Sex-specific Trends in the Use of Temporary Mechanical Circulatory Support in patients listed for Orthotopic Heart Transplant Before and After the UNOS Allocation System Change

BackgroundSince the United Network for Organ Sharing (UNOS) allocation system change patients listed for orthotopic heart transplant (OHT) are more likely to be on temporary mechanical circulatory support (tMCS). Limited sex specific data exits for use and outcomes of tMCS since the allocation change. MethodsWe queried the UNOS registry for patients listed for OHT on tMCS from October 1, 2015 to June 28, 2023, comparing baseline characteristics and outcomes between sexes pre- and post-allocation change. ResultsWomen comprised 23% of patients listed for OHT on tMCS before and after the allocation change, despite similar cardiac index (CI) compared with men (pre: 2.03 vs 2.09 L/min m2 p=0.21; post: 1.92 vs 1.92 L/min m2 p=0.89). Women were significantly younger (54 vs 57 years; p<0.001), had lower BMI (26.9 vs 27.2; p 0.006), were more likely to be on intra-aortic balloon pump (IABP) (67% vs 61% p <0.001) and had shorter waitlist times (13 vs 16 days; p <0.001). Waitlist mortality decreased similarly for both sexes (3.6% vs 3.8%; p= 0.7). There was no significant difference in 1-year post-transplant survival between the sexes in either era (HR: 0.9, 95% CI: 0.76, 1.06 p=0.2), however, 1-year post-transplant survival improved overall for patients bridged with tMCS post allocation change independent of sex (HR 0.70 (95% CI: 0.54 to 0.90; p=0.005). ConclusionDespite an increase in the use of tMCS as a bridge to OHT since the UNOS allocation change, women comprise less than a quarter of patients listed on tMCS despite similar CI, suggesting possible underuse in women. Notably, for those bridged to OHT in the post allocation era, waitlist mortality has improved for both sexes and 1-year post-transplant survival has also improved independent of sex.