Getting the Time Right: What Matters, What Doesn't, and How Should We Really Be Defining Ischemic Times in DCD Withdrawals?

Purpose: Over 100 DCD heart transplants have now been performed worldwide, with excellent early and mid-term results. However, there is a high degree of variability across units with regard to the definitions and cut-offs used for functional warm ischemic time (WIT). This study aimed to evaluate the various timepoints and definitions in a high volume single-centre cohort to determine their relationship to early graft function. Methods: Between July 2014 and September 2019, 34 heart transplants from DCD donors were performed at a single-centre. Twenty-five of the 34 donor files from the local database contained complete end-of-life withdrawal data, and were utilised for analysis. Donors were grouped into those in whom the recipient did (n=7) or did not (n=18) require peri-operative ECMO support, indicative of severe primary graft dysfunction (sPGD). Results: Despite concerns regarding the WIT DCD allografts are exposed to during withdrawal of life support (WLS), an extended WIT according to any of the current or proposed definitions (from systolic < 90 mmHg, systolic <50 mmHg or sats <70% to preservation flush; or systolic <50 mmHg to ex-situ reperfusion) was not associated with sPGD in our cohort. If fact a longer duration from WLS to circulatory arrest (CAr), systolic < 90 mmHg to CAr and sats <70% to CAr was associated with a significantly lower rate of sPGD (p=0.02, p=0.04 and p=0.02, respectively). The only period, if prolonged, associated with an increased rate of sPGD is the time between CAr and delivery of the preservation flush, in essence the asystolic WIT (aWIT) (14.6±3.1 and 11.8±2.4 min for the ΕCΜΟ and non-ΕCΜΟ groups respectively, p=0.01). Conclusion: The definition of WIT in DCD heart transplantation has proved controversial, however with more in-depth analysis of the patterns associated with WLS and performance of the donor allograft it does not appear that a prolonged WIT, as defined by any of the current or proposed definitions, is in fact associated with sPGD. At present the only clear negative predictor is a prolonged aWIT. This ought to provoke renewed discussions regarding these definitions, and an increased focus on the minimisation of aWIT during DCD allograft retrievals.