Predicted heart mass-based size matching among recipients with moderate pulmonary hypertension: Outcomes and sex effect

Background: There is a lack of evidence to guide appropriate donor sizing in recipients with moderate pulmonary hypertension (pHTN) awaiting heart transplantation (HTx). It is common practice to oversize donor hearts for such recipients to prevent post-operative right ventricular failure. Therefore, our objective was to determine if oversizing in pre-transplant moderate pHTN provides a survival advantage.

Methods: The United Network for Organ Sharing database was analyzed to include HTx recipients from 1994 to 2016. Recipients were considered as having moderate pHTN if the pulmonary vascular resistance (PVR) was 2.5 to 5 Wood units (WU) or transpulmonary gradient (TPG) was 10 to 18 mm Hg. Heart size mismatch was determined using the predicted heart mass equations. A size mismatch of ≥15% in either direction was considered undersized or oversized, respectively. Ninety-day and 1-year survival were analyzed based on size matching via univariate and Cox regression analysis. Propensity matching was performed to specifically evaluate the effect of donor sex among male transplant recipients.

Results: Among 29,441 HTx recipients, 10,666 had moderate pHTN by PVR criteria and 12,624 HTx patients had moderate pHTN according to TPG criteria. Among patients with a PVR of 2.5 to 5 WU, oversizing was not associated with lower mortality compared with matched hearts at 90 days (7.6% vs 7.4%; p = 0.75) and 1 year (12.1% vs 11.3%; p = 0.26). Conversely, undersizing the donor was associated with a higher 90-day (10.6% vs 7.6% vs 7.4%; p < 0.01) and 1-year (15.3% vs 12.1% vs 11.3%; p < 0.01) mortality than recipients receiving oversized or matched hearts, respectively. On Cox regression analysis, there was no benefit with oversizing at 90 days (hazard ratio [HR] 0.88; p = 0.23) and 1 year (HR 0.99; p = 0.90), whereas undersizing was associated with higher 90-day (HR 1.32; p = 0.02) and 1-year mortality (HR 1.23; p = 0.03) compared to size-matched controls. Among patients with moderate pHTN based on TPG of 10 to 18 mm Hg, neither undersizing nor oversizing was predictive of mortality at 90 days and 1 year according to Cox regression analysis. Propensity matching revealed that female-to-male transplantation had similar 1-year mortality to male-to-male transplantation, and there was no advantage to oversizing female donors for male recipients.

Conclusions: In this registry-based analysis, there was no benefit to oversizing donors for cardiac transplant recipients with moderate pHTN. Elimination of this restriction could increase the donor pool and reduce wait times for such recipients.