Internal Mammary Artery is also Highly Sensitive to Reperfusion Injury. Direct Comparison of Free and In situ Internal Mammary Arterial Grafts and the Improvement of Current Storage Protocols

Introduction: The in situ internal mammary artery (ITA) has better long-term patency than other arterial conduit when used for coronary bypass grafting. However, patency rate of ITA used as a free conduit has equivalent to radial artery. The study objective was to compare directly the usage of free to in situ mammary artery and to investigate the effect of daily-used preservation solution on the endothelial function after bypass surgery in a swine model.

Methods: The ITA is harvested as free/in situ graft (n = 6–8/group). Free grafts are stored for 1 hour in different preservation solutions (physiological saline, Custodiol and TiProtec). The mammary artery was anastomosed off-pump to the LAD (as an in situ/free graft) in a porcine model. Freshly harvested mammary arteries served as control. After 2 hours reperfusion, the implanted grafts were harvested. Endothelium-dependent and-independent vasorelaxations were investigated in organ bath. DNA strand breaks were assessed by TUNEL-method, mRNA expressions by quantitative real-time PCR and the expression of CD-31 by immunochemistry.

Results: Endothelial function was severely impaired after 2h reperfusion in groups with conventional storage solutions in comparison to the control, whereas was partially preserved in the TiProtec group. The in situ graft showed no impairment of endothelial function. (maximal vasorelaxation to acetylcholine: control:87 ± 5%, free graft (saline):25 ± 3%^*#, free graft (Custodiol):31 ± 4%^*#, free graft (TiProtec):44 ± 4%*, in situ:73 ± 6%; p < 0.05: *versus control, ^#versus TiProtec). Endothelial integrity was also severely damaged (CD-31 positive area: control:87 ± 2%, free graft (saline):62 ± 6%, free graft (Custodiol):70 ± 8%, free graft (TiProtec):79 ± 7%, in situ: 94 ± 2%, TUNEL positive nuclei; control:13 ± 2%, free graft (saline):71± 3%^*#, free graft (Custodiol):56 ± 4%^*#, free graft (TiProtec):38 ± 3%*, in situ: 33 ± 3%, p < 0.05: *versus control, ^#versus TiProtec). In addition, mRNA levels were significantly altered in the groups.

Conclusion: The internal mammary artery has high vulnerability against reperfusion injury. In situ usage of the ITA appears to be superior for the preservation of endothelial cells of bypass graft. Custodiol and saline as a preservation solution are not optimal, however TiProtec solution permits better storage for free grafts.