Abstract 18692: Relationship Between Fasting Time on Ketogenic Diet and Myocardial Glucose Suppression in Patients Referred for Cardiac Sarcoidosis Evaluation on FDG-PET Imaging

Abstract

Introduction: FDG-PET imaging is standard for assessing myocardial inflammation for cardiac sarcoidosis (CS). Preparation with the ketogenic diet (KD) is required to suppress physiologic myocardial glucose uptake (MGU), thereby highlighting pathologic MGU. Incomplete physiologic myocardial glucose suppression (MGS) continues to limit FDG-PET. The effect of fasting time (FT) on MSG remains unexplored. Goal: To identify if FT is an independent predictor of MGS following a KD in patients undergoing FDG-PET imaging. Methods: We prospectively included 442 consecutive patients (59.2 ± 10.9 yrs, 39% female, 55% white) who underwent 590 FDG-PET scans for the evaluation of CS after following a KD at our institution between 2021 and 2023. Time from last meal to FDG injection was documented in all patients. Serum BHB levels were measured in 516 scans. FDG PET images were classified as 1) diagnostic (complete MGS) when there was either no MGU (negative) or multifocal uptake (positive), or 2) nondiagnostic (incomplete MGS) when there was either diffuse left ventricular or nonspecific uptake. Results: The KD was followed for 1, 2 or ≥3 days in 127 (22%), 61 (10%), and 402 (68%) of cases respectively. FDG-PET scans were interpreted as the following: 436 (74%) negative; 109 (18.3%) positive; 13 (2.2%) diffuse; 32 (5.4%) nonspecific uptake. Patients on the KD for only 1 day had higher rates of MGS with increased FT (β = 0.33 ± 0.11, p <0.01); this correlation did not hold true for patients on KD for 2 days (β = -0.005 ± 0.09, p = 0.96) whereas, patients on the KD for 3 or more days showed lower rates of MGS with increased FT (β = -0.18 ±0.07, p<0.01) ( Figure 1 ). When adjusting for BHB level, the correlation between MGS and FT held true (1 day: β = 0.35 ± 0.13, p <0.01; 2 days: β = 0.26 ± 0.28, p = 0.35; 3 days: β = -0.17 ± 0.07, p = 0.02). Conclusion: Fasting time appears to be most beneficial in patients following the KD for 1-day only. Patients following the KD for 2 days or longer may not require overnight fasting.