Introduction: We investigated the difference in left ventricular ejection fraction (LVEF) and end-systolic volume(ESV) measured by gated myocardial perfusion SPECT (GSPECT) in the post-dipyridamole stress and rest periods, and compared the results with the perfusion patterns found in the conventional non-gated tomograms. Methods: 297 consecutive patients were studied with post-stress and rest 99mTc-sestamibi GSPECT using a two-day protocol. Stress images were obtained 90 min after dipyridamole infusion and radiotracer injection. All acquisitions were analyzed visually, semi-quantitatively and quantitatively using QGS software. Results: Patients were divided into 4 groups according to the perfusion patterns: Group-1 = no perfusion defects (n= 129, 43.4%); Group-2 = reversible perfusion defects (n = 85, 28.6%); Group-3=Fixed defects (n =52, 17.5%); Group 4 = partially reversible perfusion defects (n =31, 10.4%). Differences between post-stress LVEF (SEF) and rest LVEF (REF) (DEF=SEF-REF) were +3.39, -6.45, -1.61, and -0.70 for groups 1, 2, 3 and 4 respectively. Post-stress stunning (>5% decrease in LVEF) was present in 49 patients (16.5%). SEF was significantly more than REF in patients with summed difference score (SDS) <5 while patients with SDS≥5 had lower SEF (54.84) than REF (60.44). No statistical significant difference was seen between post-stress end-systolic volume (SESV) and rest end-systolic volume (RESV) in patients with SDS<5. In patients with SDS≥5, SESV was significantly more than RESV. Conclusion: LVEF as measured by GSPECT decreased slightly in post-stress period when an ischemic insult was present, while it has a mild tendency to increase when the myocardial perfusion is normal. Not only exercise stress but also dipyridamole can cause a transient decrease in LVEF in stunned patients. It was concluded that gated study be performed in both stress and rest phases of the procedure.

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