Microcirculatory alterations after orthotopic pig-to-baboon heart transplantation

Whilst macrohemodynamic function of porcine xenografts transplanted into baboons has been assessed perioperatively, the ability of the xenograft to maintain systemic microcirculatory perfusion has not been investigated after pig-to-baboon xenotransplantation so far.

We investigated the sublingual microcirculation of six baboons undergoing orthotopic transplantation of hCD46-transgenic pig hearts using orthogonal polarization spectral imaging. Microvascular measurements were performed after induction of anesthesia, in the early phase of cardiopulmonary bypass (CPB), during reperfusion of the porcine heart and 1 h after the xenograft had resumed its life-supporting function. Microvascular blood flow was analyzed semiquantitatively and the number of visualized cell-to-cell interactions was counted.

The proportion of continuously perfused microvessels was 97 (96 to 97) % at baseline and 95 (94 to 97) % in the early phase of CPB. It decreased significantly (P < 0.05) during CPB to 89 (84 to 91), and alterations were still present (P < 0.05) when CPB was terminated and the xenograft had taken over systemic perfusion 83 (81 to 85) %. The microcirculatory changes correlated with the lactate levels (y = 18.1-0.18 x; r(2) = 0.55; P < 0.001), but no correlation with macrohemodynamic parameters was found.

Microvascular blood flow is altered after orthotopic pig-to-baboon heart transplantation, despite systemic hemodynamic parameters being well maintained by the porcine xenograft. These changes are moderate but persist after termination of CPB. Further studies need to elucidate whether these changes are transient or add to the mortality associated with cardiac xenotransplantation.