Influence of cigarettes on myocardial injury in healthy population after exposure to high altitude over 5000 m

Background: Myocardial injury (MI) is a severe complication once subjected to hypoxic condition at high altitude. Little evidence exists about the association of cigarettes and MI at high altitude, especially over 5000 m. In the present study, we intend to explore the influence of cigarettes on MI in healthy population after travelling to this extreme environment. Methods: Physical examination was performed in population at Pamirs plateau during November and December 2020. All participants were divided into cigarette group or control group. MI was diagnosed based on lactate dehydrogenase (LDH), creatine kinase (CK), creatine kinase isoenzymes (CK-MB) and aspartate amino transferase (AST). Results: 311 people were included, 58 of whom developed MI, accounting for 18.6 %. Participants in cigarette group were all male, and younger than those in control group. There was longer exposure time in cigarette group. Compared with control group, red blood cell counting, hemoglobin (HGB) and hematocrit in cigarette group were significantly increased, while heart rate was significantly decreased. Cigarettes were found to significantly upregulate the level of CK-MB and LDH. After adjustment with age, sex, body mass index, altitude and exposure time as covariables, 108 male participants remained in each group, showing that none of clinical indexes had significant difference between the two groups. Logistic regression analysis revealed that female sex and oxygen saturation (SO2) were independent risk factors for MI in non-smokers while HGB was independent risk factor in smokers. By using Spearman correlation analysis, four myocardial enzymes were not relevant with the level of SO2 in non-smokers. For smokers, HGB was found to be in significant positive correlation with LDH. Conclusion: Our study suggested that exposure to high altitude over 5000 m could abrogate the impact of cigarettes on MI in healthy population. The independent factors affecting the occurrence of MI were distinctive depending on current smoking status.