Fixed Defect on Rest/Stress Tc-99m Sestamibi Study Underestimates Myocardial Ischemia: Comparison With 24-Hour Thallium-201 Study for Short- and Intermediate-term Follow-up

PURPOSE:We assessed whether a same day rest/stress gated Tc-99m sestamibi (MIBI) SPECT myocardial study underestimates reversible ischemia in patients with fixed perfusion defects compared with a 24-hour thallium-201 (Tl-201) study. The short- and intermediate-term outcome with or without Tl-201 reversibility was assessed. METHODS:Forty-nine consecutive patients with fixed MIBI defects received an additional Tl-201 study and were evaluated. Tl-201 was given to patients with a high clinical suspicion of underestimation of reversibility. Images were interpreted semiquantitatively by 3 nuclear medicine physicians using a 17-segment, 5-point model. A summed stress score (SSS) from stress MIBI images, a summed rest score (SRS) from Tl images, and a summed difference (SDS = SSS − SRS) score were calculated. SDS >3 indicated significant Tl-201 redistribution. Composite end points included acute myocardial infarction, unstable angina needing admission, cardiac death, or revascularization within 3 and 6 months. RESULTS:Fifteen of 49 patients showed no Tl-201 redistribution. Thirty-four of 49 (69%) patients had significant Tl-201 redistribution, and these patients had significantly higher cardiac events (CE) at 3 months (29% vs. 7%; P = 0.039), and higher at 6 months (32% vs. 7%; P = 0.027). These patients with CE had a larger amount of Tl-201 redistribution, mean SDS 8.6 vs. 5.3 (P = 0.047). Patients with significant Tl-201 redistribution had a lower left ventricular ejection fraction (mean 37%; P = 0.001). CONCLUSION:With short- and intermediate-term follow-up, our study shows a significant association towards fixed defects on the rest/stress MIBI study underestimating CE risk when compared with a delayed Tl-201 study, especially in patients with a large amount of Tl-201 redistribution. Hence, the addition of a Tl-201 study may be useful in the management of patients with large fixed MIBI defects, especially with a depressed left ventricular ejection fraction.