Long-Term Prognostic Value of Post-Revascularization Fractional Flow Reserve and Skin Perfusion Toe Pressure in Patients with Chronic Limb-Threatening Ischemia

<i>Background and Objectives</i>: The impact of peripheral below-the-knee (BTK) fractional flow reserve (FFR) on long-term clinical outcomes remains unknown. <i>Materials and Methods</i>: We enrolled 40 patients with severe BTK lesions (Rutherford 4-6). FFR (using 40 mg papaverin) and skin perfusion toe pressure (SPTP) by laser Doppler were measured during the index procedure. The primary outcomes were major adverse limb events (MALEs) (defined as reintervention on the index arterial segment or amputation of the index limb) and death during follow-up. <i>Results</i>: The median follow-up was 7 [IQR 4-8] years. After the index procedure, FFR increased significantly (<i>p</i> < 0.001) and post-revascularization SPTP was significantly higher in the FFR ≥ 0.80 group (<i>p</i> = 0.022). Multivariable regressions showed no association between change in FFR (absolute or percentage) and the risk of death (<i>p</i> = 0.39, <i>p</i> = 0.28) or MALEs (<i>p</i> = 0.83, <i>p</i> = 0.29), but both pre- and post-revascularization FFR values could predict MALEs at follow-up (<i>p</i> = 0.018, <i>p</i> = 0.012). Lower SPTP was also associated with the risk of MALEs (<i>p</i> = 0.027). SPTP > 97.8 mmHg was 100% specific for FFR ≥ 0.80. <i>Conclusions</i>: While there is no association between change in FFR and the risk of death or MALEs, lower FFR values either before or after revascularization were associated with higher long-term risk of MALEs. Moreover, a lower SPTP was associated with a higher risk of MALEs. Aiming for approximately 100 mmHg in SPTP represents a non-invasive surrogate of FFR ≥ 0.80. Larger studies are needed to validate the impact of post-revascularization FFR-SPTP-adjacent values on clinical outcomes.