Immediate postoperative biomarkers characterize severity of primary graft dysfunction after heart transplantation

Primary graft dysfunction (PGD) remains the leading cause of early morbidity and mortality after orthotopic heart transplantation. Postoperative lactate and the venoarterial carbon dioxide gap (Pv-a CO₂) are routinely measured indicators of hypoperfusion, yet their relationship to PGD severity is not well characterized. This study evaluated the association between immediate posttransplant (T0) and 24-hour (T24) biomarker values and the severity of PGD.

We performed a single-center retrospective study of adult recipients of orthotopic heart transplantation (May 2020 to May 2023). PGD was defined according to International Society for Heart and Lung Transplantation criteria and categorized as none, moderate, or severe. Pv-a CO₂ and serum lactate were collected at T0 for multivariable analysis and at T24 for descriptive and exploratory modeling. Patients receiving a simultaneous heart-lung transplant were excluded. Multivariable logistic regressions adjusted for age, body mass index, and sex.

Among 110 recipients, PGD occurred in 50 (45%) cases, including 39 moderate and 11 severe. At T0, both biomarkers demonstrated stepwise increases with PGD severity. Each 1-mm Hg increase in Pv-a CO₂ was associated with greater odds of any PGD (odds ratio [OR], 1.53; 95% CI, 1.22-1.92), moderate PGD (OR, 1.48; 95% CI, 1.15-1.92), and severe PGD (OR, 2.07; 95% CI, 1.45-2.97). T0 lactate was independently associated with moderate PGD (OR, 1.21; 95% CI, 1.03-1.43). By 24 hours, Pv-a CO₂ no longer independently differentiated PGD severity, whereas T24 lactate remained associated with moderate PGD (OR, 1.68; 95% CI, 1.13-2.49).

Immediate posttransplant Pv-a CO₂ is a strong discriminator of PGD severity and may serve as an early, objective adjunct to International Society for Heart and Lung Transplantation criteria. In contrast, lactate reflects both initial hypoperfusion and the subsequent trajectory of metabolic recovery, with persistent elevations at 24 hours indicating ongoing physiologic stress. Together, these readily available biomarkers provide complementary information that may improve early diagnostic stratification of PGD.