In recent years, mortality among pediatric heart transplant candidates has progressively declined. However, this improvement has not extended to infants, where waitlist mortality remains approximately 20%. This discrepancy is primarily attributed to donor shortages, leading to prolonged waitlist times. One proposed solution involves expanding donor availability by reconsidering size discrepancy criteria for donor-recipient matching. 

The International Society for Heart and Lung Transplantation (ISHLT), in its December 2022 guidelines, recommended evaluating graft size based on weight, setting a DRWR limit of 0.8–2. More recently, the ISHLT consensus has debated these guidelines, suggesting that a DRWR of 0.6–3 is not associated with worse outcomes. 

The authors hypothesize that expanding donor weight limits reduces waitlist duration and associated morbidity and mortality without increasing post-transplant complications. 

This study retrospectively analyzed data from the US Organ Procurement and Transplant Network. It included infants under one year transplanted between 2007 and 2020, categorizing them into three groups by DRWR: <1 (group A), 1–2 (group B), and >2 (group C). 

Between 2007 and 2020, 1,392 infants under one year of age received transplants with DRWR ranging from 0.5 to 4.1. Patient characteristics—including gender, race, cardiac pathology (congenital vs. dilated cardiomyopathy), renal function, and need for ECMO or long-term ventricular support before transplantation—were similar across groups. However, patients in group C were more likely to require mechanical ventilation during the waitlist period, receive ABO-incompatible transplants, and experience longer ischemic times. 

Waitlist times were significantly shorter in group C. Post-transplant complications (e.g., primary graft dysfunction, renal failure, or stroke) and 30-day mortality were comparable across groups. Multivariable analysis, adjusting for type of cardiac pathology, showed similar 30-day survival rates across groups, although pre-transplant ECMO was a significant risk factor for hospital mortality (OR 4.4). 

Survival at 1, 3, and 5 years post-transplant was also statistically similar among the groups. 

COMMENTARY: 

Currently, the donor shortage necessitates rethinking strategies to balance supply and demand, especially in the pediatric population. Without such measures, the consequences include prolonged waitlist times and higher mortality rates among infant heart transplant candidates. Expanding donor size acceptance criteria could maximize organ utilization. 

As noted, ISHLT guidelines initially recommended a DRWR of 0.8–2 but have since considered a broader range (0.6–3), as evidence suggests no adverse outcomes. 

Efforts to identify prognostically significant donor-recipient size parameters have included predictive models using MRI or CT imaging to estimate size in terms of mass or volume. These models incorporate variables such as sex, age, weight, and height, with recent findings favoring total cardiac volume (TCV) as the best measure for survival impact. However, these findings, such as those by Plasencia et al., are derived from limited cohorts and warrant cautious interpretation. 

A key strength of this study is its focus on a large cohort of over 1,300 infants, a high-risk group often excluded from prior studies. Group C (DRWR >2) included sicker infants with higher rates of mechanical ventilation, ABO-incompatible transplants, and longer ischemic times. Despite these challenges, waitlist times were significantly shorter without increased complications or reduced survival at 30 days, 1 year, 3 years, or 5 years. 

At La Paz Hospital, 22 transplants in infants under one year of age with DRWRs of 0.8–3 were performed over the last 20 years. Eight of these patients fell into group C. The mean ischemic time for group C was 239.5 minutes compared to 221.21 minutes (p > .05). Post-transplant ECMO was required in 4 patients, none of whom had a DRWR >2. Among the 22 transplants, 3 involved ABO-incompatible protocols (2 with DRWR = 2 and 1 with DRWR >2). Five-year survival was higher in group C (75% vs. 66%). 

One limitation of this study is the lack of investigation into other morbidities potentially associated with donor-recipient size mismatch, such as delayed sternal closure and related complications. 

Nevertheless, this study’s relevance lies in its focus on infants, a critical risk group where strategies to mitigate donor scarcity are crucial. At La Paz Hospital, adopting donor-recipient size mismatch strategies, along with ABO-incompatible and circulatory death donation protocols, has achieved a 5-year survival rate of 80% in infants under one year. Based on these results, future efforts may prioritize broader acceptance of DRWR (2–3), alongside other strategies like circulatory death donation and expanded ABO-incompatible protocols. 

REFERENCE: 

Alsoufi B, Kozik D, Lambert AN, Wilkens S, Trivedi J, Deshpande S. Increasing donor-recipient weight mismatch in infant heart transplantation is associated with shorter waitlist duration and no increased morbidity or mortality. Eur J Cardiothorac Surg. 2023 Dec 1;64(6):ezad316. doi: 10.1093/ejcts/ezad316.