Fractional Flow Reserve Value of Reverse Redistribution in 201-Thallium Stress Scintigraphy

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Background：Reverse redistribution (RR) is a unique finding in Thallium-201 chloride (²⁰¹TlCl) stress scintigraphy, but there is no established notion of its mechanism. We hypothesized that RR enhances blood flow in the RR area and that the fractional flow reserve (FFR) is low in the RR area if there is decreased microvascular resistance. We aimed to clarify the mechanism of RR by comparing FFR with ²⁰¹TlCl stress scintigraphy. Methods and Results：This single-center retrospective study enrolled forty consecutive patients who underwent both FFR and stress/rest ²⁰¹TlCl stress scintigraphy between April 2012 and April 2016. A total of 11 patients were excluded due to the following reasons: percutaneous coronary intervention performed between FFR and scintigraphy (n = 1), unreliable FFR value (n = 1), and severe coronary artery stenosis (n = 5). Finally, 29 patients were analyzed. Each coronary territory was classified into three groups according to the value of summed difference score (SDS): control (SDS = 0; n = 6), redistribution (SDS ≥ 1; n = 12), and RR (SDS ≤ -1; n = 11) regions. The FFR values among the 3 groups were compared using Kruskal-Wallis test. The redistribution region as well as the RR region showed significantly lower FFR value than the control region (control; 0.93 vs. redistribution; 0.85, P = 0.03, vs. RR; 0.85, P = 0.03). Conclusions：The RR region had significantly lower FFR value than the control region. Reduced microvascular resistance due to the increased collateral wash-out may be one of the mechanisms of RR.