Predicted heart mass for size matching in obese heart transplant donors and recipients

INTRODUCTION: Predicted heart mass (PHM) was neither derived nor evaluated in an obese population. Our objective was to evaluate size mismatch using actual body weight or ideal body weight (IBW)-adjusted PHM on mortality and risk assessment. METHODS: We conducted a retrospective cohort study of adult recipients with BMI ≥30 kg/m² or recipients of donors with BMI≥30 kg/m² from the ISHLT registry. We used multivariable Cox proportional hazard models to evaluate 30-day and 1-year mortality. The two models were compared using net reclassification index. RESULTS: 10,817 HT recipients, age 55 (IQR 46-62) years, 23% female, BMI 31 kg/m² (IQR 28-33) were included. Donors were age 34 (IQR 24-44) years, 31% female, and BMI 31 kg/m² (IQR 26-34). There was a significant nonlinear association between mortality and actual PHM but not IBW-adjusted PHM. Undersizing using actual PHM was associated with higher 30-day and 1-year mortality (p < .01), not seen with IBW-adjusted PHM. Actual PHM better risk classified .6% (95% CI .3-.8) patients compared to IBW-adjusted PHM. CONCLUSION: Actual PHM can be used for size matching when assessing mortality risk in obese recipients or recipients of obese donors. There is no advantage to re-calculating PHM using IBW to define candidate risk at the time of organ allocation.