Recipient Obesity and Heart Sizing: Gaining a Broader Understanding Within Heart Transplantation

Recipients of undersized hearts, measured by predicted heart mass ratio (PHMr) have been shown to have increased mortality. However, this metric has been poorly studied in obese patients. This study used data from the Scientific Registry of Transplant Recipients. Records of adult, initial/only, solitary organ heart transplant recipients between January 2000 and December 2020 were included. PHMr was stratified as undersized (≤0.85), matched (0.86-1.14), and oversized (≥1.15). Body mass index (BMI) (kg/m 2 ) was stratified as under/healthy weight (≤24.9), overweight (25.0-29.9), and obese (≥30.0). Statistical methods included χ 2 tests, analysis of variance, Kaplan-Meier, and multivariable proportional hazards regression survival models. The study included 38,952 adult heart transplant recipients. Univariate and multivariable analyses demonstrated that increasing BMI group and decreasing PHMr group were both independently associated with reduced graft survival ( P < .05). Multivariable analysis also demonstrated a notable BMI by PHMr group interaction effect ( P = .052). PHMr group-specific models demonstrated that increasing BMI was associated with increased risk of graft loss among recipients of matched and oversized hearts (both P < .001). However, increasing BMI within the undersized donor heart cohort did not further increase the risk of graft loss already observed due to undersized PHMr ( P = .124). The relationship between BMI and graft failure differs as a function of PHMr, with no increased risk in undersized recipients as BMI increases. The prognostic value of BMI in recipients of undersized hearts is not comparable to that of matched and oversized hearts.