The Study Of Cold Ischemic Preservation Of Isolated Porcine Coronary Artery

Background and objectives:Heart transplantation is an established treatment for the end-stage heart disease. Successful heart preservation is an important component of transplantation and ensures the maintenance of organ viability until implantation into the recipient. Despite many efforts to improve the preservation techniques, heart preservation for transplantation is still limited to 4 to 6 hours of cold ischemic storage, and longer periods of ischemia are known to adversely affect the survival. This markedly limits long-distance transportation of the donor hearts and expansion of the pool of potential donors. The shortage of donor hearts and the critical condition of patients on the waiting lists should have benefit of an extended geographical area for attaining donor hearts, if this shall be possible it is necessary to be able to store the heart for an extended period of time. The coronary endothelium plays an important role in regulating the coronary flow and the perfusion pressure by releasing vasoactive substances acting on the vascular smooth muscle cells, especially in freshly transplanted hearts devoid of autonomic neuronal input. Bad preservation of the coronary endothelium impairs the heart function after heart transplantation. It is therefore of the utmost importance to preserve the coronary vasculature especially the endothelium well. Optimal heart preservation for transplantation should include theprotection not only of the myocardium but also of the coronary vessels. There are many different types of preservation solutions used for heart storage. However, none of these can give perfect coronary endothelial preservation during cold heart storage, especially if a prolonged storage period is needed. Based on experimental studies, a new, intracellular heart preservation solution named HP100XD was developed by Steen and colleagues in the research center of cardiothoracic surgery in University Hospital of Lund for the protection of both the myocardium and the coronary vasculature. The present study is designed to investigate the preservation effect of this new preservation solution on coronary endothelium and smooth muscle and discuss the protective mechanism of this solution. Materials and methods:Seven Swedish domestic pigs of either sex with a weight of 26.9±1.2 kg (range 25-28 kg) were used for investigation. After anaesthesia and systemic heparinization, the median sternotomy was performed to extract the heart, followed by the immersion of a cold, oxygenated Krebs solution (4°C). Under the operative microscope, the distal part of porcine left anterior descending coronary artery (LAD) having a diameter of 1.0-1.5 mm, was dissected free from the surrounding tissue, cut into 1-mm long segments with the "no touch" technique. The vascular ring segments harvested (9-12 segments) from each pig were randomly divided into three groups (n=7 in each group): fresh controls, the ring segments were immediately after harvesting transferred to organ baths for the evaluation of endothelial and smooth muscle function. 24h and 48h preservation groups, the segments were transferred to organ baths respectively after 24 and 48 hours of storage in HP100XD solution at 4°C. Each group was subdivided into two groups (A and B) according to the presence or absence of the addition into baths of substance P. Subgroup A was used to investigate coronary endothelial and smooth muscle function. Subgroup B served as the internal control to ascertain that no spontaneous relaxation. The thromboxane A2 analogue U-46619 was used to investigate smooth muscle contractile capacity. Endothelium-dependent relaxation (EDR) was tested by cumulative addition of Substance P. Papaverine was used to elicit endothelium-independent relaxation.Results:Smooth muscle function was not affected regardless of 24 or 48 hours of cold ischemic storage in HP100XD solution (P>0.05). The maximal endothelium-dependent relaxation was not significantly reduced after 24h cold storage compared to fresh vessel segments (97.6±0.3% vs 95.6±0.7%, P>0.05). The maximal EDR was reduced to 87.2±3.8% (P<0.05) after 48 hours of storage. The sensitivity of coronary artery segments to substance P (expressed as the pECso value) was not decreased significantly after 24 hours cold storage in comparison with fresh vessels (9.93±0.17 vs 9.64±0.05, P>0.05). However, significant decrease in the sensitivity of coronary vessels was detected after 48h cold storage (9.93±0.17 vs 9.54±0.04, P<0.05). In addition, no spontaneous relaxations were seen in B subgroups. Conclusion:1. Coronary smooth muscle function was not impaired after 48h cold storage in HP100XD solution.2. HP100XD solution can provide good preservation of endothelium-dependent relaxation function in isolated porcine coronary arteries during 24h storage.3. During cold ischemic storage with HP100XD solution, the endothelial cells of porcine coronary arteries were more susceptible to the cold ischemic damage than the vascular smooth muscle cells.4. HP100XD solution has a positive effect on the protection of coronary artery endothelium and smooth muscle and is a promising solution for the preservation of coronary vasculature.