Prolonged fasting for optimizing myocardial fluorodeoxyglucose suppression.

Background: PET with 18F-fluorodeoxyglucose (18F-FDG) is widely used to evaluate inflammatory cardiac disorders such as sarcoidosis and myocarditis. However, physiologic myocardial uptake can obscure pathological uptake and must be suppressed.

Objective: To determine the effectiveness of fasting alone in suppressing physiological myocardial uptake and to establish a practical imaging protocol.

Methods: We retrospectively reviewed patients who underwent whole-body 18F-FDG PET/CT for oncologic indications between January 2019 and December 2020. Patients were categorized by fasting duration: Group A (<12 h), Group B (12-17 h), and Group C (≥18 h). Two independent readers qualitatively graded myocardial FDG uptake, with adequate suppression defined as grade 0 (no uptake) or grade 1 (uptake ≤ liver background). Uptake above liver background (grade 2) was considered inadequate. Interreader agreement was assessed using Cohen's Kappa.

Results: A total of 450 patients were included (150 per group). Adequate myocardial suppression was achieved in 77.3, 66, and 60% of patients in Groups C, B, and A, respectively (P = 0.005). Suppression was not associated with blood glucose, age, or diabetes. However, significant associations were observed with gender (P = 0.024) and BMI (P = 0.006). Interreader agreement was almost perfect (Cohen's Kappa 0.909; 95% CI: 0.868-0.950).

Conclusion: Fasting for ≥18 h is more effective than shorter durations in suppressing physiologic myocardial FDG uptake, enabling evaluation of myocardial inflammation. This simple and feasible protocol is particularly valuable in resource-limited settings. Visual grading demonstrated excellent reproducibility, supporting its role in clinical practice.