Association Of Long-term High-altitude Exposure And Outcomes In Patients Undergoing Cardiac Surgery

Objective:Ischemia and reperfusion injury(IRI)is involved in the outcomes after heart procedures requiring cardiopulmonary bypass(CPB).Ischemic/hypoxic preconditioning is considered to reduce ischemia reperfusion injury,but its clinical application is limited and its effect is controversial.Patients at high altitude has been in chronic hypoxia environment for a long time,which has a similar mechanism with hypoxic preconditioning.They are natural models of hypoxia.The purpose of this study was to retrospectively analyze whether long-term high-altitude exposure can improve the indicators of ischemia reperfusion injury and prognosis of cardiac patients undergoing cardiopulmonary bypass,and to provide the basis for further research.Method:Data of 3028 patients undergoing heart surgery between January 2013 and December 2019 was collected and a propensity score matched analysis was applied.Outcomes of the highlander and lowlander group were compared.Result:A total of 2085 patients met the inclusion criteria.Base on propensity scores,128 highlander patients were matched to 248 patients from among those 1950 patients without long-term high-altitude exposure(1:2 matched,8 highlanders only matched to 1 lowlander).There were no between-group statistical differences in the baseline characteristics after matching.Creatine kinase myocardial band(CK-MB)and troponin I(TnI)increased more in the lowlander group after surgery(79.8(57.4,108.0)vs 65.1(52.4,88.6),P=0.004;8.5(4.3,15.7)vs 5.3(3.0,9.5),P<0.05,respectively).Besides,lowlander group had a higher incidence of getting acute kidney injury(AKI)(21.8%vs 13.3%,P=0.046).There were no significant differences in new stroke,use of intra-aortic balloon pump,duration of mechanical ventilation,length of stay in the ICU and length of stay in the hospital and between the matched groups.Mortality did not differ significantly between groups,occurring in 10(4.0%)patients in the highlander group and 1(0.8%)in the lowlander group(P=0.107).Conclusion:This study shows that long-term high-altitude exposure was related to a less increase of CK-MB and TnI,a lower chance of getting AKI,and underlying trends of a lower mortality,suggesting that long-term high-altitude exposure may be beneficial for reducing IRI.