Significance of Elevated Donor-Derived Cell-Free DNA in Heart Transplant Recipients With Negative Endomyocardial Biopsies: A Dawn of a New Era.

Background: The purpose of the current study was to investigate the clinical implications of elevated donor-derived cell-free DNA (dd-cfDNA) levels in heart transplantation recipients without evidence of rejection observed on endomyocardial biopsy.

Methods: We retrospectively analyzed dd-cfDNA samples from all consecutive heart transplantation recipients between 2019 and 2023, excluding those with multiorgan transplants. Each sample was paired with an endomyocardial biopsy (<30 days). A positive biopsy was defined based on International Society for Heart and Lung Transplantation criteria of ≥1R/1B or pAMR >0. Elevated dd-cfDNA was defined as ≥0.12%, with a subanalysis using a threshold of 0.20%. Graft dysfunction was defined as an ejection fraction<50%. We excluded dd-cfDNA samples with concurrent histologically positive biopsy results, focusing on those with positive dd-cfDNA and negative biopsy findings. A mixed model Cox regression approach was applied to assess for mortality and graft dysfunction.

Results: Of 643 dd-cfDNA samples from 227 patients, 238 samples (37%) from 110 patients showed positive dd-cfDNA results with negative endomyocardial biopsy. The median age was 56 years, with 27% females and 53% White patients. The median time from heart transplantation to sample collection was 5 months (interquartile range, 3-12). Among the positive samples, the median dd-cfDNA level was 0.24% (interquartile range, 0.16%-0.53%) with 63% exceeding 0.20%. A higher prevalence of prior treated antibody-mediated rejection was observed in the dd-cfDNA positive group (15% versus 5%; P=0.002). Patients with elevated dd-cfDNA results ≥ 0.20% demonstrated a near 5-fold increased risk of mortality (hazard ratio, 4.6 [95% CI, 1.6-13.4]; P=0.005) and a 3-fold risk of graft dysfunction (hazard ratio, 3.4 [95% CI, 1.0-11.9]; P=0.054) compared with those with negative dd-cfDNA.

Conclusions: In our cohort, patients with positive dd-cfDNA levels and negative biopsy results had higher rates of adverse outcomes, including graft dysfunction and mortality.