Introduction: Prior studies have demonstrated that cold perfusion using Steen’s solution reduces initial xenograft dysfunction in heart xenotransplantation via ischemia minimization (IM). We present pilot data evaluating the cardiac injury that occurs in ex vivo xenoperfusion after IM compared to standard cold storage (CS).

Method: Hearts from TKO.GHRKO (quadruple knock-out, or QKO) pigs were compared to those from wild-type (WT) pigs using an ex vivo working heart model. Three QKO and 1 WT hearts were pre-perfused with a cold Steen solution containing human packed red blood cells for 2.5 hours after procurement, prior to the ex vivo perfusion. Two QKO and 2 WT hearts were instead placed in iced saline for the standard cold storage (CS) during this time. Once placed on the ex vivo circuit, hearts were perfused with warm human blood and converted to working heart mode (WHM) with regular blood collection and measurement of cardiac function. Cardiac injury was measured by troponin levels and function was estimated by the hearts’ ability to increase cardiac output in response to increased left atrial pressure.

Results: Troponin levels increased throughout the ex vivo perfusion in all groups, yet this rise was significantly attenuated by IM in the WT group (IM 185, CS>1000; p=0.02), with a similar non-significant trend in the QKO hearts (IM 750, CS>1000; p=0.37)(Fig.1).
One WT CS heart and 1 WT IM heart were unable to generate forward flow in WHM. One WT CS heart achieved WHM but had declining function and failed at 3 hours (Fig.2F). Cardiac function was relatively preserved over 4 hours in 2 of 3 QKO IM hearts (Fig.2A,B), and 1 of 2 QKO CS hearts (Fig.2E). All WT hearts (2 CS and 1 IM (Fig.2F)) and 2 of 5 QKO hearts (1 CS (Fig.2D) and 1 IM (Fig.2C)) failed within 4 hours. The survival to 4 hours was not significantly improved by IM compared to CS.

Conclusion: Ischemia minimization using cold Steen’s solution demonstrates evidence of heart xenograft protection during ex vivo xenoperfusion, with reduced cardiac injury in WT hearts (as troponin release), and promising functional outcomes. Although this pilot series is preliminary, the findings support prior evidence of IM benefit to prevent heart xenograft injury, and warrants further evaluation in larger ex vivo and in vivo studies. The residual troponin release in QKO hearts despite IM, as well as the incomplete physiologic protection, indicate that additional previously described mechanisms of graft injury will likely need to be targeted to prevent pig heart xenograft injury.