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

D. K. Ragheb¹, S. Rega², I. Feurer³, H. Siddiqi⁴, K. Amancherla⁴, M. Brinkley⁴, J. Lindenfeld⁴, J. Menachem⁴, H. Ooi⁴, L. Punnoose⁴, A. Rali⁴, M. Wigger⁴, S. Zalawadiya⁴, K. Schlendorf⁴, A. Shah⁵, J. Trahanas⁵, C. Pasrija^6
1Department of Thoracic and Cardiovascular Surgery, Heart, Vascular and Thoracic Institute, Cleveland Clinic, Cleveland, Ohio ²Vanderbilt University Medical Center, Vanderbilt Transplant Center, Nashville, Tennessee ³Vanderbilt University Medical Center, Departments of Surgery Biostatistics, Nashville, Tennessee ⁴Vanderbilt University Medical Center, Division of Cardiovascular Medicine, Nashville, Tennessee ⁵Vanderbilt University Medical Center, Nashville, Tennessee ⁶Vanderbilt University Medical Center, Department of Cardiac Surgery, Nashville, Tennessee

Purpose: Recipients of undersized hearts, measured by predicted heart mass (PHM) ratio, have increased mortality as compared to matched or oversized hearts. However, PHM ratio has been poorly studied in patients with a body mass index (BMI)≥30. We aim to examine the interaction of BMI, PHM, and graft loss.

Methods: This study used data from the Scientific Registry of Transplant Recipients, which includes data on all donors, wait-listed candidates, and transplant recipients in the United States, submitted by members of the Organ Procurement and Transplantation Network. Records for all adult (≥18 years), first-time heart-only recipients transplanted between January 2000 and December 2020 were included. Donor to recipient PHM ratio was stratified as: undersized (≤0.85), matched (0.86-1.14), and oversized (≥1.15). Recipient BMI was initially treated as a continuous variable (Kg/m2) and then separately stratified as under/healthy weight (≤24.9), overweight (25.0-29.9), and obese (≥30.0). Statistical methods included chi-square tests, analysis of variance, Kaplan-Meier, and multivariable proportional hazards regression survival models that tested the effects of heart size strata, BMI, and their interaction on the likelihood of graft loss. Analyses were performed using IBM SPSS Statistics (version 28, Armonk, NY).

Results: The study included 38,952 adult heart transplant recipients, with heart sizing cohorts distributed as 14% undersized, 64% matched, and 22% oversized. As compared to recipients in the matched or undersized PHM ratio cohorts, recipients belonging to the oversized PHM ratio cohort were more likely to have lower BMI, female sex, mechanical circulatory support use, greater degree of renal dysfunction, and shorter transplant waitlist times. As compared to donors in the matched or undersized PHM ratio cohorts, donors belonging to the oversized PHM ratio cohort were more likely to have higher BMI, younger age, male sex, diabetes, and shorter allograft ischemic time. Univariate and multivariable analyses demonstrated that increasing BMI group (Figure 1, Panel A) and decreasing PHM ratio group (Figure 1, Panel B) were both associated with increased graft loss (p < 0.05). Multivariable analysis also demonstrated a notable BMI by PHM ratio interaction effect (p=0.052) (Table 1). Specifically, the relationship between BMI and graft loss differed among recipients of undersized and matched hearts (interaction contrast p=0.018) but not between oversized and matched hearts. Increasing BMI was associated with increased risk of graft loss in the matched and oversized cohorts (both p< 0.001) but not in the undersized cohort (p=0.124).

Conclusion: This study demonstrates that the relationship between BMI and graft loss differs as a function of PHM ratio. In recipients who receive an undersized heart, there is increased risk of graft loss due to undersizing; however, increased BMI in these patients does not confer additional risk.

Identify the source of the funding for this research project: NA