-rest study was initially performed on them with 99mTc-SestaMIBI and both the stress as well as resting studies was gated and the resting study was augmented with 10mg of sublingual nitrate. After the resting study was over, the patient was infused with Low dose Dobutamine(5μg/kg/min), at which time the gated acquisition was started and the infusion was continued till the acquisition got completed. In the perfusion study with SestaMIBI, all infarct segments which have uptake less than 50% as compared to the maximally perfused area was deemed non-viable Results: A 17-segment Myocardial model was used for both perfusion as well as quantification of wall motion and wall thickening. 110 akinetic/dyskinetic segments were taken up for analysis. 93 of these segments were non-viable and improvement in wall motion was seen in 17 segments (15.4%) in the nitrate-augmented SPECT. Dobutamine study showed improvement in totally in 27 segments (24.5%), 10 of which were additional segments which were non-viable in Nitrate SPECT study, apart from the 17 segments which showed improvement in the Nitrate study. In Dobutamine study, there was also improvement in wall thickening in 10 (10.7%) out of 93 segments which had showed less than 50% of MIBI uptake. Conclusion: Low dose Dobutamine gated SPECT detects more areas of viable myocardium as compared to nitrate augmented resting gated SPECT