Donor heart undersizing impacts early hemodynamics but not 1-year survival in adult heart transplantation-A high-volume, single-center 5-year experience.

Abstract

Size matching in heart transplantation historically used weight or predicted heart mass ratios, with guidelines recommending against donor heart undersizing. This study evaluates the safety of using undersized hearts in the modern era. All adult heart transplants from January 2020 to June 2025 at a single institution were included, excluding those with adult congenital heart disease or multiorgan transplants. Two distinct analyses were performed with different stratification strategies: predicted heart mass ratio less than 0.80 versus 0.80 to 1.20 and weight ratio less than 0.70 versus 0.70 to 1.30. A 1:1 propensity match was performed to create balanced cohorts stratified by predicted heart mass ratio or weight ratio. A total of 527 transplants were stratified by predicted heart mass ratio, of which 107 (20.3%) had low and 420 (79.7%) had normal predicted heart mass ratio. After propensity matching, post-transplant cardiac indices, severe primary graft dysfunction, and 1-year survival (92.4% low predicted heart mass ratio vs 91.5% normal predicted heart mass ratio, P = .80) were similar. A total of 523 transplants were stratified by weight ratio, of which 137 (26.2%) had low and 386 (73.8%) had normal weight ratios. After propensity matching, post-transplant cardiac indices were lower at 24 hours (2.9 vs 3.2, P = .008) and 72 hours (3.0 vs 3.2, P = .002) in the low weight ratio group. Rates of severe primary graft dysfunction and 1-year survival (93.3% low weight vs 91.2% normal weight, P = .49) were similar between matched cohorts. The study suggests that early graft function and 1-year survival were similar between normal and undersized cardiac donors. Further study is required to determine if undersized cardiac donors may safely allow for expansion of the cardiac donor pool.