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 (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.

Traumatic brain injury (TBI) is a biomechanical problem where the initiating event is dynamic loading (blunt, inertial, blast) to the head. To understand the relationship between the mechanical parameters of the injury and the deformation patterns in the brain, we have previously developed a surrogate head (SH) model capable of measuring spatial and temporal deformation in a surrogate brain under blunt impact. The objective of this work was to examine how material properties and anatomical features affect the motion of the brain and the development of injurious deformations. The SH head model was modified to study six variables independently under blunt impact: surrogate brain stiffness, surrogate skull stiffness, inclusion of cerebrospinal fluid (CSF), head/skull size, inclusion of vasculature, and neck stiffness. Each experimental SH was either crown or frontally impacted at 1.3 m/s (3 mph) using a drop tower system. Surrogate brain material, the Hybrid III neck stiffness, and skull stiffness were measured and compared to published properties. Results show that the most significant variables affecting changes in brain deformation are skull stiffness, inclusion of CSF and surrogate brain stiffness. Interestingly, neck stiffness and SH size significantly affected the strain rate only suggesting these parameters are less important in blunt trauma. While the inclusion of vasculature locally created strain concentrations at the interface of the artery and brain, overall deformation was reduced.